Because of how files and executables work on Windows, scripts that use
an interpreter must have an extension, and that extension must be
associated with an interpreter. The full list of executable extensions
is available in the PATHEXT environment variable.
However, UNIX-like OSes use an executable bit and read the shebang to
figure out what interpreter to use, and the scripts don't need to have
extensions. We can now detect these scripts using find_program by
manually searching in PATH and reading the shebang.
This gives a clearer output when the dependency is not required or has a
fallback subproject otherwise the user is left wondering why the optional
dependency wasn't used or why the fallback subproject is being used.
Just exit immediately when there's no pkg-config file found instead of putting
everything else in a huge 'else:'. Much clearer and avoids one level of
indentation.
No code changes accompany this.
This allows a project to use the same fallbacks dependency from the same
subproject multiple times in the same way that external dependencies can be.
Also change the format of the dependency identifier to ensure that fallback
checks with different dirname/varname aren't mistakenly reused. We now use
a tuple for this because the format is simpler to construct and it gives us the
same immutability guarantees as a string which is needed for using it as
a dictionary key.
Nirbheek Chauhan