Add Steve Johnson-style parser recovery rules:

SourceUnit = Error $
    Block = '{' Error '}'
    ContractDefinition = '{' Error '}'
    Statement = Error ';'

Co-Authored-By: chriseth <chris@ethereum.org>

Changelog.md

@@ -21,7 +21,7 @@ Compiler Features:
  * Yul Optimizer: Optimize representation of numbers.
  * Yul Optimizer: Do not inline recursive functions.
  * Yul Optimizer: Do not remove instructions that affect ``msize()`` if ``msize()`` is used.
-
+ * Commandline Interface: Experimental parser error recovery via the ``--error-recovery`` commandline switch.
 
 Bugfixes:
  * Code Generator: Explicitly turn uninitialized internal function pointers into invalid functions when loaded from storage.

liblangutil/CharStream.cpp

@@ -73,6 +73,13 @@ char CharStream::rollback(size_t _amount)
 	return get();
 }
 
+char CharStream::setPosition(size_t _location)
+{
+	solAssert(_location <= m_source.size(), "Attempting to set position past end of source.");
+	m_position = _location;
+	return get();
+}
+
 string CharStream::lineAtPosition(int _position) const
 {
 	// if _position points to \n, it returns the line before the \n
@@ -106,5 +113,3 @@ tuple<int, int> CharStream::translatePositionToLineColumn(int _position) const
 	}
 	return tuple<int, int>(lineNumber, searchPosition - lineStart);
 }
-
-

liblangutil/CharStream.h

@@ -76,7 +76,13 @@ public:
 
 	char get(size_t _charsForward = 0) const { return m_source[m_position + _charsForward]; }
 	char advanceAndGet(size_t _chars = 1);
+	/// Sets scanner position to @ _amount characters backwards in source text.
+	/// @returns The character of the current location after update is returned.
 	char rollback(size_t _amount);
+	/// Sets scanner position to @ _location if it refers a valid offset in m_source.
+	/// If not, nothing is done.
+	/// @returns The character of the current location after update is returned.
+	char setPosition(size_t _location);
 
 	void reset() { m_position = 0; }
 

liblangutil/ErrorReporter.cpp

@@ -86,6 +86,11 @@ void ErrorReporter::error(Error::Type _type, SourceLocation const& _location, Se
 	m_errorList.push_back(err);
 }
 
+bool ErrorReporter::hasExcessiveErrors() const
+{
+	return m_errorCount > c_maxErrorsAllowed;
+}
+
 bool ErrorReporter::checkForExcessiveErrors(Error::Type _type)
 {
 	if (_type == Error::Type::Warning)

liblangutil/ErrorReporter.h

@@ -118,6 +118,9 @@ public:
 		return m_errorCount > 0;
 	}
 
+	// @returns true if the maximum error count has been reached.
+	bool hasExcessiveErrors() const;
+
 private:
 	void error(
 		Error::Type _type,
@@ -149,4 +152,3 @@ private:
 };
 
 }
-

liblangutil/ParserBase.cpp

@@ -47,7 +47,7 @@ Token ParserBase::peekNextToken() const
 	return m_scanner->peekNextToken();
 }
 
-std::string ParserBase::currentLiteral() const
+string ParserBase::currentLiteral() const
 {
 	return m_scanner->currentLiteral();
 }
@@ -57,34 +57,83 @@ Token ParserBase::advance()
 	return m_scanner->next();
 }
 
+string ParserBase::tokenName(Token _token)
+{
+	if (_token == Token::Identifier)
+		return "identifier";
+	else if (_token == Token::EOS)
+		return "end of source";
+	else if (TokenTraits::isReservedKeyword(_token))
+		return "reserved keyword '" + TokenTraits::friendlyName(_token) + "'";
+	else if (TokenTraits::isElementaryTypeName(_token)) //for the sake of accuracy in reporting
+	{
+		ElementaryTypeNameToken elemTypeName = m_scanner->currentElementaryTypeNameToken();
+		return "'" + elemTypeName.toString() + "'";
+	}
+	else
+		return "'" + TokenTraits::friendlyName(_token) + "'";
+}
+
 void ParserBase::expectToken(Token _value, bool _advance)
 {
 	Token tok = m_scanner->currentToken();
 	if (tok != _value)
 	{
-		auto tokenName = [this](Token _token)
-		{
-			if (_token == Token::Identifier)
-				return string("identifier");
-			else if (_token == Token::EOS)
-				return string("end of source");
-			else if (TokenTraits::isReservedKeyword(_token))
-				return string("reserved keyword '") + TokenTraits::friendlyName(_token) + "'";
-			else if (TokenTraits::isElementaryTypeName(_token)) //for the sake of accuracy in reporting
-			{
-				ElementaryTypeNameToken elemTypeName = m_scanner->currentElementaryTypeNameToken();
-				return string("'") + elemTypeName.toString() + "'";
-			}
-			else
-				return string("'") + TokenTraits::friendlyName(_token) + "'";
-		};
-
-		fatalParserError(string("Expected ") + tokenName(_value) + string(" but got ") + tokenName(tok));
+		string const expectedToken = ParserBase::tokenName(_value);
+		if (m_parserErrorRecovery)
+			parserError("Expected " + expectedToken + " but got " + tokenName(tok));
+		else
+			fatalParserError("Expected " + expectedToken + " but got " + tokenName(tok));
+		// Do not advance so that recovery can sync or make use of the current token.
+		// This is especially useful if the expected token
+		// is the only one that is missing and is at the end of a construct.
+		// "{ ... ; }" is such an example.
+		//        ^
+		_advance = false;
 	}
 	if (_advance)
 		m_scanner->next();
 }
 
