Suggest installing `rust-src` when standard library source is unavailable by sladyn98 · Pull Request #158191 · rust-lang/rust

sladyn98 · 2026-06-20T21:29:06Z

Why

A lot of diagnostics point at a span inside the standard library e.g. required by a bound in std::iter::Iterator::sum``, or JoinHandle::join takes ownership of the receiver. For toolchains installed via `rustup` std is shipped with its paths remapped to `/rustc//library/...` and the source itself is not included unless the `rust-src` component is installed.

So when an error references std, rustc tries to render that span, can't find the source on disk, and falls back to printing just the bare remapped path with no code:

  error[E0277]: a value of type String cannot be made by summing an iterator ...
   --> src/main.rs:2:20
    ...
  note: required by a bound in std::iter::Iterator::sum
   --> /rustc/<hash>/library/core/src/iter/traits/iterator.rs:3669:4

For the user this is a dead end: the path doesn't exist locally, there's no surrounding code. It is fixable: rustup component add rust-src makes the source available, after which the same diagnostic renders the real std snippet. But that capability is
invisible. This PR closes that discoverability gap by suggesting it at exactly the moment it would help.

Closes #156402

rustbot · 2026-06-20T21:29:09Z

rustc_errors::annotate_snippet_emitter_writer was changed

cc @Muscraft

rustbot · 2026-06-20T21:29:11Z

r? @tiif

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sladyn98 · 2026-06-20T21:29:50Z

r? @estebank

estebank

This looks good! Would you have time to address the nitpicks? If not, we can likely land this as is.

View changes since this review

…able When a diagnostic points into the standard library but its source isn't available locally (e.g. a rustup toolchain without the `rust-src` component), the emitter can only print the bare remapped path with no snippet. Emit a one-time `help` suggesting `rustup component add rust-src` so the next build can show the source. The hint is shown at most once per compilation (tracked with an `AtomicBool` on the emitter) and only for remapped std paths. It is added to both the primary and child-note fallbacks, since std spans usually appear in child "required by a bound in `core::...`" notes.

sladyn98 · 2026-06-29T20:12:12Z

@estebank I think we are good to merge this ?

sladyn98 · 2026-07-27T20:19:35Z

@estebank Any updates on this ?

estebank · 2026-09-09T21:29:55Z

@bors r+

rust-bors · 2026-09-09T21:29:58Z

📌 Commit 55b1daf has been approved by estebank

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 5. This pull request will be tested once the tree is reopened.

Reason for tree closure: error: could not lock gitconfig

…t, r=estebank Suggest installing `rust-src` when standard library source is unavailable ### Why A lot of diagnostics point at a span *inside* the standard library e.g. `required by a bound in `std::iter::Iterator::sum``, or `JoinHandle::join takes ownership of the receiver`. For toolchains installed via `rustup` std is shipped with its paths remapped to `/rustc/<hash>/library/...` and the source itself is **not** included unless the `rust-src` component is installed. So when an error references std, rustc tries to render that span, can't find the source on disk, and falls back to printing just the bare remapped path with no code: ``` error[E0277]: a value of type String cannot be made by summing an iterator ... --> src/main.rs:2:20 ... note: required by a bound in std::iter::Iterator::sum --> /rustc/<hash>/library/core/src/iter/traits/iterator.rs:3669:4 ``` For the user this is a dead end: the path doesn't exist locally, there's no surrounding code. It *is* fixable: `rustup component add rust-src` makes the source available, after which the same diagnostic renders the real std snippet. But that capability is invisible. This PR closes that discoverability gap by suggesting it at exactly the moment it would help. Closes rust-lang#156402

Rollup of 5 pull requests Successful merges: - #158191 (Suggest installing `rust-src` when standard library source is unavailable) - #162122 (Put manual calls of Enzyme intrinsics behind a feature gate) - #162553 (Revert "Skip rustc book on i686") - #162562 (Add regression test for higher-ranked fn pointer trait impl mismatch errors) - #162518 (Add a revision for previously fixed solver issue)

Suggest installing `rust-src` when standard library source is unavailable ### Why A lot of diagnostics point at a span *inside* the standard library e.g. `required by a bound in `std::iter::Iterator::sum``, or `JoinHandle::join takes ownership of the receiver`. For toolchains installed via `rustup` std is shipped with its paths remapped to `/rustc/<hash>/library/...` and the source itself is **not** included unless the `rust-src` component is installed. So when an error references std, rustc tries to render that span, can't find the source on disk, and falls back to printing just the bare remapped path with no code: ``` error[E0277]: a value of type String cannot be made by summing an iterator ... --> src/main.rs:2:20 ... note: required by a bound in std::iter::Iterator::sum --> /rustc/<hash>/library/core/src/iter/traits/iterator.rs:3669:4 ``` For the user this is a dead end: the path doesn't exist locally, there's no surrounding code. It *is* fixable: `rustup component add rust-src` makes the source available, after which the same diagnostic renders the real std snippet. But that capability is invisible. This PR closes that discoverability gap by suggesting it at exactly the moment it would help. Closes #156402

rust-bors · 2026-09-10T03:30:13Z

💔 Test for 8a723e4 failed: CI. Failed job:

auto - test-x86_64-gnu-llvm-22-2 (web logs, enhanced plaintext logs)

rust-log-analyzer · 2026-09-10T04:03:43Z

The job test-x86_64-gnu-llvm-22-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

help: if you don't care about this missing field, you can explicitly ignore it
   |
67 -             theme,
68 -         } = self;
67 +             theme, rust_src_hint_shown: _ } = self;
   |
help: or always ignore missing fields here
   |
67 -             theme,
68 -         } = self;

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 20, 2026

rustbot assigned tiif Jun 20, 2026

rustbot assigned estebank and unassigned tiif Jun 20, 2026

sladyn98 changed the title ~~Suggest installing rust-src when standard library source is unavail…~~ Suggest installing rust-src when standard library source is unavailable Jun 20, 2026

estebank approved these changes Jun 21, 2026

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Comment thread compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs Outdated

Comment thread compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs Outdated

sladyn98 force-pushed the issue-156402-rust-src-hint branch from 487bec6 to 55b1daf Compare June 21, 2026 20:29

sladyn98 requested a review from estebank June 21, 2026 20:32

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 9, 2026

Zalathar mentioned this pull request Sep 10, 2026

Rollup of 5 pull requests #162572

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rust-bors Bot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Sep 10, 2026

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Suggest installing `rust-src` when standard library source is unavailable - #158191

Suggest installing `rust-src` when standard library source is unavailable#158191
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