tpl: Add template function namespaces

This commit moves almost all of the template functions into separate
packages under tpl/ and adds a namespace framework.  All changes should
be backward compatible for end users, as all existing function names in
the template funcMap are left intact.

Seq and DoArithmatic have been moved out of the helpers package and into
template namespaces.

Most of the tests involved have been refactored, and many new tests have
been written.  There's still work to do, but this is a big improvement.

I got a little overzealous and added some new functions along the way:

- strings.Contains
- strings.ContainsAny
- strings.HasSuffix
- strings.TrimPrefix
- strings.TrimSuffix

Documentation is forthcoming.

Fixes #3042

6 files changed, 1454 insertions, 0 deletions

diff --git a/tpl/strings/regexp.go b/tpl/strings/regexp.go
new file mode 100644
index 000000000..7b52c9f6e
--- /dev/null
+++ b/tpl/strings/regexp.go
@@ -0,0 +1,109 @@
+// Copyright 2017 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 strings
+
+import (
+	"regexp"
+	"sync"
+
+	"github.com/spf13/cast"
+)
+
+// FindRE returns a list of strings that match the regular expression. By default all matches
+// will be included. The number of matches can be limited with an optional third parameter.
+func (ns *Namespace) FindRE(expr string, content interface{}, limit ...interface{}) ([]string, error) {
+	re, err := reCache.Get(expr)
+	if err != nil {
+		return nil, err
+	}
+
+	conv, err := cast.ToStringE(content)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(limit) == 0 {
+		return re.FindAllString(conv, -1), nil
+	}
+
+	lim, err := cast.ToIntE(limit[0])
+	if err != nil {
+		return nil, err
+	}
+
+	return re.FindAllString(conv, lim), nil
+}
+
+// ReplaceRE returns a copy of s, replacing all matches of the regular
+// expression pattern with the replacement text repl.
+func (ns *Namespace) ReplaceRE(pattern, repl, s interface{}) (_ string, err error) {
+	sp, err := cast.ToStringE(pattern)
+	if err != nil {
+		return
+	}
+
+	sr, err := cast.ToStringE(repl)
+	if err != nil {
+		return
+	}
+
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return
+	}
+
+	re, err := reCache.Get(sp)
+	if err != nil {
+		return "", err
+	}
+
+	return re.ReplaceAllString(ss, sr), nil
+}
+
+// regexpCache represents a cache of regexp objects protected by a mutex.
+type regexpCache struct {
+	mu sync.RWMutex
+	re map[string]*regexp.Regexp
+}
+
+// Get retrieves a regexp object from the cache based upon the pattern.
+// If the pattern is not found in the cache, create one
+func (rc *regexpCache) Get(pattern string) (re *regexp.Regexp, err error) {
+	var ok bool
+
+	if re, ok = rc.get(pattern); !ok {
+		re, err = regexp.Compile(pattern)
+		if err != nil {
+			return nil, err
+		}
+		rc.set(pattern, re)
+	}
+
+	return re, nil
+}
+
+func (rc *regexpCache) get(key string) (re *regexp.Regexp, ok bool) {
+	rc.mu.RLock()
+	re, ok = rc.re[key]
+	rc.mu.RUnlock()
+	return
+}
+
+func (rc *regexpCache) set(key string, re *regexp.Regexp) {
+	rc.mu.Lock()
+	rc.re[key] = re
+	rc.mu.Unlock()
+}
+
+var reCache = regexpCache{re: make(map[string]*regexp.Regexp)}
diff --git a/tpl/strings/regexp_test.go b/tpl/strings/regexp_test.go
new file mode 100644
index 000000000..3bacd2018
--- /dev/null
+++ b/tpl/strings/regexp_test.go
@@ -0,0 +1,86 @@
+// Copyright 2017 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 strings
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestFindRE(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		expr    string
+		content interface{}
+		limit   interface{}
+		expect  interface{}
+	}{
+		{"[G|g]o", "Hugo is a static site generator written in Go.", 2, []string{"go", "Go"}},
+		{"[G|g]o", "Hugo is a static site generator written in Go.", -1, []string{"go", "Go"}},
+		{"[G|g]o", "Hugo is a static site generator written in Go.", 1, []string{"go"}},
+		{"[G|g]o", "Hugo is a static site generator written in Go.", "1", []string{"go"}},
+		{"[G|g]o", "Hugo is a static site generator written in Go.", nil, []string(nil)},
+		// errors