+void ParserBase::expectTokenOrConsumeUntil(Token _value, string const& _currentNodeName, bool _advance)
+{
+	Token tok = m_scanner->currentToken();
+	if (tok != _value)
+	{
+		int startPosition = position();
+		SourceLocation errorLoc = SourceLocation{startPosition, endPosition(), source()};
+		while (m_scanner->currentToken() != _value && m_scanner->currentToken() != Token::EOS)
+			m_scanner->next();
+
+		string const expectedToken = ParserBase::tokenName(_value);
+		string const msg = "In " + _currentNodeName + ", " + expectedToken + "is expected; got " +  ParserBase::tokenName(tok) +  "instead.";
+		if (m_scanner->currentToken() == Token::EOS)
+		{
+			// rollback to where the token started, and raise exception to be caught at a higher level.
+			m_scanner->setPosition(startPosition);
+			m_inParserRecovery = true;
+			fatalParserError(errorLoc, msg);
+		}
+		else
+		{
+			if (m_inParserRecovery)
+				parserWarning("Recovered in " + _currentNodeName + " at " + expectedToken + ".");
+			else
+				parserError(errorLoc, msg + "Recovered at next " + expectedToken);
+			m_inParserRecovery = false;
+		}
+	}
+	else if (m_inParserRecovery)
+	{
+		string expectedToken = ParserBase::tokenName(_value);
+		parserWarning("Recovered in " + _currentNodeName + " at " + expectedToken + ".");
+		m_inParserRecovery = false;
+	}
+
+	if (_advance)
+		m_scanner->next();
+}
+
 void ParserBase::increaseRecursionDepth()
 {
 	m_recursionDepth++;
@@ -98,12 +147,27 @@ void ParserBase::decreaseRecursionDepth()
 	m_recursionDepth--;
 }
 
+void ParserBase::parserWarning(string const& _description)
+{
+	m_errorReporter.warning(SourceLocation{position(), endPosition(), source()}, _description);
+}
+
+void ParserBase::parserError(SourceLocation const& _location, string const& _description)
+{
+	m_errorReporter.parserError(_location, _description);
+}
+
 void ParserBase::parserError(string const& _description)
 {
-	m_errorReporter.parserError(SourceLocation{position(), endPosition(), source()}, _description);
+	parserError(SourceLocation{position(), endPosition(), source()}, _description);
 }
 
 void ParserBase::fatalParserError(string const& _description)
 {
-	m_errorReporter.fatalParserError(SourceLocation{position(), endPosition(), source()}, _description);
+	fatalParserError(SourceLocation{position(), endPosition(), source()}, _description);
+}
+
+void ParserBase::fatalParserError(SourceLocation const& _location, string const& _description)
+{
+	m_errorReporter.fatalParserError(_location, _description);
 }

liblangutil/ParserBase.h

@@ -36,7 +36,14 @@ class Scanner;
 class ParserBase
 {
 public:
-	explicit ParserBase(ErrorReporter& errorReporter): m_errorReporter(errorReporter) {}
+	/// Set @a _parserErrorRecovery to true for additional error
+	/// recovery.  This is experimental and intended for use
+	/// by front-end tools that need partial AST information even
+	/// when errors occur.
+	explicit ParserBase(ErrorReporter& errorReporter, bool _parserErrorRecovery = false): m_errorReporter(errorReporter)
+	{
+		m_parserErrorRecovery = _parserErrorRecovery;
+	}
 
 	std::shared_ptr<CharStream> source() const { return m_scanner->charStream(); }
 
@@ -62,10 +69,17 @@ protected:
 
