path/filepath: add IsLocal

IsLocal reports whether a path lexically refers to a location
contained within the directory in which it is evaluated.
It identifies paths that are absolute, escape a directory
with ".." elements, and (on Windows) paths that reference
reserved device names.

For #56219.

Change-Id: I35edfa3ce77b40b8e66f1fc8e0ff73cfd06f2313
Reviewed-on: https://go-review.googlesource.com/c/go/+/449239
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Joseph Tsai <joetsai@digital-static.net>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Joedian Reid <joedian@golang.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/src/path/filepath/path_test.go b/src/path/filepath/path_test.go
index 382381eb4e..771416770e 100644
--- a/src/path/filepath/path_test.go
+++ b/src/path/filepath/path_test.go
@@ -143,6 +143,60 @@ func TestClean(t *testing.T) {
 	}
 }
 
+type IsLocalTest struct {
+	path    string
+	isLocal bool
+}
+
+var islocaltests = []IsLocalTest{
+	{"", false},
+	{".", true},
+	{"..", false},
+	{"../a", false},
+	{"/", false},
+	{"/a", false},
+	{"/a/../..", false},
+	{"a", true},
+	{"a/../a", true},
+	{"a/", true},
+	{"a/.", true},
+	{"a/./b/./c", true},
+}
+
+var winislocaltests = []IsLocalTest{
+	{"NUL", false},
+	{"nul", false},
+	{"nul.", false},
+	{"nul.txt", false},
+	{"com1", false},
+	{"./nul", false},
+	{"a/nul.txt/b", false},
+	{`\`, false},
+	{`\a`, false},
+	{`C:`, false},
+	{`C:\a`, false},
+	{`..\a`, false},
+}
+
+var plan9islocaltests = []IsLocalTest{
+	{"#a", false},
+}
+
+func TestIsLocal(t *testing.T) {
+	tests := islocaltests
+	if runtime.GOOS == "windows" {
+		tests = append(tests, winislocaltests...)
+	}
+	if runtime.GOOS == "plan9" {
+		tests = append(tests, plan9islocaltests...)
+	}
+	for _, test := range tests {
+		if got := filepath.IsLocal(test.path); got != test.isLocal {
+			t.Errorf("IsLocal(%q) = %v, want %v", test.path, got, test.isLocal)
+		}
+	}
+}
+
 const sep = filepath.Separator
 
 var slashtests = []PathTest{