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, 3 insertions, 0 deletions

diff --git a/libbb/executable.c b/libbb/executable.c
index 87a40eeda..0a0769ef3 100644
--- a/libbb/executable.c
+++ b/libbb/executable.c
@@ -49,6 +49,9 @@ char* FAST_FUNC find_executable(const char *filename, char **PATHp)
 
                 n = strchr(p, PATH_SEP);
                 if (n) *n = '\0';
+#if ENABLE_PLATFORM_MINGW32
+                p = auto_add_system_drive(p);
+#endif
                 p = concat_path_file(
                         p[0] ? p : ".", /* handle "::" case */
                         filename