Provide context when `?` can't be called because of `Result<_, E>` #116496

estebank · 2023-10-06T20:52:57Z

When a method chain ending in ? causes an E0277 because the expression's Result::Err variant doesn't have a type that can be converted to the Result<_, E> type parameter in the return type, provide additional context of which parts of the chain can and can't support the ? operator.

error[E0277]: `?` couldn't convert the error to `String`
  --> $DIR/question-mark-result-err-mismatch.rs:27:25
   |
LL | fn bar() -> Result<(), String> {
   |             ------------------ expected `String` because of this
LL |     let x = foo();
   |             ----- this has type `Result<_, String>`
...
LL |         .map_err(|_| ())?;
   |          ---------------^ the trait `From<()>` is not implemented for `String`
   |          |
   |          this can't be annotated with `?` because it has type `Result<_, ()>`
   |
   = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
   = help: the following other types implement trait `From<T>`:
             <String as From<char>>
             <String as From<Box<str>>>
             <String as From<Cow<'a, str>>>
             <String as From<&str>>
             <String as From<&mut str>>
             <String as From<&String>>
   = note: required for `Result<(), String>` to implement `FromResidual<Result<Infallible, ()>>`

Fix #72124.

rustbot · 2023-10-06T20:53:05Z

r? @wesleywiser

(rustbot has picked a reviewer for you, use r? to override)

compiler-errors · 2023-10-06T21:00:18Z

tests/ui/traits/question-mark-result-err-mismatch.stderr

+LL |           .map(|s| ())
+   |            ----------- this can be annotated with `?` because it has type `Result<(), &str>`
+LL |           .map_err(|_| ())
+   |            --------------- this can't be annotated with `?` because it has type `Result<(), ()>`
+LL |           .map(|()| "")?;
+   |            ------------^ the trait `From<()>` is not implemented for `String`
+   |            |
+   |            this can't be annotated with `?` because it has type `Result<&str, ()>`


this seems really heavy for long chains -- do i really care about ?-ability 4 .maps down?

Probably not. I would like to add an extra check to only point at places where the E changed (like we do for assoc types in method call chains), but wanted to keep the code down to a reviewable size.

I'd rather just put a hard limit on the number of method chain to walk backwards. Maybe 2 is sensible.

Let me know what you think of the new output.

compiler-errors · 2023-10-06T21:03:13Z

Also, this doesn't really fix #72124, does it? The problem in that issue is a shortcoming of closure inference causing us to forgo suggesting removing ; in a closure body?

estebank · 2023-10-06T21:05:36Z

Also, this doesn't really fix #72124, does it?

I'm adding some checks for the specific methods that take closures and that can change the type of Result<_, E>, but we still need the general context for any other cases that have underlying reasons beyond map_err calls.

compiler-errors · 2023-10-06T21:07:41Z

I'm adding some checks for the specific methods that take closures

For what it's worth, I think those checks should be implemented in a separate PR to separate concerns.

I'm mostly just noting that the PR shouldn't close (via fixes ### in the PR summary) that issue since there's additional work that needs to be done on that case specifically.

compiler-errors · 2023-12-05T16:43:09Z

@bors r+ rollup

bors · 2023-12-05T16:43:12Z

📌 Commit cce82d8 has been approved by compiler-errors

It is now in the queue for this repository.

…text, r=compiler-errors Provide context when `?` can't be called because of `Result<_, E>` When a method chain ending in `?` causes an E0277 because the expression's `Result::Err` variant doesn't have a type that can be converted to the `Result<_, E>` type parameter in the return type, provide additional context of which parts of the chain can and can't support the `?` operator. ``` error[E0277]: `?` couldn't convert the error to `String` --> $DIR/question-mark-result-err-mismatch.rs:27:25 | LL | fn bar() -> Result<(), String> { | ------------------ expected `String` because of this LL | let x = foo(); | ----- this has type `Result<_, String>` ... LL | .map_err(|_| ())?; | ---------------^ the trait `From<()>` is not implemented for `String` | | | this can't be annotated with `?` because it has type `Result<_, ()>` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = help: the following other types implement trait `From<T>`: <String as From<char>> <String as From<Box<str>>> <String as From<Cow<'a, str>>> <String as From<&str>> <String as From<&mut str>> <String as From<&String>> = note: required for `Result<(), String>` to implement `FromResidual<Result<Infallible, ()>>` ``` Fix rust-lang#72124.