+		{"[G|go", "Hugo is a static site generator written in Go.", nil, false},
+		{"[G|g]o", t, nil, false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.FindRE(test.expr, test.content, test.limit)
+
+		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 TestReplaceRE(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		pattern interface{}
+		repl    interface{}
+		s       interface{}
+		expect  interface{}
+	}{
+		{"^https?://([^/]+).*", "$1", "http://gohugo.io/docs", "gohugo.io"},
+		{"^https?://([^/]+).*", "$2", "http://gohugo.io/docs", ""},
+		{"(ab)", "AB", "aabbaab", "aABbaAB"},
+		// errors
+		{"(ab", "AB", "aabb", false}, // invalid re
+		{tstNoStringer{}, "$2", "http://gohugo.io/docs", false},
+		{"^https?://([^/]+).*", tstNoStringer{}, "http://gohugo.io/docs", false},
+		{"^https?://([^/]+).*", "$2", tstNoStringer{}, false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.ReplaceRE(test.pattern, test.repl, 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)
+	}
+}
diff --git a/tpl/strings/strings.go b/tpl/strings/strings.go
new file mode 100644
index 000000000..32c5c00ae
--- /dev/null
+++ b/tpl/strings/strings.go
@@ -0,0 +1,380 @@
+// Copyright 2017 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 strings
+
+import (
+	"errors"
+	"fmt"
+	"html/template"
+	_strings "strings"
+	"unicode/utf8"
+
+	"github.com/spf13/cast"
+	"github.com/spf13/hugo/deps"
+	"github.com/spf13/hugo/helpers"
+)
+
+// New returns a new instance of the strings-namespaced template functions.
+func New(d *deps.Deps) *Namespace {
+	return &Namespace{deps: d}
+}
+
+// Namespace provides template functions for the "strings" namespace.
+// Most functions mimic the Go stdlib, but the order of the parameters may be
+// different to ease their use in the Go template system.
+type Namespace struct {
+	deps *deps.Deps
+}
+
+// Namespace returns a pointer to the current namespace instance.
+func (ns *Namespace) Namespace() *Namespace { return ns }
+
+// CountRunes returns the number of runes in s, excluding whitepace.
+func (ns *Namespace) CountRunes(s interface{}) (int, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return 0, fmt.Errorf("Failed to convert content to string: %s", err)
+	}
+
+	counter := 0
+	for _, r := range helpers.StripHTML(ss) {
+		if !helpers.IsWhitespace(r) {
+			counter++
+		}
+	}
+
+	return counter, nil
+}
+
+// CountWords returns the approximate word count in s.
+func (ns *Namespace) CountWords(s interface{}) (int, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return 0, fmt.Errorf("Failed to convert content to string: %s", err)
+	}
+
+	counter := 0
+	for _, word := range _strings.Fields(helpers.StripHTML(ss)) {
+		runeCount := utf8.RuneCountInString(word)
+		if len(word) == runeCount {
+			counter++
+		} else {
+			counter += runeCount
+		}
+	}
+
+	return counter, nil
+}
+
+// Chomp returns a copy of s with all trailing newline characters removed.
+func (ns *Namespace) Chomp(s interface{}) (template.HTML, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	return template.HTML(_strings.TrimRight(ss, "\r\n")), nil
+}
+
+// Contains reports whether substr is in s.
+func (ns *Namespace) Contains(s, substr interface{}) (bool, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return false, err
+	}
+
+	su, err := cast.ToStringE(substr)
+	if err != nil {
+		return false, err
+	}
+
+	return _strings.Contains(ss, su), nil
+}
+
+// ContainsAny reports whether any Unicode code points in chars are within s.
+func (ns *Namespace) ContainsAny(s, chars interface{}) (bool, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return false, err
+	}
+
+	sc, err := cast.ToStringE(chars)
+	if err != nil {
+		return false, err
+	}
+
+	return _strings.ContainsAny(ss, sc), nil
+}
+
+// HasPrefix tests whether the input s begins with prefix.
+func (ns *Namespace) HasPrefix(s, prefix interface{}) (bool, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return false, err
+	}
+
+	sx, err := cast.ToStringE(prefix)
+	if err != nil {
+		return false, err
+	}
+
+	return _strings.HasPrefix(ss, sx), nil
+}
+
