Disentangle `ForwardGenericParamBan` and `ConstParamTy` ribs #138259

compiler-errors · 2025-03-09T06:10:25Z

In #137617, the ConstParamTy rib was adjusted to act kinda like the ForwardGenericParamBan. However, this means that it no longer served its purpose banning generics from parent items. Although we still are checking for param type validity using the ConstParamTy_ trait, which means that we weren't accepting code we shouldn't, I think it's a bit strange for us not to be rejecting code like this during resolution and instead letting these malformed const generics leak into the type system:

trait Foo<T> {
  fn bar<const N: T>() {}
}

This PR does a few things:

Introduce a ForwardGenericParamBanReason enum, and start using the ForwardGenericParamBan rib to ban forward-declared params in const tys when generic_const_parameter_types is enabled.
Start using the ConstParamTy rib to ban all generics when generic_const_parameter_types is disabled.
Improve the diagnostics for both of the cases above, and for forward-declared params in parameter defaults too :3

r? @BoxyUwU or reassign

BoxyUwU · 2025-03-09T07:29:43Z

ah right 🤔 I guess at the time I thought that params would include all params in scope but that doesnt make any sense xd

BoxyUwU · 2025-03-09T07:34:22Z

#![feature(adt_const_params)]

trait Trait<const N: usize> {
    fn foo<const M: [u8; N]>() {}
}

Can you add a test that we forbid this? Apparently we don't have such a test already ^^'

rustbot · 2025-03-09T21:03:53Z

This PR changes a file inside tests/crashes. If a crash was fixed, please move into the corresponding ui subdir and add 'Fixes #' to the PR description to autoclose the issue upon merge.

BoxyUwU · 2025-03-11T14:57:19Z

@bors r+

this is much nicer now thx

bors · 2025-03-11T14:57:22Z

📌 Commit a79f97b has been approved by BoxyUwU

It is now in the queue for this repository.

…r=BoxyUwU Disentangle `ForwardGenericParamBan` and `ConstParamTy` ribs In rust-lang#137617, the `ConstParamTy` rib was adjusted to act kinda like the `ForwardGenericParamBan`. However, this means that it no longer served its purpose banning generics from *parent items*. Although we still are checking for param type validity using the `ConstParamTy_` trait, which means that we weren't accepting code we shouldn't, I think it's a bit strange for us not to be rejecting code like this during *resolution* and instead letting these malformed const generics leak into the type system: ```rust trait Foo<T> { fn bar<const N: T>() {} } ``` This PR does a few things: 1. Introduce a `ForwardGenericParamBanReason` enum, and start using the `ForwardGenericParamBan` rib to ban forward-declared params in const tys when `generic_const_parameter_types` is enabled. 2. Start using the `ConstParamTy` rib to ban *all* generics when `generic_const_parameter_types` is disabled. 3. Improve the diagnostics for both of the cases above, and for forward-declared params in parameter defaults too :3 r? `@BoxyUwU` or reassign

jieyouxu · 2025-03-12T04:41:11Z

I think this failed in rollup: #138382 (comment)

2025-03-12T04:34:54.7238690Z ---- [ui] tests/ui/const-generics/generic_const_parameter_types/references-parent-generics.rs#nofeat stdout ----
2025-03-12T04:34:54.7239912Z Saved the actual stderr to "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/const-generics/generic_const_parameter_types/references-parent-generics.nofeat/references-parent-generics.nofeat.stderr"
2025-03-12T04:34:54.7240808Z diff of stderr:
2025-03-12T04:34:54.7240928Z 
2025-03-12T04:34:54.7241108Z -	error: `Self` is forbidden as the type of a const generic parameter
2025-03-12T04:34:54.7241628Z +	error[E0770]: the type of const parameters must not depend on other generic parameters
2025-03-12T04:34:54.7242657Z 2	  --> $DIR/references-parent-generics.rs:7:25
2025-03-12T04:34:54.7242960Z 3	   |
2025-03-12T04:34:54.7243405Z 4	LL |     type Assoc<const N: Self>;
2025-03-12T04:34:54.7243593Z 
2025-03-12T04:34:54.7243683Z -	   |                         ^^^^
2025-03-12T04:34:54.7243923Z -	   |
2025-03-12T04:34:54.7244201Z -	   = note: the only supported types are integers, `bool`, and `char`
2025-03-12T04:34:54.7244646Z +	   |                         ^^^^ the type must not depend on the parameter `Self`

