fix: driver.Valuer method was being ignored (#289)

When a type had implemented custom Value func to convert the type,
then the conversion method was not being called for structs.

Fixes #281

driver.go

@@ -748,13 +748,11 @@ func (c *conn) IsValid() bool {
 	return !c.closed
 }
 
+// checkIsValidType returns true for types that do not need extra conversion
+// for spanner.
 func checkIsValidType(v driver.Value) bool {
 	switch v.(type) {
 	default:
-		// google-cloud-go/spanner knows how to deal with these
-		if isStructOrArrayOfStructValue(v) || isAnArrayOfProtoColumn(v) {
-			return true
-		}
 		return false
 	case nil:
 	case sql.NullInt64:
@@ -851,6 +849,12 @@ func (c *conn) CheckNamedValue(value *driver.NamedValue) error {
 			return nil
 		}
 	}
+
+	// google-cloud-go/spanner knows how to deal with these
+	if isStructOrArrayOfStructValue(value.Value) || isAnArrayOfProtoColumn(value.Value) {
+		return nil
+	}
+
 	return spanner.ToSpannerError(status.Errorf(codes.InvalidArgument, "unsupported value type: %T", value.Value))
 }
 

driver_test.go

@@ -467,3 +467,52 @@ func TestConn_GetCommitTimestampAfterAutocommitQuery(t *testing.T) {
 		t.Fatalf("error code mismatch\n Got: %v\nWant: %v", g, w)
 	}
 }
+
+func TestConn_CheckNamedValue(t *testing.T) {
+	c := &conn{}
+
+	type Person struct {
+		Name string
+		Age  int64
+	}
+
+	tests := []struct {
+		in   any
+		want any
+	}{
+		// basic types should stay unchanged
+		{in: int64(256), want: int64(256)},
+		// driver.Valuer types should call .Value func
+		{in: &ValuerPerson{Name: "hello", Age: 123}, want: "hello"},
+		// structs should be sent to spanner
+		{in: &Person{Name: "hello", Age: 123}, want: &Person{Name: "hello", Age: 123}},
+	}
+
+	for _, test := range tests {
+		value := &driver.NamedValue{
+			Ordinal: 1,
+			Value:   test.in,
+		}
+
+		err := c.CheckNamedValue(value)
+		if err != nil {
+			t.Errorf("expected no error, got: %v", err)
+			continue
+		}
+
+		if diff := cmp.Diff(test.want, value.Value); diff != "" {
+			t.Errorf("wrong result, got %#v expected %#v:\n%v", value.Value, test.want, diff)
+		}
+	}
+}
+
+// ValuerPerson implements driver.Valuer
+type ValuerPerson struct {
+	Name string
+	Age  int64
+}
+
+// Value implements conversion func for database.
+func (p *ValuerPerson) Value() (driver.Value, error) {
+	return p.Name, nil
+}