JS Template Literal interpolations with embedded braces are parsed wrong

[hundt]

When inside a JS Template Literal interpolation, e.g. between the braces in `${val}`, RawContextUpdater considers any "}" character to indicate an end to the interpolation and a return to the Template Literal context:

closure-templates/java/src/com/google/template/soy/parsepasses/contextautoesc/RawTextContextUpdater.java

Line 770 in 8f54ab1

new Transition("}") {

// if we are in a template, then this puts us back into the template string
// e.g.  `foo${bar}`
if (prior.jsTemplateLiteralNestDepth > 0) {
  return prior.toBuilder().withState(HtmlContext.JS_TEMPLATE_LITERAL).build();
}
// stay in js, this must be part of some control flow character
return prior;

However, any Javascript expression could appear in these interpolations, including many possible expressions with curly braces in them. For example: `${{a:1}['a']}` evaluates to "1".

A test case to see this fail is to add assertTransition("JS", "`${{a:1}", "JS jsTemplateLiteralNestDepth=1"); to RawTextContentUpdaterTest.java:

expected: JS jsTemplateLiteralNestDepth=1
but was : JS_TEMPLATE_LITERAL DIV_OP jsTemplateLiteralNestDepth=1

(I'm not sure about the DIV_OP part but the JS_TEMPLATE_LITERAL part is definitely wrong.)

I don't know if it is currently possible to trigger a real-life rendering error via this bug. When I tried I found that compiling the template generally failed with a parse error if there were any braces inside an interpolation; I'm not sure if that is by design or if that is an additional bug. But I thought I'd point out the issue since I happened to spot it while browsing the source code.