fix char to bool conversion (#2334)

Author: jycor

enginetest/queries/queries.go

@@ -9174,6 +9174,70 @@ from typestable`,
 			{36},
 		},
 	},
+	{
+		Query:    "select 1 where if('', 1, char(''));",
+		Expected: []sql.Row{},
+	},
+	{
+		Query: "select 1 where if('', char(''), 1);",
+		Expected: []sql.Row{
+			{1},
+		},
+	},
+	{
+		Query: "select 1 where if(char(''), 0, 1);",
+		Expected: []sql.Row{
+			{1},
+		},
+	},
+	{
+		Query: "select 1 where if(char('123'), 0, 1);",
+		Expected: []sql.Row{
+			{1},
+		},
+	},
+	{
+		Query: "select 1 where 0 = if('', 1, char(''));",
+		Expected: []sql.Row{
+			{1},
+		},
+	},
+	{
+		Query: "select if('', 1, char(''));",
+		Expected: []sql.Row{
+			{[]byte{0}},
+		},
+	},
+	{
+		Query: "select if(char(''), 'true', 'false');",
+		Expected: []sql.Row{
+			{"false"},
+		},
+	},
+	{
+		Query: "select if(char('0'), 'true', 'false');",
+		Expected: []sql.Row{
+			{"false"},
+		},
+	},
+	{
+		Query: "select if(char('1'), 'true', 'false');",
+		Expected: []sql.Row{
+			{"false"},
+		},
+	},
+	{
+		Query: "select if(cast(1 as binary), 'true', 'false');",
+		Expected: []sql.Row{
+			{"true"},
+		},
+	},
+	{
+		Query: "select if(cast(0 as binary), 'true', 'false');",
+		Expected: []sql.Row{
+			{"false"},
+		},
+	},
 }
 
 var KeylessQueries = []QueryTest{

sql/core.go

@@ -252,6 +252,8 @@ type Lockable interface {
 // ConvertToBool converts a value to a boolean. nil is considered false.
 func ConvertToBool(ctx *Context, v interface{}) (bool, error) {
 	switch b := v.(type) {
+	case []uint8:
+		return ConvertToBool(ctx, string(b))
 	case bool:
 		return b, nil
 	case int:

sql/types/typecheck.go

@@ -22,6 +22,9 @@ import (
 
 // IsBlobType checks if t is BLOB
 func IsBlobType(t sql.Type) bool {
+	if t == nil {
+		return false
+	}
 	switch t.Type() {
 	case sqltypes.Blob:
 		return true
@@ -113,6 +116,9 @@ func IsText(t sql.Type) bool {
 
 // IsTextBlob checks if t is one of the TEXTs or BLOBs.
 func IsTextBlob(t sql.Type) bool {
+	if t == nil {
+		return false
+	}
 	switch t.Type() {
 	case sqltypes.Text, sqltypes.Blob:
 		return true