Syntax for custom errors.

docs/grammar/Solidity.g4

@@ -19,6 +19,7 @@ sourceUnit: (
 	| constantVariableDeclaration
 	| structDefinition
 	| enumDefinition
+	| errorDefinition
 )* EOF;
 
 //@doc: inline
@@ -90,6 +91,7 @@ contractBodyElement:
 	| enumDefinition
 	| stateVariableDeclaration
 	| eventDefinition
+	| errorDefinition
 	| usingDirective;
 //@doc:inline
 namedArgument: name=identifier Colon value=expression;
@@ -289,6 +291,18 @@ eventDefinition:
 	Anonymous?
 	Semicolon;
 
+/**
+ * Parameter of an error.
+ */
+errorParameter: type=typeName name=identifier?;
+/**
+ * Definition of an error.
+ */
+errorDefinition:
+	Error name=identifier
+	LParen (parameters+=errorParameter (Comma parameters+=errorParameter)*)? RParen
+	Semicolon;
+
 /**
  * Using directive to bind library functions to types.
  * Can occur within contracts and libraries.
@@ -367,7 +381,7 @@ inlineArrayExpression: LBrack (expression ( Comma expression)* ) RBrack;
 /**
  * Besides regular non-keyword Identifiers, the 'from' keyword can also occur as identifier outside of import statements.
  */
-identifier: Identifier | From;
+identifier: Identifier | From | Error;
 
 literal: stringLiteral | numberLiteral | booleanLiteral | hexStringLiteral | unicodeStringLiteral;
 booleanLiteral: True | False;

docs/grammar/SolidityLexer.g4

@@ -29,12 +29,13 @@ Do: 'do';
 Else: 'else';
 Emit: 'emit';
 Enum: 'enum';
+Error: 'error'; // not a real keyword
 Event: 'event';
 External: 'external';
 Fallback: 'fallback';
 False: 'false';
 Fixed: 'fixed' | ('fixed' [1-9][0-9]* 'x' [1-9][0-9]*);
-From: 'from';
+From: 'from'; // not a real keyword
 /**
  * Bytes types of fixed length.
  */

libsolidity/analysis/ContractLevelChecker.cpp

@@ -25,10 +25,10 @@
 #include <libsolidity/ast/AST.h>
 #include <libsolidity/ast/TypeProvider.h>
 #include <libsolidity/analysis/TypeChecker.h>
+#include <libsolutil/FunctionSelector.h>
 #include <liblangutil/ErrorReporter.h>
 #include <boost/range/adaptor/reversed.hpp>
 
-
 using namespace std;
 using namespace solidity;
 using namespace solidity::langutil;
@@ -433,6 +433,24 @@ void ContractLevelChecker::checkHashCollisions(ContractDefinition const& _contra
 			);
 		hashes.insert(hash);
 	}
+
+	map<uint32_t, SourceLocation> errorHashes;
+	for (ErrorDefinition const* error: _contract.interfaceErrors())
+	{
+		if (!error->functionType(true)->interfaceFunctionType())
+			// Will create an error later on.
+			continue;
+		uint32_t hash = selectorFromSignature32(error->functionType(true)->externalSignature());
+		if (errorHashes.count(hash))
+			m_errorReporter.typeError(
+				4883_error,
+				_contract.location(),
+				SecondarySourceLocation{}.append("This error has the same selector: ", errorHashes[hash]),
+				string("Error signature hash collision for ") + error->functionType(true)->externalSignature()
+			);
+		else
+			errorHashes[hash] = error->location();
+	}
 }
 
 void ContractLevelChecker::checkLibraryRequirements(ContractDefinition const& _contract)

libsolidity/analysis/DeclarationContainer.cpp

@@ -124,7 +124,7 @@ bool DeclarationContainer::registerDeclaration(
 		// 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.isEventParameter());
+		bool special = _declaration.scope() && (_declaration.isStructMember() || _declaration.isEnumValue() || _declaration.isEventOrErrorParameter());
 		if (m_enclosingContainer && !special)
 			m_homonymCandidates.emplace_back(*_name, _location ? _location : &_declaration.location());
 	}

libsolidity/analysis/DeclarationTypeChecker.cpp

@@ -368,7 +368,7 @@ void DeclarationTypeChecker::endVisit(VariableDeclaration const& _variable)
 	}
 
