Tweak E0277 when predicate comes indirectly from ? #137245

estebank · 2025-02-18T20:39:00Z

When a ? operation requires an Into conversion with additional bounds (like having a concrete error but wanting to convert to a trait object), we handle it speficically and provide the same kind of information we give other ? related errors.

error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied
  --> $DIR/bad-question-mark-on-trait-object.rs:7:13
   |
LL | fn foo() -> Result<(), Box<dyn std::error::Error>> {
   |             -------------------------------------- required `E: std::error::Error` because of this
LL |     Ok(bar()?)
   |        -----^ the trait `std::error::Error` is not implemented for `E`
   |        |
   |        this has type `Result<_, E>`
   |
note: `E` needs to implement `std::error::Error`
  --> $DIR/bad-question-mark-on-trait-object.rs:1:1
   |
LL | struct E;
   | ^^^^^^^^
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
   = note: required for `Box<dyn std::error::Error>` to implement `From<E>`

Avoid talking about FromResidual when other more relevant information is being given, particularly from rust_on_unimplemented.

Fix #137238.

CC #137232, which was a smaller step related to this.

rustbot · 2025-02-18T20:39:09Z

r? @oli-obk

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When a `?` operation requires an `Into` conversion with additional bounds (like having a concrete error but wanting to convert to a trait object), we handle it speficically and provide the same kind of information we give other `?` related errors. ``` error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied --> $DIR/bad-question-mark-on-trait-object.rs:5:13 | LL | fn foo() -> Result<(), Box<dyn std::error::Error>> { | -------------------------------------- required `E: std::error::Error` because of this LL | Ok(bar()?) | ^ the trait `std::error::Error` is not implemented for `E` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = note: required for `Box<dyn std::error::Error>` to implement `From<E>` ``` Avoid talking about `FromResidual` when other more relevant information is being given, particularly from `rust_on_unimplemented`.

oli-obk

just a nit, this is gonna be very useful!

compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs

``` error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied --> $DIR/bad-question-mark-on-trait-object.rs:7:13 | LL | fn foo() -> Result<(), Box<dyn std::error::Error>> { | -------------------------------------- required `E: std::error::Error` because of this LL | Ok(bar()?) | -----^ the trait `std::error::Error` is not implemented for `E` | | | this has type `Result<_, E>` | note: `E` needs to implement `std::error::Error` --> $DIR/bad-question-mark-on-trait-object.rs:1:1 | LL | struct E; | ^^^^^^^^ = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = note: required for `Box<dyn std::error::Error>` to implement `From<E>` error[E0277]: `?` couldn't convert the error to `X` --> $DIR/bad-question-mark-on-trait-object.rs:18:13 | LL | fn bat() -> Result<(), X> { | ------------- expected `X` because of this LL | Ok(bar()?) | -----^ the trait `From<E>` is not implemented for `X` | | | this can't be annotated with `?` because it has type `Result<_, E>` | note: `X` needs to implement `From<E>` --> $DIR/bad-question-mark-on-trait-object.rs:4:1 | LL | struct X; | ^^^^^^^^ note: alternatively, `E` needs to implement `Into<X>` --> $DIR/bad-question-mark-on-trait-object.rs:1:1 | LL | struct E; | ^^^^^^^^ = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait ```

oli-obk · 2025-02-21T23:04:25Z

@bors r+

bors · 2025-02-21T23:05:14Z

📌 Commit 31febc6 has been approved by oli-obk

It is now in the queue for this repository.

…iaskrgr Rollup of 8 pull requests Successful merges: - rust-lang#136458 (Do not deduplicate list of associated types provided by dyn principal) - rust-lang#136474 ([`compiletest`-related cleanups 3/7] Make the distinction between sources root vs test suite sources root in compiletest less confusing) - rust-lang#136592 (Make sure we don't overrun the stack in canonicalizer) - rust-lang#136787 (Remove `lifetime_capture_rules_2024` feature) - rust-lang#137207 (Add #[track_caller] to Duration Div impl) - rust-lang#137245 (Tweak E0277 when predicate comes indirectly from ?) - rust-lang#137257 (Ignore fake borrows for packed field check) - rust-lang#137399 (fix ICE in layout computation with unnormalizable const) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#137245 - estebank:from-residual-note-2, r=oli-obk Tweak E0277 when predicate comes indirectly from ? When a `?` operation requires an `Into` conversion with additional bounds (like having a concrete error but wanting to convert to a trait object), we handle it speficically and provide the same kind of information we give other `?` related errors. ``` error[E0277]: `?` couldn't convert the error: `E: std::error::Error` is not satisfied --> $DIR/bad-question-mark-on-trait-object.rs:7:13 | LL | fn foo() -> Result<(), Box<dyn std::error::Error>> { | -------------------------------------- required `E: std::error::Error` because of this LL | Ok(bar()?) | -----^ the trait `std::error::Error` is not implemented for `E` | | | this has type `Result<_, E>` | note: `E` needs to implement `std::error::Error` --> $DIR/bad-question-mark-on-trait-object.rs:1:1 | LL | struct E; | ^^^^^^^^ = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = note: required for `Box<dyn std::error::Error>` to implement `From<E>` ``` Avoid talking about `FromResidual` when other more relevant information is being given, particularly from `rust_on_unimplemented`. Fix rust-lang#137238. ----- CC rust-lang#137232, which was a smaller step related to this.

rustbot assigned oli-obk Feb 18, 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 Feb 18, 2025

estebank force-pushed the from-residual-note-2 branch from dac5b70 to e565eee Compare February 20, 2025 18:15

Point out the type of more expressions on bad ?

8ef535e

estebank force-pushed the from-residual-note-2 branch from 4efe94e to 8ef535e Compare February 20, 2025 19:11

oli-obk requested changes Feb 21, 2025

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compiler/rustc_trait_selection/src/error_reporting/traits/fulfillment_errors.rs Outdated Show resolved Hide resolved

rustbot 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-review Status: Awaiting review from the assignee but also interested parties. labels Feb 21, 2025

estebank force-pushed the from-residual-note-2 branch from e28e249 to 31febc6 Compare February 21, 2025 18:30

estebank added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Feb 21, 2025

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 Feb 21, 2025

matthiaskrgr mentioned this pull request Feb 22, 2025

Rollup of 8 pull requests #137406

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bors merged commit 890c4d2 into rust-lang:master Feb 22, 2025
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rustbot added this to the 1.87.0 milestone Feb 22, 2025

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Tweak E0277 when predicate comes indirectly from ? #137245

Tweak E0277 when predicate comes indirectly from ? #137245

estebank commented Feb 18, 2025 •

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bors commented Feb 21, 2025

Tweak E0277 when predicate comes indirectly from ? #137245

Tweak E0277 when predicate comes indirectly from ? #137245

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