Question: f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R, ) -> R; <ins> fn evaluation_is_concurrent(&self) -> bool; </ins> fn expand_abstract_consts<T: TypeFoldable<Self>>(self, t: T) -> T; type GenericsOf: GenericsOf<Self>;

<!-- Thank you for finding an Internal Compiler Error! If possible, try to provide a minimal verifiable example. You can read "Rust Bug Minimization Patterns" for how to create smaller examples. --After adding to , I get the ICE. The resulting : The full project: <!-- If you're using the stable version of the compiler, you should also check if the bug also exists in the beta or nightly versions. --: <!-- Include a backtrace in the code block by setting in your environment. E.g. . --
Looks like another label: +T-types +WG-trait-system-refactor +regression-from-stable-to-nightly
Stable passes, beta passes. Nightly passes with either or Discovered with It does sporadically succeed, thus needing to clean and rerun the build to make sure. Either something is up with or it only barely exercises these conditions in the parallel frontend, even after cleaning and running the build 100 times. Meanwhile, fails something like ~50% of the time on my machine.
stable passes obviously, as -Zthreads this is a unstable nightly-only flag?
Hm, not actually obvious given that works, though I suppose that does mean it isn't a regression per se. :^)
oh I thought you knew by now that this is the forbidden env flag that should only ever be used for bootstrapping and nothing else and we should not even tell users about it. If you set the flag, your "stable" will also eat nightly-only features, but why would that make a "to-stable" regression if you explicitly tell the compiler "please act like you are NOT a stable release"? I don't think it make sense to backport fixes for untable nightly features into stable lol
who mentioned backports?
The label is used to gather regressions between release channels, which are then discussed whether they are backport-worthy or not. Is that not how the label is used?
I don't really think regression-from-stable-to-nightly nor regression-from-stable-to-stable are used for that at all? Probably regression-from-stable-to-beta is?


Question: f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R, ) -> R; <ins> fn evaluation_is_concurrent(&self) -> bool; </ins> fn expand_abstract_consts<T: TypeFoldable<Self>>(self, t: T) -> T; type GenericsOf: GenericsOf<Self>;

Pretty much what the title says, I've narrowed it down to and today's nightly with the following: I've attached some backtraces.
probably duplicate of but made more prevalent by next solver
Is it possible to provide a link to or a snippet of a reproducer? I know it probably happens to various crates, but it still would be nice to have something that reproduces.
See for an attached repro.
The repro case is basically the same as , but with other crates mentioned in the ICE logs from the issue comment.


Question: f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R, ) -> R; <ins> fn evaluation_is_concurrent(&self) -> bool; </ins> fn expand_abstract_consts<T: TypeFoldable<Self>>(self, t: T) -> T; type GenericsOf: GenericsOf<Self>;

Compile with latest Nightly got ICE like below: when compiling in code OS: x86_64-apple-darwin
cc
Wyvern, could you provide some sort of reproducer? A link to some commit in some repository or better yet a smaller stripped down version of it?
Can you provide an example which triggers this behavior?
I'm not sure which commit/PR of lead to this crash, sometimes it compiled successfully, sometimes it not. Add this info to original post, hope to help investigation.
are you running with greater than 1? The cache is broken when used with more than 1 thread (which we should fix)
Sorry, I wasn't clear. I meant a link to your project (the project you are trying to compile) if publicly accessible / not proprietary.
I can hit plenty of these while fuzzing with -Zthreads so yeah its probably that.
Yeah, I think was the culprit. Comment out this option crashes disappears.
the easiest fix to rustc is to just disable this assert when we're using more than 1 thread. I've only it for debugging purposes to detect cases where we unnecessarily recompute cache entries
just hit this while trying to bootstrap with Zthreads :sweat_smile:
cc as this also showed up in your ci test run ^^
When I just disable this assert, all relevant UI tests passed with no other bugs or ICE
samle code that triggers this in around 5 of 6 cases with -Zthreads=16


Question: ignore_binding, ); <del> let no_ambiguity = self.ambiguity_errors.len() == prev_ambiguity_errors_len; </del> <ins> let no_ambiguity = ambiguity_errors_len(&self.ambiguity_errors) == prev_ambiguity_errors_len; </ins> import.vis.set(orig_vis); let module = match path_res { PathResult::Module(module) => {

<!-- ICE: Rustc '' 'error: internal compiler error: no resolution for an import', 'error: internal compiler error: no resolution for an import' File: --auto-reduced (treereduce-rust): <details<summary<strongoriginal code</strong</summary<poriginal: </p</detailsVersion information ` Command: <!-- Include a backtrace in the code block by setting in your environment. E.g. . --<details<summary<strongProgram output</strong</summary<p</p</details<!-- query stack: --<!-- TRIAGEBOTSTART --<!-- TRIAGEBOTASSIGNSTART --<!-- TRIAGEBOTASSIGNDATASTARTTRIAGEBOTASSIGNDATAEND --<!-- TRIAGEBOTASSIGNEND --<!-- TRIAGEBOTEND --
regression in cc
I believe the root cause of this issue stems from the changes I made, so claim


Question: <del> #!/bin/bash # We use InnoSetup and its `iscc` program to also create combined installers. # Honestly at this point WIX above and `iscc` are just holdovers from # oh-so-long-ago and are required for creating installers on Windows. I think # one is MSI installers and one is EXE, but they're not used so frequently at # this point anyway so perhaps it's a wash! set -euo pipefail IFS=$'nt' source "$(cd "$(dirname "$0")" && pwd)/../shared.sh" if isWindows; then curl.exe -o is-install.exe "${MIRRORS_BASE}/2017-08-22-is.exe" cmd.exe //c "is-install.exe /VERYSILENT /SUPPRESSMSGBOXES /NORESTART /SP-" ciCommandAddPath "C:Program Files (x86)Inno Setup 5" fi </del>

The .exe installer tries to install to "C:Program Files (x86)Rust", even though it's the 64-bit version. It then fails to create the destination directory due to a permission error. The .msi installer correctly defaults to "C:Program FilesRust <channel<version", and has no problems with permissions, I would expect the .exe installer to have the same behaviour.
Rust should install to , just like Ant, Python, and many others. is the place for developer tools that have a known folder. is badly named (compare to ), poorly suited for command line tools, and clutters the already hideous PATH more than .
/cc
Neither Ant nor Python install to C:tools by default, and searching I can't find any reference to C:tools even being a thing? Both Python and Ant install to C:Python<Versionand C:ant, which is incredibly annoying, so please don't do that!
I might be mistaken, but installing both through stuck them in for me. I'd recommend anyone with a machine running Vista or later use chocolatey. And there's a trend in chocolatey to have packages extract to when they aren't self-contained enough for .
For an OS without much filesystem hierarchy, is a decent place for developer and command-line packages, similar to on some unices. But I'd much rather see a that actually obeyed chocolatey's conventions and extracted an archive to , with no installer/registry involvement. But Rust only and installers for windows. : And all packages that do this reduce PATH clutter, since chocolatey symlinks their executables into .
The idea was to deprecate the .exe installer once .msi is known to be working satisfactory.
Can we have a zip release too, that contains Rust and Cargo like the others? Linux and OS X have an archive release. Those are preferred in chocolatey because they don't involve the registry or any other Windows components.
We do produce tarballs for windows.
Seems like we should probably just stop producing the .exe's. That fix would go in
I don't see a cargo+rustc nightly tarball for windows, although I do see ones for linux and osx.
triage: We do not link to the .exe installer anymore, but we still produce them.


Question: <del> #!/bin/bash # We use InnoSetup and its `iscc` program to also create combined installers. # Honestly at this point WIX above and `iscc` are just holdovers from # oh-so-long-ago and are required for creating installers on Windows. I think # one is MSI installers and one is EXE, but they're not used so frequently at # this point anyway so perhaps it's a wash! set -euo pipefail IFS=$'nt' source "$(cd "$(dirname "$0")" && pwd)/../shared.sh" if isWindows; then curl.exe -o is-install.exe "${MIRRORS_BASE}/2017-08-22-is.exe" cmd.exe //c "is-install.exe /VERYSILENT /SUPPRESSMSGBOXES /NORESTART /SP-" ciCommandAddPath "C:Program Files (x86)Inno Setup 5" fi </del>

I don't have access to windows at the moment to check if this bug has been resolved, but it's been a long time...
Grabbing the Windows download link from and swapping the for yields a functional link to the , which is nice. Testing on win7-x64, the MSI extracts with lessmsi, but the directory structure is somewhat unusual so there's no one-liner to get the Rust folder out. The best I came up with was: This yields a Rust install rooted at . However now that exists, multiple targets aren't really an issue anymore. Someone should make a Chocolatey package for
Can someone with access to Windows check what happens here today?
The latest version installs to instead, which works, but is a terrible default.
Triage: ! This seems... fine. I'm not sure if this should stay open or not; I'll let the relevant team (infra? compiler?) decide.


