To check header files with clang-check, it is often suggested to just pass the header to clang-check. However, this does not work well when the header contains a #pragma once guard, because the compiler thinks it is in the main file:
/some/path/foo.h:1:9: warning: #pragma once in main file [-Wpragma-once-outside-header]
#pragma once
^
It might seem to be sufficient to disable the warning by adding -Wno-pragma-once-outside-header to compile_flags.txt (or the compilation database), but there may be other errors caused by the compiler ignoring the #pragma once guard in a main file. This is best explained with an example.
Consider the following mini-project structure:
foo.h:
#pragma once
class Foo
{
Foo();
};
#include "foo.hpp"
foo.hpp:
#pragma once
#include "foo.h"
Foo::Foo()
{
// do something...
}
compiler_flags.txt:
-xc++
Then running clang-check foo.h leads to these errors:
/some/path/foo.h:1:9: warning: #pragma once in main file [-Wpragma-once-outside-header]
#pragma once
^
In file included from ./foo.h:8:
In file included from ./foo.hpp:3:
./foo.h:3:7: error: redefinition of 'Foo'
class Foo
^
./foo.hpp:3:10: note: './foo.h' included multiple times, additional include site here
#include "foo.h"
^
1 warning and 1 error generated.
Error while processing /some/path/foo.h.
I think the problem could be solved by handling header files differently. An intermediate C++ source file that just includes the given header file could be created and used as an "entry point" for the analysis. Maybe this can be configured somehow?
