C++: support the search order of header files used by clang/gcc

[qwerty472123]

As a example:

• a/a.h

#include "b.h"

• a/c.h

hi_c c;

• b/b.h

#include "c.h"

• c/c.h

hello_c c;

• test.cpp

#include "a/a.h"

# clang++ -I b -I c -c test.cpp -otest
In file included from test.cpp:1:
In file included from ./a/a.h:1:
In file included from b/b.h:1:
c/c.h:1:1: error: unknown type name 'hello_c'
hello_c c;
^
1 error generated.
# g++ -I b -I c -c test.cpp -otest
In file included from b/b.h:1:0,
                 from a/a.h:1,
                 from test.cpp:1:
c/c.h:1:1: error: ‘hello_c’ does not name a type
 hello_c c;
 ^~~~~~~

however, when use codeql extractor by /usr/local/bin/codeql/cpp/tools/linux64/extractor --mimic clang++ -I b -I c -c test.cpp -otest, it shows

"a/c.h", line 1: error: identifier "hi_c" is undefined
  hi_c c;
  ^

[E 09:26:49 145792] Warning[extractor-c++]: In construct_text_message: "a/c.h", line 1: error: identifier "hi_c" is undefined
  hi_c c;
  ^

It includes a/c.h, which is the same with MSVC, but gcc/clang includes c/c.h.

Clang and GCC using a static context for search directory, but MSVC use a dynamic context, which caused the problem.

I wanna CodeQL extractor to support the behavior of Clang and GCC for more consistent result with the clang compiled ELF.

[jketema]

Hi @qwerty472123,

Thanks for your report. This indeed seems incorrect. I've opened an internal issue to track this.