Initial implementation of Template Literal support - does not work with braces inside ${}

tl.patch

diff --git a/src/html/template/context.go b/src/html/template/context.go
index 7ab3d1fed6..01ee09b5e8 100644
--- a/src/html/template/context.go
+++ b/src/html/template/context.go
@@ -16,17 +16,18 @@ import (
 // https://www.w3.org/TR/html5/syntax.html#the-end
 // where the context element is null.
 type context struct {
-	state   state
-	delim   delim
-	urlPart urlPart
-	jsCtx   jsCtx
-	attr    attr
-	element element
-	err     *Error
+	state     state
+	delim     delim
+	urlPart   urlPart
+	jsCtx     jsCtx
+	jsTLDepth uint
+	attr      attr
+	element   element
+	err       *Error
 }
 
 func (c context) String() string {
-	return fmt.Sprintf("{%v %v %v %v %v %v %v}", c.state, c.delim, c.urlPart, c.jsCtx, c.attr, c.element, c.err)
+	return fmt.Sprintf("{%v %v %v %v jsTLDepth=%v %v %v %v}", c.state, c.delim, c.urlPart, c.jsCtx, c.jsTLDepth, c.attr, c.element, c.err)
 }
 
 // eq reports whether two contexts are equal.
@@ -112,6 +113,8 @@ const (
 	stateJSDqStr
 	// stateJSSqStr occurs inside a JavaScript single quoted string.
 	stateJSSqStr
+	// stateJSBtStr occurs inside a JavaScript backtick-quoted template literal.
+	stateJSTLStr
 	// stateJSRegexp occurs inside a JavaScript regexp literal.
 	stateJSRegexp
 	// stateJSBlockCmt occurs inside a JavaScript /* block comment */.
diff --git a/src/html/template/escape.go b/src/html/template/escape.go
index f12dafa870..5829efb4b7 100644
--- a/src/html/template/escape.go
+++ b/src/html/template/escape.go
@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"html"
 	"io"
+	"log"
 	"text/template"
 	"text/template/parse"
 )
@@ -201,7 +202,7 @@ func (e *escaper) escapeAction(c context, n *parse.ActionNode) context {
 		s = append(s, "_html_template_jsvalescaper")
 		// A slash after a value starts a div operator.
 		c.jsCtx = jsCtxDivOp
-	case stateJSDqStr, stateJSSqStr:
+	case stateJSDqStr, stateJSSqStr, stateJSTLStr:
 		s = append(s, "_html_template_jsstrescaper")
 	case stateJSRegexp:
 		s = append(s, "_html_template_jsregexpescaper")
@@ -647,6 +648,7 @@ func (e *escaper) escapeText(c context, n *parse.TextNode) context {
 	s, written, i, b := n.Text, 0, 0, new(bytes.Buffer)
 	for i != len(s) {
 		c1, nread := contextAfterText(c, s[i:])
+		log.Printf("Parse \"%s\": %s", s[i:][:nread], c1)
 		i1 := i + nread
 		if c.state == stateText || c.state == stateRCDATA {
 			end := i1
diff --git a/src/html/template/js.go b/src/html/template/js.go
index 04c7c325db..e280a6a655 100644
--- a/src/html/template/js.go
+++ b/src/html/template/js.go
@@ -293,12 +293,14 @@ var jsStrReplacementTable = []string{
 	// Encode HTML specials as hex so the output can be embedded
 	// in HTML attributes without further encoding.
 	'"':  `\x22`,
+	'$':  `\x24`,
 	'&':  `\x26`,
 	'\'': `\x27`,
 	'+':  `\x2b`,
 	'/':  `\/`,
 	'<':  `\x3c`,
 	'>':  `\x3e`,
+	'`':  `\x60`,
 	'\\': `\\`,
 }
 
@@ -314,12 +316,14 @@ var jsStrNormReplacementTable = []string{
 	// Encode HTML specials as hex so the output can be embedded
 	// in HTML attributes without further encoding.
 	'"':  `\x22`,
+	'$':  `\x24`,
 	'&':  `\x26`,
 	'\'': `\x27`,
 	'+':  `\x2b`,
 	'/':  `\/`,
 	'<':  `\x3c`,
 	'>':  `\x3e`,
+	'`':  `\x60`,
 }
 
 var jsRegexpReplacementTable = []string{
diff --git a/src/html/template/transition.go b/src/html/template/transition.go
index 06df679330..5d9710ae59 100644
--- a/src/html/template/transition.go
+++ b/src/html/template/transition.go
@@ -27,6 +27,7 @@ var transitionFunc = [...]func(context, []byte) (context, int){
 	stateJS:          tJS,
 	stateJSDqStr:     tJSDelimited,
 	stateJSSqStr:     tJSDelimited,
+	stateJSTLStr:     tJSDelimited,
 	stateJSRegexp:    tJSDelimited,
 	stateJSBlockCmt:  tBlockCmt,
 	stateJSLineCmt:   tLineCmt,
@@ -262,7 +263,7 @@ func tURL(c context, s []byte) (context, int) {
 
 // tJS is the context transition function for the JS state.
 func tJS(c context, s []byte) (context, int) {
-	i := bytes.IndexAny(s, `"'/`)
+	i := bytes.IndexAny(s, "\"'/`}")
 	if i == -1 {
 		// Entire input is non string, comment, regexp tokens.
 		c.jsCtx = nextJSCtx(s, c.jsCtx)
@@ -274,6 +275,14 @@ func tJS(c context, s []byte) (context, int) {
 		c.state, c.jsCtx = stateJSDqStr, jsCtxRegexp
 	case '\'':
 		c.state, c.jsCtx = stateJSSqStr, jsCtxRegexp
+	case '`':
+		c.state, c.jsCtx, c.jsTLDepth = stateJSTLStr, jsCtxRegexp, c.jsTLDepth+1
+	case '}':
+		if c.jsTLDepth > 0 {
+			// In a placeholder. Return to template-literal-quoted state.
+			c.state, c.jsCtx = stateJSTLStr, jsCtxRegexp
+			return c, i + 1
+		}
 	case '/':
 		switch {
 		case i+1 < len(s) && s[i+1] == '/':
@@ -303,6 +312,8 @@ func tJSDelimited(c context, s []byte) (context, int) {
 	switch c.state {
 	case stateJSSqStr:
 		specials = `\'`
+	case stateJSTLStr:
+		specials = "\\`$"
 	case stateJSRegexp:
 		specials = `\/[]`
 	}
@@ -326,9 +337,17 @@ func tJSDelimited(c context, s []byte) (context, int) {
 			inCharset = true
 		case ']':
 			inCharset = false
+		case '$':
+			if c.state == stateJSTLStr && i+1 < len(s) && s[i+1] == '{' {
+				c.state, c.jsCtx = stateJS, jsCtxDivOp
+				return c, i + 2
+			}
 		default:
 			// end delimiter
 			if !inCharset {
+				if c.state == stateJSTLStr {
+					c.jsTLDepth -= 1
+				}
 				c.state, c.jsCtx = stateJS, jsCtxDivOp
 				return c, i + 1
 			}