Point at inner item when it uses generic type param from outer item or `Self` #148370

estebank · 2025-11-01T19:10:15Z

Partially address #37892.

In E0401 generated in resolve:

error[E0401]: can't use generic parameters from outer item
  --> $DIR/E0401.rs:4:39
   |
LL | fn foo<T>(x: T) {
   |        - type parameter from outer item
LL |     fn bfnr<U, V: Baz<U>, W: Fn()>(y: T) {
   |        ----                           ^ use of generic parameter from outer item
   |        |
   |        generic parameter used in this inner function
   |
help: try introducing a local generic parameter here
   |
LL |     fn bfnr<T, U, V: Baz<U>, W: Fn()>(y: T) {
   |             ++

In E0401 generated in hir_typeck:

error[E0401]: can't reference `Self` constructor from outer item
  --> $DIR/do-not-ice-on-note_and_explain.rs:6:13
   |
LL | impl<B> A<B> {
   | ------------ the inner item doesn't inherit generics from this impl, so `Self` is invalid to reference
LL |     fn d() {
LL |         fn d() {
   |            - `Self` used in this inner item
LL |             Self(1)
   |             ^^^^ help: replace `Self` with the actual type: `A`

``` error[E0401]: can't use generic parameters from outer item --> $DIR/enum-definition-with-outer-generic-parameter-5997.rs:3:16 | LL | fn f<Z>() -> bool { | - type parameter from outer item LL | enum E { V(Z) } | ^ use of generic parameter from outer item | help: try introducing a local generic parameter here | LL | enum E<Z> { V(Z) } | +++ ```

``` error[E0401]: can't use generic parameters from outer item --> $DIR/E0401.rs:4:39 | LL | fn foo<T>(x: T) { | - type parameter from outer item LL | fn bfnr<U, V: Baz, W: Fn()>(y: T) { | ---- ^ use of generic parameter from outer item | | | generic parameter used in this inner function | help: try introducing a local generic parameter here | LL | fn bfnr<T, U, V: Baz, W: Fn()>(y: T) { | ++ ```

``` error[E0401]: can't reference `Self` constructor from outer item --> $DIR/do-not-ice-on-note_and_explain.rs:6:13 | LL | impl A { | ------------ the inner item doesn't inherit generics from this impl, so `Self` is invalid to reference LL | fn d() { LL | fn d() { | - `Self` used in this inner item LL | Self(1) | ^^^^ help: replace `Self` with the actual type: `A` ```

rustbot · 2025-11-01T19:10:19Z

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estebank · 2025-11-01T19:13:16Z

tests/ui/delegation/target-expr.stderr

+help: try introducing a local generic parameter here
+   |
+LL |     reuse Trait::static_methodT,  {
+   |                               ++


Pre-existing mistake with delegation suggestion, we just make it obvious now. This needs to be fixed separately.

Is there already an issue for this? If not lets make one

Fixed it in last commit

``` error[E0401]: can't use generic parameters from outer item --> $DIR/const-param-from-outer-fn.rs:3:9 | LL | fn foo<const X: u32>() { | - const parameter from outer item LL | fn bar() -> u32 { | --- generic parameter used in this inner function LL | X | ^ use of generic parameter from outer item | help: try introducing a local generic parameter here | LL | fn bar<X>() -> u32 { | +++ ```

JonathanBrouwer

Few nits, other than that it looks good

View changes since this review

compiler/rustc_resolve/src/late.rs

compiler/rustc_resolve/src/lib.rs

JonathanBrouwer · 2025-11-02T20:02:57Z

r=me when ci is green

estebank · 2025-11-03T00:49:31Z

@bors r=JonathanBrouwer

bors · 2025-11-03T00:49:34Z

📌 Commit f171c41 has been approved by JonathanBrouwer

It is now in the queue for this repository.

Rollup of 5 pull requests Successful merges: - #144194 (Provide additional context to errors involving const traits) - #148232 (ci: add runners for vanilla LLVM 21) - #148240 (rustc_codegen: fix musttail returns for cast/indirect ABIs) - #148247 (Remove a special case and move another one out of reachable_non_generics) - #148370 (Point at inner item when it uses generic type param from outer item or `Self`) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #148370 - estebank:outer-param, r=JonathanBrouwer Point at inner item when it uses generic type param from outer item or `Self` Partially address #37892. In E0401 generated in resolve: ``` error[E0401]: can't use generic parameters from outer item --> $DIR/E0401.rs:4:39 | LL | fn foo<T>(x: T) { | - type parameter from outer item LL | fn bfnr<U, V: Baz, W: Fn()>(y: T) { | ---- ^ use of generic parameter from outer item | | | generic parameter used in this inner function | help: try introducing a local generic parameter here | LL | fn bfnr<T, U, V: Baz, W: Fn()>(y: T) { | ++ ``` In E0401 generated in hir_typeck: ``` error[E0401]: can't reference `Self` constructor from outer item --> $DIR/do-not-ice-on-note_and_explain.rs:6:13 | LL | impl A { | ------------ the inner item doesn't inherit generics from this impl, so `Self` is invalid to reference LL | fn d() { LL | fn d() { | - `Self` used in this inner item LL | Self(1) | ^^^^ help: replace `Self` with the actual type: `A` ```

Tweak E0401 More accurate span pointing at use place of outer param (at ident instead of full path). Add note explaining why outer item params can't be used in inner item. Use structured suggestion for what `Self` should have been. Follow up to rust-lang#148370. Fix rust-lang#37892.

Rollup merge of #148447 - estebank:outer-param-2, r=jackh726 Tweak E0401 More accurate span pointing at use place of outer param (at ident instead of full path). Add note explaining why outer item params can't be used in inner item. Use structured suggestion for what `Self` should have been. Follow up to #148370. Fix #37892.

Rollup of 5 pull requests Successful merges: - rust-lang/rust#144194 (Provide additional context to errors involving const traits) - rust-lang/rust#148232 (ci: add runners for vanilla LLVM 21) - rust-lang/rust#148240 (rustc_codegen: fix musttail returns for cast/indirect ABIs) - rust-lang/rust#148247 (Remove a special case and move another one out of reachable_non_generics) - rust-lang/rust#148370 (Point at inner item when it uses generic type param from outer item or `Self`) r? `@ghost` `@rustbot` modify labels: rollup

estebank added 3 commits November 1, 2025 18:23

rustbot assigned JonathanBrouwer Nov 1, 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 Nov 1, 2025

estebank changed the title ~~Outer param~~ Point at inner item when it uses generic type param from outer item or Self Nov 1, 2025

estebank commented Nov 1, 2025

View reviewed changes

estebank added 2 commits November 1, 2025 19:21

Pass DiagMetadata through in more cases

86d7556

JonathanBrouwer requested changes Nov 2, 2025

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estebank added 2 commits November 2, 2025 20:04

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c962b95

Do not suggest adding type param to fn delegation

f171c41

estebank force-pushed the outer-param branch from 543eca1 to f171c41 Compare November 2, 2025 20:05

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 Nov 3, 2025

Zalathar mentioned this pull request Nov 3, 2025

Rollup of 5 pull requests #148420

Merged

estebank mentioned this pull request Nov 3, 2025

Using type with local type parameters has confusing error #37892

Closed

bors merged commit c10e1e4 into rust-lang:master Nov 3, 2025
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rustbot added this to the 1.93.0 milestone Nov 3, 2025

estebank mentioned this pull request Nov 3, 2025

Tweak E0401 #148447

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Point at inner item when it uses generic type param from outer item or `Self` #148370

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