[PATCH v2] fix pushing to //server/share/dir on Windows

normalize_path_copy() is not prepared to keep the double-slash of a
//server/share/dir kind of path, but treats it like a regular POSIX
style path and transforms it to /server/share/dir.

The bug manifests when 'git push //server/share/dir master' is run,
because tmp_objdir_add_as_alternate() uses the path in normalized
form when it registers the quarantine object database via
link_alt_odb_entries(). Needless to say that the directory cannot be
accessed using the wrongly normalized path.

Fix it by skipping all of the root part, not just a potential drive
prefix. offset_1st_component takes care of this, see the
implementation in compat/mingw.c::mingw_offset_1st_component().

Signed-off-by: Johannes Sixt <redacted>
---
Am 14.12.2016 um 18:30 schrieb Jeff King:

Would it be reasonable to
write:

  /* Copy initial part of absolute path, converting separators on Windows */
  const char *end = src + offset_1st_component(src);
  while (src < end) {
	  char c = *src++;
	  if (c == '\\')
		  c = '/';
	  *dst++ = c;
  }

Makes a lot of sense! I haven't had an opportunity, though, to test
on Windows.

? I'm not sure if it's wrong to convert backslashes in that first
component or not (but certainly we were before). I don't think we'd need
is_dir_sep() in that "if()", because we can leave slashes as-is. But
maybe it would make the code easier to read.

is_dir_sep() is preferable, IMO.

I also changed the commit message and subject line slightly.

 path.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/path.c b/path.c
index 52d889c88e..efcedafba6 100644
--- a/path.c
+++ b/path.c

@@ -991,7 +991,7 @@ const char *remove_leading_path(const char *in, const char *prefix)
  *
  * Performs the following normalizations on src, storing the result in dst:
  * - Ensures that components are separated by '/' (Windows only)
- * - Squashes sequences of '/'.
+ * - Squashes sequences of '/' except "//server/share" on Windows
  * - Removes "." components.
  * - Removes ".." components, and the components the precede them.
  * Returns failure (non-zero) if a ".." component appears as first path

@@ -1014,17 +1014,22 @@ const char *remove_leading_path(const char *in, const char *prefix)
 int normalize_path_copy_len(char *dst, const char *src, int *prefix_len)
 {
 	char *dst0;
-	int i;
+	const char *end;
 
-	for (i = has_dos_drive_prefix(src); i > 0; i--)
-		*dst++ = *src++;
+	/*
+	 * Copy initial part of absolute path: "/", "C:/", "//server/share/".
+	 */
+	end = src + offset_1st_component(src);
+	while (src < end) {
+		char c = *src++;
+		if (is_dir_sep(c))
+			c = '/';
+		*dst++ = c;
+	}
 	dst0 = dst;
 
-	if (is_dir_sep(*src)) {
-		*dst++ = '/';
-		while (is_dir_sep(*src))
-			src++;
-	}
+	while (is_dir_sep(*src))
+		src++;
 
 	for (;;) {
 		char c = *src;

-- 
2.11.0.79.g263f27a