some APIs treat 412s as the conflict code. (#4277) (#7915)

* some APIs treat 412s as the conflict code.

it stands for 'invalid etag' in that context.

* add unit test.

Signed-off-by: Modular Magician <magic-modules@google.com>

.changelog/4277.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+iam: fixed iam conflict handling so that optimistic-locking retries will succeed more often.
+```

google/utils.go

@@ -139,11 +139,11 @@ func isFailedPreconditionError(err error) bool {
 }
 
 func isConflictError(err error) bool {
-	if e, ok := err.(*googleapi.Error); ok && e.Code == 409 {
+	if e, ok := err.(*googleapi.Error); ok && (e.Code == 409 || e.Code == 412) {
 		return true
 	} else if !ok && errwrap.ContainsType(err, &googleapi.Error{}) {
 		e := errwrap.GetType(err, &googleapi.Error{}).(*googleapi.Error)
-		if e.Code == 409 {
+		if e.Code == 409 || e.Code == 412 {
 			return true
 		}
 	}

google/utils_test.go

@@ -575,3 +575,25 @@ func TestRetryTimeDuration_URLTimeoutsShouldRetry(t *testing.T) {
 		t.Errorf("expected the retryFunc to be called %v time(s), instead was called %v time(s)", expectedRunCount, runCount)
 	}
 }
+
+func TestConflictError(t *testing.T) {
+	confErr := &googleapi.Error{
+		Code: 409,
+	}
+	if !isConflictError(confErr) {
+		t.Error("did not find that a 409 was a conflict error.")
+	}
+	if !isConflictError(errwrap.Wrapf("wrap", confErr)) {
+		t.Error("did not find that a wrapped 409 was a conflict error.")
+	}
+	confErr = &googleapi.Error{
+		Code: 412,
+	}
+	if !isConflictError(confErr) {
+		t.Error("did not find that a 412 was a conflict error.")
+	}
+	if !isConflictError(errwrap.Wrapf("wrap", confErr)) {
+		t.Error("did not find that a wrapped 412 was a conflict error.")
+	}
+	// skipping negative tests as other cases may be added later.
+}