 	///@{
 	///@name Helper functions
-	/// If current token value is not _value, throw exception otherwise advance token.
+	/// If current token value is not @a _value, throw exception otherwise advance token
+	//  @a if _advance is true and error recovery is in effect.
 	void expectToken(Token _value, bool _advance = true);
+
+	/// Like expectToken but if there is an error ignores tokens until
+	/// the expected token or EOS is seen. If EOS is encountered, back up to the error point,
+	/// and throw an exception so that a higher grammar rule has an opportunity to recover.
+	void expectTokenOrConsumeUntil(Token _value, std::string const& _currentNodeName, bool _advance = true);
 	Token currentToken() const;
 	Token peekNextToken() const;
+	std::string tokenName(Token _token);
 	std::string currentLiteral() const;
 	Token advance();
 	///@}
@@ -77,16 +91,26 @@ protected:
 	/// Creates a @ref ParserError and annotates it with the current position and the
 	/// given @a _description.
 	void parserError(std::string const& _description);
+	void parserError(SourceLocation const& _location, std::string const& _description);
+
+	/// Creates a @ref ParserWarning and annotates it with the current position and the
+	/// given @a _description.
+	void parserWarning(std::string const& _description);
 
 	/// Creates a @ref ParserError and annotates it with the current position and the
 	/// given @a _description. Throws the FatalError.
 	void fatalParserError(std::string const& _description);
+	void fatalParserError(SourceLocation const& _location, std::string const& _description);
 
 	std::shared_ptr<Scanner> m_scanner;
 	/// The reference to the list of errors and warning to add errors/warnings during parsing
 	ErrorReporter& m_errorReporter;
 	/// Current recursion depth during parsing.
 	size_t m_recursionDepth = 0;
+	/// True if we are in parser error recovery. Usually this means we are scanning for
+	/// a synchronization token like ';', or '}'. We use this to reduce cascaded error messages.
+	bool m_inParserRecovery = false;
+	bool m_parserErrorRecovery = false;
 };
 
 }

liblangutil/Scanner.cpp

@@ -156,6 +156,13 @@ void Scanner::reset()
 	next();
 }
 
+void Scanner::setPosition(size_t _offset)
+{
+	m_char = m_source->setPosition(_offset);
+	scanToken();
+	next();
+}
+
 void Scanner::supportPeriodInIdentifier(bool _value)
 {
 	m_supportPeriodInIdentifier = _value;

liblangutil/Scanner.h

@@ -110,6 +110,9 @@ public:
 	/// @returns the next token and advances input
 	Token next();
 
+	/// Set scanner to a specific offset. This is used in error recovery.
+	void setPosition(size_t _offset);
+
 	///@{
 	///@name Information about the current token
 

libsolidity/interface/CompilerStack.cpp

@@ -217,7 +217,7 @@ bool CompilerStack::parse()
 		string const& path = sourcesToParse[i];
 		Source& source = m_sources[path];
 		source.scanner->reset();
-		source.ast = Parser(m_errorReporter, m_evmVersion).parse(source.scanner);
+		source.ast = Parser(m_errorReporter, m_evmVersion, m_parserErrorRecovery).parse(source.scanner);
 		if (!source.ast)
 			solAssert(!Error::containsOnlyWarnings(m_errorReporter.errors()), "Parser returned null but did not report error.");
 		else

libsolidity/interface/CompilerStack.h

@@ -132,6 +132,14 @@ public:
 	/// Must be set before parsing.
 	void setOptimiserSettings(OptimiserSettings _settings);
 
+	/// Set whether or not parser error is desired.
+	/// When called without an argument it will revert to the default.
+	/// Must be set before parsing.
+	void setParserErrorRecovery(bool _wantErrorRecovery = false)
+	{
+		m_parserErrorRecovery = _wantErrorRecovery;
+	}
+
 	/// Set the EVM version used before running compile.
 	/// When called without an argument it will revert to the default version.
 	/// Must be set before parsing.
@@ -386,6 +394,7 @@ private:
 	langutil::ErrorList m_errorList;
 	langutil::ErrorReporter m_errorReporter;
 	bool m_metadataLiteralSources = false;
+	bool m_parserErrorRecovery = false;
 	State m_stackState = Empty;
 	bool m_release = VersionIsRelease;
 };

