Add more tests for the parallel rustc #145384

ywxt · 2025-08-14T07:31:47Z

At the moment, the parallel frontend test cases are severely lacking. Althought some reported issues have been resolved, they haven't been added into the tests.

This PR arranges the resolved ICE issues and adds tests for them.

Whether it is worthwhile to add a separate test suite for the paralel frontend still requires futher discussion. But we are trying coveraging issues being resolved through capability of the existing UI test suite.

Discussion: Zulip

Related issues:

ice: no index for a field #120760
ICE: 'only variances_of returns &[ty::Variance]' #124423 fixed by Use search_for_cycle_permutation to look for variances_of #140358
ICE: only 'variances_of' returns '&[ty::Variance]' #127971 fxied by Use search_for_cycle_permutation to look for variances_of #140358
ice: Unexpected type for constructor #120601 fixed by Avoid follow-up errors and ICEs after missing lifetime errors on data structures #127311

cc @jieyouxu

rustbot · 2025-08-14T07:31:51Z

r? @davidtwco

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rustbot · 2025-08-14T07:31:55Z

Some changes occurred in src/tools/compiletest

cc @jieyouxu

davidtwco

It would be nice if the tests could have slightly more descriptive names, though I appreciate that might be tricky.

src/tools/compiletest/src/runtest.rs

davidtwco · 2025-08-14T13:08:49Z

src/tools/compiletest/src/runtest.rs

@@ -2749,7 +2749,7 @@ impl<'test> TestCx<'test> {
        // Wrapper tools set by `runner` might provide extra output on failure,
        // for example a WebAssembly runtime might print the stack trace of an
        // `unreachable` instruction by default.
-        let compare_output_by_lines = self.config.runner.is_some();
+        let compare_output_by_lines = self.props.parallel_front_end || self.config.runner.is_some();


If this is the only thing that parallel_front_end enables, maybe exposing //@ compare-output-by-lines would be better?

I think that might be better, it's more direct in telling the test reader what the behavior is.

jieyouxu

Thanks. Some nits

jieyouxu · 2025-08-14T13:08:21Z

src/tools/compiletest/src/runtest.rs

@@ -2749,7 +2749,7 @@ impl<'test> TestCx<'test> {
        // Wrapper tools set by `runner` might provide extra output on failure,
        // for example a WebAssembly runtime might print the stack trace of an
        // `unreachable` instruction by default.
-        let compare_output_by_lines = self.config.runner.is_some();
+        let compare_output_by_lines = self.props.parallel_front_end || self.config.runner.is_some();


Problem: please document this directive and what it does in rustc-dev-guide.

tests/ui/parallel-rustc/cycle_crash.rs

jieyouxu · 2025-08-14T13:15:22Z

src/tools/compiletest/src/runtest.rs

@@ -2749,7 +2749,7 @@ impl<'test> TestCx<'test> {
        // Wrapper tools set by `runner` might provide extra output on failure,
        // for example a WebAssembly runtime might print the stack trace of an
        // `unreachable` instruction by default.
-        let compare_output_by_lines = self.config.runner.is_some();
+        let compare_output_by_lines = self.props.parallel_front_end || self.config.runner.is_some();


Remark: note that this has two potential issues:

This can mask genuine bugs, where a symptom may be diagnostics reordering.

The parallel front-end tests are still potential flaky.

I don't love (2) too much, but I recognize the pragmatic need for having some test coverage, so I don't want to block this.

My reservation is primarily that these tests can potentially fail someone else's PR, or a rollup, and can be rather confusing.

tests/ui/parallel-rustc/ty-variance-issue-127971.rs

tests/ui/parallel-rustc/undefined-function-issue-120760.rs

jieyouxu · 2025-08-14T13:19:41Z

tests/ui/parallel-rustc/undefined-function-issue-120760.rs

Remark: this is one of those that we do not know if it was genuinely fixed.

Should I remove it ?

let's keep it for now, will need to disable it if it's not actually fixed

tests/ui/parallel-rustc/unexpected-type-issue-120601.rs

davidtwco · 2025-08-14T15:08:31Z

Will re-assign to @jieyouxu, feel free to r=davidtwco,jieyouxu when you're happy with these changes

r? @jieyouxu

jieyouxu · 2025-08-14T15:11:58Z

@rustbot author

rustbot · 2025-08-14T15:12:03Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

rustbot · 2025-08-15T06:05:58Z

The rustc-dev-guide subtree was changed. If this PR only touches the dev guide consider submitting a PR directly to rust-lang/rustc-dev-guide otherwise thank you for updating the dev guide with your changes.

cc @BoxyUwU, @jieyouxu, @Kobzol, @tshepang

ywxt · 2025-08-15T07:21:18Z

@rustbot ready

jieyouxu

Thanks

jieyouxu · 2025-08-15T11:28:39Z

@bors r+ rollup=never (parallel rustc tests)

bors · 2025-08-15T11:28:43Z

📌 Commit 36ab1bf has been approved by jieyouxu

It is now in the queue for this repository.

rustbot assigned davidtwco Aug 14, 2025

davidtwco reviewed Aug 14, 2025

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ywxt force-pushed the parallel-tests branch from 99d7555 to 4c49822 Compare August 14, 2025 10:33

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rustbot assigned jieyouxu and unassigned davidtwco Aug 14, 2025

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Aug 14, 2025

ywxt force-pushed the parallel-tests branch from 4c49822 to 02c764a Compare August 15, 2025 06:05

rustbot added the A-rustc-dev-guide Area: rustc-dev-guide label Aug 15, 2025

ywxt force-pushed the parallel-tests branch from 02c764a to 28962e3 Compare August 15, 2025 06:12

ywxt added 2 commits August 15, 2025 14:16

Add the directive compare-output-by-lines

e17989e

Add more tests

36ab1bf

ywxt force-pushed the parallel-tests branch from 28962e3 to 36ab1bf Compare August 15, 2025 06:17

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Aug 15, 2025

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bors 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 Aug 15, 2025

Add more tests for the parallel rustc #145384

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