6 files changed, 115 insertions, 6 deletions

diff --git a/libsolidity/analysis/TypeChecker.cpp b/libsolidity/analysis/TypeChecker.cpp
index 8b609a31..43e894e5 100644
--- a/libsolidity/analysis/TypeChecker.cpp
+++ b/libsolidity/analysis/TypeChecker.cpp
@@ -525,6 +525,75 @@ void TypeChecker::checkDoubleStorageAssignment(Assignment const& _assignment)
 		);
 }
 
+TypePointer TypeChecker::typeCheckABIDecodeAndRetrieveReturnType(FunctionCall const& _functionCall, bool _abiEncoderV2)
+{
+	vector<ASTPointer<Expression const>> arguments = _functionCall.arguments();
+	if (arguments.size() != 2)
+		m_errorReporter.typeError(
+			_functionCall.location(),
+			"This function takes two arguments, but " +
+			toString(arguments.size()) +
+			" were provided."
+		);
+	if (arguments.size() >= 1 && !type(*arguments.front())->isImplicitlyConvertibleTo(ArrayType(DataLocation::Memory)))
+		m_errorReporter.typeError(
+			arguments.front()->location(),
+			"Invalid type for argument in function call. "
+			"Invalid implicit conversion from " +
+			type(*arguments.front())->toString() +
+			" to bytes memory requested."
+		);
+
+	TypePointer returnType = make_shared<TupleType>();
+
+	if (arguments.size() < 2)
+		return returnType;
+
+	// The following is a rather syntactic restriction, but we check it here anyway:
+	// The second argument has to be a tuple expression containing type names.
+	TupleExpression const* tupleExpression = dynamic_cast<TupleExpression const*>(arguments[1].get());
+	if (!tupleExpression)
+	{
+		m_errorReporter.typeError(
+			arguments[1]->location(),
+			"The second argument to \"abi.decode\" has to be a tuple of types."
+		);
+		return returnType;
+	}
+
+	vector<TypePointer> components;
+	for (auto const& typeArgument: tupleExpression->components())
+	{
+		solAssert(typeArgument, "");
+		if (TypeType const* argTypeType = dynamic_cast<TypeType const*>(type(*typeArgument).get()))
+		{
+			TypePointer actualType = argTypeType->actualType();
+			solAssert(actualType, "");
+			// We force memory because the parser currently cannot handle
+			// data locations. Furthermore, storage can be a little dangerous and
+			// calldata is not really implemented anyway.
+			actualType = ReferenceType::copyForLocationIfReference(DataLocation::Memory, actualType);
+			solAssert(
+				!actualType->dataStoredIn(DataLocation::CallData) &&
+				!actualType->dataStoredIn(DataLocation::Storage),
+				""
+			);
+			if (!actualType->fullEncodingType(false, _abiEncoderV2, false))
+				m_errorReporter.typeError(
+					typeArgument->location(),
+					"Decoding type " + actualType->toString(false)  + " not supported."
+				);
+			components.push_back(actualType);
+		}
+		else
+		{
+			m_errorReporter.typeError(typeArgument->location(), "Argument has to be a type name.");
+			components.push_back(make_shared<TupleType>());
+		}
+	}
+	return make_shared<TupleType>(components);
+}
+
 void TypeChecker::endVisit(InheritanceSpecifier const& _inheritance)
 {
 	auto base = dynamic_cast<ContractDefinition const*>(&dereference(_inheritance.name()));
@@ -1727,7 +1796,11 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 		}
 	}
 
-	if (functionType->takesArbitraryParameters() && arguments.size() < parameterTypes.size())
+	bool const abiEncoderV2 = m_scope->sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::ABIEncoderV2);
+
+	if (functionType->kind() == FunctionType::Kind::ABIDecode)
+		_functionCall.annotation().type = typeCheckABIDecodeAndRetrieveReturnType(_functionCall, abiEncoderV2);
+	else if (functionType->takesArbitraryParameters() && arguments.size() < parameterTypes.size())
 	{
 		solAssert(_functionCall.annotation().kind == FunctionCallKind::FunctionCall, "");
 		m_errorReporter.typeError(
@@ -1782,8 +1855,6 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 	}
 	else if (isPositionalCall)
 	{
-		bool const abiEncodeV2 = m_scope->sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::ABIEncoderV2);
-
 		for (size_t i = 0; i < arguments.size(); ++i)
 		{
 			auto const& argType = type(*arguments[i]);
@@ -1796,7 +1867,7 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 						m_errorReporter.typeError(arguments[i]->location(), "Invalid rational number (too large or division by zero).");
 						errored = true;
 					}
-				if (!errored && !argType->fullEncodingType(false, abiEncodeV2, !functionType->padArguments()))
+				if (!errored && !argType->fullEncodingType(false, abiEncoderV2, !functionType->padArguments()))
 					m_errorReporter.typeError(arguments[i]->location(), "This type cannot be encoded.");
 			}
 			else if (!type(*arguments[i])->isImplicitlyConvertibleTo(*parameterTypes[i]))
diff --git a/libsolidity/analysis/TypeChecker.h b/libsolidity/analysis/TypeChecker.h
index ed316f9c..4be0d1e4 100644
--- a/libsolidity/analysis/TypeChecker.h
+++ b/libsolidity/analysis/TypeChecker.h
@@ -91,6 +91,11 @@ private:
 	// and reports an error, if not.
 	void checkExpressionAssignment(Type const& _type, Expression const& _expression);
 
