Support configurable template parsers (#317)

Author: nicksnyder

v2/i18n/localizer.go

@@ -2,8 +2,9 @@ package i18n
 
 import (
 	"fmt"
-	"text/template"
+	texttemplate "text/template"
 
+	"github.com/nicksnyder/go-i18n/v2/i18n/template"
 	"github.com/nicksnyder/go-i18n/v2/internal/plural"
 	"golang.org/x/text/language"
 )
@@ -66,8 +67,26 @@ type LocalizeConfig struct {
 	// DefaultMessage is used if the message is not found in any message files.
 	DefaultMessage *Message
 
-	// Funcs is used to extend the Go template engine's built in functions
-	Funcs template.FuncMap
+	// Funcs is used to configure a template.TextParser if TemplateParser is not set.
+	Funcs texttemplate.FuncMap
+
+	// The TemplateParser to use for parsing templates.
+	// If one is not set, a template.TextParser is used (configured with Funcs if it is set).
+	TemplateParser template.Parser
+}
+
+var defaultTextParser = &template.TextParser{}
+
+func (lc *LocalizeConfig) getTemplateParser() template.Parser {
+	if lc.TemplateParser != nil {
+		return lc.TemplateParser
+	}
+	if lc.Funcs != nil {
+		return &template.TextParser{
+			Funcs: lc.Funcs,
+		}
+	}
+	return defaultTextParser
 }
 
 type invalidPluralCountErr struct {
@@ -152,15 +171,16 @@ func (l *Localizer) LocalizeWithTag(lc *LocalizeConfig) (string, language.Tag, e
 	}
 
 	pluralForm := l.pluralForm(tag, operands)
-	msg, err2 := template.Execute(pluralForm, templateData, lc.Funcs)
+	templateParser := lc.getTemplateParser()
+	msg, err2 := template.execute(pluralForm, templateData, templateParser)
 	if err2 != nil {
 		if err == nil {
 			err = err2
 		}
 
 		// Attempt to fallback to "Other" pluralization in case translations are incomplete.
 		if pluralForm != plural.Other {
-			msg2, err3 := template.Execute(plural.Other, templateData, lc.Funcs)
+			msg2, err3 := template.execute(plural.Other, templateData, templateParser)
 			if err3 == nil {
 				msg = msg2
 			}

v2/i18n/localizer_test.go

@@ -5,6 +5,7 @@ import (
 	"reflect"
 	"testing"
 
+	"github.com/nicksnyder/go-i18n/v2/i18n/template"
 	"github.com/nicksnyder/go-i18n/v2/internal/plural"
 	"golang.org/x/text/language"
 )
@@ -362,6 +363,56 @@ func localizerTests() []localizerTest {
 			},
 			expectedLocalized: "Hello Nick",
 		},
+		{
+			name:            "identity parser, bundle message",
+			defaultLanguage: language.English,
+			messages: map[language.Tag][]*Message{
+				language.English: {{
+					ID:    "HelloPerson",
+					Other: "Hello {{.Person}}",
+				}},
+			},
+			acceptLangs: []string{"en"},
+			conf: &LocalizeConfig{
+				MessageID: "HelloPerson",
+				TemplateData: map[string]string{
+					"Person": "Nick",
+				},
+				TemplateParser: template.IdentityParser{},
+			},
+			expectedLocalized: "Hello {{.Person}}",
+		},
+		{
+			name:            "identity parser, default message",
+			defaultLanguage: language.English,
+			acceptLangs:     []string{"en"},
+			conf: &LocalizeConfig{
+				DefaultMessage: &Message{
+					ID:    "HelloPerson",
+					Other: "Hello {{.Person}}",
+				},
+				TemplateData: map[string]string{
+					"Person": "Nick",
+				},
+				TemplateParser: template.IdentityParser{},
+			},
+			expectedLocalized: "Hello {{.Person}}",
+		},
+		{
+			name:            "custom funcs, default message",
+			defaultLanguage: language.English,
+			acceptLangs:     []string{"en"},
+			conf: &LocalizeConfig{
+				DefaultMessage: &Message{
+					ID:    "HelloWorld",
+					Other: "{{HelloWorldFunc}}",
+				},
+				Funcs: map[string]any{
+					"HelloWorldFunc": func() string { return "Hello World" },
+				},
+			},
+			expectedLocalized: "Hello World",
+		},
 		{
 			name:            "template data, custom delims, bundle message",
 			defaultLanguage: language.English,

v2/i18n/message.go

@@ -21,7 +21,7 @@ type Message struct {
 	// LeftDelim is the left Go template delimiter.
 	LeftDelim string
 
