tpl: Add strings.TrimLeft and TrimRight

tpl/strings/init.go

@@ -112,6 +112,20 @@ func init() {
 			},
 		)
 
+		ns.AddMethodMapping(ctx.TrimLeft,
+			nil,
+			[][2]string{
+				{`{{ "aabbaa" | strings.TrimLeft "a" }}`, `bbaa`},
+			},
+		)
+
+		ns.AddMethodMapping(ctx.TrimRight,
+			nil,
+			[][2]string{
+				{`{{ "aabbaa" | strings.TrimRight "a" }}`, `aabb`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.Title,
 			[]string{"title"},
 			[][2]string{

tpl/strings/strings.go

@@ -347,6 +347,22 @@ func (ns *Namespace) Trim(s, cutset interface{}) (string, error) {
 	return _strings.Trim(ss, sc), nil
 }
 
+// TrimLeft returns a slice of the string s with all leading characters
+// contained in cutset removed.
+func (ns *Namespace) TrimLeft(cutset, s interface{}) (string, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	sc, err := cast.ToStringE(cutset)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.TrimLeft(ss, sc), nil
+}
+
 // 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) {
@@ -363,6 +379,22 @@ func (ns *Namespace) TrimPrefix(s, prefix interface{}) (string, error) {
 	return _strings.TrimPrefix(ss, sx), nil
 }
 
+// TrimRight returns a slice of the string s with all trailing characters
+// contained in cutset removed.
+func (ns *Namespace) TrimRight(cutset, s interface{}) (string, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	sc, err := cast.ToStringE(cutset)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.TrimRight(ss, sc), nil
+}
+
 // 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) {

tpl/strings/strings_test.go

@@ -574,6 +574,41 @@ func TestTrim(t *testing.T) {
 	}
 }
 
+func TestTrimLeft(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		cutset interface{}
+		expect interface{}
+	}{
+		{"abba", "a", "bba"},
+		{"abba", "ab", ""},
+		{"<tag>", "<>", "tag>"},
+		{`"quote"`, `"`, `quote"`},
+		{1221, "1", "221"},
+		{1221, "12", ""},
+		{"007", "0", "7"},
+		{template.HTML("<tag>"), "<>", "tag>"},
+		{[]byte("<tag>"), "<>", "tag>"},
+		// errors
+		{"", tstNoStringer{}, false},
+		{tstNoStringer{}, "", false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.TrimLeft(test.cutset, test.s)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
 func TestTrimPrefix(t *testing.T) {
 	t.Parallel()
 
@@ -604,6 +639,41 @@ func TestTrimPrefix(t *testing.T) {
 	}
 }
 
+func TestTrimRight(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		cutset interface{}
+		expect interface{}
+	}{
+		{"abba", "a", "abb"},
+		{"abba", "ab", ""},
+		{"<tag>", "<>", "<tag"},
+		{`"quote"`, `"`, `"quote`},
+		{1221, "1", "122"},
+		{1221, "12", ""},
+		{"007", "0", "007"},
+		{template.HTML("<tag>"), "<>", "<tag"},
+		{[]byte("<tag>"), "<>", "<tag"},
+		// errors
+		{"", tstNoStringer{}, false},
+		{tstNoStringer{}, "", false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.TrimRight(test.cutset, test.s)
+
+		if b, ok := test.expect.(bool); ok && !b {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
 func TestTrimSuffix(t *testing.T) {
 	t.Parallel()