+// HasSuffix tests whether the input s begins with suffix.
+func (ns *Namespace) HasSuffix(s, suffix interface{}) (bool, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return false, err
+	}
+
+	sx, err := cast.ToStringE(suffix)
+	if err != nil {
+		return false, err
+	}
+
+	return _strings.HasSuffix(ss, sx), nil
+}
+
+// Replace returns a copy of the string s with all occurrences of old replaced
+// with new.
+func (ns *Namespace) Replace(s, old, new interface{}) (string, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	so, err := cast.ToStringE(old)
+	if err != nil {
+		return "", err
+	}
+
+	sn, err := cast.ToStringE(new)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.Replace(ss, so, sn, -1), nil
+}
+
+// SliceString slices a string by specifying a half-open range with
+// two indices, start and end. 1 and 4 creates a slice including elements 1 through 3.
+// The end index can be omitted, it defaults to the string's length.
+func (ns *Namespace) SliceString(a interface{}, startEnd ...interface{}) (string, error) {
+	aStr, err := cast.ToStringE(a)
+	if err != nil {
+		return "", err
+	}
+
+	var argStart, argEnd int
+
+	argNum := len(startEnd)
+
+	if argNum > 0 {
+		if argStart, err = cast.ToIntE(startEnd[0]); err != nil {
+			return "", errors.New("start argument must be integer")
+		}
+	}
+	if argNum > 1 {
+		if argEnd, err = cast.ToIntE(startEnd[1]); err != nil {
+			return "", errors.New("end argument must be integer")
+		}
+	}
+
+	if argNum > 2 {
+		return "", errors.New("too many arguments")
+	}
+
+	asRunes := []rune(aStr)
+
+	if argNum > 0 && (argStart < 0 || argStart >= len(asRunes)) {
+		return "", errors.New("slice bounds out of range")
+	}
+
+	if argNum == 2 {
+		if argEnd < 0 || argEnd > len(asRunes) {
+			return "", errors.New("slice bounds out of range")
+		}
+		return string(asRunes[argStart:argEnd]), nil
+	} else if argNum == 1 {
+		return string(asRunes[argStart:]), nil
+	} else {
+		return string(asRunes[:]), nil
+	}
+
+}
+
+// Split slices an input string into all substrings separated by delimiter.
+func (ns *Namespace) Split(a interface{}, delimiter string) ([]string, error) {
+	aStr, err := cast.ToStringE(a)
+	if err != nil {
+		return []string{}, err
+	}
+
+	return _strings.Split(aStr, delimiter), nil
+}
+
+// Substr extracts parts of a string, beginning at the character at the specified
+// position, and returns the specified number of characters.
+//
+// It normally takes two parameters: start and length.
+// It can also take one parameter: start, i.e. length is omitted, in which case
+// the substring starting from start until the end of the string will be returned.
+//
+// To extract characters from the end of the string, use a negative start number.
+//
+// In addition, borrowing from the extended behavior described at http://php.net/substr,
+// if length is given and is negative, then that many characters will be omitted from
+// the end of string.
+func (ns *Namespace) Substr(a interface{}, nums ...interface{}) (string, error) {
+	aStr, err := cast.ToStringE(a)
+	if err != nil {
+		return "", err
+	}
+
+	var start, length int
+
+	asRunes := []rune(aStr)
+
+	switch len(nums) {
+	case 0:
+		return "", errors.New("too less arguments")
+	case 1:
+		if start, err = cast.ToIntE(nums[0]); err != nil {
+			return "", errors.New("start argument must be integer")
+		}
+		length = len(asRunes)
+	case 2:
+		if start, err = cast.ToIntE(nums[0]); err != nil {
+			return "", errors.New("start argument must be integer")
+		}
+		if length, err = cast.ToIntE(nums[1]); err != nil {
+			return "", errors.New("length argument must be integer")
+		}
+	default:
+		return "", errors.New("too many arguments")
+	}
+
+	if start < -len(asRunes) {
+		start = 0
+	}
+	if start > len(asRunes) {
+		return "", fmt.Errorf("start position out of bounds for %d-byte string", len(aStr))
+	}
+
+	var s, e int
+	if start >= 0 && length >= 0 {
+		s = start
+		e = start + length
+	} else if start < 0 && length >= 0 {
+		s = len(asRunes) + start - length + 1
+		e = len(asRunes) + start + 1
+	} else if start >= 0 && length < 0 {
