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/htmltemplate/content.go

@@ -0,0 +1,102 @@
+// 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.
+
+package template
+
+import (
+	"fmt"
+	htmltemplate "html/template"
+	"reflect"
+)
+
+type contentType uint8
+
+const (
+	contentTypePlain contentType = iota
+	contentTypeCSS
+	contentTypeHTML
+	contentTypeHTMLAttr
+	contentTypeJS
+	contentTypeJSStr
+	contentTypeURL
+	contentTypeSrcset
+	// contentTypeUnsafe is used in attr.go for values that affect how
+	// embedded content and network messages are formed, vetted,
+	// or interpreted; or which credentials network messages carry.
+	contentTypeUnsafe
+)
+
+// indirect returns the value, after dereferencing as many times
+// as necessary to reach the base type (or nil).
+func indirect(a interface{}) interface{} {
+	if a == nil {
+		return nil
+	}
+	if t := reflect.TypeOf(a); t.Kind() != reflect.Ptr {
+		// Avoid creating a reflect.Value if it's not a pointer.
+		return a
+	}
+	v := reflect.ValueOf(a)
+	for v.Kind() == reflect.Ptr && !v.IsNil() {
+		v = v.Elem()
+	}
+	return v.Interface()
+}
+
+var (
+	errorType       = reflect.TypeOf((*error)(nil)).Elem()
+	fmtStringerType = reflect.TypeOf((*fmt.Stringer)(nil)).Elem()
+)
+
+// indirectToStringerOrError returns the value, after dereferencing as many times
+// as necessary to reach the base type (or nil) or an implementation of fmt.Stringer
+// or error,
+func indirectToStringerOrError(a interface{}) interface{} {
+	if a == nil {
+		return nil
+	}
+	v := reflect.ValueOf(a)
+	for !v.Type().Implements(fmtStringerType) && !v.Type().Implements(errorType) && v.Kind() == reflect.Ptr && !v.IsNil() {
+		v = v.Elem()
+	}
+	return v.Interface()
+}
+
+// stringify converts its arguments to a string and the type of the content.
+// All pointers are dereferenced, as in the text/template package.
+func stringify(args ...interface{}) (string, contentType) {
+	if len(args) == 1 {
+		switch s := indirect(args[0]).(type) {
+		case string:
+			return s, contentTypePlain
+		case htmltemplate.CSS:
+			return string(s), contentTypeCSS
+		case htmltemplate.HTML:
+			return string(s), contentTypeHTML
+		case htmltemplate.HTMLAttr:
+			return string(s), contentTypeHTMLAttr
+		case htmltemplate.JS:
+			return string(s), contentTypeJS
+		case htmltemplate.JSStr:
+			return string(s), contentTypeJSStr
+		case htmltemplate.URL:
+			return string(s), contentTypeURL
+		case htmltemplate.Srcset:
+			return string(s), contentTypeSrcset
+		}
+	}
+	i := 0
+	for _, arg := range args {
+		// We skip untyped nil arguments for backward compatibility.
+		// Without this they would be output as <nil>, escaped.
+		// See issue 25875.
+		if arg == nil {
+			continue
+		}
+
+		args[i] = indirectToStringerOrError(arg)
+		i++
+	}
+	return fmt.Sprint(args[:i]...), contentTypePlain
+}