Question: <ins> // compile-flags: -Z mir-opt-level=3 -Z inline-mir // ignore-wasm32-bare compiled with panic=abort by default #![crate_type = "lib"] // EMIT_MIR issue_78442.bar.RevealAll.diff // EMIT_MIR issue_78442.bar.Inline.diff pub fn bar<P>( // Error won't happen if "bar" is not generic _baz: P, ) { hide_foo()(); } fn hide_foo() -> impl Fn() { // Error won't happen if "iterate" hasn't impl Trait or has generics foo } fn foo() { // Error won't happen if "foo" isn't used in "iterate" or has generics } </ins>

Previously: Now: <!-- Thank you for finding an Internal Compiler Error! If possible, try to provide a minimal verifiable example. You can read "Rust Bug Minimization Patterns" for how to create smaller examples. --<!-- If you're using the stable version of the compiler, you should also check if the bug also exists in the beta or nightly versions. --: <!-- Include a backtrace in the code block by setting in your environment. E.g. . --<details<summary<strongBacktrace</strong</summary<p</p</details
Inlining exposes a use of unnormalized local in a call terminator (not sure if this is more of an issue with inlining or a validator): Note: revision annotation doesn't work in an auxiliary file (so it isn't tested on CI with mir-opt-level=2). modify labels: +A-mir-opt-inlining
This ICEs again because the fix was reverted Can someone reopen please?
Due to this new requires to trigger. <details<summaryICE:</summary</details
(FWIW can also trigger this: )
fixes this for and , but it still ICEs with on its own or with mir-opt-level 1/2 cc


Question: <ins> // compile-flags: -Zdrop-tracking-mir // edition:2021 use std::future::Future; trait Client { type Connecting<'a>: Future + Send where Self: 'a; fn connect(&'_ self) -> Self::Connecting<'a>; //~^ ERROR use of undeclared lifetime name `'a` } fn call_connect<C>(c: &'_ C) -> impl '_ + Future + Send where C: Client + Send + Sync, { async move { c.connect().await } //~^ ERROR `C` does not live long enough } fn main() {} </ins>

<!-- Thank you for finding an Internal Compiler Error! If possible, try to provide a minimal verifiable example. You can read "Rust Bug Minimization Patterns" for how to create smaller examples. --<!-- If you're using the stable version of the compiler, you should also check if the bug also exists in the beta or nightly versions. --: <!-- Include a backtrace in the code block by setting in your environment. E.g. . --<details<summary<strongBacktrace</strong</summary<p</p</details
Another regression of cc
Before I create a fix: is an expected/reasonable value in this ? I.e. is the right fix here just to allow ?
I don't think so. Actually just looked, think it's because we're not erasing properly. Let me put up a quick fix.


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

Following , we realized that rustdoc users would prefer to have a syntax extension rather than using plain HTML to have warning blocks. suggested the following: suggested: What do you think? cc
Personal Opinions: The first style will look fine for short forms, but I'm not sure for longer text. A possible syntax: Which to me pushes the text too far right. Not having any spacing, but just separating with newlines, seems hard to parse at a glance what is part of the WARNING, and prevents multiple line breaks inside the warning. Also, it's not as extensible. INFO can be , but if we ever want more extensions, they would increasingly possibly conflict with other things. The second style makes it immediately clear what is part of the block, and is unlikely to accidentally conflict if we ever want to add more block styles. It also supports multiple lines or inner blocks trivially. A final advantage is that it may support nested blocks, in case those ever come to be useful. Overall: I prefer the second form, both aesthetically and for future-proofing
I think I agree with in preferring the second form. I like the first form's simplicity, but it also seems surprising that is treated as a 'keyword' and will change the formatting of the docs.
That's why we have this debate. :stuckouttongue:
I personally actually prefer stabilizing a CSS class, I think we should do more of that, just because parsing can get annoying. But this is not that hard to parse anyway. The problem with is precisely that you can't scope it easily: what if you want to add code blocks? bullet points?
The problem with this is it ties rustdoc to the HTML backend; like I said nothing rustdoc currently does guarentees that it will generate HTML from the markdown. Changing that means that to make the JSON backend have the same info, we'd have to add a full HTML parser to rustdoc just to read the HTML in the markdown, because pulldown does not parse HTML for us. I really think we should avoid making the JSON backend a second-class citizen.
Also there's not much point to this if it's just a little CSS IMO, you can add that yourself with and it will look just as good and be more flexible since you can control the styles yourself.


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

I'm not a giant fan of the syntax because it looks odd when rendered by anything other than rustdoc, which I'd rather avoid, one of the major design concerns for intra-doc links was compatibility with other markdown parsers:
So, I agree, but I'm not convinced that the warning class is something that needs to be surfaced in the JSON backend as anything special. Also, bear in mind, HTML is a part of markdown: valid HTML (well a subset of HTML) is valid markdown. Users already can , and they do that in many cases. Markdown parsers already need to be able to handle HTML. There's nothing new there. Whatever consumes the JSON backend will need to be able to handle that too. I mean, yes, in theory, in practice people don't do this because of the barrier to entry (you have to get your tools to use that, including )
Also, this is incorrect, pulldown absolutely parses HTML. It has to, like I said valid HTML is valid Markdown. It doesn't parse it thoroughly, I believe you can mess it up with sufficiently complex HTML, but it parses HTML. What this changes is subtler: up till now you did not need any particular stylesheet to acceptably render rustdoc markdown from the JSON backend on your own (just use your favorite markdown renderer's stylesheet), but now you will need other css classes to handle rendering warnings as warnings.
I do not agree that this is a problem. I've used Phabricator's implementation of this approach happily and it is by design that warning banners are one paragraph. It is not the intention that you would put entire sections of documentation into a warning banner. They are for a brief callout. It's fine to refer to a subsequent section of the documentation from the callout if needed. I suppose this is a matter of taste but it's one where I believe the opinionatedness of the syntax is a positive thing.
So I discussed this a bit with on the side, we agree that the effect on the JSON backend isn't major since HTML is already a subset of markdown and docs use HTML already (especially for images and tables). My position is as follows: I strictly prefer HTML over some other scoped syntax with nuances people have to learn. I don't think there's as much value in unscoped syntax which makes my position "HTML or nothing", basically.


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

I'm not wholly against unscoped single-line syntax. We and syntax in W3C specs and you invariably need to add more stuff to it (there's an HTML class in these specs for this reason). Furthermore, Rust has a strong culture of wrapping text, so this means we need to work well while wrapped, and that means we're again introducing some form of scoping mechanism (e.g. indenting the text), which editors will have to learn, as well.
I don't know about admonitions specifically but there seems to be something of a community habit to use "magic tags" on fenced code blocks for this sort of features (e.g. github has a tag), maybe that could be an option? I don't know if pulldown_cmark has a hook for manipulating code blocks but… So a warning would be or maybe the tag would be to leave room for things like note/todo/danger/… Alternatively, take a gander at how other markdown implementations extend the language for this sort of features? e.g. seems to be using for admonitions.
Hmm, but is still for code, even if it has some extra behavior. Aside from the design concerns, this would be feasible to implement: we just extract the language string from the code block with pulldown.
Could you use something that's already built into markdown? For example, rustdoc could take and render it as an admonition.
That's what suggested: to use markdown and make some changes on rustdoc side. I think the codeblock approach is the best personally.
My bad, I didn't see that.
I wonder if it makes more sense to add this as a proc-macro. Rustdoc can still provide the CSS classes and things, and you could use them with HTML directly, but you could use or something and it would expand to the correct HTML tags and classes.
Might be better to have a then, no?
Is that going to be a special header similar to the "unsafe"/"experimental"/etc ones, or is that going to also be used within docs in an order-sensitive way? If the latter we should probably just use a CSS class; mixing and is ugly
Agreed.


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

Among the suggested ideas, my favourite one remains the code block with "warning" as tag:
Yeah, but triple backticks is also for preformatted text without further markup, so you won't be able to e.g. use text formatting (or other code) in there
True... Finding the right syntax is much more complicated than expected...
That's the issue of using markdown, for all that it has a pretty nice baseline syntax it really was not designed for extensibility.
We can always use : it'd allow to have text formatting inside it.
I would use , it's not quite kosher to invent arbitrary HTML tags (though you can use Custom Elements, which is more heavyweight)
Sounds good to me. It's funny because we kinda came back to the . :rofl:
I just thought: we could use tag in the markdown and then transform it into in the generated HTML?
My main objection to all of these is that rustdoc shouldn't be adding custom markdown syntax that no one else supports. Any new syntax we use should look reasonable even if rendered with the default renderer.
Well, it remains valid markdown since it's HTML (even though it's custom tag). I'm completely fine with , but it might be simpler/better for users to simply write .
Coming back to this (because of ), it seems like the conversation kinda agreed on adding a CSS class directly and then it would look like this in the docs: . I'll send a PR in the next days and then we can open an FCP to see if everyone is ok with it (and if not, we'll have code to help the debate).
This indeed seems like a better solution than the HTML block. It also plays better with something said about not linking it too much too HTML. This will look like a proper warning or note, mostly independent of the HTML generation.
They also seemed to not be too favourable to anything that needs some extra parsing from rustdoc iuc. I'm fine with bot the github solution and the CSS class.
Maybe one more comment to make here. The note-taking app, which uses Markdown also has a similar syntax to create these blocks. It is called . It uses a syntax similar to the syntax that is used for doc intra-links currently, and it is fully compatible with them.


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

I am uncertain if this is any better than what suggested from the GitHub syntax, but because of the similarity to the doc intra-link syntax. I do feel like this might be interesting because it should go well with backwards compatibility. However, this may look worse than the GitHub syntax solution when not going through cargo doc.
I thought I'd already left this comment, but I'd really like to avoid adding more markdown syntax where possible. This feature works fine without special syntax, I don't think we need it. edit: copying over the reasoning from the :
Although, I might not agree fully, I can fully appreciate and understand the reasoning you left in the corresponding PR. Still, I do think it might be worth to standardize some kind of syntax for some kind of warning block. This does not actually require customized markdown. Alternatively, I can suggest adding the GitHub flavor with emojis to the . This may help in standardizing short form warnings and notes within documentation. We could for example propose to standardize: which should look like the following I do value people's opinion on this. Is this a possible compromise?
That's a valid alternative, I think the yellow color is pretty important though, and it's useful for themes to be able to make styling decisions about warnings so I do think that having some way of marking it is important. I just don't think the way of marking it should be some magic invocation as opposed to CSS classes. (And I think that the bar for a feature that is adding new semantics to the Rustdoc markdown parser is much, much higher than that of one stabilizing a CSS class)
100% agree. I will look at the Rust API guidelines issue and possibly an RFC to rust to track the adoption in GitHub and possibly eventually merge. Thank you :smile:
Beyond all this discussion of third-party tools, I'd really like to make sure that whatever new syntax and presentation we add to rustdoc can also be to [mdBook]. That way, when the standard library starts using callouts, we can make sure the same style also gets used in The Book. Mostly, The Book seems to just use blockquotes, often with headings like [this one about ownership]. mdBook doesn't do anything special with it: it's [just a block quote with a header].