-	// RightDelim is the right Go template delimiter.``
+	// RightDelim is the right Go template delimiter.
 	RightDelim string
 
 	// Zero is the content of the message for the CLDR plural form "zero".

v2/i18n/message_template.go

@@ -2,9 +2,9 @@ package i18n
 
 import (
 	"fmt"
+	texttemplate "text/template"
 
-	"text/template"
-
+	"github.com/nicksnyder/go-i18n/v2/i18n/template"
 	"github.com/nicksnyder/go-i18n/v2/internal"
 	"github.com/nicksnyder/go-i18n/v2/internal/plural"
 )
@@ -53,13 +53,30 @@ func (e pluralFormNotFoundError) Error() string {
 }
 
 // Execute executes the template for the plural form and template data.
-func (mt *MessageTemplate) Execute(pluralForm plural.Form, data interface{}, funcs template.FuncMap) (string, error) {
+// Deprecated: This message is no longer used internally by go-i18n and it probably should not have been exported to
+// begin with. Its replacement is not exported. If you depend on this method for some reason and/or have
+// a use case for exporting execute, please file an issue.
+func (mt *MessageTemplate) Execute(pluralForm plural.Form, data interface{}, funcs texttemplate.FuncMap) (string, error) {
+	t := mt.PluralTemplates[pluralForm]
+	if t == nil {
+		return "", pluralFormNotFoundError{
+			pluralForm: pluralForm,
+			messageID:  mt.Message.ID,
+		}
+	}
+	parser := &template.TextParser{
+		Funcs: funcs,
+	}
+	return t.Execute(parser, data)
+}
+
+func (mt *MessageTemplate) execute(pluralForm plural.Form, data interface{}, parser template.Parser) (string, error) {
 	t := mt.PluralTemplates[pluralForm]
 	if t == nil {
 		return "", pluralFormNotFoundError{
 			pluralForm: pluralForm,
 			messageID:  mt.Message.ID,
 		}
 	}
-	return t.Execute(funcs, data)
+	return t.Execute(parser, data)
 }

v2/i18n/template/identity_parser.go

@@ -0,0 +1,21 @@
+package template
+
+// IdentityParser is an Parser that does no parsing and returns tempalte string unchanged.
+type IdentityParser struct{}
+
+func (IdentityParser) Cacheable() bool {
+	// Caching is not necessary because Parse is cheap.
+	return false
+}
+
+func (IdentityParser) Parse(src, leftDelim, rightDelim string) (ParsedTemplate, error) {
+	return &identityParsedTemplate{src: src}, nil
+}
+
+type identityParsedTemplate struct {
+	src string
+}
+
+func (t *identityParsedTemplate) Execute(data any) (string, error) {
+	return t.src, nil
+}

v2/i18n/template/parser.go

@@ -0,0 +1,17 @@
+// Package template defines a generic interface for template parsers and implementations of that interface.
+package template
+
+// Parser parses strings into executable templates.
+type Parser interface {
+	// Parse parses src and returns a ParsedTemplate.
+	Parse(src, leftDelim, rightDelim string) (ParsedTemplate, error)
+
+	// Cacheable returns true if Parse returns ParsedTemplates that are always safe to cache.
+	Cacheable() bool
+}
+
+// ParsedTemplate is an executable template.
+type ParsedTemplate interface {
+	// Execute applies a parsed template to the specified data.
+	Execute(data any) (string, error)
+}

v2/i18n/template/text_parser.go

@@ -0,0 +1,57 @@
+package template
+
+import (
+	"bytes"
+	"strings"
+	"text/template"
+)
+
+// TextParser is a Parser that uses text/template.
+type TextParser struct {
+	LeftDelim  string
+	RightDelim string
+	Funcs      template.FuncMap
+	Option     string
+}
+
+func (te *TextParser) Cacheable() bool {
+	return te.Funcs == nil
+}
+
+func (te *TextParser) Parse(src, leftDelim, rightDelim string) (ParsedTemplate, error) {
+	if leftDelim == "" {
+		leftDelim = te.LeftDelim
+	}
+	if leftDelim == "" {
+		leftDelim = "{{"
+	}
+	if !strings.Contains(src, leftDelim) {
+		// Fast path to avoid parsing a template that has no actions.
+		return &identityParsedTemplate{src: src}, nil
+	}
+
+	if rightDelim == "" {
+		rightDelim = te.RightDelim
+	}
+	if rightDelim == "" {
+		rightDelim = "}}"
+	}
+
+	tmpl, err := template.New("").Delims(leftDelim, rightDelim).Funcs(te.Funcs).Parse(src)
+	if err != nil {
+		return nil, err
+	}
+	return &parsedTextTemplate{tmpl: tmpl}, nil
+}
+
+type parsedTextTemplate struct {
+	tmpl *template.Template
+}
+
+func (t *parsedTextTemplate) Execute(data any) (string, error) {
+	var buf bytes.Buffer
+	if err := t.tmpl.Execute(&buf, data); err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}

