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Custom diagnostic for bad mut in pattern with sub-bindings #63764
Description
Given (as brought up in #63693 (comment) CC @Centril):
pub fn main() {
struct Foo { x: isize }
let mut Foo { x: x } = Foo { x: 3 };
}
We currently emit a parse error:
error: expected one of `:`, `;`, `=`, or `@`, found `{`
--> src/main.rs:3:17
|
3 | let mut Foo { x: x } = Foo { x: 3 };
| ^ expected one of `:`, `;`, `=`, or `@` here
It should instead parse as if it were let Foo { x: mut x } = Foo { x: 3 }; (medium priority), silence any complaints that mut is unnecessary (lower priority) and emit a custom error explaining that mut cannot lead a pattern with subpatterns (must have), and suggest the appropriate mut placement in the sub-bindings (nice to have):
error: incorrect `mut` pattern
--> src/main.rs:3:17
|
3 | let mut Foo { x: x } = Foo { x: 3 };
| ^^^ patterns with sub-bindings can't be marked as `mut`
help: mark the individual sub-bindings as `mut` instead
3 | let Foo { x: mut x } = Foo { x: 3 };
| -- ^^^
Activity
Centril commentedon Aug 20, 2019
This should be relatively easy to do by hooking into
rust/src/libsyntax/parse/parser/pat.rs
Line 289 in bea0372
reftoken does not follow you simply call the recursive pattern parser and then once you have parsed aPatKindyou walk (with a mutating visitor) to all the binding sites, insert amutthere, pretty print it and suggest the output.Centril commentedon Aug 20, 2019
Marking as blocked for now on #63693 so we don't get a lot of conflicts.
Rollup merge of rust-lang#63945 - Centril:recover-mut-pat, r=estebank