libsolidity/parsing/Parser.cpp

@@ -258,57 +258,75 @@ ASTPointer<ContractDefinition> Parser::parseContractDefinition()
 {
 	RecursionGuard recursionGuard(*this);
 	ASTNodeFactory nodeFactory(*this);
+	ASTPointer<ASTString> name =  nullptr;
 	ASTPointer<ASTString> docString;
-	if (m_scanner->currentCommentLiteral() != "")
-		docString = make_shared<ASTString>(m_scanner->currentCommentLiteral());
-	ContractDefinition::ContractKind contractKind = parseContractKind();
-	ASTPointer<ASTString> name = expectIdentifierToken();
 	vector<ASTPointer<InheritanceSpecifier>> baseContracts;
-	if (m_scanner->currentToken() == Token::Is)
-		do
-		{
-			m_scanner->next();
-			baseContracts.push_back(parseInheritanceSpecifier());
-		}
-		while (m_scanner->currentToken() == Token::Comma);
 	vector<ASTPointer<ASTNode>> subNodes;
-	expectToken(Token::LBrace);
-	while (true)
+	ContractDefinition::ContractKind contractKind = ContractDefinition::ContractKind::Contract;
+	try
 	{
-		Token currentTokenValue = m_scanner->currentToken();
-		if (currentTokenValue == Token::RBrace)
-			break;
-		else if (currentTokenValue == Token::Function || currentTokenValue == Token::Constructor)
-			// This can be a function or a state variable of function type (especially
-			// complicated to distinguish fallback function from function type state variable)
-			subNodes.push_back(parseFunctionDefinitionOrFunctionTypeStateVariable());
-		else if (currentTokenValue == Token::Struct)
-			subNodes.push_back(parseStructDefinition());
-		else if (currentTokenValue == Token::Enum)
-			subNodes.push_back(parseEnumDefinition());
-		else if (
-			currentTokenValue == Token::Identifier ||
-			currentTokenValue == Token::Mapping ||
-			TokenTraits::isElementaryTypeName(currentTokenValue)
-		)
+		if (m_scanner->currentCommentLiteral() != "")
+			docString = make_shared<ASTString>(m_scanner->currentCommentLiteral());
+		contractKind = parseContractKind();
+		name = expectIdentifierToken();
+		if (m_scanner->currentToken() == Token::Is)
+			do
+			{
+				m_scanner->next();
+				baseContracts.push_back(parseInheritanceSpecifier());
+			}
+			while (m_scanner->currentToken() == Token::Comma);
+		expectToken(Token::LBrace);
+		while (true)
 		{
-			VarDeclParserOptions options;
-			options.isStateVariable = true;
-			options.allowInitialValue = true;
-			subNodes.push_back(parseVariableDeclaration(options));
-			expectToken(Token::Semicolon);
+			Token currentTokenValue = m_scanner->currentToken();
+			if (currentTokenValue == Token::RBrace)
+				break;
+			else if (currentTokenValue == Token::Function || currentTokenValue == Token::Constructor)
+				// This can be a function or a state variable of function type (especially
+				// complicated to distinguish fallback function from function type state variable)
+				subNodes.push_back(parseFunctionDefinitionOrFunctionTypeStateVariable());
+			else if (currentTokenValue == Token::Struct)
+				subNodes.push_back(parseStructDefinition());
+			else if (currentTokenValue == Token::Enum)
+				subNodes.push_back(parseEnumDefinition());
+			else if (
+					currentTokenValue == Token::Identifier ||
+					currentTokenValue == Token::Mapping ||
+					TokenTraits::isElementaryTypeName(currentTokenValue)
+					)
+			{
+				VarDeclParserOptions options;
+				options.isStateVariable = true;
+				options.allowInitialValue = true;
+				subNodes.push_back(parseVariableDeclaration(options));
+				expectToken(Token::Semicolon);
+			}
+			else if (currentTokenValue == Token::Modifier)
+				subNodes.push_back(parseModifierDefinition());
+			else if (currentTokenValue == Token::Event)
+				subNodes.push_back(parseEventDefinition());
+			else if (currentTokenValue == Token::Using)
+				subNodes.push_back(parseUsingDirective());
+			else
+				fatalParserError(string("Function, variable, struct or modifier declaration expected."));
 		}
-		else if (currentTokenValue == Token::Modifier)
-			subNodes.push_back(parseModifierDefinition());
-		else if (currentTokenValue == Token::Event)
-			subNodes.push_back(parseEventDefinition());
-		else if (currentTokenValue == Token::Using)
-			subNodes.push_back(parseUsingDirective());
-		else
-			fatalParserError(string("Function, variable, struct or modifier declaration expected."));
+	}
+	catch (FatalError const&)
+	{
+		if (
+			!m_errorReporter.hasErrors() ||
+			!m_parserErrorRecovery ||
+			m_errorReporter.hasExcessiveErrors()
+		)
+			BOOST_THROW_EXCEPTION(FatalError()); /* Don't try to recover here. */
+		m_inParserRecovery = true;
 	}
 	nodeFactory.markEndPosition();
-	expectToken(Token::RBrace);
+	if (m_inParserRecovery)
+		expectTokenOrConsumeUntil(Token::RBrace, "ContractDefinition");
+	else
+		expectToken(Token::RBrace);
 	return nodeFactory.createNode<ContractDefinition>(
 		name,
 		docString,
@@ -959,10 +977,26 @@ ASTPointer<Block> Parser::parseBlock(ASTPointer<ASTString> const& _docString)
 	ASTNodeFactory nodeFactory(*this);
 	expectToken(Token::LBrace);
 	vector<ASTPointer<Statement>> statements;
-	while (m_scanner->currentToken() != Token::RBrace)
-		statements.push_back(parseStatement());
-	nodeFactory.markEndPosition();
-	expectToken(Token::RBrace);
+	try
+	{
+		while (m_scanner->currentToken() != Token::RBrace)
+			statements.push_back(parseStatement());
+		nodeFactory.markEndPosition();
+	}
+	catch (FatalError const&)
+	{
+		if (
+			!m_errorReporter.hasErrors() ||
+			!m_parserErrorRecovery ||
+			m_errorReporter.hasExcessiveErrors()
+		)
+			BOOST_THROW_EXCEPTION(FatalError()); /* Don't try to recover here. */
+		m_inParserRecovery = true;
+	}
+	if (m_parserErrorRecovery)
+		expectTokenOrConsumeUntil(Token::RBrace, "Block");
+	else
+		expectToken(Token::RBrace);
 	return nodeFactory.createNode<Block>(_docString, statements);
 }
 
