Re: [PATCH 1/2] relative_path should honor dos_drive_prefix

2013/9/13 Junio C Hamano [off-list ref]:

Jiang Xin [off-list ref] writes:

quoted

2013/9/13 Junio C Hamano [off-list ref]:

quoted

For systems that need POSIX escape hatch for Apollo Domain ;-), we
would need a bit more work.  When both path1 and path2 begin with a
double-dash, we would need to check if they match up to the next
slash, so that

 - //host1/usr/src and //host1/usr/lib share the same root and the
   former can be made to ../src relative to the latter;

 - //host1/usr/src and //host2/usr/lib are of separate roots.

or something.

But how could we know which platform supports network pathnames and
needs such implementation.

Near the end of

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_12

is this:

    If a pathname begins with two successive <slash> characters, the
    first component following the leading <slash> characters may be
    interpreted in an implementation-defined manner, although more than
    two leading <slash> characters shall be treated as a single <slash>
    character.

Two points to note are

 (1) Only paths that begin with exactly two slashes are special.

 (2) As it is "implementation-defined", we are not even allowed to
     treat that //host1/usr/src and //host1/usr/lib as sharing "the
     same root", and make the former to ../src relative to the
     latter.

So in the strictest sense, we do not have to bother. As long as we
make sure we do not molest anything that begins with exactly two
slashes.

I have checked the behavior of UNC path on Windows (msysGit):

* I can cd to a UNC path:

    cd //server1/share1/path

* can cd to other share:

    cd ../../share2/path

* and can cd to other server's share:

    cd ../../../server2/share/path

That means relative_path(path1, path2) support UNC paths out of the box.
We only need to check both path1 and path2 are UNC paths, or both not.

So, funciton “have_same_root" will write like this:


+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);
+       if (is_abs1 && is_abs2) {
+               if (is_unc_path(path1) ^ is_unc_path(path2))
+                       return 0;
+               return tolower(path1[0]) == tolower(path2[0]);
+       } else {
+               return !is_abs1 && !is_abs2;
+       }
+}


-- 
Jiang Xin