[PATCH v4 0/4] Ensure that we can build without libgen.h

This mini series adds a fall-back for the `dirname()` function that we use e.g. in git-am. This is necessary because not all platforms have a working libgen.h.

While at it, we ensure that our basename() drop-in conforms to the POSIX specifications.

In addition to Eric's style improvement, v4 also fixes the signature of skip_dos_drive_prefix() in the non-Windows case.

Johannes Schindelin (4):
  Refactor skipping DOS drive prefixes
  compat/basename: make basename() conform to POSIX
  Provide a dirname() function when NO_LIBGEN_H=YesPlease
  t0060: verify that basename() and dirname() work as expected

 compat/basename.c     |  66 ++++++++++++++++++--
 compat/mingw.c        |  14 ++---
 compat/mingw.h        |  10 ++-
 git-compat-util.h     |  10 +++
 path.c                |  14 ++---
 t/t0060-path-utils.sh |   3 +
 test-path-utils.c     | 166 ++++++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 259 insertions(+), 24 deletions(-)

Interdiff vs v3:

 diff --git a/compat/basename.c b/compat/basename.c
 index 0a2ed25..96bd953 100644
 --- a/compat/basename.c
 +++ b/compat/basename.c
 @@ -29,20 +29,15 @@ char *gitbasename (char *path)
  
  char *gitdirname(char *path)
  {
 +	static struct strbuf buf = STRBUF_INIT;
  	char *p = path, *slash = NULL, c;
  	int dos_drive_prefix;
  
  	if (!p)
  		return ".";
  
 -	if ((dos_drive_prefix = skip_dos_drive_prefix(&p)) && !*p) {
 -		static struct strbuf buf = STRBUF_INIT;
 -
 -dot:
 -		strbuf_reset(&buf);
 -		strbuf_addf(&buf, "%.*s.", dos_drive_prefix, path);
 -		return buf.buf;
 -	}
 +	if ((dos_drive_prefix = skip_dos_drive_prefix(&p)) && !*p)
 +		goto dot;
  
  	/*
  	 * POSIX.1-2001 says dirname("/") should return "/", and dirname("//")
 @@ -64,8 +59,13 @@ dot:
  				slash = tentative;
  		}
  
 -	if (!slash)
 -		goto dot;
 -	*slash = '\0';
 -	return path;
 +	if (slash) {
 +		*slash = '\0';
 +		return path;
 +	}
 +
 +dot:
 +	strbuf_reset(&buf);
 +	strbuf_addf(&buf, "%.*s.", dos_drive_prefix, path);
 +	return buf.buf;
  }
 diff --git a/git-compat-util.h b/git-compat-util.h
 index 94f311a..5f72f1c 100644
 --- a/git-compat-util.h
 +++ b/git-compat-util.h
 @@ -338,7 +338,7 @@ static inline int git_has_dos_drive_prefix(const char *path)
  #endif
  
  #ifndef skip_dos_drive_prefix
 -static inline int git_skip_dos_drive_prefix(const char **path)
 +static inline int git_skip_dos_drive_prefix(char **path)
  {
  	return 0;
  }