fixup! Add functionality for converting UNIX paths in arguments and e…

…nvironment variables to Windows form for native Win32 applications.

Let's prevent scp-style arguments from being mangled by MSYS2's path
conversion.

An argument like `me@example.com:/tmp/` is not something we should convert
into a Windows path; Use the absence of a slash before the colon as a
tell-tale that it is *not* a POSIX path list (exception: if the part
left of the colon is `.` or `..`).

This addresses the expectations of the following test cases in the test
suite of https://github.com/git/git/tree/v2.43.0:

-t5516.8 fetch with insteadOf
-t5516.16 push with insteadOf
-t5516.17 push with pushInsteadOf
-t5602.2 clone calls git upload-pack unqualified with no -u option
-t5602.3 clone calls specified git upload-pack with -u option
-t5603.31 clone of host:/ goes to host (non-bare)
-t5603.35 clone of user@host:/ goes to host (non-bare)
-t5813.81 full paths still work

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

winsup/cygwin/msys2_path_conv.cc

@@ -462,6 +462,8 @@ path_type find_path_start_and_type(const char** src, int recurse, const char* en
 
     int starts_with_minus = 0;
     int starts_with_minus_alpha = 0;
+    int only_dots = *it == '.';
+    int has_slashes = 0;
     if (*it == '-') {
       starts_with_minus = 1;
       it += 1;
@@ -505,11 +507,17 @@ path_type find_path_start_and_type(const char** src, int recurse, const char* en
                 if (ch == '/' && *(it2 + 1) == '/') {
                     return URL;
                 } else {
+                    if (!only_dots && !has_slashes)
+                        goto skip_p2w;
                     return POSIX_PATH_LIST;
                 }
             } else if (memchr(it2, '=', end - it2) == NULL) {
                 return SIMPLE_WINDOWS_PATH;
             }
+        } else if (ch != '.') {
+            only_dots = 0;
+            if (ch == '/' || ch == '\\')
+                has_slashes = 1;
         }
     }