Merge pull request #7358 from aarlt/abstract_contracts

Abstract contracts

Changelog.md

@@ -10,6 +10,7 @@ Breaking changes:
  * General: New reserved keywords: ``virtual``.
  * Standard JSON Interface: Add option to disable or choose hash method between IPFS and Swarm for the bytecode metadata.
  * Syntax: ``push(element)`` for dynamic storage arrays do not return the new length anymore.
+ * Syntax: Abstract contracts need to be marked explicitly as abstract by using the ``abstract`` keyword.
  * Inline Assembly: Only strict inline assembly is allowed.
  * Type checker: Resulting type of exponentiation is equal to the type of the base. Also allow signed types for the base.
  * Language Feature: When overriding a function or modifier, the new keyword ``override`` must be used. When overriding a function or modifier defined in multiple parallel bases, all bases must be listed in parentheses after the keyword like so: ``override(Base1, Base2)``

docs/abi-spec.rst

@@ -529,7 +529,7 @@ As an example, the code
     pragma experimental ABIEncoderV2;
 
 
-    contract Test {
+    abstract contract Test {
         struct S { uint a; uint[] b; T[] c; }
         struct T { uint x; uint y; }
         function f(S memory s, T memory t, uint a) public;

docs/contracts/abstract-contracts.rst

@@ -6,19 +6,24 @@
 Abstract Contracts
 ******************
 
-Contracts are marked as abstract when at least one of their functions lacks an implementation as in the following example (note that the function declaration header is terminated by ``;``)::
+Contracts need to be marked as abstract when at least one of their functions was not implemented.
+You can also mark contracts as abstract even though all functions are implemented.
+This can be done by using the ``abstract`` keyword as shown in the following example. Note, that this contract need to be
+defined as abstract, because the function ``utterance()`` was defined, but no implementation was
+provided (no implementation body ``{ }`` was given).::
 
     pragma solidity >=0.4.0 <0.7.0;
 
-    contract Feline {
+    abstract contract Feline {
         function utterance() public returns (bytes32);
     }
 
-Such contracts cannot be compiled (even if they contain implemented functions alongside non-implemented functions), but they can be used as base contracts::
+Such abstract contracts can not be instantiated directly. This is also true, if an abstract contract itself does implement
+all defined functions. The usage of an abstract contract as a base class is shown in the following example::
 
     pragma solidity >=0.4.0 <0.7.0;
 
-    contract Feline {
+    abstract contract Feline {
         function utterance() public returns (bytes32);
     }
 
@@ -26,7 +31,7 @@ Such contracts cannot be compiled (even if they contain implemented functions al
         function utterance() public override returns (bytes32) { return "miaow"; }
     }
 
-If a contract inherits from an abstract contract and does not implement all non-implemented functions by overriding, it will itself be abstract.
+If a contract inherits from an abstract contract and does not implement all non-implemented functions by overriding, it needs to be marked as abstract as well.
 
 Note that a function without implementation is different from a :ref:`Function Type <function_types>` even though their syntax looks very similar.
 

docs/contracts/inheritance.rst

@@ -52,12 +52,12 @@ Details are given in the following example.
     // interface known to the compiler. Note the function
     // without body. If a contract does not implement all
     // functions it can only be used as an interface.
-    contract Config {
+    abstract contract Config {
         function lookup(uint id) public returns (address adr);
     }
 
 
-    contract NameReg {
+    abstract contract NameReg {
         function register(bytes32 name) public;
         function unregister() public;
     }

docs/grammar.txt

@@ -7,7 +7,7 @@ ImportDirective = 'import' StringLiteral ('as' Identifier)? ';'
         | 'import' ('*' | Identifier) ('as' Identifier)? 'from' StringLiteral ';'
         | 'import' '{' Identifier ('as' Identifier)? ( ',' Identifier ('as' Identifier)? )* '}' 'from' StringLiteral ';'
 
-ContractDefinition = ( 'contract' | 'library' | 'interface' ) Identifier
+ContractDefinition = 'abstract'? ( 'contract' | 'library' | 'interface' ) Identifier
                      ( 'is' InheritanceSpecifier (',' InheritanceSpecifier )* )?
                      '{' ContractPart* '}'
 

docs/style-guide.rst

@@ -91,7 +91,7 @@ Yes::
 
     pragma solidity >=0.4.0 <0.7.0;
 
-    contract A {
+    abstract contract A {
         function spam() public pure;
         function ham() public pure;
     }

libsolidity/analysis/ContractLevelChecker.cpp

@@ -391,6 +391,19 @@ void ContractLevelChecker::checkAbstractFunctions(ContractDefinition const& _con
 				_contract.annotation().unimplementedFunctions.push_back(function);
 				break;
 			}
+
+	if (_contract.abstract() && _contract.contractKind() != ContractDefinition::ContractKind::Contract)
+		m_errorReporter.typeError(_contract.location(), "Only contracts can be abstract.");
+
+	if (
+		_contract.contractKind() == ContractDefinition::ContractKind::Contract &&
+		!_contract.annotation().unimplementedFunctions.empty() &&
+		!_contract.abstract()
+	)
+		m_errorReporter.typeError(
+			_contract.location(),
+			"Contract \"" + _contract.annotation().canonicalName + "\" should be marked as abstract."
+		);
 }
 
