os: fix os.dir, os.base, os.file_name, when the argument contains / on windows

vlib/os/os.v

@@ -165,10 +165,11 @@ pub fn file_ext(path string) string {
 // If the path is empty, dir returns ".". If the path consists entirely of separators,
 // dir returns a single separator.
 // The returned path does not end in a separator unless it is the root directory.
-pub fn dir(path string) string {
-	if path == '' {
+pub fn dir(opath string) string {
+	if opath == '' {
 		return '.'
 	}
+	path := opath.replace_each(['/', path_separator, r'\', path_separator])
 	pos := path.last_index(path_separator) or { return '.' }
 	if pos == 0 && path_separator == '/' {
 		return '/'
@@ -180,10 +181,11 @@ pub fn dir(path string) string {
 // Trailing path separators are removed before extracting the last element.
 // If the path is empty, base returns ".". If the path consists entirely of separators, base returns a
 // single separator.
-pub fn base(path string) string {
-	if path == '' {
+pub fn base(opath string) string {
+	if opath == '' {
 		return '.'
 	}
+	path := opath.replace_each(['/', path_separator, r'\', path_separator])
 	if path == path_separator {
 		return path_separator
 	}
@@ -198,7 +200,8 @@ pub fn base(path string) string {
 
 // file_name will return all characters found after the last occurence of `path_separator`.
 // file extension is included.
-pub fn file_name(path string) string {
+pub fn file_name(opath string) string {
+	path := opath.replace_each(['/', path_separator, r'\', path_separator])
 	return path.all_after_last(path_separator)
 }
 
@@ -363,7 +366,8 @@ fn executable_fallback() string {
 		}
 	}
 	if !is_abs_path(exepath) {
-		if exepath.contains(path_separator) {
+		rexepath := exepath.replace_each(['/', path_separator, r'\', path_separator])
+		if rexepath.contains(path_separator) {
 			exepath = join_path(os.wd_at_startup, exepath)
 		} else {
 			// no choice but to try to walk the PATH folders :-| ...

vlib/os/os_test.v

@@ -533,11 +533,15 @@ fn test_dir() {
 	$if windows {
 		assert os.dir('C:\\a\\b\\c') == 'C:\\a\\b'
 		assert os.dir('C:\\a\\b\\') == 'C:\\a\\b'
+		assert os.dir('C:/a/b/c') == 'C:\\a\\b'
+		assert os.dir('C:/a/b/') == 'C:\\a\\b'
 	} $else {
 		assert os.dir('/') == '/'
 		assert os.dir('/abc') == '/'
 		assert os.dir('/var/tmp/foo') == '/var/tmp'
 		assert os.dir('/var/tmp/') == '/var/tmp'
+		assert os.dir('C:\\a\\b\\c') == 'C:/a/b'
+		assert os.dir('C:\\a\\b\\') == 'C:/a/b'
 	}
 	assert os.dir('os') == '.'
 }
@@ -546,9 +550,13 @@ fn test_base() {
 	$if windows {
 		assert os.base('v\\vlib\\os') == 'os'
 		assert os.base('v\\vlib\\os\\') == 'os'
+		assert os.base('v/vlib/os') == 'os'
+		assert os.base('v/vlib/os/') == 'os'
 	} $else {
 		assert os.base('v/vlib/os') == 'os'
 		assert os.base('v/vlib/os/') == 'os'
+		assert os.base('v\\vlib\\os') == 'os'
+		assert os.base('v\\vlib\\os\\') == 'os'
 	}
 	assert os.base('filename') == 'filename'
 }