Support for using iwyu under various sets of compiler flags

[KierenP]

Hi, I'm using IWYU currently at my workplace and I've run into an issue. The software I am building supports various mutually exclusive targets set by compiler flags. For example, I might build the software with -DTARGET_A or -DTARGET_B.

Currently, I apply the iwyu_tool.py tool with a compilation database.

The issue is, if I am building the software with -DTARGET_A, iwyu suggests the removal of #include's that are only required by -DTARGET_B. Is there any support for combining the results of iwyu when build under multiple compiler flag sets and only removing includes if they are needed for none of the options?

As a mini example, take the following file:

#include <array>
#include <vector>

void fn()
{
#ifdef TARGET_A
    std::vector<int> v;
#endif

#ifdef TARGET_B
    std::array<int, 10> a;
#endif
}

After invoking <path to binary>/include-what-you-use test_file.cpp -DTARGET_A=1 it gives the following output:

test_file.cpp should add these lines:

test_file.cpp should remove these lines:
- #include <array>  // lines 2-2

The full include-list for test_file.cpp:
#include <vector>  // for vector
---

After invoking <path to binary>/include-what-you-use test_file.cpp -DTARGET_B=1 it gives the following output:

test_file.cpp should add these lines:

test_file.cpp should remove these lines:
- #include <vector>  // lines 3-3

The full include-list for test_file.cpp:
#include <array>  // for array
---

Is there any support or tooling to support applying iwyu recommendations across multiple runs with various compiler flag settings?

[i-ky]

As a mini example, take the following file:

#include <array>
#include <vector>

void fn()
{
#ifdef TARGET_A
    std::vector<int> v;
#endif

#ifdef TARGET_B
    std::array<int, 10> a;
#endif
}

This is my personal opinion, but I would suggest wrapping #include directives with appropriate #ifdef directives. Some people think it's ugly, I don't mind. You probably need to do a similar thing with uses of v and a to avoid "unused variable" warnings. Unless, of course, if their scope is very limited and fits inside one #ifdef with a declaration.

[kimgr]

How about running IWYU with both -DTARGET_A=1 -DTARGET_B=1 defined?

The suggestion from @i-ky also makes sense to me, and allows you to IWYU one configuration at a time.

[KierenP]

Thanks for getting back to me on this.

Without going into specifics I can't build the software with more than one target enabled at a time so @kimgr that idea is sadly not possible.

@i-ky's idea is interesting. Sadly, it would require a major refactor of our codebase to guard target specific includes with preproccessor directives so I don't think that's possible for me either.

Thank you both for your help.