Recover from typo where == is used in place of =

[chenyukang]

Fixes#101477

[rust-highfive]

r? @fee1-dead

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[fee1-dead]

Nice work! LGTM pending error message improvements. Also, could this be using SessionDiagnostics instead? cc @davidtwco

[fee1-dead]

Suggested change

	letmut err = self.struct_span_err(self.token.span,"expect `=`, found `==`");
	err.span_suggestion_short(self.token.span,"write `=` instead of `==`","=", appl)
	letmut err = self.struct_span_err(self.token.span,"unexpected `==`");
	err.span_suggestion_short(self.token.span,"try using `=` instead","=", appl)

[chenyukang]

SessionDiagnostic will print the suggestion in the same line, so it will print like this:

error: unexpected `==` --> src/test/ui/parser/issue-101477-enum.rs:6:7 |6 | B == 2 //~ ERROR unexpected `==` | ^^ help: try using `=` instead `==`: `=`

I think it's better in this format?

error: unexpected `==` --> src/test/ui/parser/issue-101477-enum.rs:6:7 |6 | B == 2 //~ ERROR unexpected `==` | ^^ help: replace `==` with a equal symbol: `=`

[chenyukang]

Resolved with @compiler-errors with advices.

[davidtwco]

Also, could this be using SessionDiagnostics instead? cc @davidtwco

This could absolutely use SessionDiagnostic, I'd appreciate it if it did - see #100717.

[chenyukang]

Also, could this be using SessionDiagnostics instead? cc @davidtwco

This could absolutely use SessionDiagnostic, I'd appreciate it if it did - see #100717.

@davidtwco
I'm fixing it to use SessionDiagnostic, I have a question when using it:

How can I keep returning an Err to avoid extra useless diagnostics?

- let mut err = self.struct_span_err(self.token.span, "unexpected `==`");- err.span_suggestion_short(self.token.span, "try using `=` instead `==`", "=", appl)- .emit();- return Err(err);+ self.sess.emit_err(UseEqInstead { span: self.token.span });+ return Ok(true);

I use return Ok now and there will be a extra diagnostics which I want to remove.

--- a/src/test/ui/parser/issue-101477-let.stderr+++ b/src/test/ui/parser/issue-101477-let.stderr@@ -2,7 +2,13 @@ error: unexpected `==`
--> $DIR/issue-101477-let.rs:4:11
|
LL | let x == 2;
- | ^^ help: try using `=` instead `==`+ | ^^ help: replace `==` with a equal symbol: `=`-error: aborting due to previous error+error: expected expression, found `==`+ --> $DIR/issue-101477-let.rs:4:11+ |+LL | let x == 2;+ | ^^ expected expression++error: aborting due to 2 previous errors

[chenyukang]

Seems we use this struct to avoid later errors:

/// Useful type to use with `Result<>` indicate that an error has already/// been reported to the user, so no need to continue checking.#[derive(Clone,Copy,Debug,Encodable,Decodable,Hash,PartialEq,Eq,PartialOrd,Ord)]#[derive(HashStable_Generic)]pubstructErrorGuaranteed(());

But parse_let_expr is:

fnparse_let_expr(&mutself) -> PResult<'a,P<Expr>>{
...self.expect(&token::Eq)?;
...Ok(self.mk_expr(span,ExprKind::Let(pat, expr, span)))}

[chenyukang]

Got it:

letmut err = self.sess.create_err(UseEqInstead{span:self.token.span});
err.emit();returnErr(err);

[rustbot]

rustc_error_messages was changed

cc @davidtwco, @compiler-errors, @JohnTitor, @estebank, @TaKO8Ki

[fee1-dead]

@bors r+

[bors]

📌 Commit ddb225f has been approved by fee1-dead

It is now in the queue for this repository.