@@ -970,67 +1004,83 @@ ASTPointer<Statement> Parser::parseStatement()
 {
 	RecursionGuard recursionGuard(*this);
 	ASTPointer<ASTString> docString;
-	if (m_scanner->currentCommentLiteral() != "")
-		docString = make_shared<ASTString>(m_scanner->currentCommentLiteral());
 	ASTPointer<Statement> statement;
-	switch (m_scanner->currentToken())
+	try
 	{
-	case Token::If:
-		return parseIfStatement(docString);
-	case Token::While:
-		return parseWhileStatement(docString);
-	case Token::Do:
-		return parseDoWhileStatement(docString);
-	case Token::For:
-		return parseForStatement(docString);
-	case Token::LBrace:
-		return parseBlock(docString);
-		// starting from here, all statements must be terminated by a semicolon
-	case Token::Continue:
-		statement = ASTNodeFactory(*this).createNode<Continue>(docString);
-		m_scanner->next();
-		break;
-	case Token::Break:
-		statement = ASTNodeFactory(*this).createNode<Break>(docString);
-		m_scanner->next();
-		break;
-	case Token::Return:
-	{
-		ASTNodeFactory nodeFactory(*this);
-		ASTPointer<Expression> expression;
-		if (m_scanner->next() != Token::Semicolon)
+		if (m_scanner->currentCommentLiteral() != "")
+			docString = make_shared<ASTString>(m_scanner->currentCommentLiteral());
+		switch (m_scanner->currentToken())
 		{
-			expression = parseExpression();
-			nodeFactory.setEndPositionFromNode(expression);
-		}
-		statement = nodeFactory.createNode<Return>(docString, expression);
-		break;
-	}
-	case Token::Throw:
-	{
-		statement = ASTNodeFactory(*this).createNode<Throw>(docString);
-		m_scanner->next();
-		break;
-	}
-	case Token::Assembly:
-		return parseInlineAssembly(docString);
-	case Token::Emit:
-		statement = parseEmitStatement(docString);
-		break;
-	case Token::Identifier:
-		if (m_insideModifier && m_scanner->currentLiteral() == "_")
-		{
-			statement = ASTNodeFactory(*this).createNode<PlaceholderStatement>(docString);
+		case Token::If:
+			return parseIfStatement(docString);
+		case Token::While:
+			return parseWhileStatement(docString);
+		case Token::Do:
+			return parseDoWhileStatement(docString);
+		case Token::For:
+			return parseForStatement(docString);
+		case Token::LBrace:
+			return parseBlock(docString);
+			// starting from here, all statements must be terminated by a semicolon
+		case Token::Continue:
+			statement = ASTNodeFactory(*this).createNode<Continue>(docString);
 			m_scanner->next();
-		}
-		else
+			break;
+		case Token::Break:
+			statement = ASTNodeFactory(*this).createNode<Break>(docString);
+			m_scanner->next();
+			break;
+		case Token::Return:
+		{
+			ASTNodeFactory nodeFactory(*this);
+			ASTPointer<Expression> expression;
+			if (m_scanner->next() != Token::Semicolon)
+				{
+					expression = parseExpression();
+					nodeFactory.setEndPositionFromNode(expression);
+				}
+			statement = nodeFactory.createNode<Return>(docString, expression);
+				break;
+			}
+		case Token::Throw:
+			{
+				statement = ASTNodeFactory(*this).createNode<Throw>(docString);
+				m_scanner->next();
+				break;
+			}
+		case Token::Assembly:
+			return parseInlineAssembly(docString);
+		case Token::Emit:
+			statement = parseEmitStatement(docString);
+			break;
+		case Token::Identifier:
+			if (m_insideModifier && m_scanner->currentLiteral() == "_")
+				{
+					statement = ASTNodeFactory(*this).createNode<PlaceholderStatement>(docString);
+					m_scanner->next();
+				}
+			else
+				statement = parseSimpleStatement(docString);
+			break;
+		default:
 			statement = parseSimpleStatement(docString);
-		break;
-	default:
-		statement = parseSimpleStatement(docString);
-		break;
+			break;
+		}
 	}
-	expectToken(Token::Semicolon);
+	catch (FatalError const&)
+	{
+		if (
+			!m_errorReporter.hasErrors() ||
+			!m_parserErrorRecovery ||
+			m_errorReporter.hasExcessiveErrors()
+		)
+			BOOST_THROW_EXCEPTION(FatalError()); /* Don't try to recover here. */
+		m_inParserRecovery = true;
+	}
+	if (m_inParserRecovery)
+		expectTokenOrConsumeUntil(Token::Semicolon, "Statement");
+	else
+		expectToken(Token::Semicolon);
 	return statement;
 }
 

