compiletest: add implied `needs-target-std` for `codegen` mode tests unless annotated with `#![no_std]`/`#![no_core]` #151294

jieyouxu · 2026-01-18T11:12:24Z

A codegen mode test (such as codegen-llvm test suite) will now by default have an implied //@ needs-target-std directive, unless the test explicitly has an #![no_std]/#![no_core] attribute which disables this behavior.

When a test has both #![no_std]/#![no_core] and //@ needs-target-std, the explicit //@ needs-target-std directive will cause the test to be ignored for targets that do not support std still.

This is to make it easier to test out-of-tree targets / custom targets (and targets not tested in r-l/r CI) without requiring target maintainers to do a bunch of manual //@ needs-target-std busywork.

Context: #t-compiler/help > `compiletest` cannot find `core` library for target != host

Implementation remarks

This is an alternative version of #150672, with some differences:

This PR applies this implied-needs-target-std behavior to all codegen test mode tests.
This PR does the synthetic directive injection in the same place as implied-codegen-run directives. Both are of course hacks, but at least they're together next to each other.

rustbot · 2026-01-18T11:12:27Z

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, @Kobzol, @tshepang

rustbot · 2026-01-18T11:12:29Z

r? @Zalathar

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jieyouxu · 2026-01-18T11:13:43Z

src/doc/rustc-dev-guide/src/tests/compiletest.md

+By default, codegen tests will infer `//@ needs-target-std` (that the target
+needs to support std), *unless* the `#![no_std]` attribute was specified in the
+test source. You can override this behavior and explicitly write `//@
+needs-target-std` to only run the test when target supports std, even if the
+test is `#![no_std]`.
+


Discussion: note that design wise, I still don't really like this kind of inferred implicit behavior, but OTOH I agree it is really annoying having to maintain explicit //@ needs-target-std for codegen tests.

jieyouxu · 2026-01-18T11:23:02Z

cc @xdoardo, lmw if you want an Co-authored-by attribution.

xdoardo · 2026-01-18T13:26:18Z

src/tools/compiletest/src/directives/file.rs

+            }
+
            if let Some(directive_line) = line_directive(path, line_number, ln) {
                lines.push(directive_line);


I haven't looked too much into it, but I noticed that the testing infrastructure looks at the directives in reverse to find reasons to ignore the test for the current target.

This means, for example, that a test like this will be ignored with the "target needs std" message if it is run for a target that does not have std and is not a 64-bit platform.

It could make sense to add the synthetic directive at the beginning of the vector instead, so that the (potential) reasons to ignore the test for the current target that are already in the file are checked first.

That seems okay, but also I think that's an orthogonal change which can benefit from a more aggressive change: I wonder if we should report the set of criteria that contributes to a test being ignored, rather than just the "first" or "last" directive.

src/tools/compiletest/src/directives/file.rs

xdoardo · 2026-01-18T13:52:28Z

I had a couple patches to push to my PR, but I am happy to close mine and comment here the bits I had patches for.

cc @xdoardo, lmw if you want an Co-authored-by attribution.

That would be great! It's not that important, though. I'm fine without the attribution if it is a hassle.

jieyouxu · 2026-01-19T01:11:59Z

@rustbot author

Zalathar · 2026-01-19T01:45:36Z

Terminology nitpick: This usage of “infer” feels subtly wrong to me, in a way that trips me up every time I read it.

E.g. if I were the one writing, I would be more likely to say that we assume the need for an implicit/implied //@ needs-target-std directive in all codegen tests, except for ones with an explicit #![no_std] attribute.

jieyouxu · 2026-01-21T01:55:05Z

Changes since last review:

Added #![no_core] to also disable the implied //@ needs-target-std.
Updated comment as requested, esp. to change "inferred" -> "implied".
Updated PR/commit title/description re. above.

@rustbot review

Zalathar · 2026-01-24T03:37:44Z

Looks good to me, thanks.

I notice there are still a few occurrences of “infer” left over; r=me after another cleanup pass to make those more consistent.

Zalathar · 2026-01-24T03:38:05Z

@rustbot author

…tests by default A `codegen-llvm` test (and other codegen test mode tests) will now by default have an implied `//@ needs-target-std` directive, *unless* the test explicitly has an `#![no_std]`/`#![no_core]` attribute which disables this implied behavior. - When a test has both `#![no_std]`/`#![no_core]` and `//@ needs-target-std`, the explicit `//@ needs-target-std` directive will cause the test to be ignored for targets that do not support std still. This is to make it easier to test out-of-tree targets / custom targets (and targets not tested in r-l/r CI) without requiring target maintainers to do a bunch of manual `//@ needs-target-std` busywork. Co-authored-by: Edoardo Marangoni <ecmm@anche.no>

rustbot · 2026-01-26T01:43:55Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

jieyouxu · 2026-01-26T01:47:23Z

Fixed the leftover "inferred" that I apparently missed, no functional changes since last review.
@bors r=Zalathar rollup

rust-bors · 2026-01-26T01:47:25Z

📌 Commit 841d781 has been approved by Zalathar

It is now in the queue for this repository.

