2 files changed, 93 insertions, 0 deletions
diff --git a/common/hstrings/strings.go b/common/hstrings/strings.go
new file mode 100644
index 000000000..6c0f820fe
--- /dev/null
+++ b/common/hstrings/strings.go
@@ -0,0 +1,57 @@
+// Copyright 2023 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hstrings
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/gohugoio/hugo/compare"
+)
+
+var _ compare.Eqer = StringEqualFold("")
+
+// StringEqualFold is a string that implements the compare.Eqer interface and considers
+// two strings equal if they are equal when folded to lower case.
+// The compare.Eqer interface is used in Hugo to compare values in templates (e.g. using the eq template function).
+type StringEqualFold string
+
+func (s StringEqualFold) EqualFold(s2 string) bool {
+	return strings.EqualFold(string(s), s2)
+}
+
+func (s StringEqualFold) String() string {
+	return string(s)
+}
+
+func (s StringEqualFold) Eq(s2 any) bool {
+	switch ss := s2.(type) {
+	case string:
+		return s.EqualFold(ss)
+	case fmt.Stringer:
+		return s.EqualFold(ss.String())
+	}
+
+	return false
+}
+
+// EqualAny returns whether a string is equal to any of the given strings.
+func EqualAny(a string, b ...string) bool {
+	for _, s := range b {
+		if a == s {
+			return true
+		}
+	}
+	return false
+}
diff --git a/common/hstrings/strings_test.go b/common/hstrings/strings_test.go
new file mode 100644
index 000000000..dc2eae6f2
--- /dev/null
+++ b/common/hstrings/strings_test.go
@@ -0,0 +1,36 @@
+// Copyright 2023 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package hstrings
+
+import (
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestStringEqualFold(t *testing.T) {
+	c := qt.New(t)
+
+	s1 := "A"
+	s2 := "a"
+
+	c.Assert(StringEqualFold(s1).EqualFold(s2), qt.Equals, true)
+	c.Assert(StringEqualFold(s1).EqualFold(s1), qt.Equals, true)
+	c.Assert(StringEqualFold(s2).EqualFold(s1), qt.Equals, true)
+	c.Assert(StringEqualFold(s2).EqualFold(s2), qt.Equals, true)
+	c.Assert(StringEqualFold(s1).EqualFold("b"), qt.Equals, false)
+	c.Assert(StringEqualFold(s1).Eq(s2), qt.Equals, true)
+	c.Assert(StringEqualFold(s1).Eq("b"), qt.Equals, false)
+
+}