lib/fs: Don't panic when watching a folder with symlinked root (#4846)

lib/fs/basicfs_watch_test.go

@@ -123,7 +123,7 @@ func TestWatchOutside(t *testing.T) {
 			}
 			cancel()
 		}()
-		fs.watchLoop(".", testDirAbs, backendChan, outChan, fakeMatcher{}, ctx)
+		fs.watchLoop(".", backendChan, outChan, fakeMatcher{}, ctx)
 	}()
 
 	backendChan <- fakeEventInfo(filepath.Join(filepath.Dir(testDirAbs), "outside"))
@@ -139,7 +139,7 @@ func TestWatchSubpath(t *testing.T) {
 	fs := newBasicFilesystem(testDirAbs)
 
 	abs, _ := fs.rooted("sub")
-	go fs.watchLoop("sub", abs, backendChan, outChan, fakeMatcher{}, ctx)
+	go fs.watchLoop("sub", backendChan, outChan, fakeMatcher{}, ctx)
 
 	backendChan <- fakeEventInfo(filepath.Join(abs, "file"))
 
@@ -208,6 +208,54 @@ func TestWatchErrorLinuxInterpretation(t *testing.T) {
 	}
 }
 
+func TestWatchSymlinkedRoot(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("Involves symlinks")
+	}
+
+	name := "symlinkedRoot"
+	if err := testFs.MkdirAll(name, 0755); err != nil {
+		panic(fmt.Sprintf("Failed to create directory %s: %s", name, err))
+	}
+	defer testFs.RemoveAll(name)
+
+	root := filepath.Join(name, "root")
+	if err := testFs.MkdirAll(root, 0777); err != nil {
+		panic(err)
+	}
+	link := filepath.Join(name, "link")
+
+	if err := testFs.CreateSymlink(filepath.Join(testFs.URI(), root), link); err != nil {
+		panic(err)
+	}
+
+	linkedFs := NewFilesystem(FilesystemTypeBasic, filepath.Join(testFs.URI(), link))
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	if _, err := linkedFs.Watch(".", fakeMatcher{}, ctx, false); err != nil {
+		panic(err)
+	}
+
+	if err := linkedFs.MkdirAll("foo", 0777); err != nil {
+		panic(err)
+	}
+
+	// Give the panic some time to happen
+	sleepMs(100)
+}
+
+func TestUnrootedChecked(t *testing.T) {
+	var unrooted string
+	defer func() {
+		if recover() == nil {
+			t.Fatal("unrootedChecked did not panic on outside path, but returned", unrooted)
+		}
+	}()
+	fs := newBasicFilesystem(testDirAbs)
+	unrooted = fs.unrootedChecked("/random/other/path")
+}
+
 // path relative to folder root, also creates parent dirs if necessary
 func createTestFile(name string, file string) string {
 	joined := filepath.Join(name, file)