Fix Go template script escaping

Fixes #6695

25 files changed, 1060 insertions, 293 deletions

diff --git a/tpl/internal/go_templates/cfg/cfg.go b/tpl/internal/go_templates/cfg/cfg.go
new file mode 100644
index 000000000..bdbe9df3e
--- /dev/null
+++ b/tpl/internal/go_templates/cfg/cfg.go
@@ -0,0 +1,64 @@
+// Copyright 2019 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 cfg holds configuration shared by the Go command and internal/testenv.
+// Definitions that don't need to be exposed outside of cmd/go should be in
+// cmd/go/internal/cfg instead of this package.
+package cfg
+
+// KnownEnv is a list of environment variables that affect the operation
+// of the Go command.
+const KnownEnv = `
+	AR
+	CC
+	CGO_CFLAGS
+	CGO_CFLAGS_ALLOW
+	CGO_CFLAGS_DISALLOW
+	CGO_CPPFLAGS
+	CGO_CPPFLAGS_ALLOW
+	CGO_CPPFLAGS_DISALLOW
+	CGO_CXXFLAGS
+	CGO_CXXFLAGS_ALLOW
+	CGO_CXXFLAGS_DISALLOW
+	CGO_ENABLED
+	CGO_FFLAGS
+	CGO_FFLAGS_ALLOW
+	CGO_FFLAGS_DISALLOW
+	CGO_LDFLAGS
+	CGO_LDFLAGS_ALLOW
+	CGO_LDFLAGS_DISALLOW
+	CXX
+	FC
+	GCCGO
+	GO111MODULE
+	GO386
+	GOARCH
+	GOARM
+	GOBIN
+	GOCACHE
+	GOENV
+	GOEXE
+	GOFLAGS
+	GOGCCFLAGS
+	GOHOSTARCH
+	GOHOSTOS
+	GOINSECURE
+	GOMIPS
+	GOMIPS64
+	GOMODCACHE
+	GONOPROXY
+	GONOSUMDB
+	GOOS
+	GOPATH
+	GOPPC64
+	GOPRIVATE
+	GOPROXY
+	GOROOT
+	GOSUMDB
+	GOTMPDIR
+	GOTOOLDIR
+	GOWASM
+	GO_EXTLINK_ENABLED
+	PKG_CONFIG
+`
diff --git a/tpl/internal/go_templates/fmtsort/sort.go b/tpl/internal/go_templates/fmtsort/sort.go
index 70a305a3a..b01229bd0 100644
--- a/tpl/internal/go_templates/fmtsort/sort.go
+++ b/tpl/internal/go_templates/fmtsort/sort.go
@@ -53,12 +53,16 @@ func Sort(mapValue reflect.Value) *SortedMap {
 	if mapValue.Type().Kind() != reflect.Map {
 		return nil
 	}
-	key := make([]reflect.Value, mapValue.Len())
-	value := make([]reflect.Value, len(key))
+	// Note: this code is arranged to not panic even in the presence
+	// of a concurrent map update. The runtime is responsible for
+	// yelling loudly if that happens. See issue 33275.
+	n := mapValue.Len()
+	key := make([]reflect.Value, 0, n)
+	value := make([]reflect.Value, 0, n)
 	iter := mapValue.MapRange()
-	for i := 0; iter.Next(); i++ {
-		key[i] = iter.Key()
-		value[i] = iter.Value()
+	for iter.Next() {
+		key = append(key, iter.Key())
+		value = append(value, iter.Value())
 	}
 	sorted := &SortedMap{
 		Key:   key,
diff --git a/tpl/internal/go_templates/fmtsort/sort_test.go b/tpl/internal/go_templates/fmtsort/sort_test.go
index 601ec9d25..364c5bf6d 100644
--- a/tpl/internal/go_templates/fmtsort/sort_test.go
+++ b/tpl/internal/go_templates/fmtsort/sort_test.go
@@ -119,7 +119,7 @@ var sortTests = []sortTest{
 		"PTR0:0 PTR1:1 PTR2:2",
 	},
 	{
-		map[toy]string{toy{7, 2}: "72", toy{7, 1}: "71", toy{3, 4}: "34"},
+		map[toy]string{{7, 2}: "72", {7, 1}: "71", {3, 4}: "34"},
 		"{3 4}:34 {7 1}:71 {7 2}:72",
 	},
 	{
diff --git a/tpl/internal/go_templates/htmltemplate/content_test.go b/tpl/internal/go_templates/htmltemplate/content_test.go
index 2a1abfbfb..b5de701d3 100644
--- a/tpl/internal/go_templates/htmltemplate/content_test.go
+++ b/tpl/internal/go_templates/htmltemplate/content_test.go
@@ -21,7 +21,7 @@ func TestTypedContent(t *testing.T) {
 		htmltemplate.HTML(`Hello, <b>World</b> &amp;tc!`),
 		htmltemplate.HTMLAttr(` dir="ltr"`),
 		htmltemplate.JS(`c && alert("Hello, World!");`),
-		htmltemplate.JSStr(`Hello, World & O'Reilly\x21`),
+		htmltemplate.JSStr(`Hello, World & O'Reilly\u0021`),
 		htmltemplate.URL(`greeting=H%69,&addressee=(World)`),
 		htmltemplate.Srcset(`greeting=H%69,&addressee=(World) 2x, https://golang.org/favicon.ico 500.5w`),
 		htmltemplate.URL(`,foo/,`),
@@ -73,7 +73,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello, <b>World</b> &amp;tc!`,
 				` dir=&#34;ltr&#34;`,
 				`c &amp;&amp; alert(&#34;Hello, World!&#34;);`,
-				`Hello, World &amp; O&#39;Reilly\x21`,
+				`Hello, World &amp; O&#39;Reilly\u0021`,
 				`greeting=H%69,&amp;addressee=(World)`,
 				`greeting=H%69,&amp;addressee=(World) 2x, https://golang.org/favicon.ico 500.5w`,
 				`,foo/,`,
@@ -103,7 +103,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello,&#32;World&#32;&amp;tc!`,
 				`&#32;dir&#61;&#34;ltr&#34;`,
 				`c&#32;&amp;&amp;&#32;alert(&#34;Hello,&#32;World!&#34;);`,
-				`Hello,&#32;World&#32;&amp;&#32;O&#39;Reilly\x21`,
+				`Hello,&#32;World&#32;&amp;&#32;O&#39;Reilly\u0021`,
 				`greeting&#61;H%69,&amp;addressee&#61;(World)`,
 				`greeting&#61;H%69,&amp;addressee&#61;(World)&#32;2x,&#32;https://golang.org/favicon.ico&#32;500.5w`,
 				`,foo/,`,
@@ -118,7 +118,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello, World &amp;tc!`,
 				` dir=&#34;ltr&#34;`,
 				`c &amp;&amp; alert(&#34;Hello, World!&#34;);`,
-				`Hello, World &amp; O&#39;Reilly\x21`,
+				`Hello, World &amp; O&#39;Reilly\u0021`,
 				`greeting=H%69,&amp;addressee=(World)`,
 				`greeting=H%69,&amp;addressee=(World) 2x, https://golang.org/favicon.ico 500.5w`,
 				`,foo/,`,
@@ -133,7 +133,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello, &lt;b&gt;World&lt;/b&gt; &amp;tc!`,
 				` dir=&#34;ltr&#34;`,
 				`c &amp;&amp; alert(&#34;Hello, World!&#34;);`,
-				`Hello, World &amp; O&#39;Reilly\x21`,
+				`Hello, World &amp; O&#39;Reilly\u0021`,
 				`greeting=H%69,&amp;addressee=(World)`,
 				`greeting=H%69,&amp;addressee=(World) 2x, https://golang.org/favicon.ico 500.5w`,
 				`,foo/,`,
@@ -149,7 +149,7 @@ func TestTypedContent(t *testing.T) {
 				// Not escaped.
 				`c && alert("Hello, World!");`,
 				// Escape sequence not over-escaped.
-				`"Hello, World & O'Reilly\x21"`,
+				`"Hello, World & O'Reilly\u0021"`,
 				`"greeting=H%69,\u0026addressee=(World)"`,
 				`"greeting=H%69,\u0026addressee=(World) 2x, https://golang.org/favicon.ico 500.5w"`,
 				`",foo/,"`,
@@ -165,7 +165,7 @@ func TestTypedContent(t *testing.T) {
 				// Not JS escaped but HTML escaped.
 				`c &amp;&amp; alert(&#34;Hello, World!&#34;);`,
 				// Escape sequence not over-escaped.
-				`&#34;Hello, World &amp; O&#39;Reilly\x21&#34;`,
+				`&#34;Hello, World &amp; O&#39;Reilly\u0021&#34;`,
 				`&#34;greeting=H%69,\u0026addressee=(World)&#34;`,
 				`&#34;greeting=H%69,\u0026addressee=(World) 2x, https://golang.org/favicon.ico 500.5w&#34;`,
 				`&#34;,foo/,&#34;`,
@@ -174,30 +174,30 @@ func TestTypedContent(t *testing.T) {
 		{
 			`<script>alert("{{.}}")</script>`,
 			[]string{
-				`\x3cb\x3e \x22foo%\x22 O\x27Reilly \x26bar;`,
-				`a[href =~ \x22\/\/example.com\x22]#foo`,
-				`Hello, \x3cb\x3eWorld\x3c\/b\x3e \x26amp;tc!`,
-				` dir=\x22ltr\x22`,
-				`c \x26\x26 alert(\x22Hello, World!\x22);`,
+				`\u003cb\u003e \u0022foo%\u0022 O\u0027Reilly \u0026bar;`,
+				`a[href =~ \u0022\/\/example.com\u0022]#foo`,
+				`Hello, \u003cb\u003eWorld\u003c\/b\u003e \u0026amp;tc!`,
+				` dir=\u0022ltr\u0022`,
+				`c \u0026\u0026 alert(\u0022Hello, World!\u0022);`,
 				// Escape sequence not over-escaped.
-				`Hello, World \x26 O\x27Reilly\x21`,
-				`greeting=H%69,\x26addressee=(World)`,
-				`greeting=H%69,\x26addressee=(World) 2x, https:\/\/golang.org\/favicon.ico 500.5w`,
+				`Hello, World \u0026 O\u0027Reilly\u0021`,
+				`greeting=H%69,\u0026addressee=(World)`,
+				`greeting=H%69,\u0026addressee=(World) 2x, https:\/\/golang.org\/favicon.ico 500.5w`,
 				`,foo\/,`,
 			},
 		},
 		{
 			`<script type="text/javascript">alert("{{.}}")</script>`,
 			[]string{
-				`\x3cb\x3e \x22foo%\x22 O\x27Reilly \x26bar;`,
-				`a[href =~ \x22\/\/example.com\x22]#foo`,
-				`Hello, \x3cb\x3eWorld\x3c\/b\x3e \x26amp;tc!`,
-				` dir=\x22ltr\x22`,
-				`c \x26\x26 alert(\x22Hello, World!\x22);`,
+				`\u003cb\u003e \u0022foo%\u0022 O\u0027Reilly \u0026bar;`,
+				`a[href =~ \u0022\/\/example.com\u0022]#foo`,
+				`Hello, \u003cb\u003eWorld\u003c\/b\u003e \u0026amp;tc!`,
+				` dir=\u0022ltr\u0022`,
+				`c \u0026\u0026 alert(\u0022Hello, World!\u0022);`,
 				// Escape sequence not over-escaped.
-				`Hello, World \x26 O\x27Reilly\x21`,
-				`greeting=H%69,\x26addressee=(World)`,
-				`greeting=H%69,\x26addressee=(World) 2x, https:\/\/golang.org\/favicon.ico 500.5w`,
+				`Hello, World \u0026 O\u0027Reilly\u0021`,
+				`greeting=H%69,\u0026addressee=(World)`,
+				`greeting=H%69,\u0026addressee=(World) 2x, https:\/\/golang.org\/favicon.ico 500.5w`,
 				`,foo\/,`,
 			},
 		},
@@ -211,7 +211,7 @@ func TestTypedContent(t *testing.T) {
 				// Not escaped.
 				`c && alert("Hello, World!");`,
 				// Escape sequence not over-escaped.
-				`"Hello, World & O'Reilly\x21"`,
+				`"Hello, World & O'Reilly\u0021"`,
 				`"greeting=H%69,\u0026addressee=(World)"`,
 				`"greeting=H%69,\u0026addressee=(World) 2x, https://golang.org/favicon.ico 500.5w"`,
 				`",foo/,"`,
@@ -227,7 +227,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello, <b>World</b> &amp;tc!`,
 				` dir=&#34;ltr&#34;`,
 				`c &amp;&amp; alert(&#34;Hello, World!&#34;);`,
-				`Hello, World &amp; O&#39;Reilly\x21`,
+				`Hello, World &amp; O&#39;Reilly\u0021`,
 				`greeting=H%69,&amp;addressee=(World)`,
 				`greeting=H%69,&amp;addressee=(World) 2x, https://golang.org/favicon.ico 500.5w`,
 				`,foo/,`,
@@ -236,15 +236,15 @@ func TestTypedContent(t *testing.T) {
 		{
 			`<button onclick='alert("{{.}}")'>`,
 			[]string{
-				`\x3cb\x3e \x22foo%\x22 O\x27Reilly \x26bar;`,
-				`a[href =~ \x22\/\/example.com\x22]#foo`,
-				`Hello, \x3cb\x3eWorld\x3c\/b\x3e \x26amp;tc!`,
-				` dir=\x22ltr\x22`,
-				`c \x26\x26 alert(\x22Hello, World!\x22);`,
+				`\u003cb\u003e \u0022foo%\u0022 O\u0027Reilly \u0026bar;`,
+				`a[href =~ \u0022\/\/example.com\u0022]#foo`,
+				`Hello, \u003cb\u003eWorld\u003c\/b\u003e \u0026amp;tc!`,
+				` dir=\u0022ltr\u0022`,
+				`c \u0026\u0026 alert(\u0022Hello, World!\u0022);`,
 				// Escape sequence not over-escaped.
-				`Hello, World \x26 O\x27Reilly\x21`,
-				`greeting=H%69,\x26addressee=(World)`,
-				`greeting=H%69,\x26addressee=(World) 2x, https:\/\/golang.org\/favicon.ico 500.5w`,
+				`Hello, World \u0026 O\u0027Reilly\u0021`,
+				`greeting=H%69,\u0026addressee=(World)`,
+				`greeting=H%69,\u0026addressee=(World) 2x, https:\/\/golang.org\/favicon.ico 500.5w`,
 				`,foo\/,`,
 			},
 		},
@@ -256,7 +256,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello%2c%20%3cb%3eWorld%3c%2fb%3e%20%26amp%3btc%21`,
 				`%20dir%3d%22ltr%22`,
 				`c%20%26%26%20alert%28%22Hello%2c%20World%21%22%29%3b`,
-				`Hello%2c%20World%20%26%20O%27Reilly%5cx21`,
+				`Hello%2c%20World%20%26%20O%27Reilly%5cu0021`,
 				// Quotes and parens are escaped but %69 is not over-escaped. HTML escaping is done.
 				`greeting=H%69,&amp;addressee=%28World%29`,
 				`greeting%3dH%2569%2c%26addressee%3d%28World%29%202x%2c%20https%3a%2f%2fgolang.org%2ffavicon.ico%20500.5w`,
@@ -271,7 +271,7 @@ func TestTypedContent(t *testing.T) {
 				`Hello%2c%20%3cb%3eWorld%3c%2fb%3e%20%26amp%3btc%21`,
 				`%20dir%3d%22ltr%22`,
 				`c%20%26%26%20alert%28%22Hello%2c%20World%21%22%29%3b`,
-				`Hello%2c%20World%20%26%20O%27Reilly%5cx21`,
+				`Hello%2c%20World%20%26%20O%27Reilly%5cu0021`,
 				// Quotes and parens are escaped but %69 is not over-escaped. HTML escaping is not done.
 				`greeting=H%69,&addressee=%28World%29`,
 				`greeting%3dH%2569%2c%26addressee%3d%28World%29%202x%2c%20https%3a%2f%2fgolang.org%2ffavicon.ico%20500.5w`,
diff --git a/tpl/internal/go_templates/htmltemplate/doc.go b/tpl/internal/go_templates/htmltemplate/doc.go
index 0a3004a9b..b6a1504f8 100644
--- a/tpl/internal/go_templates/htmltemplate/doc.go
+++ b/tpl/internal/go_templates/htmltemplate/doc.go
@@ -73,6 +73,51 @@ functions.
 For these internal escaping functions, if an action pipeline evaluates to
 a nil interface value, it is treated as though it were an empty string.
 
