Instead of passing the continuously merged initial forbidden token set
(with the new additional forbidden tokens from each parsed secondary
expression) to the next call of parse_secondary_expression(), keep a
copy of the original set and use it as the base for parsing the next
secondary expression.
This bug prevented us from properly parsing the following expression:
```js
0 ?? 0 ? 0 : 0 || 0
```
...due to LogicalExpression with LogicalOp::NullishCoalescing returning
both DoubleAmpersand and DoublePipe in its forbidden token set.
The following correct AST is now generated:
Program
(Children)
ExpressionStatement
ConditionalExpression
(Test)
LogicalExpression
NumericLiteral 0
??
NumericLiteral 0
(Consequent)
NumericLiteral 0
(Alternate)
LogicalExpression
NumericLiteral 0
||
NumericLiteral 0
An alternate solution I explored was only merging the original forbidden
token set with the one of the last parsed secondary expression which is
then passed to match_secondary_expression(); however that led to an
incorrect AST (note the alternate expression):
Program
(Children)
ExpressionStatement
LogicalExpression
ConditionalExpression
(Test)
LogicalExpression
NumericLiteral 0
??
NumericLiteral 0
(Consequent)
NumericLiteral 0
(Alternate)
NumericLiteral 0
||
NumericLiteral 0
Truth be told, I don't know enough about the inner workings of the
parser to fully explain the difference. AFAICT this patch has no
unintended side effects in its current form though.
Fixes#18087.
The same expression is not allowed to contain both the
logical && and || operators, and the coalescing ?? operator.
This patch changes how "forbidden" tokens are handled, using a
finite set instead of an Vector. This supports much more efficient
merging of the forbidden tokens when propagating forward, and
allowing the return of forbidden tokens to parent contexts.