+	/// Performs type checks for ``abi.decode(bytes memory, (...))`` and returns the
+	/// return type (which is basically the second argument) if successful. It returns
+	/// the empty tuple type or error.
+	TypePointer typeCheckABIDecodeAndRetrieveReturnType(FunctionCall const& _functionCall, bool _abiEncoderV2);
+
 	virtual void endVisit(InheritanceSpecifier const& _inheritance) override;
 	virtual void endVisit(UsingForDirective const& _usingFor) override;
 	virtual bool visit(StructDefinition const& _struct) override;
diff --git a/libsolidity/analysis/ViewPureChecker.cpp b/libsolidity/analysis/ViewPureChecker.cpp
index d936ada0..e92ad2fa 100644
--- a/libsolidity/analysis/ViewPureChecker.cpp
+++ b/libsolidity/analysis/ViewPureChecker.cpp
@@ -295,7 +295,7 @@ void ViewPureChecker::endVisit(MemberAccess const& _memberAccess)
 	{
 		// we can ignore the kind of magic and only look at the name of the member
 		set<string> static const pureMembers{
-			"encode", "encodePacked", "encodeWithSelector", "encodeWithSignature", "data", "sig", "blockhash"
+			"encode", "encodePacked", "encodeWithSelector", "encodeWithSignature", "decode", "data", "sig", "blockhash"
 		};
 		if (!pureMembers.count(member))
 			mutability = StateMutability::View;
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index 68c201a8..c9dca126 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -2553,6 +2553,7 @@ string FunctionType::richIdentifier() const
 	case Kind::ABIEncodePacked: id += "abiencodepacked"; break;
 	case Kind::ABIEncodeWithSelector: id += "abiencodewithselector"; break;
 	case Kind::ABIEncodeWithSignature: id += "abiencodewithsignature"; break;
+	case Kind::ABIDecode: id += "abidecode"; break;
 	default: solAssert(false, "Unknown function location."); break;
 	}
 	id += "_" + stateMutabilityToString(m_stateMutability);
@@ -2959,7 +2960,8 @@ bool FunctionType::isPure() const
 		m_kind == Kind::ABIEncode ||
 		m_kind == Kind::ABIEncodePacked ||
 		m_kind == Kind::ABIEncodeWithSelector ||
-		m_kind == Kind::ABIEncodeWithSignature;
+		m_kind == Kind::ABIEncodeWithSignature ||
+		m_kind == Kind::ABIDecode;
 }
 
 TypePointers FunctionType::parseElementaryTypeVector(strings const& _types)
@@ -3315,6 +3317,15 @@ MemberList::MemberMap MagicType::nativeMembers(ContractDefinition const*) const
 				FunctionType::Kind::ABIEncodeWithSignature,
 				true,
 				StateMutability::Pure
+			)},
+			{"decode", make_shared<FunctionType>(
+				TypePointers(),
+				TypePointers(),
+				strings{},
+				strings{},
+				FunctionType::Kind::ABIDecode,
+				true,
+				StateMutability::Pure
 			)}
 		});
 	default:
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index 34f862c3..d8e73ab9 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -934,6 +934,7 @@ public:
 		ABIEncodePacked,
 		ABIEncodeWithSelector,
 		ABIEncodeWithSignature,
+		ABIDecode,
 		GasLeft ///< gasleft()
 	};
 
diff --git a/libsolidity/codegen/ExpressionCompiler.cpp b/libsolidity/codegen/ExpressionCompiler.cpp
index 412a7255..7a4548f5 100644
--- a/libsolidity/codegen/ExpressionCompiler.cpp
+++ b/libsolidity/codegen/ExpressionCompiler.cpp
@@ -1070,6 +1070,27 @@ bool ExpressionCompiler::visit(FunctionCall const& _functionCall)
 			// stack now: <memory pointer>
 			break;
 		}
+		case FunctionType::Kind::ABIDecode:
+		{
+			arguments.front()->accept(*this);
+			TypePointer firstArgType = arguments.front()->annotation().type;
+			TypePointers const& targetTypes = dynamic_cast<TupleType const&>(*_functionCall.annotation().type).components();
+			if (
+				*firstArgType == ArrayType(DataLocation::CallData) ||
+				*firstArgType == ArrayType(DataLocation::CallData, true)
+			)
+				utils().abiDecode(targetTypes, false);
+			else
+			{
+				utils().convertType(*firstArgType, ArrayType(DataLocation::Memory));
+				m_context << Instruction::DUP1 << u256(32) << Instruction::ADD;
+				m_context << Instruction::SWAP1 << Instruction::MLOAD;
+				// stack now: <mem_pos> <length>
+
+				utils().abiDecode(targetTypes, true);
+			}
+			break;
+		}
 		case FunctionType::Kind::GasLeft:
 			m_context << Instruction::GAS;
 			break;