expand: Add error check if derive has wrong item by Pasta-coder · Pull Request #4359 · Rust-GCC/gccrs

Pasta-coder · 2026-01-06T10:11:23Z

The DeriveVisitor previously dispatched calls to specific handlers (like DeriveClone) without validating the input item type. This caused internal compiler errors (ICEs) when users attempted to derive traits on invalid items like functions or traits, as the handlers assumed the input was a struct, enum, or union.

This patch adds a validation predicate to the DeriveVisitor to reject invalid items gracefully with a diagnostic error before dispatching.

Fixes #3875

gcc/rust/ChangeLog:

* expand/rust-derive.h: Add validate_item prototype.
* expand/rust-derive.cc (DeriveVisitor::derive): Use visitor validation.
(DeriveVisitor::validate_item): New function to check item kind.

gcc/testsuite/ChangeLog:

* rust/compile/derive-on-invalid-item.rs: New test.

GCC development requires copyright assignment or the Developer's Certificate of Origin sign-off, see https://gcc.gnu.org/contribute.html or https://gcc.gnu.org/dco.html
Read contributing guidlines
make check-rust passes locally
Run clang-format
Added any relevant test cases to gcc/testsuite/rust/

dkm · 2026-01-06T10:24:02Z

Hello, thanks for your contribution!

Small nitpick on the Changelog part...

* expand/rust-derive.h: Add validate_item prototype.

Does not target a specific "item". You could be more precise using:

* expand/rust-derive.h (DeriveVisitor::validate_item): New.

Pasta-coder · 2026-01-06T16:08:16Z

@dkm hello,

commit message regarding changelog changed .

thanks

Pasta-coder · 2026-01-08T11:39:15Z

I realized there might be a potential false positive with Tuple Structs (e.g., struct Foo(i32);).

If AST::Item::Kind differentiates between named Structs and TupleStructs, my current whitelist might incorrectly reject valid tuple structs.

I am going to verify this locally by adding a test case for a tuple struct. If it fails, I will update validate_item to explicitly include Kind::TupleStruct and push the fix along with the test.

dkm · 2026-01-08T12:36:21Z

@dkm hello,

commit message regarding changelog changed .

thanks

Thanks!

Pasta-coder · 2026-01-09T12:20:31Z

@dkm hello,

I reverted the extra Kind check since TupleStruct falls under Kind::Struct. I kept the test case to verify that tuple structs are correctly accepted.

Open for review .

thankyou

Pasta-coder · 2026-01-13T08:25:14Z

@P-E-P please review .

thankyou .

Pasta-coder · 2026-01-23T07:16:00Z

@CohenArthur please review .

thankyou .

P-E-P

I don't really get what this PR brings on the table. Sure there is a new fancy helper function, but it has a side effect, we're emitting an error. Moving the error out of that helper means it becomes so short a function may not even be worth it anymore.

The check was already there so we didn't get anything from that.

We do get a new test which is a bit more complete compared to rust/compile/issue-3971.rs.

Am I missing something ?

Pasta-coder · 2026-01-25T22:11:03Z

introducing helper function does have a side effect .

why i did what i did ? the ICE was solved in #4211 but issue #3875 was still open with comments suggesting a helper function , also test was missing TupleStructs check . so , i opened a pr .

should i remove the helper function or return bool from helper and emit error from caller ? (do you prefer such helpers?)
or should this pr be solely for adding a new test ?

thankyou

P-E-P · 2026-01-26T12:49:46Z

introducing helper function does have a side effect .

why i did what i did ? the ICE was solved in #4211 but issue #3875 was still open with comments suggesting a helper function , also test was missing TupleStructs check . so , i opened a pr .
1. should i remove the helper function or return `bool` from helper and emit error from caller ? (do you prefer such helpers?)

2. or should this pr be solely for adding a new test ?
thankyou

I think we should definitely keep the test, but I wouldn't keep the rest of the changes.

Pasta-coder · 2026-01-27T10:01:18Z

@P-E-P now this pr only adds the test .

thankyou.

gcc/testsuite/rust/compile/issue-3875.rs

This patch adds a regression test ensuring that deriving on invalid items (such as functions or traits) triggers a diagnostic error instead of an Internal Compiler Error (ICE). It also verifies that Tuple Structs are accepted as valid targets for derivation. Fixes Rust-GCC#3875 gcc/testsuite/ChangeLog: * rust/compile/issue-3875.rs: New test. Signed-off-by: Jayant Chauhan <0001jayant@gmail.com>

Pasta-coder · 2026-02-05T11:42:47Z

@P-E-P this can also be merged .

review once , thanks .

edit - didn't see you self requested a review .

Pasta-coder · 2026-03-11T15:47:54Z

@P-E-P this pr is getting stale , any chance of merging it ?

Pasta-coder force-pushed the issue-3875 branch from 786575e to 57ad8d3 Compare January 6, 2026 10:21

Pasta-coder force-pushed the issue-3875 branch 3 times, most recently from ff0806a to 9e84d88 Compare January 6, 2026 16:06

Pasta-coder force-pushed the issue-3875 branch 5 times, most recently from 11bd185 to 475edf5 Compare January 7, 2026 04:57

Pasta-coder force-pushed the issue-3875 branch 2 times, most recently from 9cee832 to eb4177c Compare January 9, 2026 11:33

P-E-P reviewed Jan 23, 2026

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Pasta-coder force-pushed the issue-3875 branch 3 times, most recently from f4ee91d to 207332f Compare January 26, 2026 22:12

P-E-P reviewed Jan 27, 2026

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gcc/testsuite/rust/compile/issue-3875.rs Outdated Show resolved Hide resolved

Pasta-coder force-pushed the issue-3875 branch 4 times, most recently from a3e1065 to ea8c59e Compare January 27, 2026 18:30

Pasta-coder force-pushed the issue-3875 branch 4 times, most recently from c775b26 to 721a7fc Compare January 28, 2026 20:47

Pasta-coder marked this pull request as draft January 29, 2026 06:09

Pasta-coder force-pushed the issue-3875 branch from 721a7fc to 41639b7 Compare February 4, 2026 15:22

Pasta-coder marked this pull request as ready for review February 4, 2026 16:01

P-E-P self-requested a review February 5, 2026 11:39

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