libsolidity/parsing/Parser.h

@@ -41,9 +41,10 @@ class Parser: public langutil::ParserBase
 public:
 	explicit Parser(
 		langutil::ErrorReporter& _errorReporter,
-		langutil::EVMVersion _evmVersion
+		langutil::EVMVersion _evmVersion,
+		bool _errorRecovery = false
 	):
-		ParserBase(_errorReporter),
+		ParserBase(_errorReporter, _errorRecovery),
 		m_evmVersion(_evmVersion)
 	{}
 

solc/CommandLineInterface.cpp

@@ -112,6 +112,7 @@ static string const g_strBinaryRuntime = "bin-runtime";
 static string const g_strCombinedJson = "combined-json";
 static string const g_strCompactJSON = "compact-format";
 static string const g_strContracts = "contracts";
+static string const g_strErrorRecovery = "error-recovery";
 static string const g_strEVM = "evm";
 static string const g_strEVM15 = "evm15";
 static string const g_strEVMVersion = "evm-version";
@@ -163,6 +164,7 @@ static string const g_argBinary = g_strBinary;
 static string const g_argBinaryRuntime = g_strBinaryRuntime;
 static string const g_argCombinedJson = g_strCombinedJson;
 static string const g_argCompactJSON = g_strCompactJSON;
+static string const g_argErrorRecovery = g_strErrorRecovery;
 static string const g_argGas = g_strGas;
 static string const g_argHelp = g_strHelp;
 static string const g_argInputFile = g_strInputFile;
@@ -689,6 +691,7 @@ Allowed options)",
 		(g_argColor.c_str(), "Force colored output.")
 		(g_argNoColor.c_str(), "Explicitly disable colored output, disabling terminal auto-detection.")
 		(g_argNewReporter.c_str(), "Enables new diagnostics reporter.")
+		(g_argErrorRecovery.c_str(), "Enables additional parser error recovery.")
 		(g_argIgnoreMissingFiles.c_str(), "Ignore missing files.");
 	po::options_description outputComponents("Output Components");
 	outputComponents.add_options()
@@ -923,6 +926,8 @@ bool CommandLineInterface::processInput()
 		m_compiler->setSources(m_sourceCodes);
 		if (m_args.count(g_argLibraries))
 			m_compiler->setLibraries(m_libraries);
+		if (m_args.count(g_argErrorRecovery))
+			m_compiler->setParserErrorRecovery(true);
 		m_compiler->setEVMVersion(m_evmVersion);
 		// TODO: Perhaps we should not compile unless requested
 

test/InteractiveTests.h

@@ -56,6 +56,7 @@ Testsuite const g_interactiveTestsuites[] = {
 	{"Yul Interpreter",     "libyul",      "yulInterpreterTests", false, false, &yul::test::YulInterpreterTest::create},
 	{"Yul Object Compiler", "libyul",      "objectCompiler",      false, false, &yul::test::ObjectCompilerTest::create},
 	{"Syntax",              "libsolidity", "syntaxTests",         false, false, &SyntaxTest::create},
+	{"ErrorRecovery",       "libsolidity", "errorRecoveryTests",  false, false, &SyntaxTest::createErrorRecovery},
 	{"Semantic",            "libsolidity", "semanticTests",       false, true,  &SemanticTest::create},
 	{"JSON AST",            "libsolidity", "ASTJSON",             false, false, &ASTJSONTest::create},
 	{"SMT Checker",         "libsolidity", "smtCheckerTests",     true,  false, &SyntaxTest::create},
@@ -66,4 +67,3 @@ Testsuite const g_interactiveTestsuites[] = {
 }
 }
 }
-

