helpers: Add PathSpec.MakePathSegment

MakePathSegment properly sanitizes path segments (like taxonomy terms) with
slashes (and pound signs).

Updates gohugoio#4090

helpers/path.go

@@ -74,6 +74,35 @@ func (filepathBridge) Separator() string {
 
 var fpb filepathBridge
 
+// segmentReplacer replaces some URI-reserved characters in a path segments.
+var segmentReplacer = strings.NewReplacer("/", "-", "#", "-")
+
+// MakeSegment returns a copy of string s that is appropriate for a path
+// segment.  MakeSegment is similar to MakePath but disallows the '/' and
+// '#' characters because of their reserved meaning in URIs.
+func (p *PathSpec) MakeSegment(s string) string {
+	s = p.MakePathSanitized(strings.Trim(segmentReplacer.Replace(s), "- "))
+
+	var pos int
+	var last byte
+	b := make([]byte, len(s))
+
+	for i := 0; i < len(s); i++ {
+		// consolidate dashes
+		if s[i] == '-' && last == '-' {
+			continue
+		}
+
+		b[pos], last = s[i], s[i]
+		pos++
+	}
+
+	if p.disablePathToLower {
+		return string(b[:pos])
+	}
+	return strings.ToLower(string(b[:pos]))
+}
+
 // MakePath takes a string with any characters and replace it
 // so the string could be used in a path.
 // It does so by creating a Unicode-sanitized string, with the spaces replaced,

helpers/path_test.go

@@ -36,6 +36,34 @@ import (
 	"github.com/spf13/viper"
 )
 
+func TestMakeSegment(t *testing.T) {
+	v := viper.New()
+	l := NewDefaultLanguage(v)
+	p, _ := NewPathSpec(hugofs.NewMem(v), l)
+
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"  FOO bar  ", "foo-bar"},
+		{"Foo.Bar/fOO_bAr-Foo", "foo.bar-foo_bar-foo"},
+		{"FOO,bar:FooBar", "foobarfoobar"},
+		{"foo/BAR.HTML", "foo-bar.html"},
+		{"трям/трям", "трям-трям"},
+		{"은행", "은행"},
+		{"Say What??", "say-what"},
+		{"Your #1 Fan", "your-1-fan"},
+		{"Red & Blue", "red-blue"},
+	}
+
+	for _, test := range tests {
+		output := p.MakeSegment(test.input)
+		if output != test.expected {
+			t.Errorf("Expected %#v, got %#v\n", test.expected, output)
+		}
+	}
+}
+
 func TestMakePath(t *testing.T) {
 	tests := []struct {
 		input         string