Create lightweight forks of text/template and html/template

This commit also removes support for Ace and Amber templates.

Updates #6594

tpl/internal/go_templates/texttemplate/example_test.go

@@ -0,0 +1,112 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.13
+
+package template_test
+
+import (
+	"log"
+	"os"
+	"strings"
+	"text/template"
+)
+
+func ExampleTemplate() {
+	// Define a template.
+	const letter = `
+Dear {{.Name}},
+{{if .Attended}}
+It was a pleasure to see you at the wedding.
+{{- else}}
+It is a shame you couldn't make it to the wedding.
+{{- end}}
+{{with .Gift -}}
+Thank you for the lovely {{.}}.
+{{end}}
+Best wishes,
+Josie
+`
+
+	// Prepare some data to insert into the template.
+	type Recipient struct {
+		Name, Gift string
+		Attended   bool
+	}
+	var recipients = []Recipient{
+		{"Aunt Mildred", "bone china tea set", true},
+		{"Uncle John", "moleskin pants", false},
+		{"Cousin Rodney", "", false},
+	}
+
+	// Create a new template and parse the letter into it.
+	t := template.Must(template.New("letter").Parse(letter))
+
+	// Execute the template for each recipient.
+	for _, r := range recipients {
+		err := t.Execute(os.Stdout, r)
+		if err != nil {
+			log.Println("executing template:", err)
+		}
+	}
+
+	// Output:
+	// Dear Aunt Mildred,
+	//
+	// It was a pleasure to see you at the wedding.
+	// Thank you for the lovely bone china tea set.
+	//
+	// Best wishes,
+	// Josie
+	//
+	// Dear Uncle John,
+	//
+	// It is a shame you couldn't make it to the wedding.
+	// Thank you for the lovely moleskin pants.
+	//
+	// Best wishes,
+	// Josie
+	//
+	// Dear Cousin Rodney,
+	//
+	// It is a shame you couldn't make it to the wedding.
+	//
+	// Best wishes,
+	// Josie
+}
+
+// The following example is duplicated in html/template; keep them in sync.
+
+func ExampleTemplate_block() {
+	const (
+		master  = `Names:{{block "list" .}}{{"\n"}}{{range .}}{{println "-" .}}{{end}}{{end}}`
+		overlay = `{{define "list"}} {{join . ", "}}{{end}} `
+	)
+	var (
+		funcs     = template.FuncMap{"join": strings.Join}
+		guardians = []string{"Gamora", "Groot", "Nebula", "Rocket", "Star-Lord"}
+	)
+	masterTmpl, err := template.New("master").Funcs(funcs).Parse(master)
+	if err != nil {
+		log.Fatal(err)
+	}
+	overlayTmpl, err := template.Must(masterTmpl.Clone()).Parse(overlay)
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err := masterTmpl.Execute(os.Stdout, guardians); err != nil {
+		log.Fatal(err)
+	}
+	if err := overlayTmpl.Execute(os.Stdout, guardians); err != nil {
+		log.Fatal(err)
+	}
+	// Output:
+	// Names:
+	// - Gamora
+	// - Groot
+	// - Nebula
+	// - Rocket
+	// - Star-Lord
+	// Names: Gamora, Groot, Nebula, Rocket, Star-Lord
+}