git clone <url> C:\cygwin\home\USER\repo' is working (again)

A regression for cygwin users was introduced with commit 05b458c,
 "real_path: resolve symlinks by hand".

In the the commit message we read:
  The current implementation of real_path uses chdir() in order to resolve
    symlinks.  Unfortunately this isn't thread-safe as chdir() affects a
      process as a whole...

The old (and non-thread-save) OS calls chdir()/pwd() had been
replaced by a string operation.
The cygwin layer "knows" that "C:\cygwin" is an absolute path,
but the new string operation does not.

"git clone <url> C:\cygwin\home\USER\repo" fails like this:
fatal: Invalid path '/home/USER/repo/C:\cygwin\home\USER\repo'

The solution is to implement has_dos_drive_prefix(), skip_dos_drive_prefix()
is_dir_sep(), offset_1st_component() and convert_slashes() for cygwin
in the same way as it is done in 'Git for Windows' in compat/mingw.[ch]

Extract the needed code into compat/win32/path-utils.[ch] and use it
for cygwin as well.

Reported-by: Steven Penny <svnpenn@gmail.com>
Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

6 files changed, 49 insertions, 69 deletions

diff --git a/compat/cygwin.c b/compat/cygwin.c
deleted file mode 100644
index b9862d606d5..00000000000
--- a/compat/cygwin.c
+++ /dev/null
@@ -1,19 +0,0 @@
-#include "../git-compat-util.h"
-#include "../cache.h"
-
-int cygwin_offset_1st_component(const char *path)
-{
-	const char *pos = path;
-	/* unc paths */
-	if (is_dir_sep(pos[0]) && is_dir_sep(pos[1])) {
-		/* skip server name */
-		pos = strchr(pos + 2, '/');
-		if (!pos)
-			return 0; /* Error: malformed unc path */
-
-		do {
-			pos++;
-		} while (*pos && pos[0] != '/');
-	}
-	return pos + is_dir_sep(*pos) - path;
-}
diff --git a/compat/cygwin.h b/compat/cygwin.h
deleted file mode 100644
index 8e52de4644d..00000000000
--- a/compat/cygwin.h
+++ /dev/null
@@ -1,2 +0,0 @@
-int cygwin_offset_1st_component(const char *path);
-#define offset_1st_component cygwin_offset_1st_component
diff --git a/compat/mingw.c b/compat/mingw.c
index 18caf21969a..76cad1fe21f 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -294,7 +294,7 @@ static inline int needs_hiding(const char *path)
 		return 0;
 
 	/* We cannot use basename(), as it would remove trailing slashes */
-	mingw_skip_dos_drive_prefix((char **)&path);
+	win32_skip_dos_drive_prefix((char **)&path);
 	if (!*path)
 		return 0;
 
@@ -2043,33 +2043,6 @@ pid_t waitpid(pid_t pid, int *status, int options)
 	return -1;
 }
 
-int mingw_skip_dos_drive_prefix(char **path)
-{
-	int ret = has_dos_drive_prefix(*path);
-	*path += ret;
-	return ret;
-}
-
-int mingw_offset_1st_component(const char *path)
-{
-	char *pos = (char *)path;
-
-	/* unc paths */
-	if (!skip_dos_drive_prefix(&pos) &&
-			is_dir_sep(pos[0]) && is_dir_sep(pos[1])) {
-		/* skip server name */
-		pos = strpbrk(pos + 2, "\\/");
-		if (!pos)
-			return 0; /* Error: malformed unc path */
-
-		do {
-			pos++;
-		} while (*pos && !is_dir_sep(*pos));
-	}
-
-	return pos + is_dir_sep(*pos) - path;
-}
-
 int xutftowcsn(wchar_t *wcs, const char *utfs, size_t wcslen, int utflen)
 {
 	int upos = 0, wpos = 0;
diff --git a/compat/mingw.h b/compat/mingw.h
index 571019d0bdd..3387c3faeb3 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -397,32 +397,12 @@ HANDLE winansi_get_osfhandle(int fd);
  * git specific compatibility
  */
 
-#define has_dos_drive_prefix(path) \
-	(isalpha(*(path)) && (path)[1] == ':' ? 2 : 0)
-int mingw_skip_dos_drive_prefix(char **path);
-#define skip_dos_drive_prefix mingw_skip_dos_drive_prefix
-static inline int mingw_is_dir_sep(int c)
-{
-	return c == '/' || c == '\\';
-}
-#define is_dir_sep mingw_is_dir_sep
-static inline char *mingw_find_last_dir_sep(const char *path)
-{
-	char *ret = NULL;
-	for (; *path; ++path)
-		if (is_dir_sep(*path))
-			ret = (char *)path;
-	return ret;
-}
 static inline void convert_slashes(char *path)
 {
 	for (; *path; path++)
 		if (*path == '\\')
 			*path = '/';
 }
-#define find_last_dir_sep mingw_find_last_dir_sep
-int mingw_offset_1st_component(const char *path);
-#define offset_1st_component mingw_offset_1st_component
 #define PATH_SEP ';'
 #if !defined(__MINGW64_VERSION_MAJOR) && (!defined(_MSC_VER) || _MSC_VER < 1800)
 #define PRIuMAX "I64u"
diff --git a/compat/win32/path-utils.c b/compat/win32/path-utils.c
new file mode 100644
index 00000000000..d9d3641de85
--- /dev/null
+++ b/compat/win32/path-utils.c
@@ -0,0 +1,28 @@
+#include "../../git-compat-util.h"
+
+int win32_skip_dos_drive_prefix(char **path)
+{
+	int ret = has_dos_drive_prefix(*path);
+	*path += ret;
+	return ret;
+}
+
+int win32_offset_1st_component(const char *path)
+{
+	char *pos = (char *)path;
+
+	/* unc paths */
+	if (!skip_dos_drive_prefix(&pos) &&
+			is_dir_sep(pos[0]) && is_dir_sep(pos[1])) {
+		/* skip server name */
+		pos = strpbrk(pos + 2, "\\/");
+		if (!pos)
+			return 0; /* Error: malformed unc path */
+
+		do {
+			pos++;
+		} while (*pos && !is_dir_sep(*pos));
+	}
+
+	return pos + is_dir_sep(*pos) - path;
+}
diff --git a/compat/win32/path-utils.h b/compat/win32/path-utils.h
new file mode 100644
index 00000000000..0f70d439204
--- /dev/null
+++ b/compat/win32/path-utils.h
@@ -0,0 +1,20 @@
+#define has_dos_drive_prefix(path) \
+	(isalpha(*(path)) && (path)[1] == ':' ? 2 : 0)
+int win32_skip_dos_drive_prefix(char **path);
+#define skip_dos_drive_prefix win32_skip_dos_drive_prefix
+static inline int win32_is_dir_sep(int c)
+{
+	return c == '/' || c == '\\';
+}
+#define is_dir_sep win32_is_dir_sep
+static inline char *win32_find_last_dir_sep(const char *path)
+{
+	char *ret = NULL;
+	for (; *path; ++path)
+		if (is_dir_sep(*path))
+			ret = (char *)path;
+	return ret;
+}
+#define find_last_dir_sep win32_find_last_dir_sep
+int win32_offset_1st_component(const char *path);
+#define offset_1st_component win32_offset_1st_component