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

[mdBook]: [this one about ownership]: [just a block quote with a header]:
This is a good point. Once we have something merged here, I'll send a PR there to have an equivalent.
CC
I'd be happy to add some CSS rules to mdbook if that is what you are proposing.
Yeah, it is.
FYI, using a is not semantic and Microsoft GitHub is setting a bad precedence. — CommonMark Spec v0.30, denotes a in Markdown and is rendered as such. — W3C HTML spec, Unless you are quoting a source, this is not the correct element to use. While I disagree with even using altogether, at least some tools out there are at least translating the blockquote in admonition context into a (div has no semantic meaning which is unfortunately the best HTML option for admonitions). It would be ill-advised to follow Microsoft GitHub’s Markdown syntax fork—especially with their disregard for semantics. Similarly using a block would also be breaking semantics as an admonition is not preformatted text. CommonMark does have that could be used if the solution was preferred. There’s also other reasonable options noted here that don’t break semantics.
I agree that block quotes for callouts are bad, and would like to work with mdBook to roll out a common syntax (probably ) that will replace the ad-hoc, unsemantic markup that they use right now.
Using is what we agreed upon in The debate now is on the look itself.
Unfortunately isn't great because markdown has a "boundary" when HTML tags are used. I wanted to add a warning indicating that users probably wanted another trait, but intra-doc links don't work (which is the correct behavior per markdown spec).
Works perfectly fine though (well, minus the UI bug I just discovered haha): ! I used this code: I'll send a PR to improve documentation.
Ah. Well I suppose the issue wasn't with intra-doc links, but with inline code blocks. What I tried was that but with bar`, and it failed.
Works too: !
I opened which adds extra explanation on how to use markdown inside html tags. That should solve your issue.
That note is exactly what I was just looking in to. I had it inline, given my familiarity with HTML. TIL that matters.


Question: font-size: 1.25rem; } <ins> /* This class only exists for users who want to draw attention to a particular element in their documentation. */ .content .docblock .warning { border-left: 2px solid var(--warning-border-color); padding: 14px; position: relative; /* The "!important" part is required because the rule is otherwise overruled in this CSS selector: ".docblock > :not(.more-examples-toggle):not(.example-wrap)" */ overflow-x: visible !important; } .content .docblock .warning::before { color: var(--warning-border-color); content: "ⓘ"; position: absolute; left: -25px; top: 5px; font-weight: bold; font-size: 1.25rem; } </ins> a.test-arrow { visibility: hidden; position: absolute;

It doesn't hurt to have it and if it can helps users, well, why not doing it. :)


Question: use ext::tt::macro_parser::{parse, parse_failure_msg}; use ext::tt::quoted; use ext::tt::transcribe::transcribe; <del> use feature_gate::{self, emit_feature_err, Features, GateIssue}; </del> <ins> use feature_gate::Features; </ins> use parse::{Directory, ParseSess}; use parse::parser::Parser; use parse::token::{self, NtTT};

Tracking issue for rust-lang/rfcs.
Is anyone working on implementation already? If not I can take a crack at it.
I'll probably do it.
Huh oh, we have an issue already: do we mean to include potentially minus-prefixed literals? If yes, we have a problem because 1. it means we have to return an Expr instead of a Lit, which means I'm not sure one will be able to use the bound fragment in a non-expr context (for example in a static array type?) and 2. it's no longer always a single-TT, so the benefits in terms of future-proofing are a bit less good. If we don't... well, we loose expressivity. I have no idea what is more intuitive though... Would you, as a Rust user, expect to parse ? I certainly can think of use cases for this...
good point. I think I would have expected it, I also agree with the complications.
Can't we upgrade Lit to support negative literals?
I'd expect "literal" (or a future integer-literal specifier) to include (negative 5), but not (the negation of positive 5). Perhaps that expectation doesn't match reality, though. For instance, based on parsing rules for non-literals, I'd expect to act like . So, if handling both and as literals makes this easier, that works. But "literal" definitely needs to include negative numbers, or we'd have a weird user trap to explain.
I'd expect "literal" (or a future integer-literal specifier) to include -5 (negative 5), but not - 5 (the negation of positive 5). Unary operators, including minus, are processed purely by the parser at the moment, no lexer involved. So their treatment is whitespace agnostic. (I personally think this is a good thing.)
I agree with is not syntactically different from and has no reason to be. But I also agree with the fact that the user will probably expect negative numbers to work as literals (even it – syntactically – they're not).
is also supported in literal patterns while arbitrary expressions are not. It'd be reasonable to support it in fragments as well.
Another thing that won't match is a macro call, like , or any of the other macros that I think of as expanding to a literal (, ...).


Question: use ext::tt::macro_parser::{parse, parse_failure_msg}; use ext::tt::quoted; use ext::tt::transcribe::transcribe; <del> use feature_gate::{self, emit_feature_err, Features, GateIssue}; </del> <ins> use feature_gate::Features; </ins> use parse::{Directory, ParseSess}; use parse::parser::Parser; use parse::token::{self, NtTT};

I dunno, maybe this is not such a good idea after all. Re-reading the RFC in a more skeptical light, I felt like the "Motivation" section could use some more concrete use cases. Maybe this is just failure of imagination on my part, though! I think the likelihood of this feature attracting people who really want constant expressions should be acknowledged as a drawback, too.
That's fine IMO. Personally I'd like it to match only explicit literals in code to distinguish, for example, between literal and identifier and produce different code for them. Right now this is not possible because all of , , are too broad and conflict with each other.
Hi All, I have implemented this feature in my fork of Rust over 1.25.0, under this branch: Following a quick review by a rustc mentor I may have the free time to provide a full pull request for this.
BTW label has the tooltip "implemented in nightly and unstable" but I did not see it there, i.e. commits & pull requests referencing this. Did I miss it?
The implementation that I worked on was merged, yay!
Is there anything stopping an FCP for this?
It's currently merged in unstable; do you mean an FCP to declare it stable?
Yes, an FCP to stabilise. Should have clarified.
Currently, it is not possible to pass a literal from a macro to another macro. . I think this is a bug.
Interesting! That is a bug. I opened to track it.
Agreed, this should be allowed just like passing any other node types.
Is there anything else preventing this from being stabilized? The issue above has been fixed.
This has baked for some time now and I believe it should be ready for stabilization. So let's start the review. merge The feature gate test is here: Unstable book: Tests defined here:
Team member has proposed to merge this. The next step is review by the rest of the tagged teams: [x] [x] [x] [x] [x] [ ] [x] [x] [x] [ ] No concerns currently listed. Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!


Question: use ext::tt::macro_parser::{parse, parse_failure_msg}; use ext::tt::quoted; use ext::tt::transcribe::transcribe; <del> use feature_gate::{self, emit_feature_err, Features, GateIssue}; </del> <ins> use feature_gate::Features; </ins> use parse::{Directory, ParseSess}; use parse::parser::Parser; use parse::token::{self, NtTT};

See for info about what commands tagged team members can give me.
Reading through the tests, I see that is a literal. While that makes sense to me, I remember hearing that it wasn't, but was instead a negation operator and a literal. Am I misremembering?
cc on
I agree that it makes sense. I would say that even if is interpreted as negation + a literal, I would probably still want the macro matcher to accept since that behavior seems more intuitive. In other words, I would see being more as an implementation detail than what a literal is in the mental model.
I think that the nuance with causes a bit of a problem, because I don't think it should be treated as a literal, but I also don't think that the current implementation of would allow detecting it either. You could naïvely allow but that would allow which is clearly wrong.
there are tests currently implemented that verify that is detected as a literal.
I worded that wrong; I meant that only having a matcher and not being able to distinguish strings and numbers means that you can't easily make not a literal.
for procedural macros the input as lexed by the compiler is (two tokens) but procedural macros can create tokens that are negatives (like ). In that sense matching for makes sense to me.
Are literals generated by the compiler counted as true literals? A quick example would be something like: This fails to match, as the expansion, I guess, happens after the selection. I just naively assumed that would have worked.
is not a literal generated by the compiler, it is an identifier followed by an exclamation mark followed by a set of parentheses containing some tokens. See for example: If you were to use it in expression position, it would be interpreted as an invocation of which expands to a string literal. In this case and in your macro though, it is never in a syntactic position where it would be treated as an expression.
I can understand semantically why it doesn't make sense, I just thought it would have, but that being said, I already changed it to , so there's no issue. It just made more sense to me as a literal, because according to the compiler, it could generate a literal from it. I guess it was more a question than an actual issue.
This is true, but there's more to it!


