Dredd could still inject headers before Feature Test Macros

[JonathanFoo0523]

As an example, consider this adaptation from #215 (addressed by #220 )

void bar() { int x = 2; };

#define _GNU_SOURCE
#include <sys/mman.h>
void foo() {
  size_t a = 4096;
  mremap;
}

Dredd will mutate the statement in bar() and place its headers and prelude functions at the beginning of file.

Not that I encountered this problem in an actual codebase (and I believe this pattern is very unlikely), but I just opened an issue here for documentation purposes.

[afd]

As the problem of where to insert the prelude seems hard to solve in general, one option could be to allow the user to write a dummy function prototype:

void __dredd_prelude();

in a source file.

If encountered, the Dredd prelude would be inserted right after (or in place of) this function prototype. Otherwise, the current behaviour would be used.

This would allow the user to control where the prelude is emitted in tricky cases.

[afd]

Actually this is especially difficult, because of the fact that Dredd would mutate the code in bar, for which it would need its header files.

[afd]

I propose we close this as __dredd_prelude_start() offers one way to control where the prelude is placed, and the troubleshooting part of the README explains that placement of the prelude can be an issue. I don't see a way to solve this problem in full generality, meaning that this issue would just remain open indefinitely.