 	// Find correct data location.
-	if (_variable.isEventParameter())
+	if (_variable.isEventOrErrorParameter())
 	{
 		solAssert(varLoc == Location::Unspecified, "");
 		typeLoc = DataLocation::Memory;

libsolidity/analysis/DocStringAnalyser.cpp

@@ -157,6 +157,13 @@ bool DocStringAnalyser::visit(EventDefinition const& _event)
 	return true;
 }
 
+bool DocStringAnalyser::visit(ErrorDefinition const& _error)
+{
+	handleCallable(_error, _error, _error.annotation());
+
+	return true;
+}
+
 void DocStringAnalyser::handleCallable(
 	CallableDeclaration const& _callable,
 	StructurallyDocumented const& _node,

libsolidity/analysis/DocStringAnalyser.h

@@ -43,6 +43,7 @@ class DocStringAnalyser: private ASTConstVisitor
 	bool visit(VariableDeclaration const& _variable) override;
 	bool visit(ModifierDefinition const& _modifier) override;
 	bool visit(EventDefinition const& _event) override;
+	bool visit(ErrorDefinition const& _error) override;
 
 	CallableDeclaration const* resolveInheritDoc(
 		std::set<CallableDeclaration const*> const& _baseFunctions,

libsolidity/analysis/DocStringTagParser.cpp

@@ -85,6 +85,13 @@ bool DocStringTagParser::visit(EventDefinition const& _event)
 	return true;
 }
 
+bool DocStringTagParser::visit(ErrorDefinition const& _error)
+{
+	handleCallable(_error, _error, _error.annotation());
+
+	return true;
+}
+
 void DocStringTagParser::checkParameters(
 	CallableDeclaration const& _callable,
 	StructurallyDocumented const& _node,
@@ -127,11 +134,14 @@ void DocStringTagParser::handleCallable(
 )
 {
 	static set<string> const validEventTags = set<string>{"dev", "notice", "return", "param"};
+	static set<string> const validErrorTags = set<string>{"dev", "notice", "param"};
 	static set<string> const validModifierTags = set<string>{"dev", "notice", "param", "inheritdoc"};
 	static set<string> const validTags = set<string>{"dev", "notice", "return", "param", "inheritdoc"};
 
 	if (dynamic_cast<EventDefinition const*>(&_callable))
 		parseDocStrings(_node, _annotation, validEventTags, "events");
+	else if (dynamic_cast<ErrorDefinition const*>(&_callable))
+		parseDocStrings(_node, _annotation, validErrorTags, "errors");
 	else if (dynamic_cast<ModifierDefinition const*>(&_callable))
 		parseDocStrings(_node, _annotation, validModifierTags, "modifiers");
 	else

libsolidity/analysis/DocStringTagParser.h

@@ -44,6 +44,7 @@ class DocStringTagParser: private ASTConstVisitor
 	bool visit(VariableDeclaration const& _variable) override;
 	bool visit(ModifierDefinition const& _modifier) override;
 	bool visit(EventDefinition const& _event) override;
+	bool visit(ErrorDefinition const& _error) override;
 
 	void checkParameters(
 		CallableDeclaration const& _callable,

libsolidity/analysis/PostTypeChecker.cpp

@@ -23,6 +23,7 @@
 #include <liblangutil/ErrorReporter.h>
 #include <liblangutil/SemVerHandler.h>
 #include <libsolutil/Algorithms.h>
+#include <libsolutil/FunctionSelector.h>
 
 #include <boost/range/adaptor/map.hpp>
 #include <memory>
@@ -70,6 +71,11 @@ void PostTypeChecker::endVisit(VariableDeclaration const& _variable)
 	callEndVisit(_variable);
 }
 
