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Fix incorrect trait bound restriction suggestion#117505

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bors merged 1 commit intorust-lang:masterfrom
estebank:issue-117501
Nov 3, 2023
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Fix incorrect trait bound restriction suggestion#117505
bors merged 1 commit intorust-lang:masterfrom
estebank:issue-117501

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@estebank
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@estebank estebank commented Nov 2, 2023

Suggest

error[E0308]: mismatched types
  --> $DIR/restrict-assoc-type-of-generic-bound.rs:9:12
   |
LL | pub fn foo<A: MyTrait, B>(a: A) -> B {
   |                        -           - expected `B` because of return type
   |                        |
   |                        expected this type parameter
LL |     return a.bar();
   |            ^^^^^^^ expected type parameter `B`, found associated type
   |
   = note: expected type parameter `B`
             found associated type `<A as MyTrait>::T`
help: consider further restricting this bound
   |
LL | pub fn foo<A: MyTrait<T = B>, B>(a: A) -> B {
   |                      +++++++

instead of

error[E0308]: mismatched types
  --> $DIR/restrict-assoc-type-of-generic-bound.rs:9:12
   |
LL | pub fn foo<A: MyTrait, B>(a: A) -> B {
   |                        -           - expected `B` because of return type
   |                        |
   |                        expected this type parameter
LL |     return a.bar();
   |            ^^^^^^^ expected type parameter `B`, found associated type
   |
   = note: expected type parameter `B`
             found associated type `<A as MyTrait>::T`
help: consider further restricting this bound
   |
LL | pub fn foo<A: MyTrait + <T = B>, B>(a: A) -> B {
   |                      +++++++++

Fix #117501.

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@rustbot 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 2, 2023
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TaKO8Ki commented Nov 2, 2023

After resolving CI errors, r=me

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polina4096 commented Nov 2, 2023 •
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I think the message is still misleading, as it suggests restricting a trait bound instead of an associated type. The correct message is shown when a concrete type is expected.

Incorrect message:

help: consider further restricting this bound
  |
7 | fn foo<A: MyTrait<T = B>, B>(a: A) -> B {
  |                  +++++++

Correct message:

help: consider constraining the associated type `<A as MyTrait>::T` to `B`
  |
7 | fn foo<A: MyTrait<T = B>, B>(a: A) -> B {
  |                  +++++++

@estebank
Fix incorrect trait bound restriction suggestion
9e7345b 
Suggest

```
error[E0308]: mismatched types
  --> $DIR/restrict-assoc-type-of-generic-bound.rs:9:12
   |
LL | pub fn foo<A: MyTrait, B>(a: A) -> B {
   |                        -           - expected `B` because of return type
   |                        |
   |                        expected this type parameter
LL |     return a.bar();
   |            ^^^^^^^ expected type parameter `B`, found associated type
   |
   = note: expected type parameter `B`
             found associated type `<A as MyTrait>::T`
help: consider further restricting this bound
   |
LL | pub fn foo<A: MyTrait<T = B>, B>(a: A) -> B {
   |                      +++++++
```

instead of

```
error[E0308]: mismatched types
  --> $DIR/restrict-assoc-type-of-generic-bound.rs:9:12
   |
LL | pub fn foo<A: MyTrait, B>(a: A) -> B {
   |                        -           - expected `B` because of return type
   |                        |
   |                        expected this type parameter
LL |     return a.bar();
   |            ^^^^^^^ expected type parameter `B`, found associated type
   |
   = note: expected type parameter `B`
             found associated type `<A as MyTrait>::T`
help: consider further restricting this bound
   |
LL | pub fn foo<A: MyTrait + <T = B>, B>(a: A) -> B {
   |                      +++++++++
```

Fix rust-lang#117501.
@estebank
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estebank commented Nov 2, 2023

@polina4096 the wording is technically correct: we're asking to further constrain A to MyTrait<T = B> from MyTrait. It is still part of the trait bound. We should pass in more information to suggest_constraining_type_param so that the message can be more accurate in all cases.

@bors r=TaKO8Ki

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bors commented Nov 2, 2023

📌 Commit 9e7345b has been approved by TaKO8Ki

It is now in the queue for this repository.

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bors commented Nov 2, 2023

🌲 The tree is currently closed for pull requests below priority 100. This pull request will be tested once the tree is reopened.

@bors 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 Nov 2, 2023
@matthiaskrgr matthiaskrgr mentioned this pull request Nov 3, 2023
Merged
bors added a commit to rust-lang-ci/rust that referenced this pull request Nov 3, 2023
@bors
Auto merge of rust-lang#117538 - matthiaskrgr:rollup-63u77xb, r=matth…
a026bd4 
…iaskrgr

Rollup of 5 pull requests

Successful merges:

 - rust-lang#117434 (delegate `<Box<E> as Error>::provide` to `<E as Error>::provide`)
 - rust-lang#117505 (Fix incorrect trait bound restriction suggestion)
 - rust-lang#117520 (Clippy subtree update)
 - rust-lang#117523 (oli-obk is on vacation)
 - rust-lang#117533 (Revert "bootstrap: do not purge docs on CI environment")

