exp/template/html: elide comments in template source.

When templates are stored in external files, developers often embed
comments to explain&|disable code.

  <!-- Oblique reference to project code name here -->
  {{if .C}}...{{else}}<!-- commented out default -->{{end}}

This unnecessarily increases the size of shipped HTML and can leak
information.

This change elides all comments of the following types:
1. <!-- ... --> comments found in source.
2. /*...*/ and // comments found in <script> elements.
3. /*...*/ and // comments found in <style> elements.

It does not elide /*...*/ or // comments found in HTML attributes:
4. <button onclick="/*...*/">
5. <div style="/*...*/">

I can find no examples of comments in attributes in Closure Templates
code and doing so would require keeping track of character positions
post decode in

  <button onclick="/&#42;...*/">

To prevent token joining, /*comments*/ are JS and CSS comments are
replaced with a whitespace char.
HTML comments are not, but to prevent token joining we could try to
detect cases like
   <<!---->b>
   </<!---->b>
which has a well defined meaning in HTML but will cause a validator
to barf.  This is difficult, and this is a very minor case.
I have punted for now, but if we need to address this case, the best
way would be to normalize '<' in stateText to '&lt;' consistently.

The whitespace to replace a JS /*comment*/ with depends on whether
there is an embedded line terminator since
    break/*
    */foo
    ...
is equivalent to
    break;
    foo
    ...
while
    break/**/foo
    ...
is equivalent to
    break foo;
    ...

Comment eliding can interfere with IE conditional comments.
http://en.wikipedia.org/wiki/Conditional_comment

<!--[if IE 6]>
<p>You are using Internet Explorer 6.</p>
<![endif]-->

/*@cc_on
  document.write("You are using IE4 or higher");
@*/

I have not encountered these in production template code, and
the typed content change in CL 4962067 provides an escape-hatch
if conditional comments are needed.

R=nigeltao
CC=golang-dev
https://golang.org/cl/4999042

diff --git a/src/pkg/exp/template/html/escape.go b/src/pkg/exp/template/html/escape.go
index 28019f252522c84053c76e7f1b6c6f45a102ca1f..650a6acd288e82a15ff3545904b9f44c07455855 100644 (file)
--- a/src/pkg/exp/template/html/escape.go
+++ b/src/pkg/exp/template/html/escape.go
@@ -568,12 +568,43 @@ func (e *escaper) escapeText(c context, n *parse.TextNode) context {
                                        written = j + 1
                                }
                        }
+               } else if isComment(c.state) && c.delim == delimNone {
+                       switch c.state {
+                       case stateJSBlockCmt:
+                               // http://es5.github.com/#x7.4:
+                               // "Comments behave like white space and are
+                               // discarded except that, if a MultiLineComment
+                               // contains a line terminator character, then
+                               // the entire comment is considered to be a
+                               // LineTerminator for purposes of parsing by
+                               // the syntactic grammar."
+                               if bytes.IndexAny(s[written:i1], "\n\r\u2028\u2029") != -1 {
+                                       b.WriteByte('\n')
+                               } else {
+                                       b.WriteByte(' ')
+                               }
+                       case stateCSSBlockCmt:
+                               b.WriteByte(' ')
+                       }
+                       written = i1
+               }
+               if c.state != c1.state && isComment(c1.state) && c1.delim == delimNone {
+                       // Preserve the portion between written and the comment start.
+                       cs := i1 - 2
+                       if c1.state == stateHTMLCmt {
+                               // "<!--" instead of "/*" or "//"
+                               cs -= 2
+                       }
+                       b.Write(s[written:cs])
+                       written = i1
                }
                c, i = c1, i1
        }
 
        if written != 0 && c.state != stateError {
-               b.Write(n.Text[written:])
+               if !isComment(c.state) || c.delim != delimNone {
+                       b.Write(n.Text[written:])
+               }
                e.editTextNode(n, b.Bytes())
        }
        return c

