Detect missing `else` in block with `return`

[estebank]

error: expected identifier, found keyword `return`
   --> /home/gh-estebank/rust/compiler/rustc_lint/src/default_could_be_derived.rs:249:13
    |
248 |         let hir::VariantData::Struct { fields, recovered: Recovered::No } = data {
    |                                                                             ---- while parsing this struct
249 |             return;
    |             ^^^^^^ expected identifier, found keyword
    |
help: escape `return` to use it as an identifier
    |
249 |             r#return;
    |             ++

This should detect that there's a missing else: = data else {.

[11happy]

Hello @estebank I am new to Rust community & this issue looks interesting to me. Can I work on this ?
Thank you

[estebank]

@11happy you can! You should look at the parser for this. You can look at the docs https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html to set up your environment and after that you can use rustc +your-toolchain file.rs -Ztrack-diagnostics to see where the error is emitted.

[11happy]

Sure! Thank you for the headstart.

@rustbot claim