server: deletions of intentions by name using the intention API is now idempotent (#9278)

Restoring a behavior inadvertently changed while fixing #9254

.changelog/9278.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+server: deletions of intentions by name using the intention API is now idempotent
+```

agent/consul/intention_endpoint.go

@@ -413,9 +413,7 @@ func (s *Intention) computeApplyChangesDelete(
 		return nil, fmt.Errorf("Intention lookup failed: %v", err)
 	}
 	if ixn == nil {
-		src := structs.NewServiceName(exactIxn.SourceName, exactIxn.SourceEnterpriseMeta())
+		return nil, nil // by-name deletions are idempotent
-		dst := structs.NewServiceName(exactIxn.DestinationName, exactIxn.DestinationEnterpriseMeta())
-		return nil, fmt.Errorf("Cannot delete non-existent intention: source=%q, destination=%q", src.String(), dst.String())
 	}
 
 	return &structs.IntentionMutation{

agent/consul/intention_endpoint_test.go

@@ -653,14 +653,14 @@ func TestIntentionApply_WithoutIDs(t *testing.T) {
 		require.Equal(t, expect, entry)
 	}
 
-	// Delete a non existent intention should return an error
+	// Delete a non existent intention should act like it did work
-	testutil.RequireErrorContains(t, opApply(&structs.IntentionRequest{
+	require.NoError(t, opApply(&structs.IntentionRequest{
 		Op: structs.IntentionOpDelete,
 		Intention: &structs.Intention{
 			SourceName:      "ghost",
 			DestinationName: "phantom",
 		},
-	}), "Cannot delete non-existent intention")
+	}))
 
 	// Delete the original
 	require.NoError(t, opApply(&structs.IntentionRequest{

agent/intentions_endpoint_test.go

@@ -554,8 +554,8 @@ func TestIntentionDeleteExact(t *testing.T) {
 
 		resp := httptest.NewRecorder()
 		obj, err := a.srv.IntentionExact(resp, req)
-		require.Nil(t, obj)
+		require.NoError(t, err) // by-name deletions are idempotent
-		testutil.RequireErrorContains(t, err, "Cannot delete non-existent intention")
+		require.Equal(t, true, obj)
 	})
 
 	exact := ixn.ToExact()
@@ -643,6 +643,18 @@ func TestIntentionSpecificDelete(t *testing.T) {
 	ixn := structs.TestIntention(t)
 	ixn.SourceName = "foo"
 
+	t.Run("cannot delete non-existent intention", func(t *testing.T) {
+		fakeID := generateUUID()
+
+		req, err := http.NewRequest("DELETE", "/v1/connect/intentions/"+fakeID, nil)
+		require.NoError(t, err)
+
+		resp := httptest.NewRecorder()
+		obj, err := a.srv.IntentionSpecific(resp, req)
+		testutil.RequireErrorContains(t, err, "Cannot delete non-existent intention")
+		require.Nil(t, obj)
+	})
+
 	// Create an intention directly
 	var reply string
 	{