 

libsolidity/analysis/TypeChecker.cpp

@@ -88,7 +88,6 @@ bool TypeChecker::visit(ContractDefinition const& _contract)
 	for (auto const& n: _contract.subNodes())
 		n->accept(*this);
 
-
 	return false;
 }
 
@@ -2152,21 +2151,10 @@ void TypeChecker::endVisit(NewExpression const& _newExpression)
 			m_errorReporter.fatalTypeError(_newExpression.location(), "Identifier is not a contract.");
 		if (contract->isInterface())
 			m_errorReporter.fatalTypeError(_newExpression.location(), "Cannot instantiate an interface.");
-		if (!contract->annotation().unimplementedFunctions.empty())
-		{
-			SecondarySourceLocation ssl;
-			for (auto function: contract->annotation().unimplementedFunctions)
-				ssl.append("Missing implementation:", function->location());
-			string msg = "Trying to create an instance of an abstract contract.";
-			ssl.limitSize(msg);
-			m_errorReporter.typeError(
-				_newExpression.location(),
-				ssl,
-				msg
-			);
-		}
 		if (!contract->constructorIsPublic())
 			m_errorReporter.typeError(_newExpression.location(), "Contract with internal constructor cannot be created directly.");
+		if (contract->abstract() || !contract->annotation().unimplementedFunctions.empty())
+			m_errorReporter.typeError(_newExpression.location(), "Cannot instantiate an abstract contract.");
 
 		solAssert(!!m_scope, "");
 		m_scope->annotation().contractDependencies.insert(contract);

libsolidity/ast/AST.cpp

@@ -151,7 +151,7 @@ bool ContractDefinition::constructorIsPublic() const
 
 bool ContractDefinition::canBeDeployed() const
 {
-	return constructorIsPublic() && annotation().unimplementedFunctions.empty();
+	return constructorIsPublic() && annotation().unimplementedFunctions.empty() && !abstract();
 }
 
 FunctionDefinition const* ContractDefinition::fallbackFunction() const

libsolidity/ast/AST.h

@@ -388,13 +388,15 @@ public:
 		ASTPointer<ASTString> const& _documentation,
 		std::vector<ASTPointer<InheritanceSpecifier>> const& _baseContracts,
 		std::vector<ASTPointer<ASTNode>> const& _subNodes,
-		ContractKind _contractKind = ContractKind::Contract
+		ContractKind _contractKind = ContractKind::Contract,
+		bool _abstract = false
 	):
 		Declaration(_location, _name),
 		Documented(_documentation),
 		m_baseContracts(_baseContracts),
 		m_subNodes(_subNodes),
-		m_contractKind(_contractKind)
+		m_contractKind(_contractKind),
+		m_abstract(_abstract)
 	{}
 
 	void accept(ASTVisitor& _visitor) override;
@@ -441,10 +443,13 @@ public:
 
 	ContractKind contractKind() const { return m_contractKind; }
 
+	bool abstract() const { return m_abstract; }
+
 private:
 	std::vector<ASTPointer<InheritanceSpecifier>> m_baseContracts;
 	std::vector<ASTPointer<ASTNode>> m_subNodes;
 	ContractKind m_contractKind;
+	bool m_abstract{false};
 
 	mutable std::unique_ptr<std::vector<std::pair<FixedHash<4>, FunctionTypePointer>>> m_interfaceFunctionList;
 	mutable std::unique_ptr<std::vector<EventDefinition const*>> m_interfaceEvents;

libsolidity/ast/ASTJsonConverter.cpp

@@ -260,6 +260,7 @@ bool ASTJsonConverter::visit(ContractDefinition const& _node)
 		make_pair("name", _node.name()),
 		make_pair("documentation", _node.documentation() ? Json::Value(*_node.documentation()) : Json::nullValue),
 		make_pair("contractKind", contractKind(_node.contractKind())),
+		make_pair("abstract", _node.abstract()),
 		make_pair("fullyImplemented", _node.annotation().unimplementedFunctions.empty()),
 		make_pair("linearizedBaseContracts", getContainerIds(_node.annotation().linearizedBaseContracts)),
 		make_pair("baseContracts", toJson(_node.baseContracts())),

libsolidity/parsing/Parser.cpp

@@ -91,6 +91,7 @@ ASTPointer<SourceUnit> Parser::parse(shared_ptr<Scanner> const& _scanner)
 			case Token::Import:
 				nodes.push_back(parseImportDirective());
 				break;
+			case Token::Abstract:
 			case Token::Interface:
 			case Token::Contract:
 			case Token::Library:
@@ -244,9 +245,15 @@ ASTPointer<ImportDirective> Parser::parseImportDirective()
 	return nodeFactory.createNode<ImportDirective>(path, unitAlias, move(symbolAliases));
 }
 