+		s = start
+		e = len(asRunes) + length
+	} else {
+		s = len(asRunes) + start
+		e = len(asRunes) + length
+	}
+
+	if s > e {
+		return "", fmt.Errorf("calculated start position greater than end position: %d > %d", s, e)
+	}
+	if e > len(asRunes) {
+		e = len(asRunes)
+	}
+
+	return string(asRunes[s:e]), nil
+}
+
+// Title returns a copy of the input s with all Unicode letters that begin words
+// mapped to their title case.
+func (ns *Namespace) Title(s interface{}) (string, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.Title(ss), nil
+}
+
+// ToLower returns a copy of the input s with all Unicode letters mapped to their
+// lower case.
+func (ns *Namespace) ToLower(s interface{}) (string, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.ToLower(ss), nil
+}
+
+// ToUpper returns a copy of the input s with all Unicode letters mapped to their
+// upper case.
+func (ns *Namespace) ToUpper(s interface{}) (string, error) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.ToUpper(ss), nil
+}
+
+// Trim returns a string with all leading and trailing characters defined
+// contained in cutset removed.
+func (ns *Namespace) Trim(s, cutset 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.Trim(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) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	sx, err := cast.ToStringE(prefix)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.TrimPrefix(ss, sx), 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) {
+	ss, err := cast.ToStringE(s)
+	if err != nil {
+		return "", err
+	}
+
+	sx, err := cast.ToStringE(suffix)
+	if err != nil {
+		return "", err
+	}
+
+	return _strings.TrimSuffix(ss, sx), nil
+}
diff --git a/tpl/strings/strings_test.go b/tpl/strings/strings_test.go
new file mode 100644
index 000000000..9164729fe
--- /dev/null
+++ b/tpl/strings/strings_test.go
@@ -0,0 +1,639 @@
+// Copyright 2017 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 strings
+
+import (
+	"fmt"
+	"html/template"
+	"testing"
+
+	"github.com/spf13/hugo/deps"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+var ns = New(&deps.Deps{})
+
+type tstNoStringer struct{}
+
+func TestNamespace(t *testing.T) {
+	t.Parallel()
+	assert.Equal(t, ns, ns.Namespace(), "object pointers should match")
+}
+
+func TestChomp(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		expect interface{}
+	}{
+		{"\n a\n", template.HTML("\n a")},
+		{"\n a\n\n", template.HTML("\n a")},
+		{"\n a\r\n", template.HTML("\n a")},
+		{"\n a\n\r\n", template.HTML("\n a")},
+		{"\n a\r\r", template.HTML("\n a")},
+		{"\n a\r", template.HTML("\n a")},
+		// errors
+		{tstNoStringer{}, false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.Chomp(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 TestContains(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		substr interface{}
+		expect bool
+		isErr  bool
+	}{
+		{"", "", true, false},
+		{"123", "23", true, false},
+		{"123", "234", false, false},
+		{"123", "", true, false},
+		{"", "a", false, false},
+		{123, "23", true, false},
+		{123, "234", false, false},
+		{123, "", true, false},
+		{template.HTML("123"), []byte("23"), true, false},
+		{template.HTML("123"), []byte("234"), false, false},
+		{template.HTML("123"), []byte(""), true, false},
+		// errors
+		{"", tstNoStringer{}, false, true},
+		{tstNoStringer{}, "", false, true},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.Contains(test.s, test.substr)
+
+		if test.isErr {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestContainsAny(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		substr interface{}
+		expect bool
+		isErr  bool
+	}{
+		{"", "", false, false},
+		{"", "1", false, false},
+		{"", "123", false, false},
+		{"1", "", false, false},
+		{"1", "1", true, false},
+		{"111", "1", true, false},
+		{"123", "789", false, false},
+		{"123", "729", true, false},
+		{"a☺b☻c☹d", "uvw☻xyz", true, false},
+		{1, "", false, false},
+		{1, "1", true, false},
+		{111, "1", true, false},
+		{123, "789", false, false},
+		{123, "729", true, false},
