Defining an alias to _has_include fails

[martis42]

Preprocessing code which creates an alias to _has_include() via #define FOO _has_include cannot be processed with wave.
A real world example for this is googletest, see here: https://github.com/google/googletest/blob/52eb8108c5bdec04579160ae17225d66034bd723/googletest/include/gtest/internal/gtest-port.h#L277-L281

A minimal test case for this is

#define HAS_INCLUDE __has_include
#if HAS_INCLUDE(<header>)
#endif

[jefftrull]

Thanks for the bug report!

I notice first off that __has_include is a function-like macro, which this example is executing in an unusual way - that is, it defines an object-like macro which is the name, then applies the function call syntax. Have you tried any other function-like macros (e.g. defined)? I wonder if:

1. this is a more general problem or is specific to this case, and
2. whether defining HAS_INCLUDE as function-like would be a suitable workaround

[martis42]

Thanks for the fast reply!

1. this is a more general problem or is specific to this case, ..

To my understanding we are talking about the generalized case:

#define FN_MACRO(x) (x) * (x)
#define FN_MACRO_ALIAS FN_MACRO

#if FN_MACRO_ALIAS(2) == 4
#define SUCCESS
#else
#error Failure
#endif

This works. I tested this in my own project using wave as well as with a new test case for wave, see this contributed test case: #262
This also works when configuring C++ 17/20/23 standard versions for wave.

2. whether defining HAS_INCLUDE as function-like would be a suitable workaround

I do not have the failing code under control, it is located inside googletest (see link in initial message). I don't believe they will be open to change this. Plus, my tool utilizing wave is used by others to analyze their Bazel C++ projects. I can't tell my users my tool works only with a future to be released googletest version or by patching googletest.

[jefftrull]

I'm glad to hear that object-type macros and function-type macros work properly when they are not "special".

For the two special cases (defined and __has_include) I was considering, it looks like gcc and clang both accept all variations of __has_include usage, so we should support that too.

It looks like the wave "tool" produces error: ill formed preprocessor expression: 0(<0>) for uses of both object and function type variations of macros defined as __has_include

[martis42]

Now I realize I misunderstood your first message. You meant defined like in #if defined FOO didn't you?
Will create test case for this as well the next time i have a free minute.

[jefftrull]

There's no need. I have established that defined() and __has_include() are treated differently by gcc and clang and Wave is arguably compatible - at least with clang - in that regard.