fixup! Syntax for custom errors.

libsolidity/analysis/SyntaxChecker.cpp

@@ -192,6 +192,17 @@ void SyntaxChecker::endVisit(ModifierDefinition const& _modifier)
 	m_placeholderFound = false;
 }
 
+bool SyntaxChecker::visit(ErrorDefinition const& _error)
+{
+	if (_error.name() == "Error" || _error.name() == "Panic")
+		m_errorReporter.syntaxError(
+			1855_error,
+			_error.location(),
+			"The built-in errors \"Error\" and \"Panic\" cannot be re-defined."
+		);
+	return true;
+}
+
 void SyntaxChecker::checkSingleStatementVariableDeclaration(ASTNode const& _statement)
 {
 	auto varDecl = dynamic_cast<VariableDeclarationStatement const*>(&_statement);

libsolidity/analysis/SyntaxChecker.h

@@ -40,6 +40,7 @@ namespace solidity::frontend
  *  - issues deprecation warning for throw
  *  - whether the msize instruction is used and the Yul optimizer is enabled at the same time.
  *  - selection of the ABI coder through pragmas.
+ *  - whether user-defined errors are called Error or Panic.
  */
 class SyntaxChecker: private ASTConstVisitor
 {
@@ -61,6 +62,8 @@ private:
 	bool visit(ModifierDefinition const& _modifier) override;
 	void endVisit(ModifierDefinition const& _modifier) override;
 
+	bool visit(ErrorDefinition const& _error) override;
+
 	/// Reports an error if _statement is a VariableDeclarationStatement.
 	/// Used by if/while/for to check for single statement variable declarations
 	/// without a block.

test/libsolidity/syntaxTests/errors/error_reserved_name.sol

@@ -1,3 +1,4 @@
 // TODO do we want to disallow this at all?
 error Error(uint);
 // ----
+// SyntaxError 1855: (44-62): The built-in errors "Error" and "Panic" cannot be re-defined.

test/libsolidity/syntaxTests/errors/panic_reserved_name.sol

@@ -2,3 +2,4 @@
 // TODO I Think the best way would be to have Error in the global scope.
 error Panic(bytes2);
 // ----
+// SyntaxError 1855: (131-151): The built-in errors "Error" and "Panic" cannot be re-defined.