Add `core::num::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

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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.

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Usually yes.

Right, so this whole file has been set up so that, hopefully, it will be easy to review that when we deviate from clang, it's only a textual difference, not an abi difference.

mejrs

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

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teor2345

Looks good to me!

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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.

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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.

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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

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mejrs

The attribute part of this looks good to me.

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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

rustbot · 2026-08-08T21:07:01Z

Some changes occurred in compiler/rustc_attr_ir

cc @jdonszelmann, @JonathanBrouwer

workingjubilee

I don't know how an "r" got into this comment.

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workingjubilee · 2026-08-12T01:06:35Z

+                )
+                .emit();
+            }
+            cx.check_target("(complex)", &AllowedTargets::AllowList(&[Allow(Target::Struct)]));


...hm.

...What happens if I put in repr(simd, complex), or repr(C, complex)?

We don't need to make this specifically a repr attribute.

Yeah maybe a lang item is sufficient actually. Then the type could just be repr(C) and that would do the right thing for like Complex<String> etc.

Yes, if you find that impl to work out similar to this then that would also be good.

workingjubilee · 2026-08-12T01:11:06Z

+    pub re: T,
+    /// The imaginary component.
+    pub im: T,


Huh, odd. I kind of would expect r and i or real and imaginary.

There might be some value in matching the C function names real and imag, but I don't personally think it's compelling:
https://www.gnu.org/software/c-intro-and-ref/manual/html_node/Complex-Data-Types.html

I'm just following the RFC here, libs can re-litigate it later

workingjubilee · 2026-08-12T01:11:22Z

+pub struct Complex<T> {
+    /// The real component.
+    pub re: T,
+    /// The imaginary component.
+    pub im: T,
+}


Unsure if public fields is desirable here.

Having to call a method just to get the real or imaginary part seems annoying

Again this is just per the RFC #154023

Ah, OK, I didn't notice that on my scan.

leaving this open so I see it if I revisit this PR for some reason, but considering it nonblocking.

workingjubilee · 2026-08-12T01:12:18Z

Usually yes.

rustbot · 2026-08-12T19:35:24Z

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.

workingjubilee · 2026-08-12T20:33:36Z

I need to stare at this for a moment longer but I'll r+ it after assuming tests are green and nothing jumps out.

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made it through CI at least (and it's all minicore-checked so I don't expect issues on other targets)

the new `sym::complex` in the previous commit pushes some symbol from 999 to 1000, which causes the formatting change here

folkertdev · 2026-08-12T20:58:29Z

Right, so this whole file has been set up so that, hopefully, it will be easy to review that when we deviate from clang, it's only a textual difference, not an abi difference.

folkertdev · 2026-08-12T20:59:35Z

-    ($f /* 0#0 */:ident /* 0#0 */<$a /* 0#0 */:lifetime /* 0#0 */>)
-    =>
+    ($f /* 0#0 */:ident /* 0#0 */<$a /* 0#0 */:lifetime /* 0#0
+    */>) =>


this formatting change is due to some symbol now being wider (so 999 turned to 1000 or something like that). That should probably be handled more robustly, but for this PR this will do.

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workingjubilee · 2026-08-12T21:52:45Z

snrk, right, HTML

rustbot assigned workingjubilee Jul 6, 2026

folkertdev commented Jul 6, 2026

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folkertdev mentioned this pull request Jul 6, 2026

Tracking issue for RFC 3892: Complex numbers. #154023

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teor2345 mentioned this pull request Jul 6, 2026

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

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mejrs reviewed Jul 6, 2026

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

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

teor2345 approved these changes Jul 6, 2026

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asquared31415 reviewed Jul 6, 2026

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

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mejrs approved these changes Jul 7, 2026

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

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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

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folkertdev added the F-complex_numbers `#![feature(complex_numbers)]` label Jul 26, 2026

folkertdev mentioned this pull request Jul 26, 2026

Complex layout phase 2 #159981

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folkertdev force-pushed the complex-layout branch from bc52ce8 to 9a26ba5 Compare July 30, 2026 22:49

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folkertdev force-pushed the complex-layout branch from 9a26ba5 to c9a428c Compare August 8, 2026 21:06

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beetrees reviewed Aug 8, 2026

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Comment thread compiler/rustc_abi/src/layout/ty.rs Outdated

workingjubilee reviewed Aug 12, 2026

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folkertdev force-pushed the complex-layout branch from a3d076f to f422b61 Compare August 12, 2026 19:35

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folkertdev force-pushed the complex-layout branch from f422b61 to 02d6b19 Compare August 12, 2026 19:47

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workingjubilee approved these changes Aug 12, 2026

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folkertdev added 2 commits August 12, 2026 22:50

add Complex type

5b66cc1

update hygiene test

d7ec103

the new `sym::complex` in the previous commit pushes some symbol from 999 to 1000, which causes the formatting change here

folkertdev force-pushed the complex-layout branch from 02d6b19 to 15e2724 Compare August 12, 2026 20:56

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folkertdev added 6 commits August 13, 2026 00:05

define Ty::is_complex

592e138

add complex-abi.rs test

05e8259

add CHECK lines and revisions

34fab67

disable most revisions

4213ac7

Implement and test x86_64 Complex

5e8cc87

Complex return on x86

daf4a0e

folkertdev force-pushed the complex-layout branch from 15e2724 to daf4a0e Compare August 12, 2026 22:05

folkertdev changed the title ~~Add Complex type and repr(complex)~~ Add core::num::Complex Aug 12, 2026

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

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