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camc314 b20fc1950c fix(parser): reject partially parenthesized mixed coalesce expressions (#26394 )

The parser currently accepts mixed nullish and logical expressions when parentheses cover only the first operand of the logical expression:

```js
(a) || b ?? c;
a ?? (b) || c;
(a) && b ?? c;
a ?? (b) && c;
```

These expressions require a syntax error because `??` cannot be mixed directly with `||` or `&&`. Parentheses around `a` or `b` do not group the complete logical expression. This change reports the existing mixed-coalesce diagnostic for all four forms.

Fully grouped operands remain valid:

```js
(a || b) ?? c;
a ?? (b || c);
(a && b) ?? c;
a ?? (b && c);
```

### Why the existing check misses these expressions

`parse_binary_expression_rest` used `lhs_parenthesized` and `rhs_parenthesized` flags captured before parsing an operand. Those flags describe whether the initial token is `(`, but the parser can subsequently accumulate a larger logical expression outside those parentheses. Applying the initial flag to that complete expression incorrectly suppresses the diagnostic.

### Complete-operand checks

Check both operands independently for an `And` or `Or` logical expression whose span starts at the operand's starting position. A logical expression accumulated outside initial parentheses starts at that position and must be rejected. Checking both operands also prevents a grouped right operand from hiding an invalid left operand.

This works with either `preserve_parens` setting. When parentheses are preserved, a fully grouped operand is a `ParenthesizedExpression`. When they are omitted, its inner logical expression retains a span beginning after the opening `(`, so its start differs from the operand start and it remains allowed. For `(a) || b`, the complete logical expression instead starts at the opening `(` and is correctly rejected.

2026-09-07 14:34:52 +00:00

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(a) || b ?? c;