tpl: Cleanup strings.TrimPrefix and TrimSuffix

These funcs were added during the move to namespaces but were
undocumented.  This commit fixes the order of the arguments and adds the
funcs to the method mapping.

tpl/strings/init.go

@@ -119,6 +119,14 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.TrimPrefix,
+			nil,
+			[][2]string{
+				{`{{ "aabbaa" | strings.TrimPrefix "a" }}`, `abbaa`},
+				{`{{ "aabbaa" | strings.TrimPrefix "aa" }}`, `bbaa`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.TrimRight,
 			nil,
 			[][2]string{
@@ -126,6 +134,14 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.TrimSuffix,
+			nil,
+			[][2]string{
+				{`{{ "aabbaa" | strings.TrimSuffix "a" }}`, `aabba`},
+				{`{{ "aabbaa" | strings.TrimSuffix "aa" }}`, `aabb`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.Title,
 			[]string{"title"},
 			[][2]string{

tpl/strings/strings.go

@@ -365,7 +365,7 @@ func (ns *Namespace) TrimLeft(cutset, s interface{}) (string, error) {
 
 // TrimPrefix returns s without the provided leading prefix string. If s doesn't
 // start with prefix, s is returned unchanged.
-func (ns *Namespace) TrimPrefix(s, prefix interface{}) (string, error) {
+func (ns *Namespace) TrimPrefix(prefix, s interface{}) (string, error) {
 	ss, err := cast.ToStringE(s)
 	if err != nil {
 		return "", err
@@ -397,7 +397,7 @@ func (ns *Namespace) TrimRight(cutset, s interface{}) (string, error) {
 
 // TrimSuffix returns s without the provided trailing suffix string. If s
 // doesn't end with suffix, s is returned unchanged.
-func (ns *Namespace) TrimSuffix(s, suffix interface{}) (string, error) {
+func (ns *Namespace) TrimSuffix(suffix, s interface{}) (string, error) {
 	ss, err := cast.ToStringE(s)
 	if err != nil {
 		return "", err

tpl/strings/strings_test.go

@@ -627,7 +627,7 @@ func TestTrimPrefix(t *testing.T) {
 	} {
 		errMsg := fmt.Sprintf("[%d] %v", i, test)
 
-		result, err := ns.TrimPrefix(test.s, test.prefix)
+		result, err := ns.TrimPrefix(test.prefix, test.s)
 
 		if b, ok := test.expect.(bool); ok && !b {
 			require.Error(t, err, errMsg)
@@ -692,7 +692,7 @@ func TestTrimSuffix(t *testing.T) {
 	} {
 		errMsg := fmt.Sprintf("[%d] %v", i, test)
 
-		result, err := ns.TrimSuffix(test.s, test.suffix)
+		result, err := ns.TrimSuffix(test.suffix, test.s)
 
 		if b, ok := test.expect.(bool); ok && !b {
 			require.Error(t, err, errMsg)