+Namespaced and data- attributes
+
+Attributes with a namespace are treated as if they had no namespace.
+Given the excerpt
+
+  <a my:href="{{.}}"></a>
+
+At parse time the attribute will be treated as if it were just "href".
+So at parse time the template becomes:
+
+  <a my:href="{{. | urlescaper | attrescaper}}"></a>
+
+Similarly to attributes with namespaces, attributes with a "data-" prefix are
+treated as if they had no "data-" prefix. So given
+
+  <a data-href="{{.}}"></a>
+
+At parse time this becomes
+
+  <a data-href="{{. | urlescaper | attrescaper}}"></a>
+
+If an attribute has both a namespace and a "data-" prefix, only the namespace
+will be removed when determining the context. For example
+
+  <a my:data-href="{{.}}"></a>
+
+This is handled as if "my:data-href" was just "data-href" and not "href" as
+it would be if the "data-" prefix were to be ignored too. Thus at parse
+time this becomes just
+
+  <a my:data-href="{{. | attrescaper}}"></a>
+
+As a special case, attributes with the namespace "xmlns" are always treated
+as containing URLs. Given the excerpts
+
+  <a xmlns:title="{{.}}"></a>
+  <a xmlns:href="{{.}}"></a>
+  <a xmlns:onclick="{{.}}"></a>
+
+At parse time they become:
+
+  <a xmlns:title="{{. | urlescaper | attrescaper}}"></a>
+  <a xmlns:href="{{. | urlescaper | attrescaper}}"></a>
+  <a xmlns:onclick="{{. | urlescaper | attrescaper}}"></a>
+
 Errors
 
 See the documentation of ErrorCode for details.
diff --git a/tpl/internal/go_templates/htmltemplate/escape_test.go b/tpl/internal/go_templates/htmltemplate/escape_test.go
index 9e9db7800..075db4e13 100644
--- a/tpl/internal/go_templates/htmltemplate/escape_test.go
+++ b/tpl/internal/go_templates/htmltemplate/escape_test.go
@@ -242,7 +242,7 @@ func TestEscape(t *testing.T) {
 		{
 			"jsStr",
 			"<button onclick='alert(&quot;{{.H}}&quot;)'>",
-			`<button onclick='alert(&quot;\x3cHello\x3e&quot;)'>`,
+			`<button onclick='alert(&quot;\u003cHello\u003e&quot;)'>`,
 		},
 		{
 			"badMarshaler",
@@ -263,7 +263,7 @@ func TestEscape(t *testing.T) {
 		{
 			"jsRe",
 			`<button onclick='alert(/{{"foo+bar"}}/.test(""))'>`,
-			`<button onclick='alert(/foo\x2bbar/.test(""))'>`,
+			`<button onclick='alert(/foo\u002bbar/.test(""))'>`,
 		},
 		{
 			"jsReBlank",
@@ -829,7 +829,7 @@ func TestEscapeSet(t *testing.T) {
 				"main":   `<button onclick="title='{{template "helper"}}'; ...">{{template "helper"}}</button>`,
 				"helper": `{{11}} of {{"<100>"}}`,
 			},
-			`<button onclick="title='11 of \x3c100\x3e'; ...">11 of &lt;100&gt;</button>`,
+			`<button onclick="title='11 of \u003c100\u003e'; ...">11 of &lt;100&gt;</button>`,
 		},
 		// A non-recursive template that ends in a different context.
 		// helper starts in jsCtxRegexp and ends in jsCtxDivOp.
diff --git a/tpl/internal/go_templates/htmltemplate/example_test.go b/tpl/internal/go_templates/htmltemplate/example_test.go
index a3e7910ee..a93b8d2fb 100644
--- a/tpl/internal/go_templates/htmltemplate/example_test.go
+++ b/tpl/internal/go_templates/htmltemplate/example_test.go
@@ -119,9 +119,9 @@ func Example_escape() {
 	// &#34;Fran &amp; Freddie&#39;s Diner&#34; &lt;tasty@example.com&gt;
 	// &#34;Fran &amp; Freddie&#39;s Diner&#34; &lt;tasty@example.com&gt;
 	// &#34;Fran &amp; Freddie&#39;s Diner&#34;32&lt;tasty@example.com&gt;
-	// \"Fran & Freddie\'s Diner\" \x3Ctasty@example.com\x3E
-	// \"Fran & Freddie\'s Diner\" \x3Ctasty@example.com\x3E
-	// \"Fran & Freddie\'s Diner\"32\x3Ctasty@example.com\x3E
+	// \"Fran \u0026 Freddie\'s Diner\" \u003Ctasty@example.com\u003E
+	// \"Fran \u0026 Freddie\'s Diner\" \u003Ctasty@example.com\u003E
+	// \"Fran \u0026 Freddie\'s Diner\"32\u003Ctasty@example.com\u003E
 	// %22Fran+%26+Freddie%27s+Diner%2232%3Ctasty%40example.com%3E
 
 }
diff --git a/tpl/internal/go_templates/htmltemplate/js.go b/tpl/internal/go_templates/htmltemplate/js.go
index 57622d152..cfd413461 100644
--- a/tpl/internal/go_templates/htmltemplate/js.go
+++ b/tpl/internal/go_templates/htmltemplate/js.go
@@ -164,7 +164,6 @@ func jsValEscaper(args ...interface{}) string {
 	}
 	// TODO: detect cycles before calling Marshal which loops infinitely on
 	// cyclic data. This may be an unacceptable DoS risk.
-
 	b, err := json.Marshal(a)
 	if err != nil {
 		// Put a space before comment so that if it is flush against
@@ -179,8 +178,8 @@ func jsValEscaper(args ...interface{}) string {
 	// TODO: maybe post-process output to prevent it from containing
 	// "<!--", "-->", "<![CDATA[", "]]>", or "</script"
 	// in case custom marshalers produce output containing those.
-
-	// TODO: Maybe abbreviate \u00ab to \xab to produce more compact output.
+	// Note: Do not use \x escaping to save bytes because it is not JSON compatible and this escaper
+	// supports ld+json content-type.
 	if len(b) == 0 {
 		// In, `x=y/{{.}}*z` a json.Marshaler that produces "" should
 		// not cause the output `x=y/*z`.
@@ -261,6 +260,8 @@ func replace(s string, replacementTable []string) string {
 		r, w = utf8.DecodeRuneInString(s[i:])
 		var repl string
 		switch {
+		case int(r) < len(lowUnicodeReplacementTable):
+			repl = lowUnicodeReplacementTable[r]
 		case int(r) < len(replacementTable) && replacementTable[r] != "":
 			repl = replacementTable[r]
 		case r == '\u2028':
@@ -284,67 +285,80 @@ func replace(s string, replacementTable []string) string {
 	return b.String()
 }
 
