-Wmissing-declarations is not implemented to mean what GCC means

[llvmbot]

Bugzilla Link	16286
Version	unspecified
OS	Linux
Attachments	basic test case for both warnings
Reporter	LLVM Bugzilla Contributor
CC	@dwblaikie

Extended Description

Even more than the still-unfixed bug #​4803, I find -Wmissing-declarations essential in C++ to make accidental parameter mismatches compiler errors rather than linker errors.

However, -Wmissing-declarations seems to be used for something else, as in bug #​10830.

Additionally, you could emit better warnings than GCC if, when emitting the warning for -Wmissing-declarations, you also emit the location of any declarations this definition is overloading.

[dwblaikie]

I don't really understand what bug you're describing. Can you show an example of the problem this bug is about? (which code does GCC produce a missing-declaration warning on where Clang remains silent, or the other way around?)

[llvmbot]

In the attachment, GCC produces:

declarations.cpp:7:6: error: no previous declaration for ‘void foo(unsigned int)’ [-Werror=missing-declarations]

but clang (tested 3.2 and 3.3rc3) produces nothing.

[dwblaikie]

Seems we warn on 'foo(unsigned)' under -Wmissing-prototypes.\

Clang uses -Wmissing-declarations for extension warnings like "declaration does not declare anything" and "typedef requires a name"

Not sure how we should resolve that inconsistency, but there it is.

[llvmbot]

GCC documents -Wmissing-prototypes as only applying to C code, and complains if it is used with C++.

It is intended for the following C code:

int frob();
int frob(int arg) { return arg; }