Question: use ext::tt::macro_parser::{parse, parse_failure_msg}; use ext::tt::quoted; use ext::tt::transcribe::transcribe; <del> use feature_gate::{self, emit_feature_err, Features, GateIssue}; </del> <ins> use feature_gate::Features; </ins> use parse::{Directory, ParseSess}; use parse::parser::Parser; use parse::token::{self, NtTT};

A few built-in macros can expand their arguments eagerly through ~m a g i c~, so they accept and likes even if they expect string literals: Fortunately (or not), this currently cannot be done in user-defined macros.
I actually just realised that I can't change it to , as it's used in . So, I've just had to manually unroll the macro. ! It doesn't look pretty. :( Ninja edit: I just tested what actually happens if you try to pass in a non-literal with . It rejects it the exact same way. Does the already make use of this feature? If not, the seems to propagate the required token. Oh, unless the compiler steps in... That's actually probably the case... I've reverted it back to the type.
:bell: This is now entering its final comment period, as per the . :bell:
The final comment period, with a disposition to merge, as per the , is now complete.
Since you implemented this, would you be willing to write up the stabilization PR?
sure
This appears to be missing from the Rust reference


Question: <ins> #![feature(staged_api)] #![stable(feature = "libfoo", since = "1.0.0")] #[unstable(feature = "foo", reason = "...", issue = "none")] pub fn foo() {} #[stable(feature = "libfoo", since = "1.0.0")] pub struct Foo; impl Foo { #[unstable(feature = "foo", reason = "...", issue = "none")] pub fn foo(&self) {} } </ins>

It would be more helpful to suggest the method for the typo rather than a nightly-only symbol which isn't actually available. the suggestion doesn't work. method is actually available on a . method has been stable since 1.0.0. had trouble noticing the difference between and and could have used the compiler's help. No response Reproduced with 1.68.0 stable and 1.70 nightly. <!-- TRIAGEBOTSTART --<!-- TRIAGEBOTASSIGNSTART --<!-- TRIAGEBOTASSIGNDATASTARTTRIAGEBOTASSIGNDATAEND --<!-- TRIAGEBOTASSIGNEND --<!-- TRIAGEBOTEND --
cc
claim


Question: span } = *self; <del> hcx.hash_hir_item_like(attrs, |hcx| { </del> <ins> hcx.hash_hir_item_like(attrs, is_const, |hcx| { </ins> hcx.while_hashing_spans(hash_spans, |hcx| { name.hash_stable(hcx, hasher); attrs.hash_stable(hcx, hasher);

Found via rust-icci: https://travis- The commit history of the regex crate contains on changeset that only adds a comment which in turn leads to the body of a function being moved. This results in the update of the source location pointed to by a potential overflow panic message. This message is not updated properly in incremental mode: I have not found out yet why the change is not detected. HIR fingerprinting has special treatment of operations that can trigger overflows: There must be some kind of mismatch between when HIR fingerprinting thinks that an operation can panic and when we actually emit panic messages. This is another span-related papercut cc
Full IR files for reference:


Question: was_remapped, Some(&unmapped_path)); <del> return match self.source_file_by_stable_id(file_id) { </del> <ins> let lrc_sf = match self.source_file_by_stable_id(file_id) { </ins> Some(lrc_sf) => lrc_sf, None => { let source_file = Lrc::new(SourceFile::new(

I know that having huge literal in source is a bad idea, but it should not cause ICE :( It looks like something overflowed. Version: Command, output and backtrace: Here is the generator of the source:
cc
Took a quick look. We certainly have a restriction that any file can't be that large, because we use u32 for indexing. And looks like we never try to enforce it anywhere. I think the place to do that would be . Do we have any way to panic without this being marked as ICE? I don't want to thread to each , and this seems like a marginal error where it's totally OK to panic. This is even OK in the IDE context I think: IDE should enforce reasonable max size of the file (something like 10mb, not 4gb) at the virtual file system layer. The "just panic" fix is here:
Do we have any way to panic without this being marked as ICE? or if the context is available.
I tried to compile the same thing in gcc and clang: With gcc: With clang: EDIT: Opened


Question: source_file: Lrc<rustc_span::SourceFile>, override_span: Option<Span>, ) -> Self { <del> // Make sure external source is loaded first, before accessing it. // While this can't show up during normal parsing, `retokenize` may // be called with a source file from an external crate. sess.source_map().ensure_source_file_source_present(Lrc::clone(&source_file)); let src = if let Some(src) = &source_file.src { Lrc::clone(&src) } else if let Some(src) = source_file.external_src.borrow().get_source() { Lrc::clone(&src) } else { </del> <ins> let src = source_file.src.clone().unwrap_or_else(|| { </ins> sess.span_diagnostic .bug(&format!("cannot lex `source_file` without source: {}", source_file.name)); <del> }; </del> <ins> }); </ins> StringReader { sess,

contains a function, which allows to to, well, retokenize existing span: There's only caller of this function: And there's only one caller of that caller: In other words, the only reason why we need is to get the span of hir::Usewhich happens to be a glob import. ( rls needs to know the span of use foo:: with explicit list of imported items" code action. This was the first demoed code action and is still that is implemented ) I'd like to remove the function, as it is one of the few remaining things that requires to be public, and as it is very much a hack anyway. Additionally, I believe I've broken this function accidently a while ago: Rather than retokenizing a span, it retokenized file from the begining until the end of the span (whcih, as uses are usually on top, worked correctly most of the times by accident). What would be the best way to fix this? Add hir::Use-- this seem to be the "proper" solution here Move hack's implementation to where it belongs: in , just fetch the text of the file and look for ('') Remove the deglog functionlity from RLS? I don't like this option as it handicaps the RLS before we formally decided to deprecated it. But I don't completely disregard it either, as, as a whole, it seems to be a full-stack one off hack penetrating every layer of abstraction. WDYT?
I'd suggest the second alternative (move hack's implementation to in librutcsaveanalysis), save analysis is a home of many hacks already and one more until save analysis is deprecated in its entirety won't hurt. Adding span for would be ok if it were useful for anything else at least.


Question: ) => { eq_closure_binder(lb, rb) && lc == rc <del> && la.map_or(false, CoroutineKind::is_async) == ra.map_or(false, CoroutineKind::is_async) </del> <ins> && eq_coroutine_kind(*la, *ra) </ins> && lm == rm && eq_fn_decl(lf, rf) && eq_expr(le, re)

() Reproduces on the playground using . label +D-incorrect +F-gen_blocks +requires-nightly


Question: impl Foo { // @has async_fn/struct.Foo.html <del> // @has - '//*[@class="method"]' 'pub async fn complicated_lifetimes( &self, context: &impl Bar ) -> impl Iterator<Item = &usize>' </del> <ins> // @has - '//*[@class="method"]' 'pub async fn complicated_lifetimes( &self, context: &impl Bar, ) -> impl Iterator<Item = &usize>' </ins> pub async fn complicated_lifetimes(&self, context: &impl Bar) -> impl Iterator<Item = &usize> { [0].iter() }

Take a look at the docs for : Rustdoc is making good choices for whether to wrap the declarations ! But when it wraps, it doesn't include a trailing comma on the last parameter. I think it should, because the default style guide wants a comma there. (And rustdoc should continue not putting a trailing comma when the declaration is shown as a single line.) <!-- TRIAGEBOTSTART --<!-- TRIAGEBOTASSIGNSTART --<!-- TRIAGEBOTASSIGNDATASTARTTRIAGEBOTASSIGNDATAEND --<!-- TRIAGEBOTASSIGNEND --<!-- TRIAGEBOTEND --
claim


Question: with_interner(|interner| interner.gensymed(self)) } <ins> pub fn is_gensymed(self) -> bool { with_interner(|interner| interner.is_gensymed(self)) } </ins> pub fn as_str(self) -> LocalInternedString { with_interner(|interner| unsafe { LocalInternedString {

The error happens on latest stable and nightly. Steps to reproduce: ; : : returns error: The error only happens if the module is named (for instance, and work without error). The error is not produced if doesn't use in any way. If doesn't contain imports but uses the library directly (e.g. ), the error is produced. always succeeds. I don't know if this is supposed to be forbidden but the error message seems to be misleading.
The second instance is injected implicitly. The error could be better, yes.
Where exactly is injected - in the library or in the test? Why does the library work on its own? Why does conflict with in the test?
Ok, it turns out this is a legitimate bug, I misinterpreted it as a more commonly reported diagnostic issue. is injected into both the library and the test, but only the first one causes the error. If you set in , then you'll see the error immediately while compiling - conflicts with . On 2018 edition, however, is injected in more subtle way, as where is some unique symbol that still has the string representation , but doesn't clash with anything in the same crate. Unfortunately, turns into "just " after encoding into metadata in the compiled library (this is the bug). So, when we load that library from the test it looks like the library defines two conflicting items.
The solution is to either encode gensyms/hygiene into metadata properly (this is a large task and a long standing issue), or come up with some hack preventing the injected specifically from being encoded (it doesn't really need to be encoded).
Fixed in


Question: if let Res::Def(DefKind::Mod, ..) = child.res { self.resolve_doc_links_extern_inner(def_id); // Inner attribute scope } <del> // Traits are processed in `add_extern_traits_in_scope`. </del> <ins> // `DefKind::Trait`s are processed in `process_extern_impls`. </ins> if let Res::Def(DefKind::Mod | DefKind::Enum, ..) = child.res { self.process_module_children_or_reexports(def_id); } <ins> if let Res::Def(DefKind::Struct | DefKind::Union | DefKind::Variant, _) = child.res { let field_def_ids = Vec::from_iter( self.resolver .cstore() .associated_item_def_ids_untracked(def_id, self.sess), ); for field_def_id in field_def_ids { self.resolve_doc_links_extern_outer(field_def_id, scope_id); } } </ins> } } }

Here is a complete (minimized) reproducer: It can be reproduced with a workspace with two crates "a" and "b" where: The crate "a" depends on the public () crate and its code is: . The crate "b" depends on the workspace crate and its code is: With that setup, the command rightfully succeeds using the stable toolchain. But fails when using the latest (2022-04-25) nightly toolchain. The bug is observable on nightly only (works fine on stable, and beta) : <details<summary<strongBacktrace</strong</summary<p</p</details
Fixed in


Question: self.report_error_if_loan_conflicts_with_restriction( old_loan, new_loan, old_loan, new_loan) && self.report_error_if_loan_conflicts_with_restriction( <del> new_loan, old_loan, old_loan, new_loan); </del> <ins> new_loan, old_loan, old_loan, new_loan) </ins> } pub fn report_error_if_loan_conflicts_with_restriction(&self,

Ran into this when running a fauly tt muncher with ~100 items. We can now compete with C++ in the compiler spew area as well! :-P
Ran into this while demonstrating why you need raw pointers to do a singly-linked-queue: 66 Borrow check errors in this test.