+var lowUnicodeReplacementTable = []string{
+	0: `\u0000`, 1: `\u0001`, 2: `\u0002`, 3: `\u0003`, 4: `\u0004`, 5: `\u0005`, 6: `\u0006`,
+	'\a': `\u0007`,
+	'\b': `\u0008`,
+	'\t': `\t`,
+	'\n': `\n`,
+	'\v': `\u000b`, // "\v" == "v" on IE 6.
+	'\f': `\f`,
+	'\r': `\r`,
+	0xe:  `\u000e`, 0xf: `\u000f`, 0x10: `\u0010`, 0x11: `\u0011`, 0x12: `\u0012`, 0x13: `\u0013`,
+	0x14: `\u0014`, 0x15: `\u0015`, 0x16: `\u0016`, 0x17: `\u0017`, 0x18: `\u0018`, 0x19: `\u0019`,
+	0x1a: `\u001a`, 0x1b: `\u001b`, 0x1c: `\u001c`, 0x1d: `\u001d`, 0x1e: `\u001e`, 0x1f: `\u001f`,
+}
+
 var jsStrReplacementTable = []string{
-	0:    `\0`,
+	0:    `\u0000`,
 	'\t': `\t`,
 	'\n': `\n`,
-	'\v': `\x0b`, // "\v" == "v" on IE 6.
+	'\v': `\u000b`, // "\v" == "v" on IE 6.
 	'\f': `\f`,
 	'\r': `\r`,
 	// Encode HTML specials as hex so the output can be embedded
 	// in HTML attributes without further encoding.
-	'"':  `\x22`,
-	'&':  `\x26`,
-	'\'': `\x27`,
-	'+':  `\x2b`,
+	'"':  `\u0022`,
+	'&':  `\u0026`,
+	'\'': `\u0027`,
+	'+':  `\u002b`,
 	'/':  `\/`,
-	'<':  `\x3c`,
-	'>':  `\x3e`,
+	'<':  `\u003c`,
+	'>':  `\u003e`,
 	'\\': `\\`,
 }
 
 // jsStrNormReplacementTable is like jsStrReplacementTable but does not
 // overencode existing escapes since this table has no entry for `\`.
 var jsStrNormReplacementTable = []string{
-	0:    `\0`,
+	0:    `\u0000`,
 	'\t': `\t`,
 	'\n': `\n`,
-	'\v': `\x0b`, // "\v" == "v" on IE 6.
+	'\v': `\u000b`, // "\v" == "v" on IE 6.
 	'\f': `\f`,
 	'\r': `\r`,
 	// Encode HTML specials as hex so the output can be embedded
 	// in HTML attributes without further encoding.
-	'"':  `\x22`,
-	'&':  `\x26`,
-	'\'': `\x27`,
-	'+':  `\x2b`,
+	'"':  `\u0022`,
+	'&':  `\u0026`,
+	'\'': `\u0027`,
+	'+':  `\u002b`,
 	'/':  `\/`,
-	'<':  `\x3c`,
-	'>':  `\x3e`,
+	'<':  `\u003c`,
+	'>':  `\u003e`,
 }
-
 var jsRegexpReplacementTable = []string{
-	0:    `\0`,
+	0:    `\u0000`,
 	'\t': `\t`,
 	'\n': `\n`,
-	'\v': `\x0b`, // "\v" == "v" on IE 6.
+	'\v': `\u000b`, // "\v" == "v" on IE 6.
 	'\f': `\f`,
 	'\r': `\r`,
 	// Encode HTML specials as hex so the output can be embedded
 	// in HTML attributes without further encoding.
-	'"':  `\x22`,
+	'"':  `\u0022`,
 	'$':  `\$`,
-	'&':  `\x26`,
-	'\'': `\x27`,
+	'&':  `\u0026`,
+	'\'': `\u0027`,
 	'(':  `\(`,
 	')':  `\)`,
 	'*':  `\*`,
-	'+':  `\x2b`,
+	'+':  `\u002b`,
 	'-':  `\-`,
 	'.':  `\.`,
 	'/':  `\/`,
-	'<':  `\x3c`,
-	'>':  `\x3e`,
+	'<':  `\u003c`,
+	'>':  `\u003e`,
 	'?':  `\?`,
 	'[':  `\[`,
 	'\\': `\\`,
@@ -384,11 +398,11 @@ func isJSType(mimeType string) bool {
 	//   https://tools.ietf.org/html/rfc7231#section-3.1.1
 	//   https://tools.ietf.org/html/rfc4329#section-3
 	//   https://www.ietf.org/rfc/rfc4627.txt
-	mimeType = strings.ToLower(mimeType)
 	// discard parameters
 	if i := strings.Index(mimeType, ";"); i >= 0 {
 		mimeType = mimeType[:i]
 	}
+	mimeType = strings.ToLower(mimeType)
 	mimeType = strings.TrimSpace(mimeType)
 	switch mimeType {
 	case
diff --git a/tpl/internal/go_templates/htmltemplate/js_test.go b/tpl/internal/go_templates/htmltemplate/js_test.go
index 0a6f332a6..e15087f0f 100644
--- a/tpl/internal/go_templates/htmltemplate/js_test.go
+++ b/tpl/internal/go_templates/htmltemplate/js_test.go
@@ -139,7 +139,7 @@ func TestJSValEscaper(t *testing.T) {
 		{"foo", `"foo"`},
 		// Newlines.
 		{"\r\n\u2028\u2029", `"\r\n\u2028\u2029"`},
-		// "\v" == "v" on IE 6 so use "\x0b" instead.
+		// "\v" == "v" on IE 6 so use "\u000b" instead.
 		{"\t\x0b", `"\t\u000b"`},
 		{struct{ X, Y int }{1, 2}, `{"X":1,"Y":2}`},
 		{[]interface{}{}, "[]"},
@@ -175,7 +175,7 @@ func TestJSStrEscaper(t *testing.T) {
 	}{
 		{"", ``},
 		{"foo", `foo`},
-		{"\u0000", `\0`},
+		{"\u0000", `\u0000`},
 		{"\t", `\t`},
 		{"\n", `\n`},
 		{"\r", `\r`},
@@ -185,14 +185,14 @@ func TestJSStrEscaper(t *testing.T) {
 		{"\\n", `\\n`},
 		{"foo\r\nbar", `foo\r\nbar`},
 		// Preserve attribute boundaries.
-		{`"`, `\x22`},
-		{`'`, `\x27`},
+		{`"`, `\u0022`},
+		{`'`, `\u0027`},
 		// Allow embedding in HTML without further escaping.
-		{`&amp;`, `\x26amp;`},
+		{`&amp;`, `\u0026amp;`},
 		// Prevent breaking out of text node and element boundaries.
-		{"</script>", `\x3c\/script\x3e`},
-		{"<![CDATA[", `\x3c![CDATA[`},
-		{"]]>", `]]\x3e`},
+		{"</script>", `\u003c\/script\u003e`},
+		{"<![CDATA[", `\u003c![CDATA[`},
+		{"]]>", `]]\u003e`},
 		// https://dev.w3.org/html5/markup/aria/syntax.html#escaping-text-span
 		//   "The text in style, script, title, and textarea elements
 		//   must not have an escaping text span start that is not
@@ -203,11 +203,11 @@ func TestJSStrEscaper(t *testing.T) {
 		// allow regular text content to be interpreted as script
 		// allowing script execution via a combination of a JS string
 		// injection followed by an HTML text injection.
-		{"<!--", `\x3c!--`},
-		{"-->", `--\x3e`},
+		{"<!--", `\u003c!--`},
+		{"-->", `--\u003e`},
 		// From https://code.google.com/p/doctype/wiki/ArticleUtf7
 		{"+ADw-script+AD4-alert(1)+ADw-/script+AD4-",
-			`\x2bADw-script\x2bAD4-alert(1)\x2bADw-\/script\x2bAD4-`,
+			`\u002bADw-script\u002bAD4-alert(1)\u002bADw-\/script\u002bAD4-`,
 		},
 		// Invalid UTF-8 sequence
 		{"foo\xA0bar", "foo\xA0bar"},
@@ -230,7 +230,7 @@ func TestJSRegexpEscaper(t *testing.T) {
 	}{
 		{"", `(?:)`},
 		{"foo", `foo`},
-		{"\u0000", `\0`},
+		{"\u0000", `\u0000`},
 		{"\t", `\t`},
 		{"\n", `\n`},
 		{"\r", `\r`},
@@ -240,19 +240,19 @@ func TestJSRegexpEscaper(t *testing.T) {
 		{"\\n", `\\n`},
 		{"foo\r\nbar", `foo\r\nbar`},
 		// Preserve attribute boundaries.
-		{`"`, `\x22`},
-		{`'`, `\x27`},
+		{`"`, `\u0022`},
+		{`'`, `\u0027`},
 		// Allow embedding in HTML without further escaping.
-		{`&amp;`, `\x26amp;`},
+		{`&amp;`, `\u0026amp;`},
 		// Prevent breaking out of text node and element boundaries.
-		{"</script>", `\x3c\/script\x3e`},
-		{"<![CDATA[", `\x3c!\[CDATA\[`},
-		{"]]>", `\]\]\x3e`},
+		{"</script>", `\u003c\/script\u003e`},
+		{"<![CDATA[", `\u003c!\[CDATA\[`},
+		{"]]>", `\]\]\u003e`},
 		// Escaping text spans.
-		{"<!--", `\x3c!\-\-`},
-		{"-->", `\-\-\x3e`},
+		{"<!--", `\u003c!\-\-`},
+		{"-->", `\-\-\u003e`},
 		{"*", `\*`},
-		{"+", `\x2b`},
+		{"+", `\u002b`},
 		{"?", `\?`},
 		{"[](){}", `\[\]\(\)\{\}`},
 		{"$foo|x.y", `\$foo\|x\.y`},
@@ -286,27 +286,27 @@ func TestEscapersOnLower7AndSelectHighCodepoints(t *testing.T) {
 		{
 			"jsStrEscaper",
 			jsStrEscaper,
-			"\\0\x01\x02\x03\x04\x05\x06\x07" +
-				"\x08\\t\\n\\x0b\\f\\r\x0E\x0F" +
-				"\x10\x11\x12\x13\x14\x15\x16\x17" +
-				"\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f" +
-				` !\x22#$%\x26\x27()*\x2b,-.\/` +
-				`0123456789:;\x3c=\x3e?` +
+			`\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007` +
+				`\u0008\t\n\u000b\f\r\u000e\u000f` +
+				`\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017` +
+				`\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f` +
+				` !\u0022#$%\u0026\u0027()*\u002b,-.\/` +
+				`0123456789:;\u003c=\u003e?` +
 				`@ABCDEFGHIJKLMNO` +
 				`PQRSTUVWXYZ[\\]^_` +
 				"`abcdefghijklmno" +
-				"pqrstuvwxyz{|}~\x7f" +
+				"pqrstuvwxyz{|}~\u007f" +
 				"\u00A0\u0100\\u2028\\u2029\ufeff\U0001D11E",
 		},
 		{
 			"jsRegexpEscaper",
 			jsRegexpEscaper,
-			"\\0\x01\x02\x03\x04\x05\x06\x07" +
-				"\x08\\t\\n\\x0b\\f\\r\x0E\x0F" +
-				"\x10\x11\x12\x13\x14\x15\x16\x17" +
-				"\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f" +
-				` !\x22#\$%\x26\x27\(\)\*\x2b,\-\.\/` +
-				`0123456789:;\x3c=\x3e\?` +
+			`\u0000\u0001\u0002\u0003\u0004\u0005\u0006\u0007` +
+				`\u0008\t\n\u000b\f\r\u000e\u000f` +
+				`\u0010\u0011\u0012\u0013\u0014\u0015\u0016\u0017` +
+				`\u0018\u0019\u001a\u001b\u001c\u001d\u001e\u001f` +
+				` !\u0022#\$%\u0026\u0027\(\)\*\u002b,\-\.\/` +
+				`0123456789:;\u003c=\u003e\?` +
 				`@ABCDEFGHIJKLMNO` +
 				`PQRSTUVWXYZ\[\\\]\^_` +
 				"`abcdefghijklmno" +
diff --git a/tpl/internal/go_templates/htmltemplate/template_test.go b/tpl/internal/go_templates/htmltemplate/template_test.go
index 8adf3324b..589e6912a 100644
--- a/tpl/internal/go_templates/htmltemplate/template_test.go
+++ b/tpl/internal/go_templates/htmltemplate/template_test.go
@@ -8,6 +8,7 @@ package template_test
 
 import (
 	"bytes"
+	"encoding/json"
 	"strings"
 	"testing"
 