+void PostTypeChecker::endVisit(ErrorDefinition const& _error)
+{
+	callEndVisit(_error);
+}
+
 bool PostTypeChecker::visit(EmitStatement const& _emit)
 {
 	return callVisit(_emit);
@@ -362,6 +368,33 @@ struct NoVariablesInInterfaceChecker: public PostTypeChecker::Checker
 	/// Flag indicating whether we are currently inside a StructDefinition.
 	int m_insideStruct = 0;
 };
+
+struct ReservedErrorSelector: public PostTypeChecker::Checker
+{
+	ReservedErrorSelector(ErrorReporter& _errorReporter):
+		Checker(_errorReporter)
+	{}
+
+	void endVisit(ErrorDefinition const& _error) override
+	{
+		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."
+			);
+		else
+		{
+			uint32_t selector = selectorFromSignature32(_error.functionType(true)->externalSignature());
+			if (selector == 0 || ~selector == 0)
+				m_errorReporter.syntaxError(
+					2855_error,
+					_error.location(),
+					"The selector " + to_string(selector) + " is reserved. Please rename the error to avoid the collision."
+				);
+		}
+	}
+};
 }
 
 PostTypeChecker::PostTypeChecker(langutil::ErrorReporter& _errorReporter): m_errorReporter(_errorReporter)
@@ -371,4 +404,5 @@ PostTypeChecker::PostTypeChecker(langutil::ErrorReporter& _errorReporter): m_err
 	m_checkers.push_back(make_shared<ModifierContextChecker>(_errorReporter));
 	m_checkers.push_back(make_shared<EventOutsideEmitChecker>(_errorReporter));
 	m_checkers.push_back(make_shared<NoVariablesInInterfaceChecker>(_errorReporter));
+	m_checkers.push_back(make_shared<ReservedErrorSelector>(_errorReporter));
 }

libsolidity/analysis/PostTypeChecker.h

@@ -40,6 +40,7 @@ namespace solidity::frontend
  *  - whether a modifier is in a function header
  *  - whether an event is used outside of an emit statement
  *  - whether a variable is declared in a interface
+ *  - whether an error uses a reserved signature
  *
  *  When adding a new checker, make sure a visitor that forwards calls that your
  *  checker uses exists in PostTypeChecker. Add missing ones.
@@ -77,6 +78,8 @@ class PostTypeChecker: private ASTConstVisitor
 	bool visit(VariableDeclaration const& _variable) override;
 	void endVisit(VariableDeclaration const& _variable) override;
 
+	void endVisit(ErrorDefinition const& _error) override;
+
 	bool visit(EmitStatement const& _emit) override;
 	void endVisit(EmitStatement const& _emit) override;
 

libsolidity/analysis/SyntaxChecker.cpp

@@ -29,6 +29,7 @@
 #include <liblangutil/SemVerHandler.h>
 
 #include <libsolutil/UTF8.h>
+#include <libsolutil/FunctionSelector.h>
 
 #include <boost/algorithm/string.hpp>
 

libsolidity/analysis/TypeChecker.cpp

@@ -42,6 +42,7 @@
 
 #include <range/v3/view/zip.hpp>
 #include <range/v3/view/drop_exactly.hpp>
+#include <range/v3/algorithm/count_if.hpp>
 
 #include <memory>
 #include <vector>
@@ -681,37 +682,26 @@ void TypeChecker::visitManually(
 bool TypeChecker::visit(EventDefinition const& _eventDef)
 {
 	solAssert(_eventDef.visibility() > Visibility::Internal, "");
-	unsigned numIndexed = 0;
-	for (ASTPointer<VariableDeclaration> const& var: _eventDef.parameters())
-	{
-		if (var->isIndexed())
-			numIndexed++;
-		if (type(*var)->containsNestedMapping())
-			m_errorReporter.typeError(
-				3448_error,
-				var->location(),
-				"Type containing a (nested) mapping is not allowed as event parameter type."
-			);
-		if (!type(*var)->interfaceType(false))
-			m_errorReporter.typeError(3417_error, var->location(), "Internal or recursive type is not allowed as event parameter type.");
-		if (
-			!useABICoderV2() &&
-			!typeSupportedByOldABIEncoder(*type(*var), false /* isLibrary */)
-		)
-			m_errorReporter.typeError(
-				3061_error,
-				var->location(),
-				"This type is only supported in ABI coder v2. "
-				"Use \"pragma abicoder v2;\" to enable the feature."
-			);
-	}
+	checkErrorAndEventParameters(_eventDef);
+
+	auto numIndexed = ranges::count_if(
+		_eventDef.parameters(),
+		[](ASTPointer<VariableDeclaration> const& var) { return var->isIndexed(); }
+	);
 	if (_eventDef.isAnonymous() && numIndexed > 4)
 		m_errorReporter.typeError(8598_error, _eventDef.location(), "More than 4 indexed arguments for anonymous event.");
 	else if (!_eventDef.isAnonymous() && numIndexed > 3)
 		m_errorReporter.typeError(7249_error, _eventDef.location(), "More than 3 indexed arguments for event.");
 	return true;
 }
 
