exp/template/html: tolerate '/' ambiguity in JS when it doesn't matter.
Often, division/regexp ambiguity doesn't matter in JS because the next
token is not a slash.
For example, in
<script>var global{{if .InitVal}} = {{.InitVal}}{{end}}</script>
When there is an initial value, the {{if}} ends with jsCtxDivOp
since a '/' following {{.InitVal}} would be a division operator.
When there is none, the empty {{else}} branch ends with jsCtxRegexp
since a '/' would start a regular expression. A '/' could result
in a valid program if it were on a new line to allow semicolon
insertion to terminate the VarDeclaration.
There is no '/' though, so we can ignore the ambiguity.
There are cases where a missing semi can result in ambiguity that
we should report.
<script>
{{if .X}}var x = {{.X}}{{end}}
/...{{.Y}}
</script>
where ... could be /foo/.test(bar) or /divisor. Disambiguating in
this case is hard and is required to sanitize {{.Y}}.
Note, that in the case where there is a '/' in the script tail but it
is not followed by any interpolation, we already don't care. So we
are already tolerant of
<script>{{if .X}}var x = {{.X}}{{end}}/a-bunch-of-text</script>
because tJS checks for </script> before looking in /a-bunch-of-text.
This CL
- Adds a jsCtx value: jsCtxUnknown
- Changes joinContext to join contexts that only differ by jsCtx.
- Changes tJS to return an error when a '/' is seen in jsCtxUnknown.
- Adds tests for both the happy and sad cases.
R=nigeltao
CC=golang-dev
https://golang.org/cl/
4956077