[PATCH v1/RFC 1/1] 'git clone <url> C:\cygwin\home\USER\repo' is working (again)

[tboegi@web.de]

From: Torsten Bögershausen <tboegi@web.de>

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The old (and non-thread-save) OS calls chdir()/pwd() had been
replaced by a string operation.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]

Reported-By: Steven Penny <svnpenn@gmail.com>
Signed-off-by: Torsten Bögershausen <tboegi@web.de>
---

This is the first vesion of a patch.
Is there a chance that you test it ?

abspath.c       |  2 +-
 compat/cygwin.c | 18 ++++++++++++++----
 compat/cygwin.h | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/abspath.c b/abspath.c
index 9857985329..77a281f789 100644
--- a/abspath.c
+++ b/abspath.c
@@ -55,7 +55,7 @@ static void get_root_part(struct strbuf *resolved, struct strbuf *remaining)
 
 	strbuf_reset(resolved);
 	strbuf_add(resolved, remaining->buf, offset);
-#ifdef GIT_WINDOWS_NATIVE
+#if defined(GIT_WINDOWS_NATIVE) || defined(__CYGWIN__)
 	convert_slashes(resolved->buf);
 #endif
 	strbuf_remove(remaining, 0, offset);
diff --git a/compat/cygwin.c b/compat/cygwin.c
index b9862d606d..c4a10cb5a1 100644
--- a/compat/cygwin.c
+++ b/compat/cygwin.c
@@ -1,19 +1,29 @@
 #include "../git-compat-util.h"
 #include "../cache.h"
 
+int cygwin_skip_dos_drive_prefix(char **path)
+{
+	int ret = has_dos_drive_prefix(*path);
+	*path += ret;
+	return ret;
+}
+
 int cygwin_offset_1st_component(const char *path)
 {
-	const char *pos = path;
+	char *pos = (char *)path;
+
 	/* unc paths */
-	if (is_dir_sep(pos[0]) && is_dir_sep(pos[1])) {
+	if (!skip_dos_drive_prefix(&pos) &&
+			is_dir_sep(pos[0]) && is_dir_sep(pos[1])) {
 		/* skip server name */
-		pos = strchr(pos + 2, '/');
+		pos = strpbrk(pos + 2, "\\/");
 		if (!pos)
 			return 0; /* Error: malformed unc path */
 
 		do {
 			pos++;
-		} while (*pos && pos[0] != '/');
+		} while (*pos && !is_dir_sep(*pos));
 	}
+
 	return pos + is_dir_sep(*pos) - path;
 }
diff --git a/compat/cygwin.h b/compat/cygwin.h
index 8e52de4644..46f29c0a90 100644
--- a/compat/cygwin.h
+++ b/compat/cygwin.h
@@ -1,2 +1,34 @@
+#define has_dos_drive_prefix(path) \
+	(isalpha(*(path)) && (path)[1] == ':' ? 2 : 0)
+
+
+int cygwin_offset_1st_component(const char *path);
+#define offset_1st_component cygwin_offset_1st_component
+
+
+#define has_dos_drive_prefix(path) \
+	(isalpha(*(path)) && (path)[1] == ':' ? 2 : 0)
+int cygwin_skip_dos_drive_prefix(char **path);
+#define skip_dos_drive_prefix cygwin_skip_dos_drive_prefix
+static inline int cygwin_is_dir_sep(int c)
+{
+	return c == '/' || c == '\\';
+}
+#define is_dir_sep cygwin_is_dir_sep
+static inline char *cygwin_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 cygwin_find_last_dir_sep
 int cygwin_offset_1st_component(const char *path);
 #define offset_1st_component cygwin_offset_1st_component
-- 
2.19.0.271.gfe8321ec05