@@ -124,6 +125,44 @@ func TestNumbers(t *testing.T) {
 	c.mustExecute(c.root, nil, "12.34 7.5")
 }
 
+func TestStringsInScriptsWithJsonContentTypeAreCorrectlyEscaped(t *testing.T) {
+	// See #33671 and #37634 for more context on this.
+	tests := []struct{ name, in string }{
+		{"empty", ""},
+		{"invalid", string(rune(-1))},
+		{"null", "\u0000"},
+		{"unit separator", "\u001F"},
+		{"tab", "\t"},
+		{"gt and lt", "<>"},
+		{"quotes", `'"`},
+		{"ASCII letters", "ASCII letters"},
+		{"Unicode", "ʕ⊙ϖ⊙ʔ"},
+		{"Pizza", "🍕"},
+	}
+	const (
+		prefix = `<script type="application/ld+json">`
+		suffix = `</script>`
+		templ  = prefix + `"{{.}}"` + suffix
+	)
+	tpl := Must(New("JS string is JSON string").Parse(templ))
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var buf bytes.Buffer
+			if err := tpl.Execute(&buf, tt.in); err != nil {
+				t.Fatalf("Cannot render template: %v", err)
+			}
+			trimmed := bytes.TrimSuffix(bytes.TrimPrefix(buf.Bytes(), []byte(prefix)), []byte(suffix))
+			var got string
+			if err := json.Unmarshal(trimmed, &got); err != nil {
+				t.Fatalf("Cannot parse JS string %q as JSON: %v", trimmed[1:len(trimmed)-1], err)
+			}
+			if got != tt.in {
+				t.Errorf("Serialization changed the string value: got %q want %q", got, tt.in)
+			}
+		})
+	}
+}
+
 type testCase struct {
 	t    *testing.T
 	root *Template
diff --git a/tpl/internal/go_templates/testenv/testenv.go b/tpl/internal/go_templates/testenv/testenv.go
new file mode 100644
index 000000000..90044570d
--- /dev/null
+++ b/tpl/internal/go_templates/testenv/testenv.go
@@ -0,0 +1,272 @@
+// Copyright 2015 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 testenv provides information about what functionality
+// is available in different testing environments run by the Go team.
+//
+// It is an internal package because these details are specific
+// to the Go team's test setup (on build.golang.org) and not
+// fundamental to tests in general.
+package testenv
+
+import (
+	"errors"
+	"flag"
+	"github.com/gohugoio/hugo/tpl/internal/go_templates/cfg"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+)
+
+// Builder reports the name of the builder running this test
+// (for example, "linux-amd64" or "windows-386-gce").
+// If the test is not running on the build infrastructure,
+// Builder returns the empty string.
+func Builder() string {
+	return os.Getenv("GO_BUILDER_NAME")
+}
+
+// HasGoBuild reports whether the current system can build programs with ``go build''
+// and then run them with os.StartProcess or exec.Command.
+func HasGoBuild() bool {
+	if os.Getenv("GO_GCFLAGS") != "" {
+		// It's too much work to require every caller of the go command
+		// to pass along "-gcflags="+os.Getenv("GO_GCFLAGS").
+		// For now, if $GO_GCFLAGS is set, report that we simply can't
+		// run go build.
+		return false
+	}
+	switch runtime.GOOS {
+	case "android", "js":
+		return false
+	case "darwin":
+		if runtime.GOARCH == "arm64" {
+			return false
+		}
+	}
+	return true
+}
+
+// MustHaveGoBuild checks that the current system can build programs with ``go build''
+// and then run them with os.StartProcess or exec.Command.
+// If not, MustHaveGoBuild calls t.Skip with an explanation.
+func MustHaveGoBuild(t testing.TB) {
+	if os.Getenv("GO_GCFLAGS") != "" {
+		t.Skipf("skipping test: 'go build' not compatible with setting $GO_GCFLAGS")
+	}
+	if !HasGoBuild() {
+		t.Skipf("skipping test: 'go build' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+// HasGoRun reports whether the current system can run programs with ``go run.''
+func HasGoRun() bool {
+	// For now, having go run and having go build are the same.
+	return HasGoBuild()
+}
+
+// MustHaveGoRun checks that the current system can run programs with ``go run.''
+// If not, MustHaveGoRun calls t.Skip with an explanation.
+func MustHaveGoRun(t testing.TB) {
+	if !HasGoRun() {
+		t.Skipf("skipping test: 'go run' not available on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+// GoToolPath reports the path to the Go tool.
+// It is a convenience wrapper around GoTool.
+// If the tool is unavailable GoToolPath calls t.Skip.
+// If the tool should be available and isn't, GoToolPath calls t.Fatal.
+func GoToolPath(t testing.TB) string {
+	MustHaveGoBuild(t)
+	path, err := GoTool()
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Add all environment variables that affect the Go command to test metadata.
+	// Cached test results will be invalidate when these variables change.
+	// See golang.org/issue/32285.
+	for _, envVar := range strings.Fields(cfg.KnownEnv) {
+		os.Getenv(envVar)
+	}
+	return path
+}
+
+// GoTool reports the path to the Go tool.
+func GoTool() (string, error) {
+	if !HasGoBuild() {
+		return "", errors.New("platform cannot run go tool")
+	}
+	var exeSuffix string
+	if runtime.GOOS == "windows" {
+		exeSuffix = ".exe"
+	}
+	path := filepath.Join(runtime.GOROOT(), "bin", "go"+exeSuffix)
+	if _, err := os.Stat(path); err == nil {
+		return path, nil
+	}
+	goBin, err := exec.LookPath("go" + exeSuffix)
+	if err != nil {
+		return "", errors.New("cannot find go tool: " + err.Error())
+	}
+	return goBin, nil
+}
+
+// HasExec reports whether the current system can start new processes
+// using os.StartProcess or (more commonly) exec.Command.
+func HasExec() bool {
+	switch runtime.GOOS {
+	case "js":
+		return false
+	case "darwin":
+		if runtime.GOARCH == "arm64" {
+			return false
+		}
+	}
+	return true
+}
+
+// HasSrc reports whether the entire source tree is available under GOROOT.
+func HasSrc() bool {
+	switch runtime.GOOS {
+	case "darwin":
+		if runtime.GOARCH == "arm64" {
+			return false
+		}
+	}
+	return true
+}
+
+// MustHaveExec checks that the current system can start new processes
+// using os.StartProcess or (more commonly) exec.Command.
+// If not, MustHaveExec calls t.Skip with an explanation.
+func MustHaveExec(t testing.TB) {
+	if !HasExec() {
+		t.Skipf("skipping test: cannot exec subprocess on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+var execPaths sync.Map // path -> error
+
+// MustHaveExecPath checks that the current system can start the named executable
+// using os.StartProcess or (more commonly) exec.Command.
+// If not, MustHaveExecPath calls t.Skip with an explanation.
+func MustHaveExecPath(t testing.TB, path string) {
+	MustHaveExec(t)
+
+	err, found := execPaths.Load(path)
+	if !found {
+		_, err = exec.LookPath(path)
+		err, _ = execPaths.LoadOrStore(path, err)
+	}
+	if err != nil {
+		t.Skipf("skipping test: %s: %s", path, err)
+	}
+}
+
+// HasExternalNetwork reports whether the current system can use
+// external (non-localhost) networks.
+func HasExternalNetwork() bool {
+	return !testing.Short() && runtime.GOOS != "js"
+}
+
+// MustHaveExternalNetwork checks that the current system can use
+// external (non-localhost) networks.
+// If not, MustHaveExternalNetwork calls t.Skip with an explanation.
+func MustHaveExternalNetwork(t testing.TB) {
+	if runtime.GOOS == "js" {
+		t.Skipf("skipping test: no external network on %s", runtime.GOOS)
+	}
+	if testing.Short() {
+		t.Skipf("skipping test: no external network in -short mode")
+	}
+}
+
+var haveCGO bool
+
+// HasCGO reports whether the current system can use cgo.
+func HasCGO() bool {
+	return haveCGO
+}
+
+// MustHaveCGO calls t.Skip if cgo is not available.
+func MustHaveCGO(t testing.TB) {
+	if !haveCGO {
+		t.Skipf("skipping test: no cgo")
+	}
+}
+
+// HasSymlink reports whether the current system can use os.Symlink.
+func HasSymlink() bool {
+	ok, _ := hasSymlink()
+	return ok
+}
+
+// MustHaveSymlink reports whether the current system can use os.Symlink.
+// If not, MustHaveSymlink calls t.Skip with an explanation.
+func MustHaveSymlink(t testing.TB) {
+	ok, reason := hasSymlink()
+	if !ok {
+		t.Skipf("skipping test: cannot make symlinks on %s/%s%s", runtime.GOOS, runtime.GOARCH, reason)
+	}
+}
+
+// HasLink reports whether the current system can use os.Link.
+func HasLink() bool {
+	// From Android release M (Marshmallow), hard linking files is blocked
+	// and an attempt to call link() on a file will return EACCES.
+	// - https://code.google.com/p/android-developer-preview/issues/detail?id=3150
+	return runtime.GOOS != "plan9" && runtime.GOOS != "android"
+}
+
+// MustHaveLink reports whether the current system can use os.Link.
+// If not, MustHaveLink calls t.Skip with an explanation.
+func MustHaveLink(t testing.TB) {
+	if !HasLink() {
+		t.Skipf("skipping test: hardlinks are not supported on %s/%s", runtime.GOOS, runtime.GOARCH)
+	}
+}
+
+var flaky = flag.Bool("flaky", false, "run known-flaky tests too")
+
+func SkipFlaky(t testing.TB, issue int) {
+	t.Helper()
+	if !*flaky {
+		t.Skipf("skipping known flaky test without the -flaky flag; see golang.org/issue/%d", issue)
+	}
+}
+
+func SkipFlakyNet(t testing.TB) {
+	t.Helper()
+	if v, _ := strconv.ParseBool(os.Getenv("GO_BUILDER_FLAKY_NET")); v {
+		t.Skip("skipping test on builder known to have frequent network failures")
+	}
+}
+
+// CleanCmdEnv will fill cmd.Env with the environment, excluding certain
+// variables that could modify the behavior of the Go tools such as
+// GODEBUG and GOTRACEBACK.
+func CleanCmdEnv(cmd *exec.Cmd) *exec.Cmd {
+	if cmd.Env != nil {
+		panic("environment already set")
+	}
+	for _, env := range os.Environ() {
+		// Exclude GODEBUG from the environment to prevent its output
+		// from breaking tests that are trying to parse other command output.
+		if strings.HasPrefix(env, "GODEBUG=") {
+			continue
+		}
+		// Exclude GOTRACEBACK for the same reason.
+		if strings.HasPrefix(env, "GOTRACEBACK=") {
+			continue
+		}
+		cmd.Env = append(cmd.Env, env)
+	}
+	return cmd
+}
diff --git a/tpl/internal/go_templates/testenv/testenv_cgo.go b/tpl/internal/go_templates/testenv/testenv_cgo.go
new file mode 100644
index 000000000..e3d4d16b3
--- /dev/null
+++ b/tpl/internal/go_templates/testenv/testenv_cgo.go
@@ -0,0 +1,11 @@
+// Copyright 2017 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 cgo
+
+package testenv
+
+func init() {
+	haveCGO = true
+}
diff --git a/tpl/internal/go_templates/testenv/testenv_notwin.go b/tpl/internal/go_templates/testenv/testenv_notwin.go
new file mode 100644
index 000000000..ccb5d5585
--- /dev/null
+++ b/tpl/internal/go_templates/testenv/testenv_notwin.go
@@ -0,0 +1,20 @@
+// Copyright 2016 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 !windows
+
+package testenv
+
+import (
+	"runtime"
+)
+
+func hasSymlink() (ok bool, reason string) {
+	switch runtime.GOOS {
+	case "android", "plan9":
+		return false, ""
+	}
+
+	return true, ""
+}
diff --git a/tpl/internal/go_templates/testenv/testenv_windows.go b/tpl/internal/go_templates/testenv/testenv_windows.go
new file mode 100644
index 000000000..eb8d6ac16
--- /dev/null
+++ b/tpl/internal/go_templates/testenv/testenv_windows.go
@@ -0,0 +1,48 @@
+// Copyright 2016 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 testenv
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sync"
+	"syscall"
+)
+
+var symlinkOnce sync.Once
+var winSymlinkErr error
+
+func initWinHasSymlink() {
+	tmpdir, err := ioutil.TempDir("", "symtest")
+	if err != nil {
+		panic("failed to create temp directory: " + err.Error())
+	}
+	defer os.RemoveAll(tmpdir)
+
+	err = os.Symlink("target", filepath.Join(tmpdir, "symlink"))
+	if err != nil {
+		err = err.(*os.LinkError).Err
+		switch err {
+		case syscall.EWINDOWS, syscall.ERROR_PRIVILEGE_NOT_HELD:
+			winSymlinkErr = err
+		}
+	}
+}
+
+func hasSymlink() (ok bool, reason string) {
+	symlinkOnce.Do(initWinHasSymlink)
+
+	switch winSymlinkErr {
+	case nil:
+		return true, ""
+	case syscall.EWINDOWS:
+		return false, ": symlinks are not supported on your version of Windows"
+	case syscall.ERROR_PRIVILEGE_NOT_HELD:
+		return false, ": you don't have enough privileges to create symlinks"
+	}
+
+	return false, ""
+}
diff --git a/tpl/internal/go_templates/texttemplate/doc.go b/tpl/internal/go_templates/texttemplate/doc.go
index dbffaa495..4b0efd2df 100644
--- a/tpl/internal/go_templates/texttemplate/doc.go
+++ b/tpl/internal/go_templates/texttemplate/doc.go
@@ -102,8 +102,8 @@ data, defined in detail in the corresponding sections that follow.
 		If the value of the pipeline has length zero, nothing is output;
 		otherwise, dot is set to the successive elements of the array,
 		slice, or map and T1 is executed. If the value is a map and the
-		keys are of basic type with a defined order ("comparable"), the
-		elements will be visited in sorted key order.
+		keys are of basic type with a defined order, the elements will be
+		visited in sorted key order.
 
