function: make array_length not fail with literal null

Signed-off-by: Miguel Molina <miguel@erizocosmi.co>

Author: erizocosmico

engine_test.go

@@ -1230,6 +1230,14 @@ var queries = []struct {
 		`SELECT (NULL+1)`,
 		[]sql.Row{{nil}},
 	},
+	{
+		`SELECT ARRAY_LENGTH(null)`,
+		[]sql.Row{{nil}},
+	},
+	{
+		`SELECT ARRAY_LENGTH("foo")`,
+		[]sql.Row{{nil}},
+	},
 }
 
 func TestQueries(t *testing.T) {

sql/expression/function/arraylength.go

@@ -2,7 +2,6 @@ package function // import "github.com/src-d/go-mysql-server/sql/expression/func
 
 import (
 	"fmt"
-	"reflect"
 
 	"github.com/src-d/go-mysql-server/sql"
 	"github.com/src-d/go-mysql-server/sql/expression"
@@ -39,7 +38,7 @@ func (f *ArrayLength) TransformUp(fn sql.TransformExprFunc) (sql.Expression, err
 // Eval implements the Expression interface.
 func (f *ArrayLength) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 	if t := f.Child.Type(); !sql.IsArray(t) && t != sql.JSON {
-		return nil, sql.ErrInvalidType.New(f.Child.Type().Type().String())
+		return nil, nil
 	}
 
 	child, err := f.Child.Eval(ctx, row)
@@ -53,7 +52,7 @@ func (f *ArrayLength) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 
 	array, ok := child.([]interface{})
 	if !ok {
-		return nil, sql.ErrInvalidType.New(reflect.TypeOf(child))
+		return nil, nil
 	}
 
 	return int32(len(array)), nil

sql/expression/function/arraylength_test.go

@@ -3,10 +3,10 @@ package function
 import (
 	"testing"
 
-	"github.com/stretchr/testify/require"
-	errors "gopkg.in/src-d/go-errors.v1"
 	"github.com/src-d/go-mysql-server/sql"
 	"github.com/src-d/go-mysql-server/sql/expression"
+	"github.com/stretchr/testify/require"
+	errors "gopkg.in/src-d/go-errors.v1"
 )
 
 func TestArrayLength(t *testing.T) {
@@ -19,7 +19,7 @@ func TestArrayLength(t *testing.T) {
 		err      *errors.Kind
 	}{
 		{"array is nil", sql.NewRow(nil), nil, nil},
-		{"array is not of right type", sql.NewRow(5), nil, sql.ErrInvalidType},
+		{"array is not of right type", sql.NewRow(5), nil, nil},
 		{"array is ok", sql.NewRow([]interface{}{1, 2, 3}), int32(3), nil},
 	}
 
@@ -40,7 +40,7 @@ func TestArrayLength(t *testing.T) {
 
 	f = NewArrayLength(expression.NewGetField(0, sql.Tuple(sql.Int64, sql.Int64), "", false))
 	require := require.New(t)
-	_, err := f.Eval(sql.NewEmptyContext(), []interface{}{int64(1), int64(2)})
-	require.Error(err)
-	require.True(sql.ErrInvalidType.Is(err))
+	v, err := f.Eval(sql.NewEmptyContext(), []interface{}{int64(1), int64(2)})
+	require.NoError(err)
+	require.Nil(v)
 }