feat(forge): add APIError stringers

Co-Authored-By: Virgil <virgil@lethean.io>

client.go

@@ -33,9 +33,26 @@ type APIError struct {
 //
 //	err := (&forge.APIError{StatusCode: 404, Message: "not found", URL: "/api/v1/repos/x/y"}).Error()
 func (e *APIError) Error() string {
+	if e == nil {
+		return "forge.APIError{<nil>}"
+	}
 	return core.Concat("forge: ", e.URL, " ", strconv.Itoa(e.StatusCode), ": ", e.Message)
 }
 
+// String returns a safe summary of the API error.
+//
+// Usage:
+//
+//	s := err.String()
+func (e *APIError) String() string { return e.Error() }
+
+// GoString returns a safe Go-syntax summary of the API error.
+//
+// Usage:
+//
+//	s := fmt.Sprintf("%#v", err)
+func (e *APIError) GoString() string { return e.Error() }
+
 // IsNotFound returns true if the error is a 404 response.
 //
 // Usage:

client_test.go

@@ -248,6 +248,15 @@ func TestAPIError_Error_Good(t *testing.T) {
 	if got != want {
 		t.Errorf("got %q, want %q", got, want)
 	}
+	if got := e.String(); got != want {
+		t.Errorf("got String()=%q, want %q", got, want)
+	}
+	if got := fmt.Sprint(e); got != want {
+		t.Errorf("got fmt.Sprint=%q, want %q", got, want)
+	}
+	if got := fmt.Sprintf("%#v", e); got != want {
+		t.Errorf("got GoString=%q, want %q", got, want)
+	}
 }
 
 func TestIsConflict_Match_Good(t *testing.T) {

stringer_nil_test.go

@@ -46,3 +46,17 @@ func TestResource_String_NilSafe(t *testing.T) {
 		t.Fatalf("got GoString=%q, want %q", got, want)
 	}
 }
+
+func TestAPIError_String_NilSafe(t *testing.T) {
+	var e *APIError
+	want := "forge.APIError{<nil>}"
+	if got := e.String(); got != want {
+		t.Fatalf("got String()=%q, want %q", got, want)
+	}
+	if got := fmt.Sprint(e); got != want {
+		t.Fatalf("got fmt.Sprint=%q, want %q", got, want)
+	}
+	if got := fmt.Sprintf("%#v", e); got != want {
+		t.Fatalf("got GoString=%q, want %q", got, want)
+	}
+}