+		{[]byte("123"), template.HTML("789"), false, false},
+		{[]byte("123"), template.HTML("729"), true, false},
+		{[]byte("a☺b☻c☹d"), template.HTML("uvw☻xyz"), true, false},
+		// errors
+		{"", tstNoStringer{}, false, true},
+		{tstNoStringer{}, "", false, true},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.ContainsAny(test.s, test.substr)
+
+		if test.isErr {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestCountRunes(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		expect interface{}
+	}{
+		{"foo bar", 6},
+		{"旁边", 2},
+		{`<div class="test">旁边</div>`, 2},
+		// errors
+		{tstNoStringer{}, false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test.s)
+
+		result, err := ns.CountRunes(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 TestCountWords(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		expect interface{}
+	}{
+		{"Do Be Do Be Do", 5},
+		{"旁边", 2},
+		{`<div class="test">旁边</div>`, 2},
+		// errors
+		{tstNoStringer{}, false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test.s)
+
+		result, err := ns.CountWords(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 TestHasPrefix(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		prefix interface{}
+		expect interface{}
+		isErr  bool
+	}{
+		{"abcd", "ab", true, false},
+		{"abcd", "cd", false, false},
+		{template.HTML("abcd"), "ab", true, false},
+		{template.HTML("abcd"), "cd", false, false},
+		{template.HTML("1234"), 12, true, false},
+		{template.HTML("1234"), 34, false, false},
+		{[]byte("abcd"), "ab", true, false},
+		// errors
+		{"", tstNoStringer{}, false, true},
+		{tstNoStringer{}, "", false, true},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.HasPrefix(test.s, test.prefix)
+
+		if test.isErr {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestHasSuffix(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		suffix interface{}
+		expect interface{}
+		isErr  bool
+	}{
+		{"abcd", "cd", true, false},
+		{"abcd", "ab", false, false},
+		{template.HTML("abcd"), "cd", true, false},
+		{template.HTML("abcd"), "ab", false, false},
+		{template.HTML("1234"), 34, true, false},
+		{template.HTML("1234"), 12, false, false},
+		{[]byte("abcd"), "cd", true, false},
+		// errors
+		{"", tstNoStringer{}, false, true},
+		{tstNoStringer{}, "", false, true},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.HasSuffix(test.s, test.suffix)
+
+		if test.isErr {
+			require.Error(t, err, errMsg)
+			continue
+		}
+
+		require.NoError(t, err, errMsg)
+		assert.Equal(t, test.expect, result, errMsg)
+	}
+}
+
+func TestReplace(t *testing.T) {
+	t.Parallel()
+
+	for i, test := range []struct {
+		s      interface{}
+		old    interface{}
+		new    interface{}
+		expect interface{}
+	}{
+		{"aab", "a", "b", "bbb"},
+		{"11a11", 1, 2, "22a22"},
+		{12345, 1, 2, "22345"},
+		// errors
+		{tstNoStringer{}, "a", "b", false},
+		{"a", tstNoStringer{}, "b", false},
+		{"a", "b", tstNoStringer{}, false},
+	} {
+		errMsg := fmt.Sprintf("[%d] %v", i, test)
+
+		result, err := ns.Replace(test.s, test.old, test.new)
+
+		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 TestSliceString(t *testing.T) {
+	t.Parallel()
+
+	var err error
+	for i, test := range []struct {
+		v1     interface{}
+		v2     interface{}
+		v3     interface{}
+		expect interface{}
+	}{
+		{"abc", 1, 2, "b"},
+		{"abc", 1, 3, "bc"},
+		{"abcdef", 1, int8(3), "bc"},
+		{"abcdef", 1, int16(3), "bc"},
+		{"abcdef", 1, int32(3), "bc"},
+		{"abcdef", 1, int64(3), "bc"},
+		{"abc", 0, 1, "a"},
+		{"abcdef", nil, nil, "abcdef"},
+		{"abcdef", 0, 6, "abcdef"},
+		{"abcdef", 0, 2, "ab"},
+		{"abcdef", 2, nil, "cdef"},
+		{"abcdef", int8(2), nil, "cdef"},
+		{"abcdef", int16(2), nil, "cdef"},
+		{"abcdef", int32(2), nil, "cdef"},
+		{"abcdef", int64(2), nil, "cdef"},
+		{123, 1, 3, "23"},
+		{"abcdef", 6, nil, false},
+		{"abcdef", 4, 7, false},
+		{"abcdef", -1, nil, false},
+		{"abcdef", -1, 7, false},
+		{"abcdef", 1, -1, false},
+		{tstNoStringer{}, 0, 1, false},
+		{"ĀĀĀ", 0, 1, "Ā"}, // issue #1333
+		{"a", t, nil, false},
+		{"a", 1, t, false},
+	} {
+		err