Rollup of 6 pull requests Successful merges: - #151611 (Improve is_ascii performance on x86_64 with explicit SSE2 intrinsics) - #150705 (Add missing mut to pin.rs docs) - #151294 (compiletest: add implied `needs-target-std` for `codegen` mode tests unless annotated with `#![no_std]`/`#![no_core]`) - #151589 (Add a `documentation` remapping path scope for rustdoc usage) - #151639 (Fix broken WASIp1 reference link) - #151645 (Update `sysinfo` version to `0.38.0`)

Rollup merge of #151294 - jieyouxu:infer-needs-target-std, r=Zalathar compiletest: add implied `needs-target-std` for `codegen` mode tests unless annotated with `#![no_std]`/`#![no_core]` A `codegen` mode test (such as `codegen-llvm` test suite) will now by default have an implied `//@ needs-target-std` directive, *unless* the test explicitly has an `#![no_std]`/`#![no_core]` attribute which disables this behavior. - When a test has both `#![no_std]`/`#![no_core]` and `//@ needs-target-std`, the explicit `//@ needs-target-std` directive will cause the test to be ignored for targets that do not support std still. This is to make it easier to test out-of-tree targets / custom targets (and targets not tested in r-l/r CI) without requiring target maintainers to do a bunch of manual `//@ needs-target-std` busywork. Context: [#t-compiler/help > `compiletest` cannot find `core` library for target != host](https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/.60compiletest.60.20cannot.20find.20.60core.60.20library.20for.20target.20!.3D.20host/with/568652419) ## Implementation remarks This is an alternative version of #150672, with some differences: - *This* PR applies this implied-`needs-target-std` behavior to all `codegen` test mode tests. - *This* PR does the synthetic directive injection in the same place as implied-`codegen-run` directives. Both are of course hacks, but at least they're together next to each other.

Rollup of 6 pull requests Successful merges: - rust-lang/rust#151611 (Improve is_ascii performance on x86_64 with explicit SSE2 intrinsics) - rust-lang/rust#150705 (Add missing mut to pin.rs docs) - rust-lang/rust#151294 (compiletest: add implied `needs-target-std` for `codegen` mode tests unless annotated with `#![no_std]`/`#![no_core]`) - rust-lang/rust#151589 (Add a `documentation` remapping path scope for rustdoc usage) - rust-lang/rust#151639 (Fix broken WASIp1 reference link) - rust-lang/rust#151645 (Update `sysinfo` version to `0.38.0`)

rustbot assigned Zalathar Jan 18, 2026

jieyouxu commented Jan 18, 2026

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jieyouxu force-pushed the infer-needs-target-std branch 2 times, most recently from 101f610 to c2d972b Compare January 18, 2026 11:18

jieyouxu changed the title ~~compiletest: infer needs-target-std for codegen-{gcc,llvm,cranelift} tests~~ compiletest: infer needs-target-std for codegen mode tests Jan 18, 2026

jieyouxu mentioned this pull request Jan 18, 2026

compiletest/codegen-llvm: automatically add needs-target-std if needed #150672

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jieyouxu changed the title ~~compiletest: infer needs-target-std for codegen mode tests~~ compiletest: infer needs-target-std for codegen mode tests without #![no_std] Jan 18, 2026

xdoardo reviewed Jan 18, 2026

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src/tools/compiletest/src/directives/file.rs Outdated Show resolved Hide resolved

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jieyouxu changed the title ~~compiletest: infer needs-target-std for codegen mode tests without #![no_std]~~ compiletest: assume needs-target-std for codegen mode tests unless explicit directive or annotated with #![no_std] Jan 21, 2026

jieyouxu changed the title ~~compiletest: assume needs-target-std for codegen mode tests unless explicit directive or annotated with #![no_std]~~ compiletest: assume needs-target-std for codegen mode tests unless annotated with #![no_std] Jan 21, 2026

jieyouxu changed the title ~~compiletest: assume needs-target-std for codegen mode tests unless annotated with #![no_std]~~ compiletest: assume needs-target-std for codegen mode tests unless annotated with #![no_{std,core}] Jan 21, 2026

jieyouxu force-pushed the infer-needs-target-std branch from c2d972b to 8923124 Compare January 21, 2026 01:48

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jieyouxu force-pushed the infer-needs-target-std branch from 8923124 to 9cfd996 Compare January 21, 2026 01:52

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jieyouxu changed the title ~~compiletest: assume needs-target-std for codegen mode tests unless annotated with #![no_{std,core}]~~ compiletest: assume needs-target-std for codegen mode tests unless annotated with #![no_std]/#![no_core] Jan 21, 2026

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jieyouxu force-pushed the infer-needs-target-std branch from 9cfd996 to 841d781 Compare January 26, 2026 01:43

jieyouxu changed the title ~~compiletest: assume needs-target-std for codegen mode tests unless annotated with #![no_std]/#![no_core]~~ compiletest: add implied needs-target-std for codegen mode tests unless annotated with #![no_std]/#![no_core] Jan 26, 2026

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Rollup of 6 pull requests #151667

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rust-bors bot merged commit 504c7fe into rust-lang:main Jan 26, 2026
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jieyouxu deleted the infer-needs-target-std branch January 26, 2026 09:51

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compiletest: add implied needs-target-std for codegen mode tests unless annotated with #![no_std]/#![no_core] #151294

compiletest: add implied needs-target-std for codegen mode tests unless annotated with #![no_std]/#![no_core] #151294

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compiletest: add implied `needs-target-std` for `codegen` mode tests unless annotated with `#![no_std]`/`#![no_core]` #151294

compiletest: add implied `needs-target-std` for `codegen` mode tests unless annotated with `#![no_std]`/`#![no_core]` #151294

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