 	{{range pipeline}} T1 {{else}} T0 {{end}}
 		The value of the pipeline must be an array, slice, map, or channel.
@@ -385,14 +385,12 @@ returning in effect
 (Unlike with || in Go, however, eq is a function call and all the
 arguments will be evaluated.)
 
-The comparison functions work on basic types only (or named basic
-types, such as "type Celsius float32"). They implement the Go rules
-for comparison of values, except that size and exact type are
-ignored, so any integer value, signed or unsigned, may be compared
-with any other integer value. (The arithmetic value is compared,
-not the bit pattern, so all negative integers are less than all
-unsigned integers.) However, as usual, one may not compare an int
-with a float32 and so on.
+The comparison functions work on any values whose type Go defines as
+comparable. For basic types such as integers, the rules are relaxed:
+size and exact type are ignored, so any integer value, signed or unsigned,
+may be compared with any other integer value. (The arithmetic value is compared,
+not the bit pattern, so all negative integers are less than all unsigned integers.)
+However, as usual, one may not compare an int with a float32 and so on.
 
 Associated templates
 
diff --git a/tpl/internal/go_templates/texttemplate/exec.go b/tpl/internal/go_templates/texttemplate/exec.go
index f400abd9c..879cd0884 100644
--- a/tpl/internal/go_templates/texttemplate/exec.go
+++ b/tpl/internal/go_templates/texttemplate/exec.go
@@ -5,7 +5,6 @@
 package template
 
 import (
-	"bytes"
 	"fmt"
 	"github.com/gohugoio/hugo/tpl/internal/go_templates/fmtsort"
 	"github.com/gohugoio/hugo/tpl/internal/go_templates/texttemplate/parse"
@@ -230,21 +229,19 @@ func (t *Template) DefinedTemplates() string {
 	if t.common == nil {
 		return ""
 	}
-	var b bytes.Buffer
+	var b strings.Builder
 	for name, tmpl := range t.tmpl {
 		if tmpl.Tree == nil || tmpl.Root == nil {
 			continue
 		}
-		if b.Len() > 0 {
+		if b.Len() == 0 {
+			b.WriteString("; defined templates are: ")
+		} else {
 			b.WriteString(", ")
 		}
 		fmt.Fprintf(&b, "%q", name)
 	}
-	var s string
-	if b.Len() > 0 {
-		s = "; defined templates are: " + b.String()
-	}
-	return s
+	return b.String()
 }
 
 // Walk functions step through the major pieces of the template structure,
@@ -464,7 +461,8 @@ func (s *state) evalCommand(dot reflect.Value, cmd *parse.CommandNode, final ref
 		// Must be a function.
 		return s.evalFunction(dot, n, cmd, cmd.Args, final)
 	case *parse.PipeNode:
-		// Parenthesized pipeline. The arguments are all inside the pipeline; final is ignored.
+		// Parenthesized pipeline. The arguments are all inside the pipeline; final must be absent.
+		s.notAFunction(cmd.Args, final)
 		return s.evalPipeline(dot, n)
 	case *parse.VariableNode:
 		return s.evalVariableNode(dot, n, cmd.Args, final)
@@ -499,20 +497,29 @@ func (s *state) idealConstant(constant *parse.NumberNode) reflect.Value {
 	switch {
 	case constant.IsComplex:
 		return reflect.ValueOf(constant.Complex128) // incontrovertible.
-	case constant.IsFloat && !isHexInt(constant.Text) && strings.ContainsAny(constant.Text, ".eEpP"):
+
+	case constant.IsFloat &&
+		!isHexInt(constant.Text) && !isRuneInt(constant.Text) &&
+		strings.ContainsAny(constant.Text, ".eEpP"):
 		return reflect.ValueOf(constant.Float64)
+
 	case constant.IsInt:
 		n := int(constant.Int64)
 		if int64(n) != constant.Int64 {
 			s.errorf("%s overflows int", constant.Text)
 		}
 		return reflect.ValueOf(n)
+
 	case constant.IsUint:
 		s.errorf("%s overflows int", constant.Text)
 	}
 	return zero
 }
 
+func isRuneInt(s string) bool {
+	return len(s) > 0 && s[0] == '\''
+}
+
 func isHexInt(s string) bool {
 	return len(s) > 2 && s[0] == '0' && (s[1] == 'x' || s[1] == 'X') && !strings.ContainsAny(s, "pP")
 }
diff --git a/tpl/internal/go_templates/texttemplate/exec_test.go b/tpl/internal/go_templates/texttemplate/exec_test.go
index 504967db6..940a1de6a 100644
--- a/tpl/internal/go_templates/texttemplate/exec_test.go
+++ b/tpl/internal/go_templates/texttemplate/exec_test.go
@@ -354,6 +354,12 @@ var execTests = []execTest{
 	{"field on interface", "{{.foo}}", "<no value>", nil, true},
 	{"field on parenthesized interface", "{{(.).foo}}", "<no value>", nil, true},
 
+	// Issue 31810: Parenthesized first element of pipeline with arguments.
+	// See also TestIssue31810.
+	{"unparenthesized non-function", "{{1 2}}", "", nil, false},
+	{"parenthesized non-function", "{{(1) 2}}", "", nil, false},
+	{"parenthesized non-function with no args", "{{(1)}}", "1", nil, true}, // This is fine.
+
 	// Method calls.
 	{".Method0", "-{{.Method0}}-", "-M0-", tVal, true},
 	{".Method1(1234)", "-{{.Method1 1234}}-", "-1234-", tVal, true},
@@ -498,6 +504,7 @@ var execTests = []execTest{
 	{"map MUI64S", "{{index .MUI64S 3}}", "ui643", tVal, true},
 	{"map MI8S", "{{index .MI8S 3}}", "i83", tVal, true},
 	{"map MUI8S", "{{index .MUI8S 2}}", "u82", tVal, true},
+	{"index of an interface field", "{{index .Empty3 0}}", "7", tVal, true},
 
 	// Slicing.
 	{"slice[:]", "{{slice .SI}}", "[3 4 5]", tVal, true},
@@ -523,12 +530,14 @@ var execTests = []execTest{
 	{"string[1:2]", "{{slice .S 1 2}}", "y", tVal, true},
 	{"out of range", "{{slice .S 1 5}}", "", tVal, false},
 	{"3-index slice of string", "{{slice .S 1 2 2}}", "", tVal, false},
+	{"slice of an interface field", "{{slice .Empty3 0 1}}", "[7]", tVal, true},
 
 	// Len.
 	{"slice", "{{len .SI}}", "3", tVal, true},
 	{"map", "{{len .MSI }}", "3", tVal, true},
 	{"len of int", "{{len 3}}", "", tVal, false},
 	{"len of nothing", "{{len .Empty0}}", "", tVal, false},
+	{"len of an interface field", "{{len .Empty3}}", "2", tVal, true},
 
 	// With.
 	{"with true", "{{with true}}{{.}}{{end}}", "true", tVal, true},
@@ -665,6 +674,12 @@ var execTests = []execTest{
 	{"bug17c", "{{len .NonEmptyInterfacePtS}}", "2", tVal, true},
 	{"bug17d", "{{index .NonEmptyInterfacePtS 0}}", "a", tVal, true},
 	{"bug17e", "{{range .NonEmptyInterfacePtS}}-{{.}}-{{end}}", "-a--b-", tVal, true},
+
+	// More variadic function corner cases. Some runes would get evaluated
+	// as constant floats instead of ints. Issue 34483.
+	{"bug18a", "{{eq . '.'}}", "true", '.', true},
+	{"bug18b", "{{eq . 'e'}}", "true", 'e', true},
+	{"bug18c", "{{eq . 'P'}}", "true", 'P', true},
 }
 
 func zeroArgs() string {
@@ -898,7 +913,9 @@ func TestJSEscaping(t *testing.T) {
 		{`Go "jump" \`, `Go \"jump\" \\`},
 		{`Yukihiro says "今日は世界"`, `Yukihiro says \"今日は世界\"`},
 		{"unprintable \uFDFF", `unprintable \uFDFF`},
-		{`<html>`, `\x3Chtml\x3E`},
+		{`<html>`, `\u003Chtml\u003E`},
+		{`no = in attributes`, `no \u003D in attributes`},
+		{`&#x27; does not become HTML entity`, `\u0026#x27; does not become HTML entity`},
 	}
 	for _, tc := range testCases {
 		s := JSEscapeString(tc.in)
@@ -1158,19 +1175,41 @@ var cmpTests = []cmpTest{
 	{"ge .Uthree .NegOne", "true", true},
 	{"eq (index `x` 0) 'x'", "true", true}, // The example that triggered this rule.
 	{"eq (index `x` 0) 'y'", "false", true},
+	{"eq .V1 .V2", "true", true},
+	{"eq .Ptr .Ptr", "true", true},
+	{"eq .Ptr .NilPtr", "false", true},
+	{"eq .NilPtr .NilPtr", "true", true},
+	{"eq .Iface1 .Iface1", "true", true},
+	{"eq .Iface1 .Iface2", "false", true},
+	{"eq .Iface2 .Iface2", "true", true},
 	// Errors
-	{"eq `xy` 1", "", false},    // Different types.
-	{"eq 2 2.0", "", false},     // Different types.
-	{"lt true true", "", false}, // Unordered types.
-	{"lt 1+0i 1+0i", "", false}, // Unordered types.
+	{"eq `xy` 1", "", false},       // Different types.
+	{"eq 2 2.0", "", false},        // Different types.
+	{"lt true true", "", false},    // Unordered types.
+	{"lt 1+0i 1+0i", "", false},    // Unordered types.
+	{"eq .Ptr 1", "", false},       // Incompatible types.
+	{"eq .Ptr .NegOne", "", false}, // Incompatible types.
+	{"eq .Map .Map", "", false},    // Uncomparable types.
+	{"eq .Map .V1", "", false},     // Uncomparable types.
 }
 
