Pass through try-compatible errors

try/try.go

@@ -47,7 +47,14 @@ type call struct {
 }
 
 // FromErr wraps a standard error into a try-compatible one with extended stack info.
-func FromErr(err error) *tryErr {
+func FromErr(err error) Err {
+	// If the error is already try-compatible, return
+	//nolint:errorlint
+	cterr, ok := err.(Err)
+	if ok {
+		return cterr
+	}
+
 	terr := &tryErr{err: err, callStack: []call{}}
 
 	pc, _, _, ok := runtime.Caller(0)
@@ -82,7 +89,7 @@ func FromErr(err error) *tryErr {
 }
 
 // NewErr creates a new try-compatible error with extended stack info.
-func NewErr(msg string) *tryErr {
+func NewErr(msg string) Err {
 	return FromErr(errors.New(msg))
 }
 

try/try_test.go

@@ -220,6 +220,22 @@ func TestReturnStd(t *testing.T) {
 	}
 }
 
+func TestCheckTryErr(t *testing.T) {
+	testErr := NewErr("TestErr")
+
+	tf := func() (err Err) {
+		defer Return(&err)
+		Check(testErr)
+		return
+	}
+
+	err := tf()
+
+	if err != testErr {
+		t.Fail()
+	}
+}
+
 func ExampleReturn() {
 	var err Err
 	defer Return(&err)