add path.Base, analogous to Unix basename

R=rsc
CC=golang-dev
https://golang.org/cl/1633042

src/pkg/path/path.go

@@ -186,3 +186,25 @@ func Walk(root string, v Visitor, errors chan<- os.Error) {
 	}
 	walk(root, f, v, errors)
 }
+
+// Base returns the last path element of the slash-separated name.
+// Trailing slashes are removed before extracting the last element.  If the name is
+// empty, "." is returned.  If it consists entirely of slashes, "/" is returned.
+func Base(name string) string {
+	if name == "" {
+		return "."
+	}
+	// Strip trailing slashes.
+	for len(name) > 0 && name[len(name)-1] == '/' {
+		name = name[0 : len(name)-1]
+	}
+	// Find the last element
+	if i := strings.LastIndex(name, "/"); i >= 0 {
+		name = name[i+1:]
+	}
+	// If empty now, it had only slashes.
+	if name == "" {
+		return "/"
+	}
+	return name
+}

src/pkg/path/path_test.go

@@ -284,3 +284,26 @@ func TestWalk(t *testing.T) {
 		t.Errorf("removeTree: %v", err)
 	}
 }
+
+var basetests = []CleanTest{
+	// Already clean
+	CleanTest{"", "."},
+	CleanTest{".", "."},
+	CleanTest{"/.", "."},
+	CleanTest{"/", "/"},
+	CleanTest{"////", "/"},
+	CleanTest{"x/", "x"},
+	CleanTest{"abc", "abc"},
+	CleanTest{"abc/def", "def"},
+	CleanTest{"a/b/.x", ".x"},
+	CleanTest{"a/b/c.", "c."},
+	CleanTest{"a/b/c.x", "c.x"},
+}
+
+func TestBase(t *testing.T) {
+	for _, test := range basetests {
+		if s := Base(test.path); s != test.clean {
+			t.Errorf("Base(%q) = %q, want %q", test.path, s, test.clean)
+		}
+	}
+}