html/template: track brace depth for each nested expression
We need to track the brace depth for each individual nested expression,
since a string interpolation expression may be nested inside of an
object.
e.g. `${ {1:`${}`}}` has brace depths [1, 0] when inside of the inner
${} expression. When we exit the inner expression, we need to reset to
the previous brace depth (1) so that we know that the following } closes
the object, but not the outer expression.
Note that if you write a broken expression (i.e. `${ { }`) escaping will
clearly not work as expected (or depending on your interpretation, since
it is broken, it will work as expected). Since the JS parser doesn't
catch syntax errors, it's up to the user to write a valid template.
Updates #61619
Change-Id: I4c33723d12aff49facdcb1134d9ca82b7a0dffc4
Reviewed-on: https://go-review.googlesource.com/c/go/+/532995 Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>