entc/gen: propagate nodes post-save mutations (#2525)

* Failing test

* Fix propagating entirely models from OpCreate hook

* Apply suggestions from code review

Co-authored-by: Ariel Mashraki <7413593+a8m@users.noreply.github.com>

* whitespace

* Failing test for updateone

* fix for updateone

* Regnerate

* regen from root

Co-authored-by: Ariel Mashraki <7413593+a8m@users.noreply.github.com>

entc/gen/template/builder/create.tmpl

@@ -83,9 +83,15 @@ func ({{ $receiver }} *{{ $builder }}) Save(ctx context.Context) (*{{ $.Name }},
 			}
 			mut = {{ $receiver }}.hooks[i](mut)
 		}
-		if _, err := mut.Mutate(ctx, {{ $mutation }}); err != nil {
+		v, err := mut.Mutate(ctx, {{ $mutation }})
+		if err != nil {
 			return nil, err
 		}
+		nv, ok := v.(*{{ $.Name }})
+		if !ok {
+			return nil, fmt.Errorf("unexpected node type %T returned from {{ $.MutationName }}", v)
+		}
+		node = nv
 	}
 	return node, err
 }

entc/gen/template/builder/update.tmpl

@@ -197,9 +197,15 @@ func ({{ $receiver }} *{{ $onebuilder }} ) Save(ctx context.Context) (*{{ $.Name
 			}
 			mut = {{ $receiver }}.hooks[i](mut)
 		}
-		if _, err := mut.Mutate(ctx, {{ $mutation }}); err != nil {
+		v, err := mut.Mutate(ctx, {{ $mutation }})
+		if err != nil {
 			return nil, err
 		}
+		nv, ok := v.(*{{ $.Name }})
+		if !ok {
+			return nil, fmt.Errorf("unexpected node type %T returned from {{ $.MutationName }}", v)
+		}
+		node = nv
 	}
 	return node, err
 }