v2/internal/template.go

@@ -1,51 +1,36 @@
 package internal
 
 import (
-	"bytes"
-	"strings"
 	"sync"
-	gotemplate "text/template"
+
+	"github.com/nicksnyder/go-i18n/v2/i18n/template"
 )
 
-// Template stores the template for a string.
+// Template stores the template for a string and a cached version of the parsed template if they are cacheable.
 type Template struct {
 	Src        string
 	LeftDelim  string
 	RightDelim string
 
 	parseOnce      sync.Once
-	parsedTemplate *gotemplate.Template
+	parsedTemplate template.ParsedTemplate
 	parseError     error
 }
 
-func (t *Template) Execute(funcs gotemplate.FuncMap, data interface{}) (string, error) {
-	leftDelim := t.LeftDelim
-	if leftDelim == "" {
-		leftDelim = "{{"
-	}
-	if !strings.Contains(t.Src, leftDelim) {
-		// Fast path to avoid parsing a template that has no actions.
-		return t.Src, nil
-	}
-
-	var gt *gotemplate.Template
+func (t *Template) Execute(parser template.Parser, data interface{}) (string, error) {
+	var pt template.ParsedTemplate
 	var err error
-	if funcs == nil {
+	if parser.Cacheable() {
 		t.parseOnce.Do(func() {
-			// If funcs is nil, then we only need to parse this template once.
-			t.parsedTemplate, t.parseError = gotemplate.New("").Delims(t.LeftDelim, t.RightDelim).Parse(t.Src)
+			t.parsedTemplate, t.parseError = parser.Parse(t.Src, t.LeftDelim, t.RightDelim)
 		})
-		gt, err = t.parsedTemplate, t.parseError
+		pt, err = t.parsedTemplate, t.parseError
 	} else {
-		gt, err = gotemplate.New("").Delims(t.LeftDelim, t.RightDelim).Funcs(funcs).Parse(t.Src)
+		pt, err = parser.Parse(t.Src, t.LeftDelim, t.RightDelim)
 	}
 
 	if err != nil {
 		return "", err
 	}
-	var buf bytes.Buffer
-	if err := gt.Execute(&buf, data); err != nil {
-		return "", err
-	}
-	return buf.String(), nil
+	return pt.Execute(data)
 }

v2/internal/template_test.go

@@ -3,13 +3,15 @@ package internal
 import (
 	"strings"
 	"testing"
-	"text/template"
+	texttemplate "text/template"
+
+	"github.com/nicksnyder/go-i18n/v2/i18n/template"
 )
 
 func TestExecute(t *testing.T) {
 	tests := []struct {
 		template *Template
-		funcs    template.FuncMap
+		parser   template.Parser
 		data     interface{}
 		result   string
 		err      string
@@ -35,9 +37,11 @@ func TestExecute(t *testing.T) {
 			template: &Template{
 				Src: "hello {{world}}",
 			},
-			funcs: template.FuncMap{
-				"world": func() string {
-					return "world"
+			parser: &template.TextParser{
+				Funcs: texttemplate.FuncMap{
+					"world": func() string {
+						return "world"
+					},
 				},
 			},
 			result: "hello world",
@@ -53,15 +57,18 @@ func TestExecute(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.template.Src, func(t *testing.T) {
-			result, err := test.template.Execute(test.funcs, test.data)
+			if test.parser == nil {
+				test.parser = &template.TextParser{}
+			}
+			result, err := test.template.Execute(test.parser, test.data)
 			if actual := str(err); !strings.Contains(str(err), test.err) {
 				t.Errorf("expected err %q to contain %q", actual, test.err)
 			}
 			if result != test.result {
 				t.Errorf("expected result %q; got %q", test.result, result)
 			}
 			allocs := testing.AllocsPerRun(10, func() {
-				_, _ = test.template.Execute(test.funcs, test.data)
+				_, _ = test.template.Execute(test.parser, test.data)
 			})
 			if test.noallocs && allocs > 0 {
 				t.Errorf("expected no allocations; got %f", allocs)