@bors r-

BoxyUwU · 2025-03-12T04:49:02Z

gamer

compiler-errors · 2025-03-12T16:56:41Z

@bors r=BoxyUwU

bors · 2025-03-12T16:56:45Z

📌 Commit 42773bf has been approved by BoxyUwU

It is now in the queue for this repository.

…earth Rollup of 12 pull requests Successful merges: - rust-lang#134076 (Stabilize `std::io::ErrorKind::InvalidFilename`) - rust-lang#137504 (Move methods from Map to TyCtxt, part 4.) - rust-lang#138175 (Support rmeta inputs for --crate-type=bin --emit=obj) - rust-lang#138259 (Disentangle `ForwardGenericParamBan` and `ConstParamTy` ribs) - rust-lang#138280 (fix ICE in pretty-printing `global_asm!`) - rust-lang#138318 (Rustdoc: remove a bunch of `@ts-expect-error` from main.js) - rust-lang#138331 (Use `RUSTC_LINT_FLAGS` more) - rust-lang#138357 (merge `TypeChecker` and `TypeVerifier`) - rust-lang#138394 (remove unnecessary variant) - rust-lang#138403 (Delegation: one more ICE fix for `MethodCall` generation) - rust-lang#138407 (Delegation: reject C-variadics) - rust-lang#138409 (Use sa_sigaction instead of sa_union.__su_sigaction for AIX) r? `@ghost` `@rustbot` modify labels: rollup

compiler-errors · 2025-03-13T01:13:52Z

@bors rollup

…earth Rollup of 12 pull requests Successful merges: - rust-lang#134076 (Stabilize `std::io::ErrorKind::InvalidFilename`) - rust-lang#137504 (Move methods from Map to TyCtxt, part 4.) - rust-lang#138175 (Support rmeta inputs for --crate-type=bin --emit=obj) - rust-lang#138259 (Disentangle `ForwardGenericParamBan` and `ConstParamTy` ribs) - rust-lang#138280 (fix ICE in pretty-printing `global_asm!`) - rust-lang#138318 (Rustdoc: remove a bunch of `@ts-expect-error` from main.js) - rust-lang#138331 (Use `RUSTC_LINT_FLAGS` more) - rust-lang#138357 (merge `TypeChecker` and `TypeVerifier`) - rust-lang#138394 (remove unnecessary variant) - rust-lang#138403 (Delegation: one more ICE fix for `MethodCall` generation) - rust-lang#138407 (Delegation: reject C-variadics) - rust-lang#138409 (Use sa_sigaction instead of sa_union.__su_sigaction for AIX) r? `@ghost` `@rustbot` modify labels: rollup

rustbot assigned BoxyUwU Mar 9, 2025

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 9, 2025

compiler-errors force-pushed the disentangle-ribs branch from 7cf39de to ea88485 Compare March 9, 2025 20:31

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compiler-errors force-pushed the disentangle-ribs branch from ea88485 to a79f97b Compare March 9, 2025 21:03

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 Mar 11, 2025

jieyouxu mentioned this pull request Mar 12, 2025

Rollup of 26 pull requests #138382

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bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Mar 12, 2025

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Disentangle ForwardGenericParamBan and ConstParamTy ribs

42773bf

compiler-errors force-pushed the disentangle-ribs branch from a79f97b to 42773bf Compare March 12, 2025 16:56

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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 12, 2025

Manishearth mentioned this pull request Mar 12, 2025

Rollup of 12 pull requests #138416

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bors merged commit 2d7a592 into rust-lang:master Mar 13, 2025
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Disentangle `ForwardGenericParamBan` and `ConstParamTy` ribs #138259

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