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Suggest the correct name if _ is used in a struct literal #98282

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scottmcm opened this issue Jun 20, 2022 · 3 comments · May be fixed by #122288
Open

Suggest the correct name if _ is used in a struct literal #98282

scottmcm opened this issue Jun 20, 2022 · 3 comments · May be fixed by #122288
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@fmease
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A-diagnostics Area: Messages for errors, warnings, and lints A-inference Area: Type inference A-parser Area: The parsing of Rust source code to an AST A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@scottmcm
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scottmcm commented Jun 20, 2022 •
edited by rustbot
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Given the following code: 

mod blah {
    pub struct Stuff { x: i32 }
    pub fn do_stuff(_: Stuff) {}
}

fn main() {
    blah::do_stuff(_ { x: 10 });
}

The current output is:

error: struct literal body without path
 --> src/main.rs:7:22
  |
7 |     blah::do_stuff(_ { x: 10 });
  |                      ^^^^^^^^^
  |
help: you might have forgotten to add the struct literal inside the block
  |
7 |     blah::do_stuff(_ { SomeStruct { x: 10 } });
  |                      ++++++++++++           +

error: expected one of `)`, `,`, `.`, `?`, or an operator, found `{`
 --> src/main.rs:7:22
  |
7 |     blah::do_stuff(_ { x: 10 });
  |                     -^ expected one of `)`, `,`, `.`, `?`, or an operator
  |                     |
  |                     help: missing `,`

warning: unnecessary braces around function argument
 --> src/main.rs:7:22
  |
7 |     blah::do_stuff(_ { x: 10 });
  |                      ^        ^
  |
  = note: `#[warn(unused_braces)]` on by default
help: remove these braces
  |
7 -     blah::do_stuff(_ { x: 10 });
7 +     blah::do_stuff(_ { x: 10 });
  |

error: in expressions, `_` can only be used on the left-hand side of an assignment
 --> src/main.rs:7:20
  |
7 |     blah::do_stuff(_ { x: 10 });
  |                    ^ `_` not allowed here

error[[E0061]](https://doc.rust-lang.org/nightly/error-index.html#E0061): this function takes 1 argument but 2 arguments were supplied
 --> src/main.rs:7:5
  |
7 |     blah::do_stuff(_ { x: 10 });
  |     ^^^^^^^^^^^^^^   --------- argument unexpected
  |
note: function defined here
 --> src/main.rs:3:12
  |
3 |     pub fn do_stuff(_: Stuff) {}
  |            ^^^^^^^^ --------
help: remove the extra argument
  |
7 |     blah::do_stuff(_);
  |     ~~~~~~~~~~~~~~~~~

Ideally the output should look like:

error[E0121]: the placeholder `_` is not allowed in struct literals
 --> src/main.rs:5:22
  |
9 |     blah::do_stuff(_ { x: 10 });
  |                    ^
  |                    |
  |                    not allowed in struct literals
  |                    help: replace with the correct struct type: `blah::Stuff`

Like how rustc will suggest the correct type if you use -> _ in a function definition.

(Opened after this thread: https://internals.rust-lang.org/t/enum-path-inference-with-variant-syntax/16851/4?u=scottmcm )
@scottmcm scottmcm added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 20, 2022
@estebank estebank added A-parser Area: The parsing of Rust source code to an AST A-inference Area: Type inference A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` D-verbose Diagnostics: Too much output caused by a single piece of incorrect code. labels Jun 20, 2022
@TaKO8Ki TaKO8Ki self-assigned this Jun 21, 2022
@alexwlchan alexwlchan mentioned this issue Dec 6, 2022
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@abs0luty
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abs0luty commented Dec 4, 2023

@rustbot claim

@rustbot rustbot assigned abs0luty and unassigned TaKO8Ki Dec 4, 2023
@fmease
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fmease commented Feb 29, 2024 •
edited
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We'd somehow need to stash the parse error without accidentally accepting this malformed input syntactically (relevant for #[cfg]'ed-out code) and steal it during type checking where we should have the necessary information available in theory. However, this looks non-trivial to fix from an architectural standpoint.

@fmease fmease assigned fmease and unassigned abs0luty Mar 9, 2024
@fmease fmease linked a pull request Mar 10, 2024 that will close this issue
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@estebank
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estebank commented Dec 4, 2024

Current output is at least less verbose:

error: expected one of `)`, `,`, `.`, `?`, or an operator, found `{`
 --> src/main.rs:7:22
  |
7 |     blah::do_stuff(_ { x: 10 });
  |                      ^ expected one of `)`, `,`, `.`, `?`, or an operator

@estebank estebank removed the D-verbose Diagnostics: Too much output caused by a single piece of incorrect code. label Dec 4, 2024
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A-diagnostics Area: Messages for errors, warnings, and lints A-inference Area: Type inference A-parser Area: The parsing of Rust source code to an AST A-suggestion-diagnostics Area: Suggestions generated by the compiler applied by `cargo fix` T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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[Proof of concept] Recover from struct literals with placeholder path fmease/rust
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@estebank @fmease @scottmcm @TaKO8Ki @abs0luty