Add `Complex` type and `repr(complex)` by folkertdev · Pull Request #158885 · rust-lang/rust

folkertdev · 2026-07-06T21:56:26Z

tracking issue: #154023

See also #t-compiler > representing `_Complex`. The RFC states that the Complex type should match the ABI of _Complex in C, but provides little detail on how to actually achieve this. We concluded that repr(complex) is probably the best approach. Like clang, that means we "desugar" the representation early: _Complex is not natively represented in LLVM IR.

I've derived the ABI from clang for 28 targets, a decent sample of what we actually support. For now I'm only actually testing x86_64 because (as you'll see) updating the tests is quite labor-intensive. If we're happy with this direction I can fill more of them in, likely in a separate PR.

The libs side of the type is very bare-bones: I'm not as interested in that part. Others can fill in the various instances, methods, write tests for those, and improve the docs.

r? workingjubilee

rustbot · 2026-07-06T21:56:32Z

workingjubilee is currently at their maximum review capacity.
They may take a while to respond.

folkertdev · 2026-07-06T22:00:43Z

Commit e4c802f shows how our LLVM IR representation differs from clang. For instance instead of <2 x float> we just use double, and sometimes we pass { double, double} instead of two separate double arguments.

Based on what I know that is perfectly compatible on an ABI-level, it's just textually different from clang.

View changes since the review

mejrs

Please also add #[repr(complex)] to tests/ui/attributes/attr-on-mac-call.rs

View changes since this review

teor2345

Looks good to me!

View changes since this review

bjorn3 · 2026-07-06T22:34:24Z

Is it me or is the callconv implementation missing? I don't see any users of fn is_complex().

folkertdev · 2026-07-06T22:41:23Z

Is it me or is the callconv implementation missing? I don't see any users of fn is_complex().

For x86_64 we only need custom behavior for f80. I've not yet implemented a target where it is needed, and I'd kind of prefer to do that in a follow-up

asquared31415 · 2026-07-06T22:52:12Z

        use FfiResult::*;

-        if !def.repr().c() && !def.repr().transparent() {
+        if !def.repr().c() && !def.repr().transparent() && !def.repr().complex() {


This likely needs some work, for example Complex<{integer}> or even weirder types like Complex<String> (if that's even allowed by the compiler) should not be considered FFI safe. Easily done in a followup however.

View changes since the review

Actually Complex<{integer}> might be de-facto fine under GCC and Clang, I'm not certain. It's a non-standard C extension though, so not sure what we want to do about that.

I recommend we err conservatively and treat it as nonsense for now until anyone asks for it.

Right, takes some more logic but we now only accept (transparently wrapped) float types, anything else triggers improper_ctypes.

btw it is my intention to make Complex<{integer}> just be abi-compatible in practice, but whether we actually guarantee it can be discussed later.

Part 18: runs rust-lang/rust#158885 (Add Complex type / repr(complex), a novel feature) through the full pipeline. Critic emits 26 comments; base judge keeps 6 (6 accept / 20 reject). The 6 survivors are a real maintainer review; the rejects expose a NEW failure mode distinct from Part 17's knowledge blind spot — grounding failures, where the critic asks for what the diff already contains because it's pattern-matching the form of a review, not reading the hunk. Argues the judge's accept rate (8/12 cookbook vs 6/26 here) is a distribution meter: an unlabeled readout of how far out of depth the critic is on a given PR. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

folkertdev · 2026-07-07T12:12:09Z

+    // repr(complex) is internal, so this check is not as thorough as we'd require if it were
+    // user-facing.


Lmk if we should be more thorough here, but given that we never want to stabilize repr(complex), only Complex<T>, this seems (more than) adequate.

View changes since the review

folkertdev · 2026-07-07T12:12:40Z

        use FfiResult::*;

-        if !def.repr().c() && !def.repr().transparent() {
+        if !def.repr().c() && !def.repr().transparent() && !def.repr().complex() {


Right, takes some more logic but we now only accept (transparently wrapped) float types, anything else triggers improper_ctypes.

folkertdev · 2026-07-07T12:14:08Z

+    #[repr(complex)]
+    //~^ ERROR attribute cannot be used on macro calls
+    //~| ERROR `repr(complex)` is experimental
+    unreachable!();


added this, it's already an error because there is no compatibility concern

View changes since the review

mejrs

The attribute part of this looks good to me.