 func TestComparison(t *testing.T) {
 	b := new(bytes.Buffer)
 	var cmpStruct = struct {
-		Uthree, Ufour uint
-		NegOne, Three int
-	}{3, 4, -1, 3}
+		Uthree, Ufour  uint
+		NegOne, Three  int
+		Ptr, NilPtr    *int
+		Map            map[int]int
+		V1, V2         V
+		Iface1, Iface2 fmt.Stringer
+	}{
+		Uthree: 3,
+		Ufour:  4,
+		NegOne: -1,
+		Three:  3,
+		Ptr:    new(int),
+		Iface1: b,
+	}
 	for _, test := range cmpTests {
 		text := fmt.Sprintf("{{if %s}}true{{else}}false{{end}}", test.expr)
 		tmpl, err := New("empty").Parse(text)
@@ -1622,3 +1661,41 @@ func TestExecutePanicDuringCall(t *testing.T) {
 		}
 	}
 }
+
+// Issue 31810. Check that a parenthesized first argument behaves properly.
+func TestIssue31810(t *testing.T) {
+	// A simple value with no arguments is fine.
+	var b bytes.Buffer
+	const text = "{{ (.)  }}"
+	tmpl, err := New("").Parse(text)
+	if err != nil {
+		t.Error(err)
+	}
+	err = tmpl.Execute(&b, "result")
+	if err != nil {
+		t.Error(err)
+	}
+	if b.String() != "result" {
+		t.Errorf("%s got %q, expected %q", text, b.String(), "result")
+	}
+
+	// Even a plain function fails - need to use call.
+	f := func() string { return "result" }
+	b.Reset()
+	err = tmpl.Execute(&b, f)
+	if err == nil {
+		t.Error("expected error with no call, got none")
+	}
+
+	// Works if the function is explicitly called.
+	const textCall = "{{ (call .)  }}"
+	tmpl, err = New("").Parse(textCall)
+	b.Reset()
+	err = tmpl.Execute(&b, f)
+	if err != nil {
+		t.Error(err)
+	}
+	if b.String() != "result" {
+		t.Errorf("%s got %q, expected %q", textCall, b.String(), "result")
+	}
+}
diff --git a/tpl/internal/go_templates/texttemplate/funcs.go b/tpl/internal/go_templates/texttemplate/funcs.go
index 248dbcf22..1b6940a84 100644
--- a/tpl/internal/go_templates/texttemplate/funcs.go
+++ b/tpl/internal/go_templates/texttemplate/funcs.go
@@ -12,6 +12,7 @@ import (
 	"net/url"
 	"reflect"
 	"strings"
+	"sync"
 	"unicode"
 	"unicode/utf8"
 )
@@ -29,31 +30,49 @@ import (
 // type can return interface{} or reflect.Value.
 type FuncMap map[string]interface{}
 
-var builtins = FuncMap{
-	"and":      and,
-	"call":     call,
-	"html":     HTMLEscaper,
-	"index":    index,
-	"slice":    slice,
-	"js":       JSEscaper,
-	"len":      length,
-	"not":      not,
-	"or":       or,
-	"print":    fmt.Sprint,
-	"printf":   fmt.Sprintf,
-	"println":  fmt.Sprintln,
-	"urlquery": URLQueryEscaper,
-
-	// Comparisons
-	"eq": eq, // ==
-	"ge": ge, // >=
-	"gt": gt, // >
-	"le": le, // <=
-	"lt": lt, // <
-	"ne": ne, // !=
-}
-
-var builtinFuncs = createValueFuncs(builtins)
+// builtins returns the FuncMap.
+// It is not a global variable so the linker can dead code eliminate
+// more when this isn't called. See golang.org/issue/36021.
+// TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
+func builtins() FuncMap {
+	return FuncMap{
+		"and":      and,
+		"call":     call,
+		"html":     HTMLEscaper,
+		"index":    index,
+		"slice":    slice,
+		"js":       JSEscaper,
+		"len":      length,
+		"not":      not,
+		"or":       or,
+		"print":    fmt.Sprint,
+		"printf":   fmt.Sprintf,
+		"println":  fmt.Sprintln,
+		"urlquery": URLQueryEscaper,
+
+		// Comparisons
+		"eq": eq, // ==
+		"ge": ge, // >=
+		"gt": gt, // >
+		"le": le, // <=
+		"lt": lt, // <
+		"ne": ne, // !=
+	}
+}
+
+var builtinFuncsOnce struct {
+	sync.Once
+	v map[string]reflect.Value
+}
+
+// builtinFuncsOnce lazily computes & caches the builtinFuncs map.
+// TODO: revert this back to a global map once golang.org/issue/2559 is fixed.
+func builtinFuncs() map[string]reflect.Value {
+	builtinFuncsOnce.Do(func() {
+		builtinFuncsOnce.v = createValueFuncs(builtins())
+	})
+	return builtinFuncsOnce.v
+}
 
 // createValueFuncs turns a FuncMap into a map[string]reflect.Value
 func createValueFuncs(funcMap FuncMap) map[string]reflect.Value {
@@ -125,7 +144,7 @@ func findFunction(name string, tmpl *Template) (reflect.Value, bool) {
 			return fn, true
 		}
 	}
-	if fn := builtinFuncs[name]; fn.IsValid() {
+	if fn := builtinFuncs()[name]; fn.IsValid() {
 		return fn, true
 	}
 	return reflect.Value{}, false
@@ -185,41 +204,41 @@ func indexArg(index reflect.Value, cap int) (int, error) {
 // arguments. Thus "index x 1 2 3" is, in Go syntax, x[1][2][3]. Each
 // indexed item must be a map, slice, or array.
 func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
-	v := indirectInterface(item)
-	if !v.IsValid() {
+	item = indirectInterface(item)
+	if !item.IsValid() {
 		return reflect.Value{}, fmt.Errorf("index of untyped nil")
 	}
-	for _, i := range indexes {
-		index := indirectInterface(i)
+	for _, index := range indexes {
+		index = indirectInterface(index)
 		var isNil bool
-		if v, isNil = indirect(v); isNil {
+		if item, isNil = indirect(item); isNil {
 			return reflect.Value{}, fmt.Errorf("index of nil pointer")
 		}
-		switch v.Kind() {
+		switch item.Kind() {
 		case reflect.Array, reflect.Slice, reflect.String:
-			x, err := indexArg(index, v.Len())
+			x, err := indexArg(index, item.Len())
 			if err != nil {
 				return reflect.Value{}, err
 			}
-			v = v.Index(x)
+			item = item.Index(x)
 		case reflect.Map:
-			index, err := prepareArg(index, v.Type().Key())
+			index, err := prepareArg(index, item.Type().Key())
 			if err != nil {
 				return reflect.Value{}, err
 			}
-			if x := v.MapIndex(index); x.IsValid() {
-				v = x
+			if x := item.MapIndex(index); x.IsValid() {
+				item = x
 			} else {
-				v = reflect.Zero(v.Type().Elem())
+				item = reflect.Zero(item.Type().Elem())
 			}
 		case reflect.Invalid:
-			// the loop holds invariant: v.IsValid()
+			// the loop holds invariant: item.IsValid()
 			panic("unreachable")
 		default:
-			return reflect.Value{}, fmt.Errorf("can't index item of type %s", v.Type())
+			return reflect.Value{}, fmt.Errorf("can't index item of type %s", item.Type())
 		}
 	}
-	return v, nil
+	return item, nil
 }
 
 // Slicing.
@@ -229,29 +248,27 @@ func index(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error)
 // is x[:], "slice x 1" is x[1:], and "slice x 1 2 3" is x[1:2:3]. The first
 // argument must be a string, slice, or array.
 func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error) {
-	var (
-		cap int
-		v   = indirectInterface(item)
-	)
-	if !v.IsValid() {
+	item = indirectInterface(item)
+	if !item.IsValid() {
 		return reflect.Value{}, fmt.Errorf("slice of untyped nil")
 	}
 	if len(indexes) > 3 {
 		return reflect.Value{}, fmt.Errorf("too many slice indexes: %d", len(indexes))
 	}
-	switch v.Kind() {
+	var cap int
+	switch item.Kind() {
 	case reflect.String:
 		if len(indexes) == 3 {
 			return reflect.Value{}, fmt.Errorf("cannot 3-index slice a string")
 		}
-		cap = v.Len()
+		cap = item.Len()
 	case reflect.Array, reflect.Slice:
-		cap = v.Cap()
+		cap = item.Cap()
 	default:
-		return reflect.Value{}, fmt.Errorf("can't slice item of type %s", v.Type())
+		return reflect.Value{}, fmt.Errorf("can't slice item of type %s", item.Type())
 	}
 	// set default values for cases item[:], item[i:].
-	idx := [3]int{0, v.Len()}
+	idx := [3]int{0, item.Len()}
 	for i, index := range indexes {
 		x, err := indexArg(index, cap)
 		if err != nil {
@@ -276,20 +293,16 @@ func slice(item reflect.Value, indexes ...reflect.Value) (reflect.Value, error)
 // Length
 
 // length returns the length of the item, with an error if it has no defined length.
-func length(item interface{}) (int, error) {
-	v := reflect.ValueOf(item)
-	if !v.IsValid() {
-		return 0, fmt.Errorf("len of untyped nil")
-	}
-	v, isNil := indirect(v)
+func length(item reflect.Value) (int, error) {
+	item, isNil := indirect(item)
 	if isNil {
 		return 0, fmt.Errorf("len of nil pointer")
 	}
-	switch v.Kind() {
+	switch item.Kind() {
 	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
-		return v.Len(), nil
+		return item.Len(), nil
 	}
-	return 0, fmt.Errorf("len of type %s", v.Type())
+	return 0, fmt.Errorf("len of type %s", item.Type())
 }
 
 // Function invocation
@@ -297,11 +310,11 @@ func length(item interface{}) (int, error) {
 // call returns the result of evaluating the first argument as a function.
 // The function must return 1 result, or 2 results, the second of which is an error.
 func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
-	v := indirectInterface(fn)
-	if !v.IsValid() {
+	fn = indirectInterface(fn)
+	if !fn.IsValid() {
 		return reflect.Value{}, fmt.Errorf("call of nil")
 	}
-	typ := v.Type()
+	typ := fn.Type()
 	if typ.Kind() != reflect.Func {
 		return reflect.Value{}, fmt.Errorf("non-function of type %s", typ)
 	}
@@ -322,7 +335,7 @@ func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
 	}
 	argv := make([]reflect.Value, len(args))
 	for i, arg := range args {
-		value := indirectInterface(arg)
+		arg = indirectInterface(arg)
 		// Compute the expected type. Clumsy because of variadics.
 		argType := dddType
 		if !typ.IsVariadic() || i < numIn-1 {
@@ -330,11 +343,11 @@ func call(fn reflect.Value, args ...reflect.Value) (reflect.Value, error) {
 		}
 
 		var err error
-		if argv[i], err = prepareArg(value, argType); err != nil {
+		if argv[i], err = prepareArg(arg, argType); err != nil {
 			return reflect.Value{}, fmt.Errorf("arg %d: %s", i, err)
 		}
 	}
-	return safeCall(v, argv)
+	return safeCall(fn, argv)
 }
 
