Warn on YUL switch statement with only default statement

libyul/AsmAnalysis.cpp

@@ -359,6 +359,13 @@ void AsmAnalyzer::operator()(Switch const& _switch)
 {
 	yulAssert(_switch.expression, "");
 
+	if (_switch.cases.size() == 1 && !_switch.cases[0].value)
+		m_errorReporter.warning(
+			1878_error,
+			_switch.location,
+			"\"switch\" statement with only a default case."
+		);
+
 	YulString valueType = expectExpression(*_switch.expression);
 
 	set<u256> cases;

test/libsolidity/syntaxTests/controlFlow/localStorageVariables/assembly/switch_declaration_fine.sol

@@ -29,3 +29,4 @@ contract C {
     }
 }
 // ----
+// Warning: (141-190): "switch" statement with only a default case.

test/libsolidity/syntaxTests/controlFlow/storageReturn/assembly/switch_fine.sol

@@ -23,3 +23,4 @@ contract C {
     }
 }
 // ----
+// Warning: (142-191): "switch" statement with only a default case.