test/liblangutil/CharStream.cpp

@@ -0,0 +1,53 @@
+/*
+	This file is part of solidity.
+
+	solidity is free software: you can redistribute it and/or modify
+	it under the terms of the GNU General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	solidity is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with solidity.  If not, see <http://www.gnu.org/licenses/>.
+*/
+/**
+ * @author Rocky Bernstein <rocky.bernstein@consensys.net>
+ * @date 2019
+ * Unit tests for the CharStream class.
+ */
+
+#include <liblangutil/CharStream.h>
+#include <liblangutil/Exceptions.h>
+
+#include <test/Options.h>
+
+namespace langutil
+{
+namespace test
+{
+
+BOOST_AUTO_TEST_SUITE(CharStreamtest)
+
+BOOST_AUTO_TEST_CASE(test_fail)
+{
+	auto const source = std::make_shared<CharStream>("now is the time for testing", "source");
+
+	BOOST_CHECK('n' == source->get());
+	BOOST_CHECK('n' == source->get());
+	BOOST_CHECK('o' == source->advanceAndGet());
+	BOOST_CHECK('n' == source->rollback(1));
+	BOOST_CHECK('w' == source->setPosition(2));
+	BOOST_REQUIRE_THROW(
+		source->setPosition(200),
+		::langutil::InternalCompilerError
+	);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
+
+}
+} // end namespaces

test/libsolidity/AnalysisFramework.cpp

@@ -44,12 +44,15 @@ AnalysisFramework::parseAnalyseAndReturnError(
 	string const& _source,
 	bool _reportWarnings,
 	bool _insertVersionPragma,
-	bool _allowMultipleErrors
+	bool _allowMultipleErrors,
+	bool _allowRecoveryErrors
 )
 {
 	compiler().reset();
 	compiler().setSources({{"", _insertVersionPragma ? "pragma solidity >=0.0;\n" + _source : _source}});
 	compiler().setEVMVersion(dev::test::Options::get().evmVersion());
+	compiler().setParserErrorRecovery(_allowRecoveryErrors);
+	_allowMultipleErrors = _allowMultipleErrors || _allowRecoveryErrors;
 	if (!compiler().parse())
 	{
 		BOOST_FAIL("Parsing contract failed in analysis test suite:" + formatErrors());

test/libsolidity/AnalysisFramework.h

@@ -50,7 +50,8 @@ protected:
 		std::string const& _source,
 		bool _reportWarnings = false,
 		bool _insertVersionPragma = true,
-		bool _allowMultipleErrors = false
+		bool _allowMultipleErrors = false,
+		bool _allowRecoveryErrors = false
 	);
 	virtual ~AnalysisFramework() = default;
 

test/libsolidity/SMTChecker.cpp

@@ -42,14 +42,16 @@ protected:
 		std::string const& _source,
 		bool _reportWarnings = false,
 		bool _insertVersionPragma = true,
-		bool _allowMultipleErrors = false
+		bool _allowMultipleErrors = false,
+		bool _allowRecoveryErrors = false
 	)
 	{
 		return AnalysisFramework::parseAnalyseAndReturnError(
 			"pragma experimental SMTChecker;\n" + _source,
 			_reportWarnings,
 			_insertVersionPragma,
-			_allowMultipleErrors
+			_allowMultipleErrors,
+			_allowRecoveryErrors
 		);
 	}
 };

test/libsolidity/SyntaxTest.cpp

@@ -52,7 +52,7 @@ int parseUnsignedInteger(string::iterator& _it, string::iterator _end)
 
 }
 
-SyntaxTest::SyntaxTest(string const& _filename, langutil::EVMVersion _evmVersion): m_evmVersion(_evmVersion)
+SyntaxTest::SyntaxTest(string const& _filename, langutil::EVMVersion _evmVersion, bool _errorRecovery): m_evmVersion(_evmVersion)
 {
 	ifstream file(_filename);
 	if (!file)
@@ -67,6 +67,7 @@ SyntaxTest::SyntaxTest(string const& _filename, langutil::EVMVersion _evmVersion
 		m_settings.erase("optimize-yul");
 	}
 	m_expectations = parseExpectations(file);
+	m_errorRecovery = _errorRecovery;
 }
 
 TestCase::TestResult SyntaxTest::run(ostream& _stream, string const& _linePrefix, bool _formatted)
@@ -75,6 +76,7 @@ TestCase::TestResult SyntaxTest::run(ostream& _stream, string const& _linePrefix
 	compiler().reset();
 	compiler().setSources({{"", versionPragma + m_source}});
 	compiler().setEVMVersion(m_evmVersion);
+	compiler().setParserErrorRecovery(m_errorRecovery);
 	compiler().setOptimiserSettings(
 		m_optimiseYul ?
 		OptimiserSettings::full() :

test/libsolidity/SyntaxTest.h

@@ -54,8 +54,14 @@ class SyntaxTest: AnalysisFramework, public EVMVersionRestrictedTestCase
 {
 public:
 	static std::unique_ptr<TestCase> create(Config const& _config)
-	{ return std::make_unique<SyntaxTest>(_config.filename, _config.evmVersion); }
-	SyntaxTest(std::string const& _filename, langutil::EVMVersion _evmVersion);
+	{
+		return std::make_unique<SyntaxTest>(_config.filename, _config.evmVersion, false);
+	}
+	static std::unique_ptr<TestCase> createErrorRecovery(Config const& _config)
+	{
+		return std::make_unique<SyntaxTest>(_config.filename, _config.evmVersion, true);
+	}
+	SyntaxTest(std::string const& _filename, langutil::EVMVersion _evmVersion, bool _errorRecovery = false);
 
