Report warning if contract uses abicoder v1, but IR is requested

libsolidity/ast/ASTAnnotations.h

@@ -94,6 +94,7 @@ struct SourceUnitAnnotation: ASTAnnotation
 	SetOnce<std::map<ASTString, std::vector<Declaration const*>>> exportedSymbols;
 	/// Experimental features.
 	std::set<ExperimentalFeature> experimentalFeatures;
+	/// Using the new ABI coder. Set to `false` if using ABI coder v1.
 	SetOnce<bool> useABICoderV2;
 };
 

libsolidity/interface/CompilerStack.cpp

@@ -1249,6 +1249,14 @@ void CompilerStack::generateIR(ContractDefinition const& _contract)
 	if (!compiledContract.yulIR.empty())
 		return;
 
+	if (!*_contract.sourceUnit().annotation().useABICoderV2)
+		m_errorReporter.warning(
+			2066_error,
+			_contract.location(),
+			"Contract requests the ABI coder v1, which is incompatible with the IR. "
+			"Using ABI coder v2 instead."
+		);
+
 	string dependenciesSource;
 	for (auto const* dependency: _contract.annotation().contractDependencies)
 		generateIR(*dependency);