 // safeCall runs fun.Call(args), and returns the resulting value and error, if
@@ -440,47 +453,53 @@ func basicKind(v reflect.Value) (kind, error) {
 
 // eq evaluates the comparison a == b || a == c || ...
 func eq(arg1 reflect.Value, arg2 ...reflect.Value) (bool, error) {
-	v1 := indirectInterface(arg1)
-	k1, err := basicKind(v1)
-	if err != nil {
-		return false, err
+	arg1 = indirectInterface(arg1)
+	if arg1 != zero {
+		if t1 := arg1.Type(); !t1.Comparable() {
+			return false, fmt.Errorf("uncomparable type %s: %v", t1, arg1)
+		}
 	}
 	if len(arg2) == 0 {
 		return false, errNoComparison
 	}
+	k1, _ := basicKind(arg1)
 	for _, arg := range arg2 {
-		v2 := indirectInterface(arg)
-		k2, err := basicKind(v2)
-		if err != nil {
-			return false, err
-		}
+		arg = indirectInterface(arg)
+		k2, _ := basicKind(arg)
 		truth := false
 		if k1 != k2 {
 			// Special case: Can compare integer values regardless of type's sign.
 			switch {
 			case k1 == intKind && k2 == uintKind:
-				truth = v1.Int() >= 0 && uint64(v1.Int()) == v2.Uint()
+				truth = arg1.Int() >= 0 && uint64(arg1.Int()) == arg.Uint()
 			case k1 == uintKind && k2 == intKind:
-				truth = v2.Int() >= 0 && v1.Uint() == uint64(v2.Int())
+				truth = arg.Int() >= 0 && arg1.Uint() == uint64(arg.Int())
 			default:
 				return false, errBadComparison
 			}
 		} else {
 			switch k1 {
 			case boolKind:
-				truth = v1.Bool() == v2.Bool()
+				truth = arg1.Bool() == arg.Bool()
 			case complexKind:
-				truth = v1.Complex() == v2.Complex()
+				truth = arg1.Complex() == arg.Complex()
 			case floatKind:
-				truth = v1.Float() == v2.Float()
+				truth = arg1.Float() == arg.Float()
 			case intKind:
-				truth = v1.Int() == v2.Int()
+				truth = arg1.Int() == arg.Int()
 			case stringKind:
-				truth = v1.String() == v2.String()
+				truth = arg1.String() == arg.String()
 			case uintKind:
-				truth = v1.Uint() == v2.Uint()
+				truth = arg1.Uint() == arg.Uint()
 			default:
-				panic("invalid kind")
+				if arg == zero {
+					truth = arg1 == arg
+				} else {
+					if t2 := arg.Type(); !t2.Comparable() {
+						return false, fmt.Errorf("uncomparable type %s: %v", t2, arg)
+					}
+					truth = arg1.Interface() == arg.Interface()
+				}
 			}
 		}
 		if truth {
@@ -499,13 +518,13 @@ func ne(arg1, arg2 reflect.Value) (bool, error) {
 
 // lt evaluates the comparison a < b.
 func lt(arg1, arg2 reflect.Value) (bool, error) {
-	v1 := indirectInterface(arg1)
-	k1, err := basicKind(v1)
+	arg1 = indirectInterface(arg1)
+	k1, err := basicKind(arg1)
 	if err != nil {
 		return false, err
 	}
-	v2 := indirectInterface(arg2)
-	k2, err := basicKind(v2)
+	arg2 = indirectInterface(arg2)
+	k2, err := basicKind(arg2)
 	if err != nil {
 		return false, err
 	}
@@ -514,9 +533,9 @@ func lt(arg1, arg2 reflect.Value) (bool, error) {
 		// Special case: Can compare integer values regardless of type's sign.
 		switch {
 		case k1 == intKind && k2 == uintKind:
-			truth = v1.Int() < 0 || uint64(v1.Int()) < v2.Uint()
+			truth = arg1.Int() < 0 || uint64(arg1.Int()) < arg2.Uint()
 		case k1 == uintKind && k2 == intKind:
-			truth = v2.Int() >= 0 && v1.Uint() < uint64(v2.Int())
+			truth = arg2.Int() >= 0 && arg1.Uint() < uint64(arg2.Int())
 		default:
 			return false, errBadComparison
 		}
@@ -525,13 +544,13 @@ func lt(arg1, arg2 reflect.Value) (bool, error) {
 		case boolKind, complexKind:
 			return false, errBadComparisonType
 		case floatKind:
-			truth = v1.Float() < v2.Float()
+			truth = arg1.Float() < arg2.Float()
 		case intKind:
-			truth = v1.Int() < v2.Int()
+			truth = arg1.Int() < arg2.Int()
 		case stringKind:
-			truth = v1.String() < v2.String()
+			truth = arg1.String() < arg2.String()
 		case uintKind:
-			truth = v1.Uint() < v2.Uint()
+			truth = arg1.Uint() < arg2.Uint()
 		default:
 			panic("invalid kind")
 		}
@@ -634,8 +653,10 @@ var (
 	jsBackslash = []byte(`\\`)
 	jsApos      = []byte(`\'`)
 	jsQuot      = []byte(`\"`)
-	jsLt        = []byte(`\x3C`)
-	jsGt        = []byte(`\x3E`)
+	jsLt        = []byte(`\u003C`)
+	jsGt        = []byte(`\u003E`)
+	jsAmp       = []byte(`\u0026`)
+	jsEq        = []byte(`\u003D`)
 )
 
 // JSEscape writes to w the escaped JavaScript equivalent of the plain text data b.
@@ -664,6 +685,10 @@ func JSEscape(w io.Writer, b []byte) {
 				w.Write(jsLt)
 			case '>':
 				w.Write(jsGt)
+			case '&':
+				w.Write(jsAmp)
+			case '=':
+				w.Write(jsEq)
 			default:
 				w.Write(jsLowUni)
 				t, b := c>>4, c&0x0f
@@ -698,7 +723,7 @@ func JSEscapeString(s string) string {
 
 func jsIsSpecial(r rune) bool {
 	switch r {
-	case '\\', '\'', '"', '<', '>':
+	case '\\', '\'', '"', '<', '>', '&', '=':
 		return true
 	}
 	return r < ' ' || utf8.RuneSelf <= r
diff --git a/tpl/internal/go_templates/texttemplate/hugo_template.go b/tpl/internal/go_templates/texttemplate/hugo_template.go
index 37fa969da..7cd6df0fb 100644
--- a/tpl/internal/go_templates/texttemplate/hugo_template.go
+++ b/tpl/internal/go_templates/texttemplate/hugo_template.go
@@ -30,7 +30,7 @@ package is auto generated.
 */
 
 // Export it so we can populate Hugo's func map with it, which makes it faster.
-var GoFuncs = builtinFuncs
+var GoFuncs = builtinFuncs()
 
 // Preparer prepares the template before execution.
 type Preparer interface {
diff --git a/tpl/internal/go_templates/texttemplate/multi_test.go b/tpl/internal/go_templates/texttemplate/multi_test.go
index e41bb9d8e..7323be379 100644
--- a/tpl/internal/go_templates/texttemplate/multi_test.go
+++ b/tpl/internal/go_templates/texttemplate/multi_test.go
@@ -244,7 +244,7 @@ func TestAddParseTree(t *testing.T) {
 		t.Fatal(err)
 	}
 	// Add a new parse tree.
-	tree, err := parse.Parse("cloneText3", cloneText3, "", "", nil, builtins)
+	tree, err := parse.Parse("cloneText3", cloneText3, "", "", nil, builtins())
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/tpl/internal/go_templates/texttemplate/parse/lex.go b/tpl/internal/go_templates/texttemplate/parse/lex.go
index 3d5770879..30371f286 100644
--- a/tpl/internal/go_templates/texttemplate/parse/lex.go
+++ b/tpl/internal/go_templates/texttemplate/parse/lex.go
@@ -411,7 +411,6 @@ func lexInsideAction(l *lexer) stateFn {
 		}
 	case r <= unicode.MaxASCII && unicode.IsPrint(r):
 		l.emit(itemChar)
-		return lexInsideAction
 	default:
 		return l.errorf("unrecognized character in action: %#U", r)
 	}
diff --git a/tpl/internal/go_templates/texttemplate/parse/node.go b/tpl/internal/go_templates/texttemplate/parse/node.go
index 1174a4b97..1c116ea6f 100644
--- a/tpl/internal/go_templates/texttemplate/parse/node.go
+++ b/tpl/internal/go_templates/texttemplate/parse/node.go
@@ -7,7 +7,6 @@
 package parse
 
 import (
-	"bytes"
 	"fmt"
 	"strconv"
 	"strings"
@@ -29,6 +28,8 @@ type Node interface {
 	// tree returns the containing *Tree.
 	// It is unexported so all implementations of Node are in this package.
 	tree() *Tree
+	// writeTo writes the String output to the builder.
+	writeTo(*strings.Builder)
 }
 
 // NodeType identifies the type of a parse tree node.
@@ -94,11 +95,15 @@ func (l *ListNode) tree() *Tree {
 }
 
 func (l *ListNode) String() string {
-	b := new(bytes.Buffer)
+	var sb strings.Builder
+	l.writeTo(&sb)
+	return sb.String()
+}
+
+func (l *ListNode) writeTo(sb *strings.Builder) {
 	for _, n := range l.Nodes {
-		fmt.Fprint(b, n)
+		n.writeTo(sb)
 	}
-	return b.String()
 }
 
 func (l *ListNode) CopyList() *ListNode {
@@ -132,6 +137,10 @@ func (t *TextNode) String() string {
 	return fmt.Sprintf(textFormat, t.Text)
 }
 
+func (t *TextNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(t.String())
+}
+
 func (t *TextNode) tree() *Tree {
 	return t.tr
 }
@@ -160,23 +169,27 @@ func (p *PipeNode) append(command *CommandNode) {
 }
 
 func (p *PipeNode) String() string {
-	s := ""
+	var sb strings.Builder
+	p.writeTo(&sb)
+	return sb.String()
+}
+
+func (p *PipeNode) writeTo(sb *strings.Builder) {
 	if len(p.Decl) > 0 {
 		for i, v := range p.Decl {
 			if i > 0 {
-				s += ", "
+				sb.WriteString(", ")
 			}
-			s += v.String()
+			v.writeTo(sb)
 		}
-		s += " := "
+		sb.WriteString(" := ")
 	}
 	for i, c := range p.Cmds {
 		if i > 0 {
-			s += " | "
+			sb.WriteString(" | ")
 		}
-		s += c.String()
+		c.writeTo(sb)
 	}
-	return s
 }
 
 func (p *PipeNode) tree() *Tree {
@@ -187,9 +200,9 @@ func (p *PipeNode) CopyPipe() *PipeNode {
 	if p == nil {
 		return p
 	}
-	var vars []*VariableNode
-	for _, d := range p.Decl {
-		vars = append(vars, d.Copy().(*VariableNode))
+	vars := make([]*VariableNode, len(p.Decl))
+	for i, d := range p.Decl {
+		vars[i] = d.Copy().(*VariableNode)
 	}
 	n := p.tr.newPipeline(p.Pos, p.Line, vars)
 	n.IsAssign = p.IsAssign
@@ -219,8 +232,15 @@ func (t *Tree) newAction(pos Pos, line int, pipe *PipeNode) *ActionNode {
 }
 
 func (a *ActionNode) String() string {
-	return fmt.Sprintf("{{%s}}", a.Pipe)
+	var sb strings.Builder
+	a.writeTo(&sb)
+	return sb.String()
+}
 
