printf.h: definition of ATTR_PRINTF is invalid without __GNUC__

[smcpeak]

As of commit 87878b2, printf.h when preprocessed without __GNUC__ has this macro definition:

# define ATTR_PRINTF((one_based_format_index), (first_arg))

This is invalid since the macro parameters have extra parentheses. cpp -undef (which does not set __GNUC__) complains:

$ cpp -undef printf.h >/dev/null
printf.h:56:22: error: expected parameter name, found "("
   56 | # define ATTR_PRINTF((one_based_format_index), (first_arg))
      |                      ^
Exit 1
$ cpp --version
cpp (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

In the original commit, that line should not have been changed.

Ideally, there should also be an automated test that exercises this printf implementation without __GNUC__, as that would have caught this error.

[eyalroz]

First, thank you for reporting this bug.

Now, would you like to submit a PR? Indeed, I currently only test on GNUC-ish compilers. Perhaps I should work on creating an MSVC workflow.

[smcpeak]

I hesitate to submit a PR since (ideally) it should include a test and I'm not sure what would fit best in this project. (And, as I'm working on other things, I'm not able to properly explore that currently.)

However, as for how to test, one suggestion is to preprocess with cpp -undef to get a "compiler-agnostic" version and then feed that to GCC. That's effectively what I was doing when I ran into this.

[eyalroz]

@smcpeak : Well, I don't know about cpp -undef. It` will break the library in a dozen ways. I think it undefines more than you might expect.