diff --git a/src/pkg/exp/template/html/escape_test.go b/src/pkg/exp/template/html/escape_test.go
index 84bf6b7a4ab67174a0e03e17407da3977109c03d..8a64515dec972ae1608931797b9e235b98678cb1 100644 (file)
--- a/src/pkg/exp/template/html/escape_test.go
+++ b/src/pkg/exp/template/html/escape_test.go
@@ -363,13 +363,12 @@ func TestEscape(t *testing.T) {
                {
                        "HTML comment",
                        "<b>Hello, <!-- name of world -->{{.C}}</b>",
-                       // TODO: Elide comment.
-                       "<b>Hello, <!-- name of world -->&lt;Cincinatti&gt;</b>",
+                       "<b>Hello, &lt;Cincinatti&gt;</b>",
                },
                {
                        "HTML comment not first < in text node.",
                        "<<!-- -->!--",
-                       "&lt;<!-- -->!--",
+                       "&lt;!--",
                },
                {
                        "HTML normalization 1",
@@ -384,18 +383,18 @@ func TestEscape(t *testing.T) {
                {
                        "HTML normalization 3",
                        "a<<!-- --><!-- -->b",
-                       "a&lt;<!-- --><!-- -->b",
+                       "a&lt;b",
                },
                {
                        "Split HTML comment",
                        "<b>Hello, <!-- name of {{if .T}}city -->{{.C}}{{else}}world -->{{.W}}{{end}}</b>",
-                       "<b>Hello, <!-- name of city -->&lt;Cincinatti&gt;</b>",
+                       "<b>Hello, &lt;Cincinatti&gt;</b>",
                },
                {
                        "JS line comment",
                        "<script>for (;;) { if (c()) break// foo not a label\n" +
                                "foo({{.T}});}</script>",
-                       "<script>for (;;) { if (c()) break// foo not a label\n" +
+                       "<script>for (;;) { if (c()) break\n" +
                                "foo( true );}</script>",
                },
                {
@@ -405,8 +404,8 @@ func TestEscape(t *testing.T) {
                        // Newline separates break from call. If newline
                        // removed, then break will consume label leaving
                        // code invalid.
-                       "<script>for (;;) { if (c()) break/* foo not a label\n" +
-                               " */foo( true );}</script>",
+                       "<script>for (;;) { if (c()) break\n" +
+                               "foo( true );}</script>",
                },
                {
                        "JS single-line block comment",
@@ -417,25 +416,25 @@ func TestEscape(t *testing.T) {
                        // removed, then break will consume label leaving
                        // code invalid.
                        "<script>for (;;) {\n" +
-                               "if (c()) break/* foo a label */foo;" +
+                               "if (c()) break foo;" +
                                "x( true );}</script>",
                },
                {
                        "JS block comment flush with mathematical division",
                        "<script>var a/*b*//c\nd</script>",
-                       "<script>var a/*b*//c\nd</script>",
+                       "<script>var a /c\nd</script>",
                },
                {
                        "JS mixed comments",
                        "<script>var a/*b*///c\nd</script>",
-                       "<script>var a/*b*///c\nd</script>",
+                       "<script>var a \nd</script>",
                },
                {
                        "CSS comments",
                        "<style>p// paragraph\n" +
                                `{border: 1px/* color */{{"#00f"}}}</style>`,
-                       "<style>p// paragraph\n" +
-                               "{border: 1px/* color */#00f}</style>",
+                       "<style>p\n" +
+                               "{border: 1px #00f}</style>",
                },
                {
                        "JS attr block comment",
@@ -462,12 +461,12 @@ func TestEscape(t *testing.T) {
                {
                        "HTML substitution commented out",
                        "<p><!-- {{.H}} --></p>",
-                       "<p><!--  --></p>",
+                       "<p></p>",
                },
                {
                        "Comment ends flush with start",
                        "<!--{{.}}--><script>/*{{.}}*///{{.}}\n</script><style>/*{{.}}*///{{.}}\n</style><a onclick='/*{{.}}*///{{.}}' style='/*{{.}}*///{{.}}'>",
-                       "<!----><script>/**///\n</script><style>/**///\n</style><a onclick='/**///' style='/**///'>",
+                       "<script> \n</script><style> \n</style><a onclick='/**///' style='/**///'>",
                },
                {
                        "typed HTML in text",