fs: improve executable search on Windows

Ensure that when we look for an executable on Windows that we add
executable suffixes (`.exe`, `.cmd`). Without this, we would not support
looking for (eg) `ssh`, since we actually need to identify a file named
`ssh.exe` (or `ssh.cmd`) in `PATH`.

src/util/fs_path.c

@@ -611,6 +611,23 @@ bool git_fs_path_isfile(const char *path)
 	return S_ISREG(st.st_mode) != 0;
 }
 
+#ifdef GIT_WIN32
+
+bool git_fs_path_isexecutable(const char *path)
+{
+	struct stat st;
+
+	GIT_ASSERT_ARG_WITH_RETVAL(path, false);
+
+	if (git__suffixcmp_icase(path, ".exe") != 0 &&
+	    git__suffixcmp_icase(path, ".cmd") != 0)
+		return false;
+
+	return (p_stat(path, &st) == 0);
+}
+
+#else
+
 bool git_fs_path_isexecutable(const char *path)
 {
 	struct stat st;
@@ -623,6 +640,8 @@ bool git_fs_path_isexecutable(const char *path)
 	       ((st.st_mode & S_IXUSR) != 0);
 }
 
+#endif
+
 bool git_fs_path_islink(const char *path)
 {
 	struct stat st;
@@ -2032,9 +2051,10 @@ int git_fs_path_owner_is_system(bool *out, const char *path)
 	return git_fs_path_owner_is(out, path, GIT_FS_PATH_OWNER_ADMINISTRATOR);
 }
 
-int git_fs_path_find_executable(git_str *fullpath, const char *executable)
-{
 #ifdef GIT_WIN32
+
+static int find_executable(git_str *fullpath, const char *executable)
+{
 	git_win32_path fullpath_w, executable_w;
 	int error;
 
@@ -2047,20 +2067,17 @@ int git_fs_path_find_executable(git_str *fullpath, const char *executable)
 		error = git_str_put_w(fullpath, fullpath_w, wcslen(fullpath_w));
 
 	return error;
+}
+
 #else
+
+static int find_executable(git_str *fullpath, const char *executable)
+{
 	git_str path = GIT_STR_INIT;
 	const char *current_dir, *term;
 	size_t current_dirlen;
 	bool found = false;
 
-	/* For qualified paths we do not look in PATH */
-	if (strchr(executable, '/') != NULL) {
-		if (!git_fs_path_isexecutable(executable))
-			return GIT_ENOTFOUND;
-
-		return git_str_puts(fullpath, executable);
-	}
-
 	if (git__getenv(&path, "PATH") < 0)
 		return -1;
 
@@ -2102,5 +2119,19 @@ int git_fs_path_find_executable(git_str *fullpath, const char *executable)
 
 	git_str_clear(fullpath);
 	return GIT_ENOTFOUND;
-#endif
+}
+
+#endif
+
+int git_fs_path_find_executable(git_str *fullpath, const char *executable)
+{
+	/* For qualified paths we do not look in PATH */
+	if (strchr(executable, '/') != NULL) {
+		if (!git_fs_path_isexecutable(executable))
+			return GIT_ENOTFOUND;
+
+		return git_str_puts(fullpath, executable);
+	}
+
+	return find_executable(fullpath, executable);
 }

src/util/win32/path_w32.c

@@ -253,26 +253,67 @@ static void win32_path_iter_dispose(struct win32_path_iter *iter)
 	iter->current_dir = NULL;
 }
 
+struct executable_suffix {
+	const wchar_t *suffix;
+	size_t len;
+};
+
 int git_win32_path_find_executable(git_win32_path fullpath, wchar_t *exe)
 {
 	struct win32_path_iter path_iter;
 	const wchar_t *dir;
 	size_t dir_len, exe_len = wcslen(exe);
 	bool found = false;
+	static struct executable_suffix suffixes[] = { { NULL, 0 }, { L".exe", 4 }, { L".cmd", 4 } };
+	size_t skip_bare = 1, i;
 
 	if (win32_path_iter_init(&path_iter) < 0)
 		return -1;
 
-	while (win32_path_iter_next(&dir, &dir_len, &path_iter) != GIT_ITEROVER) {
-		if (git_win32_path_join(fullpath, dir, dir_len, exe, exe_len) < 0)
+	/* see if the given executable has an executable suffix; if so we will
+	 * look for the explicit name directly, as well as with added suffixes.
+	 */
+	for (i = 0; i < ARRAY_SIZE(suffixes); i++) {
+		struct executable_suffix *suffix = &suffixes[i];
+
+		if (!suffix->len)
 			continue;
 
-		if (_waccess(fullpath, 0) == 0) {
-			found = true;
+		if (exe_len < suffix->len)
+			continue;
+
+		if (memcmp(&exe[exe_len - suffix->len], suffix->suffix, suffix->len) == 0) {
+			skip_bare = 0;
 			break;
 		}
 	}
 
+	while (win32_path_iter_next(&dir, &dir_len, &path_iter) != GIT_ITEROVER && !found) {
+		/*
+		 * if the given name has an executable suffix, then try looking for it
+		 * directly. in all cases, append executable extensions
+		 * (".exe", ".cmd"...)
+		 */
+		for (i = skip_bare; i < ARRAY_SIZE(suffixes); i++) {
+			struct executable_suffix *suffix = &suffixes[i];
+
+			if (git_win32_path_join(fullpath, dir, dir_len, exe, exe_len) < 0)
+				continue;
+
+			if (suffix->len) {
+				if (dir_len + exe_len + 1 + suffix->len > MAX_PATH)
+					continue;
+
+				wcscat(fullpath, suffix->suffix);
+			}
+
+			if (_waccess(fullpath, 0) == 0) {
+				found = true;
+				break;
+			}
+		}
+	}
+
 	win32_path_iter_dispose(&path_iter);
 
 	if (found)