diagnostic for referring to nested class before that type is complete refers to wrong type

[llvmbot]

Bugzilla Link	11399
Resolution	FIXED
Resolved on	Jun 29, 2013 23:26
Version	unspecified
OS	All
Reporter	LLVM Bugzilla Contributor
CC	@DougGregor,@efriedma-quic

Extended Description

clang provides a slightly noisy set of diagnostics for the following

class Foo {
Foo(Bar const &p);
class Bar {};
};

The results are:

automata.cpp:79:10: error: expected ')'
Foo(Bar const &p);
^
automata.cpp:79:5: note: to match this '('
Foo(Bar const &p);
^
automata.cpp:79:6: error: field has incomplete type 'Foo'
Foo(Bar const &p);
^
automata.cpp:78:7: note: definition of 'Foo' is not complete until the closing '}'
class Foo {
^

The third diagnostic points out the issue that the type 'Bar' is incomplete, however the diagnostic says it has the incomplete type 'Foo'. The attached note then refers to 'Foo' again to point out when exactly the type becomes complete, however because clang got the wrong type it's pointing at the wrong thing.

Also, the first two diagnostics are just unhelpful noise. A better result might be just the following two diagnostics:

automata.cpp:79:6: error: field has incomplete type 'Bar'
Foo(Bar const &p);
^
automata.cpp:80:8: note: definition of 'Bar' is not complete until the closing '}'
class Bar {};
^

[efriedma-quic]

The diagnostics here are bad because the parser starts looking at "Foo(Bar" and immediately concludes it's not a constructor declaration because "Bar" isn't a decl-specifier.

I think it's feasible to look one token further and see that "Foo(Bar const" can't be a field declaration, and we can therefore assume that Bar is a type whose declaration is accidentally missing. It's impossible to handle every case of this sort of mistake, though: the meaning of "Foo(Bar(Foo));" inside a class Foo, for example, changes drastically depending on whether Bar resolves to the name of a type.

[llvmbot]

I don't know when this was fixed but it is as of e103979ceac63c98873f3307ee897eab559356a0, or r185264

clang's output is now:

---

main.cpp:2:6: error: unknown type name 'Bar'
Foo(Bar const &);
^
main.cpp:2:10: error: expected ')'
Foo(Bar const &);
^
main.cpp:2:5: note: to match this '('
Foo(Bar const &);
^
2 errors generated.

Although I notice that without the const the extraneous "error: expected ')'" also disappears:

---

main.cpp:2:6: error: unknown type name 'Bar'
Foo(Bar &);
^
1 error generated.