Use go 1.13 features to improve IsOfType checks

error.go

@@ -106,17 +106,9 @@ func (e *Error) HasTrait(key Trait) bool {
 // IsOfType is a proper type check for an errorx-based errors.
 // It takes the transparency and error types hierarchy into account,
 // so that type check against any supertype of the original cause passes.
+// Go 1.13 and above: it also tolerates non-errorx errors in chain if those errors support errors unwrap.
 func (e *Error) IsOfType(t *Type) bool {
-cause := e
-for cause != nil {
-if !cause.transparent {
-return cause.errorType.IsOfType(t)
-}
-
-cause = Cast(cause.Cause())
-}
-
-return false
+return e.isOfType(t)
 }
 
 // Type returns the exact type of this error.

error_112.go

@@ -0,0 +1,23 @@
+// +build !go1.13
+
+package errorx
+
+func isOfType(err error, t *Type) bool {
+e := Cast(err)
+return e != nil && e.IsOfType(t)
+}
+
+func (e *Error) isOfType(t *Type) bool {
+cause := e
+for cause != nil {
+if !cause.transparent {
+return cause.errorType.IsOfType(t)
+}
+
+cause = Cast(cause.Cause())
+}
+
+return false
+}
+
+

error_113.go

@@ -0,0 +1,38 @@
+// +build go1.13
+
+package errorx
+
+import "errors"
+
+func isOfType(err error, t *Type) bool {
+e := burrowForTyped(err)
+return e != nil && e.IsOfType(t)
+}
+
+func (e *Error) isOfType(t *Type) bool {
+cause := e
+for cause != nil {
+if !cause.transparent {
+return cause.errorType.IsOfType(t)
+}
+
+cause = burrowForTyped(cause.Cause())
+}
+
+return false
+}
+
+// burrowForTyped returns either the first *Error in unwrap chain or nil
+func burrowForTyped(err error) *Error {
+raw := err
+for raw != nil {
+typed := Cast(raw)
+if typed != nil {
+return typed
+}
+
+raw = errors.Unwrap(raw)
+}
+
+return nil
+}

error_113_test.go

@@ -4,6 +4,7 @@ package errorx
 
 import (
 "errors"
+"fmt"
 "io"
 "testing"
 
@@ -103,3 +104,28 @@ func TestErrorIs(t *testing.T) {
 require.True(t, errors.Is(err, io.EOF))
 })
 }
+
+func TestErrorsAndErrorx(t *testing.T) {
+t.Run("DecoratedForeign", func(t *testing.T) {
+err := fmt.Errorf("error test: %w", testType.NewWithNoMessage())
+require.True(t, errors.Is(err, testType.NewWithNoMessage()))
+require.True(t, IsOfType(err, testType))
+})
+
+t.Run("LayeredDecorate", func(t *testing.T) {
+err := Decorate(fmt.Errorf("error test: %w", testType.NewWithNoMessage()), "test")
+require.True(t, errors.Is(err, testType.NewWithNoMessage()))
+require.True(t, IsOfType(err, testType))
+})
+
+t.Run("LayeredDecorateAgain", func(t *testing.T) {
+err := fmt.Errorf("error test: %w", Decorate(io.EOF, "test"))
+require.True(t, errors.Is(err, io.EOF))
+})
+
+t.Run("Wrap", func(t *testing.T) {
+err := fmt.Errorf("error test: %w", testType.Wrap(io.EOF, "test"))
+require.False(t, errors.Is(err, io.EOF))
+require.True(t, errors.Is(err, testType.NewWithNoMessage()))
+})
+}

type.go

@@ -97,10 +97,10 @@ func (t *Type) HasTrait(key Trait) bool {
 
 // IsOfType is a type check for errors.
 // Returns true either if both are of exactly the same type, or if the same is true for one of current type's ancestors.
-// For an error that does not have an errorx type, returns false.
+// Go 1.12 and below: for an error that does not have an errorx type, returns false.
+// Go 1.13 and above: for an error that does not have an errorx type, returns false unless it wraps another error of errorx type.
 func IsOfType(err error, t *Type) bool {
-e := Cast(err)
-return e != nil && e.IsOfType(t)
+return isOfType(err, t)
 }
 
 // Supertype returns a parent type, if present.