+bool TypeChecker::visit(ErrorDefinition const& _errorDef)
+{
+	solAssert(_errorDef.visibility() > Visibility::Internal, "");
+	checkErrorAndEventParameters(_errorDef);
+	return true;
+}
+
 void TypeChecker::endVisit(FunctionTypeName const& _funType)
 {
 	FunctionType const& fun = dynamic_cast<FunctionType const&>(*_funType.annotation().type);
@@ -2248,7 +2238,8 @@ void TypeChecker::typeCheckFunctionGeneralChecks(
 		_functionType->kind() == FunctionType::Kind::DelegateCall ||
 		_functionType->kind() == FunctionType::Kind::External ||
 		_functionType->kind() == FunctionType::Kind::Creation ||
-		_functionType->kind() == FunctionType::Kind::Event;
+		_functionType->kind() == FunctionType::Kind::Event ||
+		_functionType->kind() == FunctionType::Kind::Error;
 
 	if (callRequiresABIEncoding && !useABICoderV2())
 	{
@@ -3392,6 +3383,32 @@ void TypeChecker::endVisit(UsingForDirective const& _usingFor)
 		);
 }
 
+void TypeChecker::checkErrorAndEventParameters(CallableDeclaration const& _callable)
+{
+	string kind = dynamic_cast<EventDefinition const*>(&_callable) ? "event" : "error";
+	for (ASTPointer<VariableDeclaration> const& var: _callable.parameters())
+	{
+		if (type(*var)->containsNestedMapping())
+			m_errorReporter.typeError(
+				3448_error,
+				var->location(),
+				"Type containing a (nested) mapping is not allowed as " + kind + " parameter type."
+			);
+		if (!type(*var)->interfaceType(false))
+			m_errorReporter.typeError(3417_error, var->location(), "Internal or recursive type is not allowed as " + kind + " parameter type.");
+		if (
+			!useABICoderV2() &&
+			!typeSupportedByOldABIEncoder(*type(*var), false /* isLibrary */)
+		)
+			m_errorReporter.typeError(
+				3061_error,
+				var->location(),
+				"This type is only supported in ABI coder v2. "
+				"Use \"pragma abicoder v2;\" to enable the feature."
+			);
+	}
+}
+
 bool TypeChecker::contractDependenciesAreCyclic(
 	ContractDefinition const& _contract,
 	std::set<ContractDefinition const*> const& _seenContracts

libsolidity/analysis/TypeChecker.h

@@ -119,6 +119,7 @@ class TypeChecker: private ASTConstVisitor
 	/// case this is a base constructor call.
 	void visitManually(ModifierInvocation const& _modifier, std::vector<ContractDefinition const*> const& _bases);
 	bool visit(EventDefinition const& _eventDef) override;
+	bool visit(ErrorDefinition const& _errorDef) override;
 	void endVisit(FunctionTypeName const& _funType) override;
 	bool visit(InlineAssembly const& _inlineAssembly) override;
 	bool visit(IfStatement const& _ifStatement) override;
@@ -147,6 +148,8 @@ class TypeChecker: private ASTConstVisitor
 	void endVisit(Literal const& _literal) override;
 	void endVisit(UsingForDirective const& _usingForDirective) override;
 
+	void checkErrorAndEventParameters(CallableDeclaration const& _callable);
+
 	bool contractDependenciesAreCyclic(
 		ContractDefinition const& _contract,
 		std::set<ContractDefinition const*> const& _seenContracts = std::set<ContractDefinition const*>()