schemadiff: add EntityDiffByStatement, a testing friendly utility

go/vt/schemadiff/diff.go

@@ -174,3 +174,25 @@ func DiffSchemas(env *Environment, schema1 *Schema, schema2 *Schema, hints *Diff
 	}
 	return schema1.SchemaDiff(schema2, hints)
 }
+
+// EntityDiffByStatement is a helper function that returns a simplified and incomplete EntityDiff based on the given SQL statement.
+// It is useful for testing purposes as a quick mean to wrap a statement with a diff.
+func EntityDiffByStatement(statement sqlparser.Statement) EntityDiff {
+	switch stmt := statement.(type) {
+	case *sqlparser.CreateTable:
+		return &CreateTableEntityDiff{createTable: stmt}
+	case *sqlparser.RenameTable:
+		return &RenameTableEntityDiff{renameTable: stmt}
+	case *sqlparser.AlterTable:
+		return &AlterTableEntityDiff{alterTable: stmt}
+	case *sqlparser.DropTable:
+		return &DropTableEntityDiff{dropTable: stmt}
+	case *sqlparser.CreateView:
+		return &CreateViewEntityDiff{createView: stmt}
+	case *sqlparser.AlterView:
+		return &AlterViewEntityDiff{alterView: stmt}
+	case *sqlparser.DropView:
+		return &DropViewEntityDiff{dropView: stmt}
+	}
+	return nil
+}

go/vt/schemadiff/diff_test.go

@@ -1158,3 +1158,43 @@ func TestSchemaApplyError(t *testing.T) {
 		})
 	}
 }
+
+func TestEntityDiffByStatement(t *testing.T) {
+	env := NewTestEnv()
+
+	{
+		queries := []string{
+			"create table t1(id int primary key)",
+			"alter table t1 add column i int",
+			"rename table t1 to t2",
+			"drop table t1",
+			"create view v1 as select * from t1",
+			"alter view v1 as select * from t2",
+			"drop view v1",
+		}
+		for _, query := range queries {
+			t.Run(query, func(t *testing.T) {
+				stmt, err := env.Parser().ParseStrictDDL(query)
+				require.NoError(t, err)
+				entityDiff := EntityDiffByStatement(stmt)
+				require.NotNil(t, entityDiff)
+				require.NotNil(t, entityDiff.Statement())
+				require.Equal(t, stmt, entityDiff.Statement())
+			})
+		}
+	}
+	{
+		queries := []string{
+			"drop database d1",
+			"optimize table t1",
+		}
+		for _, query := range queries {
+			t.Run(query, func(t *testing.T) {
+				stmt, err := env.Parser().ParseStrictDDL(query)
+				require.NoError(t, err)
+				entityDiff := EntityDiffByStatement(stmt)
+				require.Nil(t, entityDiff)
+			})
+		}
+	}
+}