Go: Better check for path prefixes

Author: mbg

go/extractor/project/project.go

@@ -481,7 +481,7 @@ func getBuildRoots(emitDiagnostics bool) (goWorkspaces []GoWorkspace, totalModul
 // Determines whether `str` starts with any of `prefixes`.
 func startsWithAnyOf(str string, prefixes []string) bool {
 	for _, prefix := range prefixes {
-		if strings.HasPrefix(str, prefix) {
+		if relPath, err := filepath.Rel(str, prefix); err == nil && !strings.HasPrefix(relPath, "..") {
 			return true
 		}
 	}

go/extractor/project/project_test.go

@@ -0,0 +1,27 @@
+package project
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func testStartsWithAnyOf(t *testing.T, path string, prefix string, expectation bool) {
+	result := startsWithAnyOf(path, []string{prefix})
+	if result != expectation {
+		t.Errorf("Expected startsWithAnyOf(%s, %s) to be %t, but it is %t.", path, prefix, expectation, result)
+	}
+}
+
+func TestStartsWithAnyOf(t *testing.T) {
+	testStartsWithAnyOf(t, ".", ".", true)
+	testStartsWithAnyOf(t, ".", "dir", true)
+	testStartsWithAnyOf(t, ".", filepath.Join("foo", "bar"), true)
+	testStartsWithAnyOf(t, "dir", "dir", true)
+	testStartsWithAnyOf(t, "foo", filepath.Join("foo", "bar"), true)
+	testStartsWithAnyOf(t, filepath.Join("foo", "bar"), filepath.Join("foo", "bar"), true)
+	testStartsWithAnyOf(t, filepath.Join("foo", "bar"), filepath.Join("foo", "bar", "baz"), true)
+
+	testStartsWithAnyOf(t, filepath.Join("foo", "bar"), "foo", false)
+	testStartsWithAnyOf(t, filepath.Join("foo", "bar"), "bar", false)
+	testStartsWithAnyOf(t, filepath.Join("foo", "bar"), filepath.Join("foo", "baz"), false)
+}