compiler-errors · 2023-12-05T19:34:06Z

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

+                hir::intravisit::walk_expr(self, ex);
+            }
+        }
+        let hir_id = self.tcx.hir().local_def_id_to_hir_id(obligation.cause.body_id);


This needs a rebase.

compiler-errors

please amend commit 2faaea9 after rebasing because local_def_id_to_hir_id has moved onto TyCtxt.

compiler-errors · 2023-12-05T19:34:59Z

@bors r-

r=me after fixing up that first commit

compiler-errors · 2023-12-05T19:36:11Z

(also if you're already changing this, pls squash the formatting commits down into more relevant ones)

When a method chain ending in `?` causes an E0277 because the expression's `Result::Err` variant doesn't have a type that can be converted to the `Result<_, E>` type parameter in the return type, provide additional context of which parts of the chain can and can't support the `?` operator. ``` error[E0277]: `?` couldn't convert the error to `String` --> $DIR/question-mark-result-err-mismatch.rs:28:25 | LL | fn bar() -> Result<(), String> { | ------------------ expected `String` because of this LL | let x = foo(); | ----- this can be annotated with `?` because it has type `Result<String, String>` LL | let one = x LL | .map(|s| ()) | ----------- this can be annotated with `?` because it has type `Result<(), String>` LL | .map_err(|_| ())?; | ---------------^ the trait `From<()>` is not implemented for `String` | | | this can't be annotated with `?` because it has type `Result<(), ()>` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = help: the following other types implement trait `From<T>`: <String as From<char>> <String as From<Box<str>>> <String as From<Cow<'a, str>>> <String as From<&str>> <String as From<&mut str>> <String as From<&String>> = note: required for `Result<(), String>` to implement `FromResidual<Result<Infallible, ()>>` ``` Fix rust-lang#72124.

compiler-errors · 2023-12-05T22:23:13Z

Thanks!

@bors r+

bors · 2023-12-05T22:23:16Z

📌 Commit 23fa94f has been approved by compiler-errors

It is now in the queue for this repository.

Fix rust-lang#72124.

estebank · 2023-12-05T22:26:21Z

Pushed again (squashed the comment adding commit too)

@bors r=compiler-errors

bors · 2023-12-05T22:26:23Z

📌 Commit 70fe624 has been approved by compiler-errors

It is now in the queue for this repository.

…iaskrgr Rollup of 7 pull requests Successful merges: - rust-lang#116496 (Provide context when `?` can't be called because of `Result<_, E>`) - rust-lang#117563 (docs: clarify explicitly freeing heap allocated memory) - rust-lang#117874 (`riscv32` platform support) - rust-lang#118516 (Add ADT variant infomation to StableMIR and finish implementing TyKind::internal()) - rust-lang#118650 (add comment about keeping flags in sync between bootstrap.py and bootstrap.rs) - rust-lang#118664 (docs: remove rust-lang#110800 from release notes) - rust-lang#118669 (library: fix comment about const assert in win api) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of rust-lang#116496 - estebank:question-method-chain-context, r=compiler-errors Provide context when `?` can't be called because of `Result<_, E>` When a method chain ending in `?` causes an E0277 because the expression's `Result::Err` variant doesn't have a type that can be converted to the `Result<_, E>` type parameter in the return type, provide additional context of which parts of the chain can and can't support the `?` operator. ``` error[E0277]: `?` couldn't convert the error to `String` --> $DIR/question-mark-result-err-mismatch.rs:27:25 | LL | fn bar() -> Result<(), String> { | ------------------ expected `String` because of this LL | let x = foo(); | ----- this has type `Result<_, String>` ... LL | .map_err(|_| ())?; | ---------------^ the trait `From<()>` is not implemented for `String` | | | this can't be annotated with `?` because it has type `Result<_, ()>` | = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait = help: the following other types implement trait `From<T>`: <String as From<char>> <String as From<Box<str>>> <String as From<Cow<'a, str>>> <String as From<&str>> <String as From<&mut str>> <String as From<&String>> = note: required for `Result<(), String>` to implement `FromResidual<Result<Infallible, ()>>` ``` Fix rust-lang#72124.

rustbot assigned wesleywiser Oct 6, 2023

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 Oct 6, 2023

This comment has been minimized.

Sign in to view

compiler-errors reviewed Oct 6, 2023

View reviewed changes

estebank force-pushed the question-method-chain-context branch from bd7a587 to 19f23b6 Compare October 6, 2023 21:06

estebank force-pushed the question-method-chain-context branch from bb20f12 to b09ff86 Compare October 7, 2023 04:12

This comment was marked as resolved.