Question: fn eof_err(&mut self) -> PErr<'psess> { let msg = "this file contains an unclosed delimiter"; let mut err = self.string_reader.dcx().struct_span_err(self.token.span, msg); <del> for &(_, sp) in &self.diag_info.open_braces { err.span_label(sp, "unclosed delimiter"); </del> <ins> let unclosed_delimiter_show_limit = 5; let len = usize::min(unclosed_delimiter_show_limit, self.diag_info.open_braces.len()); for &(_, span) in &self.diag_info.open_braces[..len] { err.span_label(span, "unclosed delimiter"); </ins> self.diag_info.unmatched_delims.push(UnmatchedDelim { found_delim: None, found_span: self.token.span, <del> unclosed_span: Some(sp), </del> <ins> unclosed_span: Some(span), </ins> candidate_span: None, }); } <ins> if let Some((_, span)) = self.diag_info.open_braces.get(unclosed_delimiter_show_limit) && self.diag_info.open_braces.len() >= unclosed_delimiter_show_limit + 2 { err.span_label( *span, format!( "another {} unclosed delimiters begin from here", self.diag_info.open_braces.len() - unclosed_delimiter_show_limit ), ); } </ins> if let Some((delim, _)) = self.diag_info.open_braces.last() { report_suspicious_mismatch_block( &mut err,

In my Fedora installation ended up being a corrupted file. It took me hours to realize, given that the output does not bring any clarity to it. rustc should really have ratelimit detection or something to detect corrupted file instead and inform about this to the user. !
This indeed seems quite confusing; and counter-productive to try to show this blob of errors. Would you be able to provide us with a reproducible example of the issue? Or if you still have it the corrupted file. labels +T-compiler +A-diagnostics +D-verbose +D-confusing +S-needs-repro -needs-triage
So this a problem because I unfortunately deleted the trashed file before someone told me that I should report this as a bug. I regret that I did not store it :-/ BUT I recalled that it was probably for reason a long string of ANSI escape codes. So I did a test string: This creates somewhat similar output as I got, except probably the string was a bit longer in my case.
OK doubling that starts to be almost perfect match:
! ... I'm considering T-shirt design ;-) Made by me and rustc. EDIT: and rendered by excellent terminal emulator foot
Somehow rustc should be able to detect corrupted file in cargo's source repository (or whatever it is called). It was pretty bizarre sight when I encountered this by accident.
Thanks for the repro. label -S-needs-repro
Yeah I mean it is really a huge corner case but it can happen in the case of data corruption (e.g. power outage in middle of write operation). I'd detect frequency of errors and maybe a threshold parameter when it is interpreted as corruption with a sane default value.
yeah, I believe this error comes out from the phase of lexing, which rustc are trying to find all the mismatched delimiters, maybe a threshold is ok for resolve it.


Question: <ins> 1|       |// Verify that the entry point injected by the test harness doesn't cause 2|       |// weird artifacts in the coverage report (e.g. issue #10749). 3|       | 4|       |// compile-flags: --test 5|       | 6|       |#[allow(dead_code)] 7|      0|fn unused() {} 8|       | 9|      1|#[test] 10|      1|fn my_test() {} </ins>

<!-- Thank you for filing a bug report! Please provide a short summary of the bug, along with any information you feel relevant to replicating the bug. --Take this simple crate: If I try to gather code coverage for , I end up with the first line mysteriously duplicated as a covered region: (I'm using for convenience, but the same thing happens when I use and process the coverage data manually with and .) Note that in the report produced by , the first line of the file appears twice. It is marked as having executed once, even though it is a comment. Instead, the line should only appear once, and its execution count (if any) should be the execution count of the actual code on that line. <!-- If you're using the stable version of the compiler, you should also check if the bug also exists in the beta or nightly versions. --<!-- Include a backtrace in the code block by setting in your environment. E.g. . --<!-- <details<summaryBacktrace</summary<p</p</details--
I did some initial investigation, and discovered a few things: The coverage mapping that embeds in the test binary contains entries for two different functions named . One is the actual that appears in the file, and the other is the that is injected by the test harness. The mapping for the injected function spans from (1,0) to (1,1). Coverage mapping regions use 1-based line numbers and column numbers, so a column number of 0 should be impossible. This unexpected column number confuses the processing code in , and results in line 1 being duplicated in the output. : There are special circumstances where it's legal for a region to have 0 for its start column and its end column, but that isn't what's happening here.
The origin of the bogus (1,0) to (1,1) region seems to be: The test harness entry point is created with a dummy span: When that dummy span is converted into a region, its 0-based start is decremented in an attempt to make the region non-empty. This decrement overflows to , and a subsequent increment (to make it 1-based) overflows back to 0.
My first thought was to sidestep the whole issue by adding to the test harness's injected .


Question: <ins> 1|       |// Verify that the entry point injected by the test harness doesn't cause 2|       |// weird artifacts in the coverage report (e.g. issue #10749). 3|       | 4|       |// compile-flags: --test 5|       | 6|       |#[allow(dead_code)] 7|      0|fn unused() {} 8|       | 9|      1|#[test] 10|      1|fn my_test() {} </ins>

However, I couldn’t get that to work, because is unstable and can't necessarily be used by the crate it is being injected into. So I think the fix will involve having the instrumentor detect and skip code with dummy spans.
label +A-code-coverage
fixes the overflow, which gets rid of the duplicate line. However, the instrumentor still ends up emitting an empty region from (1,1) to (1,1) for the test harness's , so I'd still like to find a way to avoid instrumenting that function.
I think the empty region now confusing the reporter in more subtle ways, because now I see weird stuff like this: It makes sense that line 1 is “covered” (via the injected ), but it's strange that lines 2 and 3 also have non-zero counts.
It looks like does have special handling for empty regions, but it doesn't properly anticipate the first region being empty, and ends up in a slightly confused state.


Question: sym::coverage => self.check_coverage(hir_id, attr, span, target), sym::non_exhaustive => self.check_non_exhaustive(hir_id, attr, span, target), sym::marker => self.check_marker(hir_id, attr, span, target), <del> sym::target_feature => self.check_target_feature(hir_id, attr, span, target), </del> <ins> sym::target_feature => self.check_target_feature(hir_id, attr, span, target, attrs), </ins> sym::thread_local => self.check_thread_local(attr, span, target), sym::track_caller => { self.check_track_caller(hir_id, attr.span, attrs, span, target)

This works (but it shouldn't): similar to , cc (tracking issue) label T-lang T-compiler C-bug I-unsound F-targetfeature11
cc , author of Note that this is about the nostd panic handler, not about the function. This fails as it should: gives
ugh we really need a way to make sure that every single "this is called by rust" function gets a check... I assume that these functions can't be unsafe, so I guess those checks are a food way to start looking and make sure to deduplicate the logic there?
Yeah sadly we do need to make sure, not just for the constructs that we have now but also it needs to be kept in mind for the future constructs we add or stabilize. A lot thankfully goes through either the trait system (operators or the GlobalAlloc trait used by ) or function pointers (alloc error hook, std panic hook). Functions that you can make callable solely by setting an attribute, those are rare. The best list of lang items I could find was in the , so that would be a great start for such an exhaustive search. Thankfully most of them are unstable, but still it needs to be addressed for each of them before stabilization (if that is a target).
WG-prioritization assigning priority (). label -I-prioritize +P-medium
label +requires-nightly
There is also another table of lang items in the source code, .


Question: }; } ast::UnNot => { <del> oprnd_t = structurally_resolved_type(fcx, oprnd.span, oprnd_t); if !(ty::type_is_integral(oprnd_t) || ty::get(oprnd_t).sty == ty::ty_bool) { oprnd_t = check_user_unop(fcx, "!", "not", tcx.lang_items.not_trait(), expr, &**oprnd, oprnd_t); </del> <ins> if !ty::type_is_bot(oprnd_t) { oprnd_t = structurally_resolved_type(fcx, oprnd.span, oprnd_t); if !(ty::type_is_integral(oprnd_t) || ty::get(oprnd_t).sty == ty::ty_bool) { oprnd_t = check_user_unop(fcx, "!", "not", tcx.lang_items.not_trait(), expr, &**oprnd, oprnd_t); } </ins> } } ast::UnNeg => { <del> oprnd_t = structurally_resolved_type(fcx, oprnd.span, oprnd_t); if !(ty::type_is_integral(oprnd_t) || ty::type_is_fp(oprnd_t)) { oprnd_t = check_user_unop(fcx, "-", "neg", tcx.lang_items.neg_trait(), expr, &**oprnd, oprnd_t); </del> <ins> if !ty::type_is_bot(oprnd_t) { oprnd_t = structurally_resolved_type(fcx, oprnd.span, oprnd_t); if !(ty::type_is_integral(oprnd_t) || ty::type_is_fp(oprnd_t)) { oprnd_t = check_user_unop(fcx, "-", "neg", tcx.lang_items.neg_trait(), expr, &**oprnd, oprnd_t); } </ins> } } }

Taking a look.
Probably the best fix for now is to disallow deref of outright. I'll work up a PR that fixes this and a few other ICEs surrounding .
This is fixed with a test, closing.


