Make TypeId const comparable #142789

oli-obk · 2025-06-20T16:13:56Z

This should unblock stabilizing const TypeId::of and allow us to progress into any possible future we want to take TypeId to.

To achieve that TypeId now contains 16 / size_of<usize>() pointers which each are actually just size_of<usize>() bytes of the stable hash. At compile-time the first of these pointers cannot be dereferenced or otherwise inspected (at present doing so might ICE the compiler). Preventing inspection of this data allows us to refactor TypeId to any other scheme in the future without breaking anyone who was tempted to transmute TypeId to obtain the hash at compile-time.

cc @eddyb for their previous work on #95845 (which we still can do in the future if we want to get rid of the hash as the final thing that declares two TypeIds as equal).

Tracking Issue for const fn type_id #77125

r? @RalfJung

rustbot · 2025-06-20T16:14:02Z

Some changes occurred to the intrinsics. Make sure the CTFE / Miri interpreter
gets adapted for the changes, if necessary.

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

library/core/src/intrinsics/mod.rs

library/core/src/any.rs

RalfJung · 2025-06-21T10:37:29Z

It will be a while until I have the capacity to review a PR of this scale.

Meanwhile, could you say a bit more about the architecture of the change? It seems you want for the "new kind of allocation" approach, but it's not clear from the PR description how exactly that shows up in TypeId.

Also, I am definitely not comfortable landing this by myself, I can only review the const-eval parts. Changing the representation of TypeId has ramifications well beyond that that I do not feel qualified to evaluate -- I think an MCP would be justified.

rustbot · 2025-06-21T11:17:11Z

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

oli-obk · 2025-06-21T11:18:41Z

Well, I got private feedback yesterday that instead of encoding a 16 byte value as an 8 byte pointer to the 16 byte value and an 8 byte hash, I should just do the thing where we split up type id internally into pointer sized chunks and codegen will make a hash out of it again.

TLDR: no changes to runtime type id anymore in the latest revision of this PR. Only compile-time type id is now a bit funny

oli-obk · 2025-06-21T11:22:11Z

It will be a while until I have the capacity to review a PR of this scale.

I'm splitting unrelated parts out, so the high level feedback is already useful and I'll look for libs and codegen ppl to review the appropriate parts

compiler/rustc_codegen_gcc/src/common.rs

compiler/rustc_codegen_cranelift/src/constant.rs

Make `PartialEq` a `const_trait` r? `@fee1-dead` or `@compiler-errors` something generally useful but also required for rust-lang#142789

Make `PartialEq` a `const_trait` r? ``@fee1-dead`` or ``@compiler-errors`` something generally useful but also required for rust-lang#142789

Rollup merge of #142822 - oli-obk:const-partial-eq, r=fee1-dead Make `PartialEq` a `const_trait` r? ``@fee1-dead`` or ``@compiler-errors`` something generally useful but also required for #142789

bors · 2025-06-23T16:57:20Z

☔ The latest upstream changes (presumably #142906) made this pull request unmergeable. Please resolve the merge conflicts.

compiler/rustc_codegen_cranelift/src/constant.rs

RalfJung · 2025-07-09T06:04:33Z

library/core/src/intrinsics/mod.rs

+#[rustc_intrinsic]
+#[rustc_do_not_const_check]
+pub const fn type_id_eq(a: crate::any::TypeId, b: crate::any::TypeId) -> bool {
+    a.data == b.data


This now compares the arrays, so it may compare in more chunks than it used to. Might be worth transmuting tom(u64, u64) for the comparison?

I transmuted to u128 which results in a single table lookup without the secondary check for the second part of the hash.

Nice; r=me when CI is happy.

…n the interpreter

RalfJung · 2025-07-09T13:31:01Z

@bors2 try jobs=test-various

rust-bors · 2025-07-09T13:31:06Z

⌛ Trying commit b1aec1a with merge a7f53f1…

To cancel the try build, run the command @bors2 try cancel.

Make TypeId const comparable This should unblock stabilizing const `TypeId::of` and allow us to progress into any possible future we want to take `TypeId` to. To achieve that `TypeId` now contains `16 / size_of<usize>()` pointers which each are actually just `size_of<usize>()` bytes of the stable hash. At compile-time the first of these pointers cannot be dereferenced or otherwise inspected (at present doing so might ICE the compiler). Preventing inspection of this data allows us to refactor `TypeId` to any other scheme in the future without breaking anyone who was tempted to transmute `TypeId` to obtain the hash at compile-time. cc `@eddyb` for their previous work on #95845 (which we still can do in the future if we want to get rid of the hash as the final thing that declares two TypeIds as equal). * #77125 r? `@RalfJung` try-job: test-various

bors · 2025-07-09T13:31:57Z

⌛ Trying commit b1aec1a with merge 048b879...

rust-bors · 2025-07-09T15:13:09Z

☀️ Try build successful (CI)
Build commit: a7f53f1 (a7f53f1f7ee6a32481341457ba4408f9241dd3f4, parent: 6b3ae3f6e45a33c2d95fa0362c9b2593e567fd34)

oli-obk · 2025-07-09T15:15:10Z

@bors r=RalfJung

bors · 2025-07-09T15:15:14Z

📌 Commit b1aec1a has been approved by RalfJung

It is now in the queue for this repository.

bors · 2025-07-09T15:50:05Z

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing 048b879 to master...

rust-log-analyzer · 2025-07-09T15:52:22Z

A job failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

oli-obk · 2025-07-09T15:52:28Z

uh

oli-obk · 2025-07-09T15:54:21Z

@bors treeclosed

Kobzol · 2025-07-09T16:04:23Z

@bors treeclosed=100 Wrong commit appeared in master.

RalfJung · 2025-07-09T16:17:40Z

I accidentally triggered a try job on both bors' above... and I guess the one on old bors was still running when the PR got r+'d, and then we got the known issue that bors mixes up try builds and approvals and gets really confused.

Given that new bors has been doing pretty well with try jobs, can we just forbid them on old bors? Or is even that redeploy too risky?^^

oli-obk · 2025-07-09T16:20:39Z

@bors treeclosed-

Kobzol · 2025-07-09T16:23:33Z

This PR is bricked and bors doesn't listen here anymore 😆 But please don't reopen yet.

oli-obk · 2025-07-09T16:23:49Z

I will create a new PR in general

oli-obk · 2025-07-09T16:23:55Z

not touching this one anymore :D

jdonszelmann · 2025-07-09T16:31:43Z

forced pushed to master from the mobile command centre :3

@pietroalbini, @scrabsha

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Make PartialEq a const_trait #142822

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bors added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Jul 8, 2025

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oli-obk added 2 commits July 9, 2025 13:23

Add opaque TypeId handles for CTFE

38ac469

Avoid creating a helper allocation for creating new TypeId values i…

b1aec1a

…n the interpreter

oli-obk force-pushed the constable-type-id branch from 04db802 to b1aec1a Compare July 9, 2025 13:23

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 Jul 9, 2025

bors added the merged-by-bors This PR was explicitly merged by bors. label Jul 9, 2025

bors merged commit 048b879 into rust-lang:master Jul 9, 2025
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rustbot added this to the 1.90.0 milestone Jul 9, 2025

oli-obk deleted the constable-type-id branch July 9, 2025 15:54

oli-obk mentioned this pull request Jul 9, 2025

Add opaque TypeId handles for CTFE #143696

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Make TypeId const comparable #142789

Make TypeId const comparable #142789

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