+func (a *ActionNode) writeTo(sb *strings.Builder) {
+	sb.WriteString("{{")
+	a.Pipe.writeTo(sb)
+	sb.WriteString("}}")
 }
 
 func (a *ActionNode) tree() *Tree {
@@ -249,18 +269,24 @@ func (c *CommandNode) append(arg Node) {
 }
 
 func (c *CommandNode) String() string {
-	s := ""
+	var sb strings.Builder
+	c.writeTo(&sb)
+	return sb.String()
+}
+
+func (c *CommandNode) writeTo(sb *strings.Builder) {
 	for i, arg := range c.Args {
 		if i > 0 {
-			s += " "
+			sb.WriteByte(' ')
 		}
 		if arg, ok := arg.(*PipeNode); ok {
-			s += "(" + arg.String() + ")"
+			sb.WriteByte('(')
+			arg.writeTo(sb)
+			sb.WriteByte(')')
 			continue
 		}
-		s += arg.String()
+		arg.writeTo(sb)
 	}
-	return s
 }
 
 func (c *CommandNode) tree() *Tree {
@@ -311,6 +337,10 @@ func (i *IdentifierNode) String() string {
 	return i.Ident
 }
 
+func (i *IdentifierNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(i.String())
+}
+
 func (i *IdentifierNode) tree() *Tree {
 	return i.tr
 }
@@ -333,14 +363,18 @@ func (t *Tree) newVariable(pos Pos, ident string) *VariableNode {
 }
 
 func (v *VariableNode) String() string {
-	s := ""
+	var sb strings.Builder
+	v.writeTo(&sb)
+	return sb.String()
+}
+
+func (v *VariableNode) writeTo(sb *strings.Builder) {
 	for i, id := range v.Ident {
 		if i > 0 {
-			s += "."
+			sb.WriteByte('.')
 		}
-		s += id
+		sb.WriteString(id)
 	}
-	return s
 }
 
 func (v *VariableNode) tree() *Tree {
@@ -373,6 +407,10 @@ func (d *DotNode) String() string {
 	return "."
 }
 
+func (d *DotNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(d.String())
+}
+
 func (d *DotNode) tree() *Tree {
 	return d.tr
 }
@@ -403,6 +441,10 @@ func (n *NilNode) String() string {
 	return "nil"
 }
 
+func (n *NilNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(n.String())
+}
+
 func (n *NilNode) tree() *Tree {
 	return n.tr
 }
@@ -426,11 +468,16 @@ func (t *Tree) newField(pos Pos, ident string) *FieldNode {
 }
 
 func (f *FieldNode) String() string {
-	s := ""
+	var sb strings.Builder
+	f.writeTo(&sb)
+	return sb.String()
+}
+
+func (f *FieldNode) writeTo(sb *strings.Builder) {
 	for _, id := range f.Ident {
-		s += "." + id
+		sb.WriteByte('.')
+		sb.WriteString(id)
 	}
-	return s
 }
 
 func (f *FieldNode) tree() *Tree {
@@ -469,14 +516,23 @@ func (c *ChainNode) Add(field string) {
 }
 
 func (c *ChainNode) String() string {
-	s := c.Node.String()
+	var sb strings.Builder
+	c.writeTo(&sb)
+	return sb.String()
+}
+
+func (c *ChainNode) writeTo(sb *strings.Builder) {
 	if _, ok := c.Node.(*PipeNode); ok {
-		s = "(" + s + ")"
+		sb.WriteByte('(')
+		c.Node.writeTo(sb)
+		sb.WriteByte(')')
+	} else {
+		c.Node.writeTo(sb)
 	}
 	for _, field := range c.Field {
-		s += "." + field
+		sb.WriteByte('.')
+		sb.WriteString(field)
 	}
-	return s
 }
 
 func (c *ChainNode) tree() *Tree {
@@ -506,6 +562,10 @@ func (b *BoolNode) String() string {
 	return "false"
 }
 
+func (b *BoolNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(b.String())
+}
+
 func (b *BoolNode) tree() *Tree {
 	return b.tr
 }
@@ -639,6 +699,10 @@ func (n *NumberNode) String() string {
 	return n.Text
 }
 
+func (n *NumberNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(n.String())
+}
+
 func (n *NumberNode) tree() *Tree {
 	return n.tr
 }
@@ -666,6 +730,10 @@ func (s *StringNode) String() string {
 	return s.Quoted
 }
 
+func (s *StringNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(s.String())
+}
+
 func (s *StringNode) tree() *Tree {
 	return s.tr
 }
@@ -690,6 +758,10 @@ func (e *endNode) String() string {
 	return "{{end}}"
 }
 
+func (e *endNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(e.String())
+}
+
 func (e *endNode) tree() *Tree {
 	return e.tr
 }
@@ -718,6 +790,10 @@ func (e *elseNode) String() string {
 	return "{{else}}"
 }
 
+func (e *elseNode) writeTo(sb *strings.Builder) {
+	sb.WriteString(e.String())
+}
+
 func (e *elseNode) tree() *Tree {
 	return e.tr
 }
@@ -738,6 +814,12 @@ type BranchNode struct {
 }
 
 func (b *BranchNode) String() string {
+	var sb strings.Builder
+	b.writeTo(&sb)
+	return sb.String()
+}
+
+func (b *BranchNode) writeTo(sb *strings.Builder) {
 	name := ""
 	switch b.NodeType {
 	case NodeIf:
@@ -749,10 +831,17 @@ func (b *BranchNode) String() string {
 	default:
 		panic("unknown branch type")
 	}
+	sb.WriteString("{{")
+	sb.WriteString(name)
+	sb.WriteByte(' ')
+	b.Pipe.writeTo(sb)
+	sb.WriteString("}}")
+	b.List.writeTo(sb)
 	if b.ElseList != nil {
-		return fmt.Sprintf("{{%s %s}}%s{{else}}%s{{end}}", name, b.Pipe, b.List, b.ElseList)
+		sb.WriteString("{{else}}")
+		b.ElseList.writeTo(sb)
 	}
-	return fmt.Sprintf("{{%s %s}}%s{{end}}", name, b.Pipe, b.List)
+	sb.WriteString("{{end}}")
 }
 
 func (b *BranchNode) tree() *Tree {
@@ -826,10 +915,19 @@ func (t *Tree) newTemplate(pos Pos, line int, name string, pipe *PipeNode) *Temp
 }
 
 func (t *TemplateNode) String() string {
-	if t.Pipe == nil {
-		return fmt.Sprintf("{{template %q}}", t.Name)
+	var sb strings.Builder
+	t.writeTo(&sb)
+	return sb.String()
+}
+
+func (t *TemplateNode) writeTo(sb *strings.Builder) {
+	sb.WriteString("{{template ")
+	sb.WriteString(strconv.Quote(t.Name))
+	if t.Pipe != nil {
+		sb.WriteByte(' ')
+		t.Pipe.writeTo(sb)
 	}
-	return fmt.Sprintf("{{template %q %s}}", t.Name, t.Pipe)
+	sb.WriteString("}}")
 }
 
 func (t *TemplateNode) tree() *Tree {
diff --git a/tpl/internal/go_templates/texttemplate/parse/parse.go b/tpl/internal/go_templates/texttemplate/parse/parse.go
index 7c35b0ff3..c9b80f4a2 100644
--- a/tpl/internal/go_templates/texttemplate/parse/parse.go
+++ b/tpl/internal/go_templates/texttemplate/parse/parse.go
@@ -108,13 +108,8 @@ func (t *Tree) nextNonSpace() (token item) {
 }
 
 // peekNonSpace returns but does not consume the next non-space token.
-func (t *Tree) peekNonSpace() (token item) {
-	for {
-		token = t.next()
-		if token.typ != itemSpace {
-			break
-		}
-	}
+func (t *Tree) peekNonSpace() item {
+	token := t.nextNonSpace()
 	t.backup()
 	return token
 }
diff --git a/tpl/internal/go_templates/texttemplate/parse/parse_test.go b/tpl/internal/go_templates/texttemplate/parse/parse_test.go
index 5d3b59b63..79e7bb5ae 100644
--- a/tpl/internal/go_templates/texttemplate/parse/parse_test.go
+++ b/tpl/internal/go_templates/texttemplate/parse/parse_test.go
@@ -306,7 +306,8 @@ var parseTests = []parseTest{
 }
 
 var builtins = map[string]interface{}{
-	"printf": fmt.Sprintf,
+	"printf":   fmt.Sprintf,
+	"contains": strings.Contains,
 }
 
 func testParse(doCopy bool, t *testing.T) {
@@ -555,3 +556,52 @@ func BenchmarkParseLarge(b *testing.B) {
 		}
 	}
 }
+
+var sinkv, sinkl string
+
+func BenchmarkVariableString(b *testing.B) {
+	v := &VariableNode{
+		Ident: []string{"$", "A", "BB", "CCC", "THIS_IS_THE_VARIABLE_BEING_PROCESSED"},
+	}
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		sinkv = v.String()
+	}
+	if sinkv == "" {
+		b.Fatal("Benchmark was not run")
+	}
+}
+
+func BenchmarkListString(b *testing.B) {
+	text := `
+{{(printf .Field1.Field2.Field3).Value}}
+{{$x := (printf .Field1.Field2.Field3).Value}}
+{{$y := (printf $x.Field1.Field2.Field3).Value}}
+{{$z := $y.Field1.Field2.Field3}}
+{{if contains $y $z}}
+	{{printf "%q" $y}}
+{{else}}
+	{{printf "%q" $x}}
+{{end}}
+{{with $z.Field1 | contains "boring"}}
+	{{printf "%q" . | printf "%s"}}
+{{else}}
+	{{printf "%d %d %d" 11 11 11}}
+	{{printf "%d %d %s" 22 22 $x.Field1.Field2.Field3 | printf "%s"}}
+	{{printf "%v" (contains $z.Field1.Field2 $y)}}
+{{end}}
+`
+	tree, err := New("bench").Parse(text, "", "", make(map[string]*Tree), builtins)
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.ResetTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		sinkl = tree.Root.String()
+	}
+	if sinkl == "" {
+		b.Fatal("Benchmark was not run")
+	}
+}
diff --git a/tpl/internal/go_templates/texttemplate/template.go b/tpl/internal/go_templates/texttemplate/template.go
index 4df8a9ed0..9c6ba6dfc 100644
--- a/tpl/internal/go_templates/texttemplate/template.go
+++ b/tpl/internal/go_templates/texttemplate/template.go
@@ -110,20 +110,21 @@ func (t *Template) Clone() (*Template, error) {
 
 // copy returns a shallow copy of t, with common set to the argument.
 func (t *Template) copy(c *common) *Template {
-	nt := New(t.name)
-	nt.Tree = t.Tree
-	nt.common = c
-	nt.leftDelim = t.leftDelim
-	nt.rightDelim = t.rightDelim
-	return nt
+	return &Template{
+		name:       t.name,
+		Tree:       t.Tree,
+		common:     c,
+		leftDelim:  t.leftDelim,
+		rightDelim: t.rightDelim,
+	}
 }
 
-// AddParseTree adds parse tree for template with given name and associates it with t.
-// If the template does not already exist, it will create a new one.
-// If the template does exist, it will be replaced.
+// AddParseTree associates the argument parse tree with the template t, giving
+// it the specified name. If the template has not been defined, this tree becomes
+// its definition. If it has been defined and already has that name, the existing
+// definition is replaced; otherwise a new template is created, defined, and returned.
 func (t *Template) AddParseTree(name string, tree *parse.Tree) (*Template, error) {
 	t.init()
-	// If the name is the name of this template, overwrite this template.
 	nt := t
 	if name != t.name {
 		nt = t.New(name)
@@ -197,7 +198,7 @@ func (t *Template) Lookup(name string) *Template {
 func (t *Template) Parse(text string) (*Template, error) {
 	t.init()
 	t.muFuncs.RLock()
-	trees, err := parse.Parse(t.name, text, t.leftDelim, t.rightDelim, t.parseFuncs, builtins)
+	trees, err := parse.Parse(t.name, text, t.leftDelim, t.rightDelim, t.parseFuncs, builtins())
 	t.muFuncs.RUnlock()
 	if err != nil {
 		return nil, err