Question: #[unsafe_destructor] //~^ ERROR `#[unsafe_destructor]` does nothing anymore <del> //~| HELP: add #![feature(unsafe_destructor)] to the crate attributes to enable // (but of couse there is no point in doing so) </del> impl<'a> Drop for D<'a> { fn drop(&mut self) { } }

Steps to reproduce: The output of is: does as suggested by the message, but that fails too (as expected): Proposed fix: in the beta and stable channels (i.e. whenever is forbidden), the message that suggests adding should not be shown. (Clean up the test case with .) CC
Gonna milestone this real quick, as it seems quite important.
I might be able to whip up a quick fix, though I'm not 100% sure about testing it properly ... (I've never actually tried building something for a non-dev release channel before...)
after chatting with it seems like I have a patch, building it now
gonna leave to it
Hello good Rust folks :smile: Before the beta, I used which is in . Is there any way to use this trait during the beta ? I'm not sure how I can get the code to compile. Thanks for any tip / hints you can offer :+1:
Hi Commenting on random unrelated issues is usually not the right thing to do. You should rather open a new issue, or ask on . But to answer your question anyway, that trait only has : … and is stable and can be used on beta. So I’d recommend you copy/paste the trait into your code, or make a function.
Thanks for taking the time to answer. I appreciate it. I don't see how this is unrelated. This is related, since the code I'm talking about used to compile with and the compiler suggests to do that, during the beta period. Thanks for your tip on copying the function :+1: I guess I'll just do that if nothing better is available and change this again when the trait is stable.
This specific issue is about fixing one of the compiler’s error message, not about fixing code that triggers that error. It really helps everyone to keep discussions on topic.
Alright. I understand. I'll make sure to open a new issue or go on StackOverflow next time if appropriate. Thanks again :+1:
This doesn't seem to be properly fixed in the beta channel. I'm still being recommended to add in the errors, and then told it's not available in the beta channel. Rust version: The code I used (snappy example in the docs with the extra addition on the first line:
This happened after Beta release.


Question: #[unsafe_destructor] //~^ ERROR `#[unsafe_destructor]` does nothing anymore <del> //~| HELP: add #![feature(unsafe_destructor)] to the crate attributes to enable // (but of couse there is no point in doing so) </del> impl<'a> Drop for D<'a> { fn drop(&mut self) { } }

We'll see the effect of this patch in 1.0 and afterwards Beta, etc.
Whoops, I thought this made it in before beta. Thanks!
are there plans to release updates to the beta channel within a given 6 weeks cycle? Either this one or in the future.
I'm certain there will be updates; see discussion from last night here:
So how does one fix this error? I'm a new user of the rust library and I can't seem to use the collections library during the beta due to this problem. Given this git issue is a top google result, it would be nice if there were a solution here. Edit: Looks like the solution is to switch to the rust nightly. Is the entire collections library off-limits in the beta?
by design, you have access to the parts of that are re-exported from (and are stable).


Question: <ins> // Copyright 2015 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. #![feature(reflect_marker)] use std::any::TypeId; use std::marker::Reflect; use std::rc::Rc; type Fp<T> = Rc<T>; struct Engine; trait Component: 'static + Reflect {} impl Component for Engine {} trait Env { fn get_component_type_id(&self, type_id: TypeId) -> Option<Fp<Component>>; } impl<'a> Env+'a { fn get_component<T: Component>(&self) -> Option<Fp<T>> { let x = self.get_component_type_id(TypeId::of::<T>()); None } } trait Figment { fn init(&mut self, env: &Env); } struct MyFigment; impl Figment for MyFigment { fn init(&mut self, env: &Env) { let engine = env.get_component::<Engine>(); } } fn main() {} </ins>

Error: Reproduces with:
cc
I just now noticed that does not actually yet allow unsized . Might be related.
This doesn't compile, but it doesn't ICE.
It looks like no longer exists. Did it get replaced by something else? I imagine there's not much value in adding a regression test with a broken import
from


Question: <ins> // issue-52240: Can turn immutable into mut with `ref mut` enum Foo { Bar(i32), } fn main() { let arr = vec!(Foo::Bar(0)); if let (Some(Foo::Bar(ref mut val)), _) = (&arr.get(0), 0) { //~^ ERROR cannot borrow field of immutable binding as mutable *val = 9001; } match arr[0] { Foo::Bar(ref s) => println!("{}", s) } } </ins>

I expected just a compiler error . Compiler panicked: Meta
This is fixed in the beta version (1.30).


Question: <ins> // issue-52240: Can turn immutable into mut with `ref mut` enum Foo { Bar(i32), } fn main() { let arr = vec!(Foo::Bar(0)); if let (Some(Foo::Bar(ref mut val)), _) = (&arr.get(0), 0) { //~^ ERROR cannot borrow field of immutable binding as mutable *val = 9001; } match arr[0] { Foo::Bar(ref s) => println!("{}", s) } } </ins>

This lets you get a mutable reference to an immutable value under a specific case. Code: From what I can tell, the tuple and at least two depths of Enums are necessary, along with an on the right side. There's probably other variations, but that seems to work well enough. Expected output would be a compile error, instead output is This works on both stable and nightly
would fix this as well?
Fixed by . Off: I wonder why we can't ship nll yet. It would solve so many issues right now, because of the match ergonomics sigh Match ergonomics produces roughly 10% of all errors/unsoundness/ICEs atm (at least it feels like this)
Yes correctly fixed this issue.


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

Implemented in rust impl<T: PartialEqVec<T{ pub fn remove_item(&mut self, item: &T) -Option<T{ /…/ } }
PR moved to due to reasons
Comments from original thread: think that we should add this method to too. desired?
for you can simply do
I meant specifically a method that searches for the item from the end of the vec instead of the beginning
What do you think about adding ? Just as reduces the runtime complexity from O(n) to O(1) compared to , would reduce it from O(n + (n-m)) to O(n).
I like .
It would be nice if this was more generic. let v: Vec<String= Vec::new(); v.removeitem("s"); <-- fails because &str is not a &String we really want the removeitem "item: &T" to be "something that we can compare equality with the type in the container". This would let remove_item() walk the T items, compare equality, and remove if equal.
Seems reasonable to change the signature to
Reviewing the naming used in method names and the docs, it would seem that iterators yield items while vecs contain elements. Considering that we then we should also remove elements and the method should be called . That name is a bit long so I'd propose simply . However I wonder if we should favor a more general , or have both.
Any plan to stabilize this?
This has been in nightly for a year with no issue reported on the method itself. There are proposals for additional methods, but that shouldn’t block this one. Please submit separate PRs or RFCs. fcp merge
Team member has proposed to merge this. The next step is review by the rest of the tagged team members: [x] [x] [ ] [x] [x] [x] [x] Concerns: resolved by Once a majority of reviewers approve (and none object), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See for info about what commands tagged team members can give me.
Are we switching to a bound?
Oops, sorry I missed that. Yes, let’s.


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

Again here, as a maintainer of collections that offer the Vec and VecDeque APIs I'd like at least a summary comment explaining what this method does, why this design was followed, alternatives, and addressing the issues mentioned here that have received zero replies: should this method be to ? : naming issue: why s instead of elements? why instead of , etc.
concern rationale-and-vecdeque Just gonna formally register concern above
Not an issue with the method per se, but it may need to be very clearly documented that the reference is not supposed to be to an item that is in the already, as it creates impossible borrow-checker conundrum. Users coming from the C world of pointers but no proper equality comparison, may be confused by this method, e.g. The name mentioned previously would help.
as the proposer for FCP, do you have thoughts on concern?
My thinking is that the suggested by would sidestep most of the issues here.
cc re.
I don’t have a strong desire for this particular feature myself, I proposed FCP as an effort to reduce the number of features in "unstable limbo". That said: Regarding , sure, I don’t see a reason not to add it there as well. as proposed in sounds good to me. It is more general, and goes with precedent of also taking a boolean callable predicate rather than relying on . (Even further, the precedent of not having a method like that would rely on .)
I notice two things: are a lot of methods similar to this we could add, and its not obvious to me which set of those methods is the ideal set. has sat in FCP concern limbo for 8 months without anyone complaining. I think we should not stabilize this just because it exists, but instead someone should come up with a well justified explanation of exactly what the best "find and remove" set of methods of vec-likes would be.
Good points. (which is stable) and also fit the "find and remove" description, and we had a similar concern about the combinations of filtering v.s. non-filtering and self-exhausting on drop () v.s. not.
resolve rationale-and-vecdeque I don't want to personally be on the hook for blocking this any more
:bell: This is now entering its final comment period, as per the .


