Re: [PATCH v2 2/3] relative_path should honor dos_drive_prefix

Tvangeste found that the "relative_path" function could not work
properly on Windows if "in" and "prefix" have dos driver prefix.
($gmane/234434)

e.g., When execute: test-path-utils relative_path "C:/a/b" "D:/x/y",
should return "C:/a/b", but returns "../../C:/a/b", which is wrong.

So make relative_path honor dos_drive_prefix, and add test cases
for it in t0060.

Reported-by: Tvangeste <redacted>
Helped-by: Johannes Sixt [off-list ref]
Signed-off-by: Jiang Xin <redacted>
---
 path.c                | 20 ++++++++++++++++++++
 t/t0060-path-utils.sh |  4 ++++
 2 files changed, 24 insertions(+)

diff --git a/path.c b/path.c
index 9fd28bcd..65d376d 100644
--- a/path.c
+++ b/path.c

@@ -434,6 +434,16 @@ int adjust_shared_perm(const char *path)
 	return 0;
 }
 
+static int have_same_root(const char *path1, const char *path2)
+{
+	int is_abs1, is_abs2;
+
+	is_abs1 = is_absolute_path(path1);
+	is_abs2 = is_absolute_path(path2);
+	return (is_abs1 && is_abs2 && tolower(path1[0]) == tolower(path2[0])) ||
+	       (!is_abs1 && !is_abs2);
+}
+

 	while (i < prefix_len && j < in_len && prefix[i] == in[j]) {
 		if (is_dir_sep(prefix[i])) {
 			while (is_dir_sep(prefix[i]))

diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index 82a6f21..0187d11 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh

@@ -210,6 +210,10 @@ relative_path foo/a/b/		foo/a/b		./
 relative_path foo/a		foo/a/b		../
 relative_path foo/x/y		foo/a/b		../../x/y
 relative_path foo/a/c		foo/a/b		../c
+relative_path foo/a/b		/foo/x/y	foo/a/b
+relative_path /foo/a/b		foo/x/y		/foo/a/b
+relative_path d:/a/b		D:/a/c		../b		MINGW
+relative_path C:/a/b		D:/a/c		C:/a/b		MINGW