Type Checker: skip zero-param bindings in operatorDefinitions matching scan

[genisis0x]

Description

Fixes #16613.

In a global using { ..., g as <op> } for T directive that mixes a valid binding (f as -, two parameters of T) with a zero-parameter binding (g as -), solc --bin panics with an internal compiler error before the user-visible 4731 (The function "g" does not have any parameters...) is emitted:

Internal compiler error:
libsolidity/ast/Types.cpp(409): Throw in function ... operatorDefinitions(...)
Solidity assertion failed

TypeChecker::endVisit(UsingForDirective) walks the bindings in order. For f it reaches the per-binding cross-scan at libsolidity/analysis/TypeChecker.cpp:4224 and calls Type::operatorDefinitions(_token, _scope, _unary). That helper iterates every binding of every using-for directive on T (including g), and asserted on !functionType->parameterTypes().empty(). The fatal 4731 for g is only fired later, when the outer loop reaches it.

This change keeps the assertion that the binding still maps to a FunctionType, but treats the empty-parameter case as a no-op for the matching scan. The TypeChecker still emits 4731 from endVisit(UsingForDirective), so the user-visible diagnostic is unchanged for the well-typed binding paths and for the standalone zero-parameter case (operator_taking_no_parameters_unary.sol is unaffected).

Tests

• New test/libsolidity/syntaxTests/operators/userDefined/operator_zero_param_alongside_valid_binding_no_ice.sol reproduces the issue MRE (one valid - binding + one zero-parameter - binding) and asserts the expected TypeError 4731 instead of the prior ICE.

Checklist

• I have read the contributing guidelines and the review checklist
• I have personally reviewed, understood, and tested every change in this PR

AI Disclosure

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