From 2c5acdc624ed498936b8a8021925bedab321a403 Mon Sep 17 00:00:00 2001
From: genisis0x <manietdavv@gmail.com>
Date: Fri, 15 May 2026 15:32:21 +0530
Subject: [PATCH] Type Checker: skip zero-param free functions in
 attachedFunctions resolution

When a using-for directive binds a zero-parameter free function and the
call site (`x.zero()`) appears earlier in the contract body than the
directive itself, member resolution runs before TypeChecker visits the
directive. attachedFunctions reaches addFunction(), which calls
FunctionType::withBoundFirstArgument() and asserts on
`!m_parameterTypes.empty()`, triggering an internal compiler error
before the user-visible 4731 ("function does not have any parameters")
is emitted.

Library-bound resolution already filters out zero-parameter functions in
the loop above; mirror the same filter for the non-library branch. The
TypeChecker's endVisit(UsingForDirective) still reports 4731 for the
directive itself, and the call-site separately reports 9582 ("member not
found"). The user-visible diagnostics are unchanged for well-typed code.

Fixes #16610
---
 libsolidity/ast/Types.cpp                          | 14 ++++++++++----
 ...ee_no_parameters_call_site_before_directive.sol | 11 +++++++++++
 2 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 test/libsolidity/syntaxTests/using/using_free_no_parameters_call_site_before_directive.sol

diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index 3fa068491d9f..cfc62b469fb3 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -457,10 +457,16 @@ MemberList::MemberMap Type::attachedFunctions(Type const& _type, ASTNode const&
 				}
 			}
 			else
-				addFunction(
-					dynamic_cast<FunctionDefinition const&>(*declaration),
-					identifierPath->path().back()
-				);
+			{
+				auto const& functionDefinition = dynamic_cast<FunctionDefinition const&>(*declaration);
+				// Zero-parameter functions are rejected by TypeChecker::endVisit(UsingForDirective)
+				// with error 4731, but member resolution can run before the directive is visited
+				// when the call site precedes the directive in the contract body. Skip these here
+				// so addFunction() does not assert in withBoundFirstArgument() (#16610).
+				if (functionDefinition.parameters().empty())
+					continue;
+				addFunction(functionDefinition, identifierPath->path().back());
+			}
 		}
 
 	return members;
diff --git a/test/libsolidity/syntaxTests/using/using_free_no_parameters_call_site_before_directive.sol b/test/libsolidity/syntaxTests/using/using_free_no_parameters_call_site_before_directive.sol
new file mode 100644
index 000000000000..eb853b75481b
--- /dev/null
+++ b/test/libsolidity/syntaxTests/using/using_free_no_parameters_call_site_before_directive.sol
@@ -0,0 +1,11 @@
+function zero() pure returns (uint) { return 0; }
+
+contract C {
+    function f(uint z) pure external returns (uint) {
+        return z.zero();
+    }
+    using {zero} for uint;
+}
+// ----
+// TypeError 9582: (133-139): Member "zero" not found or not visible after argument-dependent lookup in uint256.
+// TypeError 4731: (160-164): The function "zero" does not have any parameters, and therefore cannot be attached to the type "uint256".