Fix segmentation fault when resolving to empty left hand side tuple-type

Changelog.md

@@ -14,6 +14,7 @@ Bugfixes:
  * SMTChecker: Fix internal error when using bitwise operators with an array element as argument.
  * Standard JSON Interface: Fix ICE when the optimizer is disabled and an empty/blank string is used for ``optimizerSteps`` sequence.
  * StaticAnalyzer: Only raise a compile time error for division and modulo by zero when it's between literals.
+ * TypeChecker: Fix segmentation fault when assigning to complex left side tuple expression that resolves to empty.
  * Yul Optimizer: Fix the order of assignments generated by ``SSATransform`` being dependent on AST IDs, sometimes resulting in different (but equivalent) bytecode when unrelated files were added to the compilation pipeline.
 
 

libsolidity/analysis/TypeChecker.cpp

@@ -116,7 +116,8 @@ void TypeChecker::checkDoubleStorageAssignment(Assignment const& _assignment)
 		TupleType const& lhsType = dynamic_cast<TupleType const&>(*type(_lhs));
 		TupleExpression const* lhsResolved = dynamic_cast<TupleExpression const*>(resolveOuterUnaryTuples(&_lhs));
 
-		if (lhsType.components().size() != _rhs.components().size() || lhsResolved->components().size() != _rhs.components().size())
+		solAssert(!lhsResolved || lhsResolved->components().size() == lhsType.components().size());
+		if (lhsType.components().size() != _rhs.components().size())
 		{
 			solAssert(m_errorReporter.hasErrors(), "");
 			return;

test/libsolidity/syntaxTests/tupleAssignments/empty_tuples_lhs_resolved.sol

@@ -0,0 +1,34 @@
+contract C {
+	uint[] public array;
+
+	function f() public {
+		(f()) = ();
+	}
+
+	function g() public {
+		(revert()) = ();
+	}
+
+	function h() internal returns (uint, uint) {}
+
+	function i() public {
+		(h()) = (1, 1);
+	}
+
+	function j() public returns (uint, uint) {
+		(j()) = (1, 1);
+	}
+
+	function m() public {
+		(uint x, uint y) = (1, 1); // OK
+	}
+
+	function n() public {
+		((array.push(), array.push())) = (1, 1); // OK
+	}
+}
+// ----
+// TypeError 4247: (62-65): Expression has to be an lvalue.
+// TypeError 4247: (103-111): Expression has to be an lvalue.
+// TypeError 4247: (197-200): Expression has to be an lvalue.
+// TypeError 4247: (263-266): Expression has to be an lvalue.