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

:bell:
The final comment period, with a disposition to merge, as per the , is now complete. As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed. The RFC will be merged soon.
I still think this should be called instead of .
My problem with that name is that it only removes the first matching item, not all that are (though I haven't read the relevant RFC to know whether the name has been hashed out already; I assume it has been).
I don't think the naming issue has been resolved. The implementation is still using the name. then?
Can someone clarify what the status of this is wrt. the conversation above?
An example: I'm writing a proc macro attribute, and amongst the tokens, I expect other attribute to be there. This would be useful to add:
Until we sort this out, you can use
Ping. What's the status of this? Could we stabilize something?
? Given we already have drainfilter for accepting a predicate, it would be nice to have a method that removed a single object from the vector (if there). Removing something from a vec is exceedingly common code. Getting the position and then removing that position is longwinded for such a common operation. (Btw, I think bit of naming is excellent as it highlights that there may be others still in the vec - a method name that prompts one to think is a good thing.)
I use for this, and haven't found it too cumbersome. It differs in that it removes all copies of a given item, but is very easy for many purposes.
Retain everything but the object? As work-arounds go that's shorter, but it's not ideal for expressing intent. Still keen on and .
Just to bring up a different opinion: how about removing this method instead of stabilizing it? While yes, it would be convenient to have, it might not be worth it. For one, is not a good name, as many already said. The name doesn't imply that the first item from the start is removed. is better in that regard, but still doesn't feel completely right. More importantly, if we have , we should certainly also have . Having one but not the other feels arbitrary to me and makes for a surprising API (that's bad).


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

Similarly, we would also want to add the variant of both of those methods. Potentially, we also want to add a variant that removes all items equal to the given . And as also already mentioned, we can also add all those methods to . And why not (without the versions)? Consequently, we would have to add 10 or 15 new methods. Adding fewer would make the API inconsistent IMO. All the functionality can be implemented with very little extra code with iterators.
How do you propose this be implemented with iterators? How about this signature: This uses to make it clear exactly what is removed. The argument and the return type makes it clear that we remove many items. The user has the option of how many to remove ( means all). The returned iterator can be implemented efficiently by shifting the items and then pulling a similar trick (using ) to to yield the removed items.
already mentioned this : I think that one is too complex. Especially when considering the call site, I think it's fairly hard to understand. And the name still does not imply that the search begins at the beginning, which is a big nono for me.
Removing an item from a vec is a very common codepath. Somehow it needs to be a one liner. Having swapremovefirst() and not having removefirst() would be nudging people in the direction of great performance. That seems quite rustic to me. swapremovelast is interesting as there maybe no swap needed if it happens to be the last item - cute. Just have those two functions. That’s the 80% case covered. People who wish to maintain order will just have to have slightly more code. On Fri, 15 Nov 2019 at 19:20, Lukas Kalbertodt <:
I don't understand the focus on removing here. Vec has a lot more members taking an index than and , and only a few to get hold of an index value ( variants and , sort of). Most of the complication in the "workaround" for this remove_item is finding the first index of something: v.iter().position( n == 2) Not too bad, the reminds you it's a linear search, but could be easier.


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

<delWorse for the last index: ().rev().position( v.len() - i - 1) Contrast to the and in that famous vector called string that (ugly names but at least they convey that a search is involved). I've vary rarely needed this, I don't advocate making linear searches easy, it just seems more useful to try to make searching easier, before making search-and-removing easier.
(so does ). And even if it didn't exist, that has no relevance to whether should exist or not, they're separate features, so they can both exist, it isn't either/or. (I personally have had many cases where would have been useful, it's a common operation in any language.)
Waaait! It's getting stabilized without fixing the confusing name! Please please don't call it , as this is the same name as in other languages that can remove item from an array by presenting an item from the same array. Rust's version can't do that due to borrow checker and it's a trap for users.
I absolutely wouldn't call it a trap.
It seems like many people agree that the name should at least be up for debate again. Really unfortunate how the name discussion was somehow forgotten during FCP. So I guess we should revert stabilization as soon as possible so it won't end up in beta?
Sounds reasonable. Maybe someone wants to volunteer to lead the process about settling on a name for this ?
The next release is scheduled for Jan 30th. So we have about 3 weeks to figure out a new name.
I went through the thread again and it seems like the following names are suggestions for the method as it currently exists: (iterators have "items", Vec has "elements") - Personally, I would absolutely include , as that's an important information and . I have no preference between and . However, from reading the thread again it seems there are plenty of other concerns and suggestions that haven't been resolved yet: Adding similar methods: ? ? Replace the method with:  (although I don't understand that one. Is it just a with flipped predicate? In that case I don't think it's useful. If it just removes the first element, then absolutely needs to be in the name IMO.) Do not stabilize this method at all: ,
mentioned : also raised some more concerns , and I raised some concerns .


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

I don't see where these concerns have been resolved. From re-reading this whole discussion, it isn't clear to me what the goal of adding this method is nor what problem does this method solve or whether this is a problem worth solving. What's more or less clear to me is that there is at least some design work to be done to at least ensure that libstd exposes a consistent API, and that sounds like this would warrant an RFC to me. The current discussion about using a method hints that these APIs might not only want to be consistent for the ordered collections (Vec, VecDeque, List) for which a notion of a "first" element makes sense, but might also want to be consistent with the e.g. and methods of slices. The main arguments for FCPing this appear to be that this has sit on nightly for too long without anybody complaining, and the main argument for stabilizing this has been that this has been in FCP for too long. I think it would be better to just encourage and support those that want to land this feature to write a small RFC for it. If somebody is interested in doing that, I would be able to help and give feedback.
Unless a concern is made with by a relevant team member, then it won't stop FCP. And it won't go into FCP unless the majority of team members have voted for it (and there aren't any formal concerns listed). So the fact it passed FCP means that all relevant team members that they were okay with the current design and did not have any outstanding concerns at the time. Things do not go into FCP simply because it's been "sitting around too long". Of course if any team members do have any concerns, now would be the best time to make them.
Mistakes happen. And to me this thread clearly looks like many concerns were overlooked accidentally and no one explicitly marked them as concerns for rfcbot. Luckily those mistakes were caught.
Reopening because
The current signature is missing a ?Sized bound. Could I ask for a PR to fix the bound and add a test that covers remove_item("...") on a Vec<String? This use case was requested in and
Separately: I am leaning toward removing removeitem.


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

I agree with and The currently design involves: start with a reference to a value not in the vec, use its PartialEq impl to do a linear scan, remove the first found, shift everything after the removed element. To generalize almost all of the discussion above, people are questioning whether the conjunction of all 5 of these decisions is really as common as a name like removeitem would suggest, whether a different permutation of choices might be more widely applicable, and how to adjust naming to leave room for all the other equally or more common permutations: ones where the ref we want to remove is a ref to a vec element, or we want to remove by FnMut instead of PartialEq, or we want a binary search, or we want to remove the last, or all matches, or we want the more efficient swapremove behavior. Fortunately Vec already supports all permutations of these use cases equally well, with nice independent APIs for searching and removing. Many people have voiced opinions equivalent to "removing an item from a vec is so common that there absolutely must be a function for it". I think what they mean is that the union of all permutations of the above 5 choices is common, which is true; they don't necessarily mean the specific choices that go into removeitem as it exists would justify a method specific to those choices. points out that satisfying the set of use cases which all together are common would take a much larger number of new methods.
Per , I think we should go ahead and remove . fcp close
That is not what I meant. When I said that I need in my code, I meant exactly that: that I could take my existing code and replace it with and it would have exactly the same behavior, because I really do need specifically, not the other fancier methods. I'm perfectly fine with changing the name so that we can accommodate other fancier methods in the future, but why would that mean that we shouldn't have at all?
fcp cancel
proposal cancelled.
Per , I think we should go ahead and remove . fcp close
Team member has proposed to close this. The next step is review by the rest of the tagged team members: [x] [x] [x] [x] [ ] [x] No concerns currently listed. Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period.


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

If you spot a major issue that hasn't been raised at any point in this process, please speak up! See for info about what commands tagged team members can give me.
Checking KodrAus’ checkbox per
:bell: This is now entering its final comment period, as per the . :bell:
The final comment period, with a disposition to close, as per the , is now complete. As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.
Since we've merged the deprecation would we like to close this tracking issue now? Or keep it open until the unstable deprecated method is removed entirely?
I think keeping this open until we removed the method is a good idea. How long do we want to wait with that by the way? I guess a couple of cycles is sufficient?
Before closing, it would be great if someone could suggest a "one clean and obvious" way to remove the first/last occurance of an item from a Vector. Irrespective of the arguments made here, a method removing the first/last occurance of an item is provided across all major programming languages, and is to be "expected" Anyone new to rust is bound to google "remove from vec rust" and end up on this discussion which would only leave them more confused.
should answer those questions. But here is a copy of my answer for convenience: You can of course handle the case however you like (panic and ignoring are not the only possibilities). Like the first element, but replace with . Remember that has a runtime of O(n) as all elements after the index need to be shifted. has a runtime of O(1) as it swaps the to-be-removed element with the last one. If the order of elements is not important in your case, use instead of !
It might be worth adding more examples (maybe all of the ones above) to the docs.
I'd like to add those to the docs, should they go along the example that we currently have?
What examples are you referring to? I could imagine those "remove examples" either going on the type (as a new section "Removing elements" or something like that) or directly on the method (below the existing docs). And by the way, feel free to add (parts of) my text/examples verbatim.
Thank you.