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 6cb627b into rust-lang:master Nov 3, 2023
@rustbot rustbot added this to the 1.75.0 milestone Nov 3, 2023
rust-timer added a commit to rust-lang-ci/rust that referenced this pull request Nov 3, 2023
@rust-timer
Unrolled build for rust-lang#117505
98772f8 
Rollup merge of rust-lang#117505 - estebank:issue-117501, r=TaKO8Ki

Fix incorrect trait bound restriction suggestion

Suggest

```
error[E0308]: mismatched types
  --> $DIR/restrict-assoc-type-of-generic-bound.rs:9:12
   |
LL | pub fn foo<A: MyTrait, B>(a: A) -> B {
   |                        -           - expected `B` because of return type
   |                        |
   |                        expected this type parameter
LL |     return a.bar();
   |            ^^^^^^^ expected type parameter `B`, found associated type
   |
   = note: expected type parameter `B`
             found associated type `<A as MyTrait>::T`
help: consider further restricting this bound
   |
LL | pub fn foo<A: MyTrait<T = B>, B>(a: A) -> B {
   |                      +++++++
```

instead of

```
error[E0308]: mismatched types
  --> $DIR/restrict-assoc-type-of-generic-bound.rs:9:12
   |
LL | pub fn foo<A: MyTrait, B>(a: A) -> B {
   |                        -           - expected `B` because of return type
   |                        |
   |                        expected this type parameter
LL |     return a.bar();
   |            ^^^^^^^ expected type parameter `B`, found associated type
   |
   = note: expected type parameter `B`
             found associated type `<A as MyTrait>::T`
help: consider further restricting this bound
   |
LL | pub fn foo<A: MyTrait + <T = B>, B>(a: A) -> B {
   |                      +++++++++
```

Fix rust-lang#117501.
@github-actions github-actions bot mentioned this pull request Nov 6, 2023
Merged
bors-ferrocene bot added a commit to ferrocene/ferrocene that referenced this pull request Nov 6, 2023
@bors-ferrocene @BenWiederhake
@SabrinaJewson @J-ZhengLi @koka831 @bjorn3 @joshlf @lengyijun @Zalathar @oli-obk @flip1995 @y21 @bors @bvanjoi
Merge #84
a01e81f 
84: Automated pull from upstream `master` r=Dajamante a=github-actions[bot]


This PR pulls the following changes from the upstream repository:

* rust-lang/rust#117585
* rust-lang/rust#117576
* rust-lang/rust#96979
* rust-lang/rust#117191
* rust-lang/rust#117179
* rust-lang/rust#117574
* rust-lang/rust#117537
* rust-lang/rust#117608
  * rust-lang/rust#117596
  * rust-lang/rust#117588
  * rust-lang/rust#117524
  * rust-lang/rust#116017
* rust-lang/rust#117504
* rust-lang/rust#117469
* rust-lang/rust#116218
* rust-lang/rust#117589
* rust-lang/rust#117581
* rust-lang/rust#117503
* rust-lang/rust#117590
  * rust-lang/rust#117583
  * rust-lang/rust#117570
  * rust-lang/rust#117562
  * rust-lang/rust#117534
  * rust-lang/rust#116894
  * rust-lang/rust#110340
* rust-lang/rust#113343
* rust-lang/rust#117579
* rust-lang/rust#117094
* rust-lang/rust#117566
* rust-lang/rust#117564
  * rust-lang/rust#117554
  * rust-lang/rust#117550
  * rust-lang/rust#117343
* rust-lang/rust#115274
* rust-lang/rust#117540
* rust-lang/rust#116412
* rust-lang/rust#115333
* rust-lang/rust#117507
* rust-lang/rust#117538
  * rust-lang/rust#117533
  * rust-lang/rust#117523
  * rust-lang/rust#117520
  * rust-lang/rust#117505
  * rust-lang/rust#117434
* rust-lang/rust#117535
* rust-lang/rust#117510
* rust-lang/rust#116439
* rust-lang/rust#117508



Co-authored-by: Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
Co-authored-by: SabrinaJewson <sejewson@gmail.com>
Co-authored-by: J-ZhengLi <lizheng135@huawei.com>
Co-authored-by: koka <koka.code@gmail.com>
Co-authored-by: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Co-authored-by: Joshua Liebow-Feeser <joshlf@users.noreply.github.com>
Co-authored-by: lengyijun <sjtu5140809011@gmail.com>
Co-authored-by: Zalathar <Zalathar@users.noreply.github.com>
Co-authored-by: Oli Scherer <git-spam-no-reply9815368754983@oli-obk.de>
Co-authored-by: Philipp Krones <hello@philkrones.com>
Co-authored-by: y21 <30553356+y21@users.noreply.github.com>
Co-authored-by: bors <bors@rust-lang.org>
Co-authored-by: bohan <bohan-zhang@foxmail.com>
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Suggestion for E0308 produces invalid syntax for traits with unconstrained associated types, when a type parameter is expected

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@estebank @rustbot @rust-log-analyzer @TaKO8Ki @polina4096 @bors