win32: handle Unix-style absolute paths for executables

As noted in commit 548ec7045 (win32: interpret absolute paths as
relative to %SYSTEMDRIVE%) a path starting with a '/' in the Unix
world is treated as relative to the current drive by Windows.
To avoid ambiguity that commit considered certain such paths to
be relative to %SYSTEMDRIVE%.  Extend this to paths representing
executables.

Add the functions need_system_drive() and auto_add_system_drive()
to detect the need for a system drive prefix and to add it if
necessary.  Use these functions in:

- the 'which' applet
- the find_executable() function
- tab-completion code
- PATH look-up, shellexec(), describe_command() and find_command() in ash
- parse_interpreter() and mingw_spawn_1()

With these changes executable paths starting with a slash are
handled consistently, whatever the current drive.

1 files changed, 15 insertions, 0 deletions

diff --git a/win32/mingw.c b/win32/mingw.c
index 8501ecdd4..e63ffa0ac 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1698,6 +1698,21 @@ const char *get_system_drive(void)
         return drive;
 }
 
+/* Return pointer to system drive if path is of form '/file', else NULL */
+const char *need_system_drive(const char *path)
+{
+        if (root_len(path) == 0 && (path[0] == '/' || path[0] == '\\'))
+                return get_system_drive();
+        return NULL;
+}
+
+/* Add a system drive prefix to 'path' if necessary, else return 'path' */
+char *auto_add_system_drive(const char *path)
+{
+        const char *sd = need_system_drive(path);
+        return sd ? auto_string(concat_path_file(sd, path)) : (char *)path;
+}
+
 int chdir_system_drive(void)
 {
         const char *sd = get_system_drive();