Syntax: ignoring tuple index with a suffix (a.1lolololol)

[kpp]

fn main() {
    let a = (1, 2, 3);
    println!("{}", a.1lolololol);
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=4280ded6698f9f9f3877ad0498769cb7

Expected:

ERROR: tuple index with a suffix is invalid

Got:

Output: 2\n

All thanks to: https://linuxrocks.online/@carl/101569506337640753

UPD:

The same error arises with tuple struct:

struct X(i32,i32,i32);

fn main() {
    let a = X(1, 2, 3);
    let b = a.1lolololol;
    println!("{}", b);
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=ad7f39e8edad0d98f2919bd4fdfded30

Expected:

ERROR: tuple index with a suffix is invalid

Got:

Output: 2\n

[estebank]

Introduced in 1.27. Output in 1.26:

error: tuple index with a suffix is invalid
 --> <source>:3:22
  |
3 |     println!("{}", a.1lolololol);
  |                      ^^^^^^^^^^

[varkor]

I have a fix for this.

Edit: ah, @estebank's already self-assigned — I'll leave it to them. One thing I would do, as well as introducing a custom error message, is make sure the suffix isn't ignored in the main code path. E.g.

rust/src/libsyntax/parse/parser.rs

Lines 3210 to 3215 in 7a4df3b

	token::Literal(token::Integer(name), _) => {
	let span = self.span;
	self.bump();
	let field = ExprKind::Field(e, Ident::new(name, span));
	e = self.mk_expr(lo.to(span), field, ThinVec::new());
	}

would be better changed to something like:

token::Literal(token::Integer(name), suf) => {
    let span = self.span;
    self.bump();
    // Affix the suffix to the integer. This means that the suffix will
    // be treated as part of the field name and will not simply be ignored.
    let name = name.as_str().to_string() + suf.map_or("", |s| s.as_str().get());
    let field = ExprKind::Field(e, Ident::new(Symbol::intern(&name), span));
    e = self.mk_expr(lo.to(span), field, ThinVec::new());
}

so that even without the custom error message, the suffix is still taken into account when resolving the field name.

[estebank]

@varkor I have the fix, just waiting for --bless to finish:

                    token::Literal(token::Integer(name), suffix) => {
                        let span = self.span;
                        self.bump();
                        let field = ExprKind::Field(e, Ident::new(name, span));
                        e = self.mk_expr(lo.to(span), field, ThinVec::new());
+                       if let Some(suffix) = suffix {
+                           let mut err = self.diagnostic().struct_span_err(
+                               span,
+                               "tuple index with a suffix is invalid",
+                           );
+                           err.span_label(span, format!("invalid suffix `{}`", suffix));
+                           err.emit();
+                       }
                    }