Sign in to view

estebank force-pushed the question-method-chain-context branch from 9688267 to c55e70e Compare October 15, 2023 22:36

This comment was marked as resolved.

Sign in to view

estebank force-pushed the question-method-chain-context branch from c55e70e to 0e8b80a Compare October 27, 2023 17:39

This comment was marked as resolved.

Sign in to view

estebank force-pushed the question-method-chain-context branch from 0e8b80a to eff708f Compare November 6, 2023 17:47

estebank force-pushed the question-method-chain-context branch from eff708f to cce82d8 Compare November 16, 2023 17:01

compiler-errors assigned compiler-errors and unassigned wesleywiser Nov 30, 2023

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 Dec 5, 2023

matthiaskrgr mentioned this pull request Dec 5, 2023

Rollup of 7 pull requests #118651

Closed

compiler-errors mentioned this pull request Dec 5, 2023

Rollup of 8 pull requests #118652

Closed

compiler-errors reviewed Dec 5, 2023

View reviewed changes

compiler-errors requested changes Dec 5, 2023

View reviewed changes

rustbot added the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Dec 5, 2023

bors removed the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Dec 5, 2023

estebank added 2 commits December 5, 2023 22:22

Point at fewer methods in the chain, only those that change the E type

5381796

estebank force-pushed the question-method-chain-context branch from cce82d8 to 23fa94f Compare December 5, 2023 22:22

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 Dec 5, 2023

estebank added 2 commits December 5, 2023 22:24

Detect incorrect ; in Option::ok_or_else and Result::map_err

98e5317

Fix rust-lang#72124.

Reduce verbosity of error

70fe624

estebank force-pushed the question-method-chain-context branch from 23fa94f to 70fe624 Compare December 5, 2023 22:24

matthiaskrgr mentioned this pull request Dec 6, 2023

Rollup of 7 pull requests #118679

Merged

bors merged commit f1e1804 into rust-lang:master Dec 6, 2023
11 checks passed

rustbot added this to the 1.76.0 milestone Dec 6, 2023

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Provide context when `?` can't be called because of `Result<_, E>` #116496

Provide context when `?` can't be called because of `Result<_, E>` #116496

estebank commented Oct 6, 2023 •

edited

rustbot commented Oct 6, 2023

This comment has been minimized.

compiler-errors Oct 6, 2023

estebank Oct 6, 2023

compiler-errors Oct 6, 2023

estebank Oct 7, 2023

compiler-errors commented Oct 6, 2023

estebank commented Oct 6, 2023

compiler-errors commented Oct 6, 2023

This comment was marked as resolved.

This comment was marked as resolved.

This comment was marked as resolved.

compiler-errors commented Dec 5, 2023

bors commented Dec 5, 2023

compiler-errors Dec 5, 2023

compiler-errors left a comment

compiler-errors commented Dec 5, 2023

compiler-errors commented Dec 5, 2023

compiler-errors commented Dec 5, 2023

bors commented Dec 5, 2023

estebank commented Dec 5, 2023

bors commented Dec 5, 2023

Provide context when ? can't be called because of Result<_, E> #116496

Provide context when ? can't be called because of Result<_, E> #116496

Conversation

estebank commented Oct 6, 2023 • edited

rustbot commented Oct 6, 2023

This comment has been minimized.

compiler-errors Oct 6, 2023

Choose a reason for hiding this comment

estebank Oct 6, 2023

Choose a reason for hiding this comment

compiler-errors Oct 6, 2023

Choose a reason for hiding this comment

estebank Oct 7, 2023

Choose a reason for hiding this comment

compiler-errors commented Oct 6, 2023

estebank commented Oct 6, 2023

compiler-errors commented Oct 6, 2023

This comment was marked as resolved.

This comment was marked as resolved.

This comment was marked as resolved.

compiler-errors commented Dec 5, 2023

bors commented Dec 5, 2023

compiler-errors Dec 5, 2023

Choose a reason for hiding this comment

compiler-errors left a comment

Choose a reason for hiding this comment

compiler-errors commented Dec 5, 2023

compiler-errors commented Dec 5, 2023

compiler-errors commented Dec 5, 2023

bors commented Dec 5, 2023

estebank commented Dec 5, 2023

bors commented Dec 5, 2023

Provide context when `?` can't be called because of `Result<_, E>` #116496

Provide context when `?` can't be called because of `Result<_, E>` #116496

estebank commented Oct 6, 2023 •

edited