non-dependent name treated as if it were dependent, requiring use of template keyword

[llvmbot]

Bugzilla Link	38299
Resolution	DUPLICATE
Resolved on	Aug 16, 2018 07:52
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@dwblaikie,@DougGregor,@zygoloid,@steveire

Extended Description

This example fails to compile on the marked line, but nothing here is dependent.

struct X {
template
void foo();
};

struct Base {
X get();
};

template
struct Derived : Base
{
void foo() {
auto result = Base::get();
result.foo(); // (*)
}
};

template struct Derived;

The error message is:

error: use 'template' keyword to treat 'foo' as a dependent template name
result.foo(); // (*)
^
template
1 error generated.

BTW, g++ accepts the code.

[dwblaikie]

*** Bug #37644 has been marked as a duplicate of this bug. ***

[dwblaikie]

Reduced this a little further:

struct foo {
template void f1();
};
template struct bar {
foo f2();
void f1() {
f2().f1();
}
};
template struct bar;

You can assign the result of f2() to a local, so long as the type is written as 'auto' and not 'foo' the behavior is still the same - the f1 call is considered dependent and needs the 'template' keyword when it seems like it shouldn't?

Maybe this test case is less convincing than the original - the original, using a (non-templated/non-depnedent) base class to contain 'f2' maybe makes it clearer that 'f2' is not dependent, whereas I guess the call to f2 could be dependent in some sense? Not sure.

[zygoloid]

FWIW, there's a FIXME in include/clang/AST/Redeclarable.h where we're working around this bug in Clang's own source code.

[steveire]

I hit exactly this issue too.

https://bugs.llvm.org//show_bug.cgi?id=17401 also exists, but it doesn't seem to be an exact duplicate as it does not use inheritance in the repro.

*** This bug has been marked as a duplicate of bug #17775 ***

[steveire]

Another maybe-interesting datapoint - CL.exe 19.14.26430 (ie Visual Studio 15.7 I think) with /permissive- rejected code with the incorrect template keyword.

CL.exe 19.15.26726 (Visual Studio 15.8) with /permissive- accepts it and ignores the extra template keyword.

Presumably customers added the keyword to fix their clang build, and when VC++ permissive mode rejected it, customers complained and the change was backed out.

I hit this issue in FBX SDK headers.