View changes since this review

rustbot · 2026-07-07T16:13:33Z

Some changes occurred in compiler/rustc_passes/src/check_attr.rs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

rust-bors · 2026-07-11T20:16:32Z

☔ The latest upstream changes (presumably #159142) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

add Complex type

ce847ff

rustbot assigned workingjubilee Jul 6, 2026

folkertdev commented Jul 6, 2026

View reviewed changes

folkertdev mentioned this pull request Jul 6, 2026

Tracking issue for RFC 3892: Complex numbers. #154023

Open

7 tasks

teor2345 mentioned this pull request Jul 6, 2026

Use the C _Complex number type rustfoundation/interop-initiative#72

Open

mejrs reviewed Jul 6, 2026

View reviewed changes

Comment thread compiler/rustc_attr_parsing/src/attributes/repr.rs

Comment thread tests/ui/feature-gates/feature-gate-repr-complex.rs Outdated

teor2345 approved these changes Jul 6, 2026

View reviewed changes

This comment has been minimized.

Sign in to view

asquared31415 reviewed Jul 6, 2026

View reviewed changes

folkertdev force-pushed the complex-layout branch 2 times, most recently from 7300c0a to a63e0f1 Compare July 7, 2026 12:21

folkertdev commented Jul 7, 2026

View reviewed changes

This comment has been minimized.

Sign in to view

mejrs approved these changes Jul 7, 2026

View reviewed changes

add repr(complex)

b7731ed

folkertdev force-pushed the complex-layout branch from a63e0f1 to 39d6ddf Compare July 7, 2026 13:14

This comment has been minimized.

Sign in to view

folkertdev added 4 commits July 7, 2026 16:39

make repr(complex) an error on macro calls

3cf6e74

validate the struct repr(complex) is applied to

bf8f77c

make improper_ctypes only accept Complex<{float}>

d25cbcc

add Complex to minicore.rs

665d04a

folkertdev added 4 commits July 7, 2026 16:40

add complex-abi.rs test

76b9275

add CHECK lines and revisions

af37a40

disable most revisions

3150260

Implement and test x86_64 Complex

faadfa3

folkertdev force-pushed the complex-layout branch from 39d6ddf to faadfa3 Compare July 7, 2026 14:45

folkertdev marked this pull request as ready for review July 7, 2026 16:13

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 7, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Jul 7, 2026

		// repr(complex) is internal, so this check is not as thorough as we'd require if it were
		// user-facing.

Uh oh!

Uh oh!

Conversation

folkertdev commented Jul 6, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rustbot commented Jul 6, 2026

Uh oh!

folkertdev Jul 6, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

mejrs left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

teor2345 left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

bjorn3 commented Jul 6, 2026

Uh oh!

This comment has been minimized.

folkertdev commented Jul 6, 2026

Uh oh!

asquared31415 Jul 6, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

asquared31415 Jul 6, 2026

Choose a reason for hiding this comment

Uh oh!

workingjubilee Jul 7, 2026

Choose a reason for hiding this comment

Uh oh!

folkertdev Jul 7, 2026

Choose a reason for hiding this comment

Uh oh!

folkertdev Jul 7, 2026

Choose a reason for hiding this comment

Uh oh!

Uh oh!

folkertdev Jul 7, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

folkertdev Jul 7, 2026

Choose a reason for hiding this comment

Uh oh!

folkertdev Jul 7, 2026 • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Uh oh!

This comment has been minimized.

mejrs left a comment • edited by rustbot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

This comment has been minimized.

rustbot commented Jul 7, 2026

Uh oh!

rust-bors Bot commented Jul 11, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

8 participants

folkertdev commented Jul 6, 2026 •

edited by rustbot

Loading

folkertdev Jul 6, 2026 •

edited by rustbot

Loading

mejrs left a comment •

edited by rustbot

Loading

teor2345 left a comment •

edited by rustbot

Loading

asquared31415 Jul 6, 2026 •

edited by rustbot

Loading

folkertdev Jul 7, 2026 •

edited by rustbot

Loading

folkertdev Jul 7, 2026 •

edited by rustbot

Loading

mejrs left a comment •

edited by rustbot

Loading