Question: #![feature(nll)] #![feature(set_stdio)] #![feature(test)] <del> #![feature(vec_remove_item)] </del> #![feature(ptr_offset_from)] #![feature(crate_visibility_modifier)] #![feature(const_fn)]

I was referring to those "remove examples" as to whether I should append them to what we currently have in docs for , put them somewhere else or perhaps modify examples for to include removal of specific element
That sounds fine to me. Feel free to just open a PR and we can still see about the specifics then :)


Question: } } <del> #[unstable(feature = "panic_info_message", issue = "66745")] </del> <ins> #[stable(feature = "panic_info_message", since = "CURRENT_RUSTC_VERSION")] </ins> impl Display for PanicMessage<'_> { #[inline] fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {

was closed when stabilized the corresponding language feature, but we didn’t realize that it was also the tracking issue for this standard library feature: History: [x] Original tracking issue: [x] Discussion of payload vs message [x] Making .message() infallible: [x] Split core/std PanicInfo into two types: This made core::panic::PanicInfo::message() infallible. [x] Use opaque return type: [x] FCP [x] Stablization PR: Unresolved questions: [x] Should it be infallible? Yes, by making std::panic::PanicHookInfo a different type. [x] What should the return type be? or an opaque ? The first is simpler, but the latter allows a bit more flexibility for future changes.
Instead of making a PR go through the queue to fix the tracking issue, should we stabilize this method? fcp merge The doc-comment is slightly wrong or out of date. Its second line shoudl be removed. always creates a where is , regardless of the number of arguments given. In the single-argument case, that argument is required to have type . At first returning seemed unusual to me and I considered that we could make the method return instead, on the basis that calling its impl is almost the only useful thing to do with a . But has been stable and documented as the return type of since 1.0.0, so maybe it’s fine.
Team member has proposed to merge this. The next step is review by the rest of the tagged team members: [x] [ ] [ ] [x] [x] [ ] [ ] [ ] Concerns: single-arg core::panic () Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See for info about what commands tagged team members can give me.
The module also links to that closed tracking issue. Let’s consider the pFCP above to also include stabilizing it. ( is stable.)
concern single-arg core::panic Should we change libcore’s macro so that its single-argument form creates a with a instead of one with a ?


Question: } } <del> #[unstable(feature = "panic_info_message", issue = "66745")] </del> <ins> #[stable(feature = "panic_info_message", since = "CURRENT_RUSTC_VERSION")] </ins> impl Display for PanicMessage<'_> { #[inline] fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {

CC Pushing this idea further, it’s tempting to maybe remove entirely and instead have a whose dynamic type can be . But that doesn’t work because is a method of and is not .
I thought the point of the message field was that core can't make a payload since it can't allocate?
The struct is: Both the and fields involve borrowing. As far as is concerned, they could both be borrowing form a stack frame. (And as far as I understand they are, in practice today.) It’s in the case of unwinding that there’s an owned that can return, which requires allocating.
Based on the timing of it looks like you may have thoughts on this :)
Ah, goes into how and why the panic handler in libstd (which is called by if libstd is linked) ignores the it receives. We could probably change this but it gets tricky: while most implementations of for environments would be fine with receiving a borrowed payload, libstd wants to potentially take ownership and box it for unwinding.
I have zero recollection for why this is the way it is, and I'm not really particularly interested in doing all the archaeology to dig up why it is the way it is. I'm not a huge fan of just stabilizing things because they happen to be there, but I don't really see why we wouldn't want to stabilize this. If there were a reason to not stabilize this though an investigation would presumably turn that up, but I'm not up to do that investigation myself.
That’s totally fair. I’m confident that this was more likely forgotten than deliberately left unstable. If deliberate we would have kept the tracking issue open or made a new one for the remaining bits. This is what lead me to propose stabilization. Having dug a little more, and thanks to Ralf’s blog post, I think we may want at some point to revisit what data we expect to contain or not in various situation. In particular it could be interesting to extend to support payloads other than and make it closer to . Given those possibly-desirable changes, it may not be the time to add more constraints: fcp cancel
proposal cancelled.
Lol, I had no idea. ;) So, indeed, I was wondering if we could do something about the duality of the and fields in . I assume we cannot change the fact that the same type is used both of panic handlers and panic hooks.


Question: } } <del> #[unstable(feature = "panic_info_message", issue = "66745")] </del> <ins> #[stable(feature = "panic_info_message", since = "CURRENT_RUSTC_VERSION")] </ins> impl Display for PanicMessage<'_> { #[inline] fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {

Concretely, I was thinking of adjusting somewhat like this: That would at least remove the need for the hack in . (The hack would likely move to instead, but that is a smaller hack IMO: the hack is now not encoded in the state of any more, just in its dynamic API.) I think this would retain all current functionality while clarifying the invariant of wrt. the payload (and explicitly calling the message a "payload"; right now it seems to be something that sits next to the payload which is inaccruate). But there are enough subtleties here that we'll only really know once someone implements this. With this change, the panic hook would always get a . We should likely provide a method somewhere in libstd to factor out this code: I was imagining something like an extension trait on with a type like . However, the panic hook is not the only place where that conversion is useful; another situation is code that caught a panic and wants to extract the message. I expect most instances of that to just handle payloads, not knowing that payloads are also common (that is certainly what happened when I wrote such code). So ideally we'd have a method that takes and returns , but I do not have a good idea where to put that. This is the hard part, as we cannot use . I wonder if we can use a take-based approach, similar to ? Conceptually, would put the panic into an , and somehow pass an to the panic handler, and the implementation of said handler could then the payload if it needs full ownership (like for unwinding). Except the panic handler cannot be generic, so it would have to be , which is not a thing. But with enough unsafe code we could re-implement something that behaves like that. I don't see any way to do this entirely safely; the panic handler that wants to take out the payload and put it somewhere needs to dynamically determine the size of the payload and arrange for there to be enough space. In liballoc, we could provide a safe wrapper for this that puts things into a , but in libcore, I don't think there is a safe API that we could provide to grab ownership.


Question: } } <del> #[unstable(feature = "panic_info_message", issue = "66745")] </del> <ins> #[stable(feature = "panic_info_message", since = "CURRENT_RUSTC_VERSION")] </ins> impl Display for PanicMessage<'_> { #[inline] fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {

But maybe it is enough for the public API to expose ways to borrow the payload (should work for all non-unwinding handlers); if only libstd needs to take the payload (for unwinding) we could keep the unsafe part of the API internal. Also, we certainly do not want a panic hook to the payload out of its . At this point it seems to be quite a problem that panic hook and panic handler both use the same type. In fact, a panic handler likely wants a to be able to things without interior mutability. Is there any way we could make the attribute support both signatures, and then (based on the types of the methods) only -based implementations will actually be able to or the payload?
I agree, but it’s can easily be an inherent method of nor of because those are in libcore which doesn’t have access to . It feels slightly unfortunate that we’d need an extension trait just for this. I considered this yesterday and come to pretty much the same conclusions. To take ownership of a payload of unknown size through a non-generic API we pretty much heap allocation, which for libcore means something like receiving an , unsafely using , and returning that is to be passed to . It’s not pretty, but if only libcore and libstd deal with this internally maybe that’s ok? Is there a use case for a other than libstd’s to take ownership of the payload?
I was thinking of a slightly different API actually: Here, does to put the payload into caller-allocated storage; that storage must have (at least) size and align as given by . What I did not consider is how to get out the vtable, so maybe that higher-order approach is better.
We discussed this in the libs-api meeting today. We concluded that before stabilizing this, we need to make sure it works (doesn't return ) for std::panic!() as well. That is already the case with Rust 2021's std::panic!() (since it's identical to core::panic!() in this edition), but not for Rust 2015/2018's std::panic!(). Once that is fixed, we feel okay with returning a placeholder message for non-string panics (panics from or Rust 2015/2018's ), at which point the function can return an unconditionally, rather than an .


Question: } } <del> #[unstable(feature = "panic_info_message", issue = "66745")] </del> <ins> #[stable(feature = "panic_info_message", since = "CURRENT_RUSTC_VERSION")] </ins> impl Display for PanicMessage<'_> { #[inline] fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {

(And also, should be returned by value, not by reference.)
Any progress on stabilization?
It would great to have this little feature.
Still nothing? What's missing?
can this be stabilized after was resolved in the pull request ?
Yes, soon, hopefully! I've updated the overview at the top of this tracking issue. The main question left before stabilization is the return type of the method. Should this return (as the unstable method does today), or should it return an opaque type that wraps that fmt::Arguments, so we can still change in the future? (In case we want to support different types of no_std panic, such as panicking with an Error or something.)
Can it return or so?
I would vote for an opaque type that would also implement .
Did that in this PR:
merge
Team member has proposed to merge this. The next step is review by the rest of the tagged team members: [ ] [x] [x] [x] [x] No concerns currently listed. Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See for info about what commands tagged team members can give me.
:bell: This is now entering its final comment period, as per the . :bell:
The final comment period, with a disposition to merge, as per the , is now complete. As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed. This will be merged soon.


Question: <ins> // Copyright 2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. fn main() { (return)[0u]; //~ ERROR cannot index a value of type `!` } </ins>

Taking a look.
Probably the best fix for now is to disallow deref of outright. I'll work up a PR that fixes this and a few other ICEs surrounding .
This is fixed with a test, closing.


Question: <ins> // Regression test for https://github.com/rust-lang/rust/issues/70673. // run-pass #![feature(thread_local)] #[thread_local] static A: &u8 = &42; fn main() { dbg!(*A); } </ins>

When running on of the crate, panics: Platform: macos
FYI, this appears to be a macOS-specific bug:
Minimal repro:


Question: } } <ins> fn eq_coroutine_kind(a: Option<CoroutineKind>, b: Option<CoroutineKind>) -> bool { match (a, b) { (Some(CoroutineKind::Async { .. }), Some(CoroutineKind::Async { .. })) | (Some(CoroutineKind::Gen { .. }), Some(CoroutineKind::Gen { .. })) | (Some(CoroutineKind::AsyncGen { .. }), Some(CoroutineKind::AsyncGen { .. })) | (None, None) => true, _ => false, } } </ins> pub fn eq_field(l: &ExprField, r: &ExprField) -> bool { l.is_placeholder == r.is_placeholder && eq_id(l.ident, r.ident)

() Reproduces on the playground using . label +D-incorrect +F-gen_blocks +requires-nightly