 	TestResult run(std::ostream& _stream, std::string const& _linePrefix = "", bool _formatted = false) override;
 
@@ -84,6 +90,7 @@ protected:
 	std::vector<SyntaxTestError> m_errorList;
 	bool m_optimiseYul = false;
 	langutil::EVMVersion const m_evmVersion;
+	bool m_errorRecovery = false;
 };
 
 }

test/libsolidity/errorRecoveryTests/constructor_recovers.sol

@@ -0,0 +1,20 @@
+pragma solidity >=0.0.0;
+
+contract Error1 {
+  constructor() public {
+    balances[tx.origin] = ; // missing RHS.
+  }
+
+  // Without error recovery we stop due to the above error.
+  // Error recovery however recovers at the above ';'
+  // There should be an AST for the above, albeit with error
+  // nodes.
+
+  // This function parses properly and should give AST info.
+  function five() public view returns(uint) {
+    return 5;
+  }
+}
+// ----
+// ParserError: (95-96): Expected primary expression.
+// Warning: (95-96): Recovered in Statement at ';'.

test/libsolidity/errorRecoveryTests/contract_recovery.sol

@@ -0,0 +1,7 @@
+contract Errort6 {
+  using foo for  ; // missing type name
+}
+
+// ----
+// ParserError: (36-37): Expected type name
+// Warning: (59-60): Recovered in ContractDefinition at '}'.

test/libsolidity/errorRecoveryTests/do_not_delete_at_error.sol

@@ -0,0 +1,13 @@
+pragma solidity >=0.0.0;
+
+// Example to show why deleting the token at the
+// is bad when error recovery is in effect. Here, ")" is missing
+// and there is a ";" instead. That causes us to
+// not be able to synchronize to ';'. Advance again and
+// '}' is deleted and then we can't synchronize the contract.
+// There should be an an AST created this contract (with errors).
+contract Error2 {
+	mapping (address => uint balances; // missing ) before "balances"
+}
+// ----
+// ParserError: (417-425): Expected ')' but got identifier

test/libsolidity/errorRecoveryTests/error_to_eos.sol

@@ -0,0 +1,23 @@
+// Example which where scanning hits EOS, so we reset.
+// Here we recover in the contractDefinition.
+// There should be an an AST created this contract (with errors).
+contract Error2 {
+  mapping (address => uint balances) // missing ;
+}
+
+// There is no error in this contract
+contract SendCoin {
+  function sendCoin(address receiver, uint amount) public returns(bool sufficient) {
+    if (balances[msg.sender] < amount) return false;
+    balances[msg.sender] -= amount;
+    balances[receiver] += amount;
+    emit Transfer(msg.sender, receiver, amount);
+    return true;
+  }
+}
+
+// ----
+// ParserError: (212-220): Expected ')' but got identifier
+// ParserError: (220-221): Expected ';' but got ')'
+// ParserError: (220-221): Function, variable, struct or modifier declaration expected.
+// Warning: (235-236): Recovered in ContractDefinition at '}'.

test/libsolidity/errorRecoveryTests/missing_rhs.sol

@@ -0,0 +1,11 @@
+pragma solidity >=0.0.0;
+
+contract Error3 {
+	constructor() public {
+	    balances[tx.origin] = ; // missing RHS.
+	}
+
+}
+// ----
+// ParserError: (95-96): Expected primary expression.
+// Warning: (95-96): Recovered in Statement at ';'.

test/libsolidity/errorRecoveryTests/multiple_errors.sol

@@ -0,0 +1,29 @@
+// An example with multiple errors.
+// Most are caught by inserting an expected token.
+// However some us S C Johnson recovery to
+// skip over tokens.
+
+pragma solidity >=0.0.0;
+
+contract Error4 {
+  constructor() public {
+    balances[tx.origin] = 1 2; // missing operator
+  }
+
+  function sendCoin(address receiver, uint amount) public returns(bool sufficient) {
+    if (balances[msg.sender] < amount) return false;
+    balances[msg.sender] -= amount   // Missing ";"
+    balances[receiver] += amount   // Another missing ";"
+    emit Transfer(msg.sender  // truncated line
+    return true;
+  }
+
+
+}
+// ----
+// ParserError: (249-250): Expected ';' but got 'Number'
+// ParserError: (471-479): Expected ';' but got identifier
+// ParserError: (529-533): Expected ';' but got 'emit'
+// ParserError: (577-583): Expected ',' but got 'return'
+// ParserError: (577-583): Expected primary expression.
+// Warning: (588-589): Recovered in Statement at ';'.