Do not warn about shadowing parameters in functions without implementation

libsolidity/analysis/DeclarationContainer.cpp

@@ -120,11 +120,7 @@ bool DeclarationContainer::registerDeclaration(
 		if (conflictingDeclaration(_declaration, _name))
 			return false;
 
-		// Do not warn about shadowing for structs and enums because their members are
-		// not accessible without prefixes. Also do not warn about event parameters
-		// because they do not participate in any proper scope.
-		bool special = _declaration.scope() && (_declaration.isStructMember() || _declaration.isEnumValue() || _declaration.isEventOrErrorParameter());
-		if (m_enclosingContainer && !special)
+		if (m_enclosingContainer && _declaration.isVisibleAsUnqualifiedName())
 			m_homonymCandidates.emplace_back(*_name, _location ? _location : &_declaration.location());
 	}
 

libsolidity/ast/AST.cpp

@@ -606,6 +606,18 @@ bool Declaration::isEventOrErrorParameter() const
 	return dynamic_cast<EventDefinition const*>(scope()) || dynamic_cast<ErrorDefinition const*>(scope());
 }
 
+bool Declaration::isVisibleAsUnqualifiedName() const
+{
+	if (!scope())
+		return true;
+	if (isStructMember() || isEnumValue() || isEventOrErrorParameter())
+		return false;
+	if (auto const* functionDefinition = dynamic_cast<FunctionDefinition const*>(scope()))
+		if (!functionDefinition->isImplemented())
+			return false; // parameter of a function without body
+	return true;
+}
+
 DeclarationAnnotation& Declaration::annotation() const
 {
 	return initAnnotation<DeclarationAnnotation>();

libsolidity/ast/AST.h

@@ -265,6 +265,12 @@ public:
 	/// @returns true if this is a declaration of a parameter of an event.
 	bool isEventOrErrorParameter() const;
 
+	/// @returns false if the declaration can never be referenced without being qualified with a scope.
+	/// Usually the name alone can be used to refer to the corresponding entity.
+	/// But, for example, struct member names or enum member names always require a prefix.
+	/// Another example is event parameter names, which do not participate in any proper scope.
+	bool isVisibleAsUnqualifiedName() const;
+
 	/// @returns the type of expressions referencing this declaration.
 	/// This can only be called once types of variable declarations have already been resolved.
 	virtual Type const* type() const = 0;

test/libsolidity/syntaxTests/scoping/name_shadowing_function_parameter_name_vs_contract.sol

@@ -0,0 +1,20 @@
+interface I {
+    function f(uint I) external;         // OK
+}
+
+library L {
+    function f(uint L) public pure {}    // warning
+}
+
+abstract contract A {
+    function f(uint A) public pure {}    // warning
+    function g(uint A) public virtual;   // OK
+}
+
+contract C {
+    function f(uint C) public pure {}    // warning
+}
+// ----
+// Warning 2519: (91-97): This declaration shadows an existing declaration.
+// Warning 2519: (168-174): This declaration shadows an existing declaration.
+// Warning 2519: (283-289): This declaration shadows an existing declaration.

test/libsolidity/syntaxTests/scoping/name_shadowing_function_parameter_vs_its_function.sol

@@ -0,0 +1,5 @@
+contract C {
+    function f(uint f) pure public {}
+}
+// ----
+// Warning 2519: (28-34): This declaration shadows an existing declaration.