-ContractDefinition::ContractKind Parser::parseContractKind()
+std::pair<ContractDefinition::ContractKind, bool> Parser::parseContractKind()
 {
 	ContractDefinition::ContractKind kind;
+	bool abstract = false;
+	if (m_scanner->currentToken() == Token::Abstract)
+	{
+		abstract = true;
+		m_scanner->next();
+	}
 	switch(m_scanner->currentToken())
 	{
 	case Token::Interface:
@@ -262,7 +269,7 @@ ContractDefinition::ContractKind Parser::parseContractKind()
 		solAssert(false, "Invalid contract kind.");
 	}
 	m_scanner->next();
-	return kind;
+	return std::make_pair(kind, abstract);
 }
 
 ASTPointer<ContractDefinition> Parser::parseContractDefinition()
@@ -273,7 +280,7 @@ ASTPointer<ContractDefinition> Parser::parseContractDefinition()
 	ASTPointer<ASTString> docString;
 	vector<ASTPointer<InheritanceSpecifier>> baseContracts;
 	vector<ASTPointer<ASTNode>> subNodes;
-	ContractDefinition::ContractKind contractKind = ContractDefinition::ContractKind::Contract;
+	std::pair<ContractDefinition::ContractKind, bool> contractKind{};
 	try
 	{
 		if (m_scanner->currentCommentLiteral() != "")
@@ -343,7 +350,8 @@ ASTPointer<ContractDefinition> Parser::parseContractDefinition()
 		docString,
 		baseContracts,
 		subNodes,
-		contractKind
+		contractKind.first,
+		contractKind.second
 	);
 }
 

libsolidity/parsing/Parser.h

@@ -85,7 +85,9 @@ private:
 	void parsePragmaVersion(langutil::SourceLocation const& _location, std::vector<Token> const& _tokens, std::vector<std::string> const& _literals);
 	ASTPointer<PragmaDirective> parsePragmaDirective();
 	ASTPointer<ImportDirective> parseImportDirective();
-	ContractDefinition::ContractKind parseContractKind();
+	/// @returns an std::pair<ContractDefinition::ContractKind, bool>, where
+	/// result.second is set to true, if an abstract contract was parsed, false otherwise.
+	std::pair<ContractDefinition::ContractKind, bool> parseContractKind();
 	ASTPointer<ContractDefinition> parseContractDefinition();
 	ASTPointer<InheritanceSpecifier> parseInheritanceSpecifier();
 	Declaration::Visibility parseVisibilitySpecifier();

test/cmdlineTests/recovery_ast_constructor/output

@@ -34,6 +34,7 @@ JSON AST:
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/cmdlineTests/recovery_standard_json/output.json

@@ -4,4 +4,4 @@ pragma solidity >=0.0; contract Errort6 { using foo for  ; /* missing type name
 ","message":"Expected type name","severity":"error","sourceLocation":{"end":58,"file":"A","start":57},"type":"ParserError"},{"component":"general","formattedMessage":"A:1:84: Warning: Recovered in ContractDefinition at '}'.
 pragma solidity >=0.0; contract Errort6 { using foo for  ; /* missing type name */ }
                                                                                    ^
-","message":"Recovered in ContractDefinition at '}'.","severity":"warning","sourceLocation":{"end":84,"file":"A","start":83},"type":"Warning"}],"sources":{"A":{"ast":{"absolutePath":"A","exportedSymbols":{"Errort6":[3]},"id":4,"nodeType":"SourceUnit","nodes":[{"id":1,"literals":["solidity",">=","0.0"],"nodeType":"PragmaDirective","src":"0:22:0"},{"baseContracts":[],"contractDependencies":[],"contractKind":"contract","documentation":null,"fullyImplemented":true,"id":3,"linearizedBaseContracts":[3],"name":"Errort6","nodeType":"ContractDefinition","nodes":[],"scope":4,"src":"23:35:0"}],"src":"0:84:0"},"id":0}}}
+","message":"Recovered in ContractDefinition at '}'.","severity":"warning","sourceLocation":{"end":84,"file":"A","start":83},"type":"Warning"}],"sources":{"A":{"ast":{"absolutePath":"A","exportedSymbols":{"Errort6":[3]},"id":4,"nodeType":"SourceUnit","nodes":[{"id":1,"literals":["solidity",">=","0.0"],"nodeType":"PragmaDirective","src":"0:22:0"},{"abstract":false,"baseContracts":[],"contractDependencies":[],"contractKind":"contract","documentation":null,"fullyImplemented":true,"id":3,"linearizedBaseContracts":[3],"name":"Errort6","nodeType":"ContractDefinition","nodes":[],"scope":4,"src":"23:35:0"}],"src":"0:84:0"},"id":0}}}

test/cmdlineTests/standard_only_ast_requested/output.json

@@ -1 +1 @@
-{"sources":{"A":{"ast":{"absolutePath":"A","exportedSymbols":{"C":[6]},"id":7,"nodeType":"SourceUnit","nodes":[{"id":1,"literals":["solidity",">=","0.0"],"nodeType":"PragmaDirective","src":"0:22:0"},{"baseContracts":[],"contractDependencies":[],"contractKind":"contract","documentation":null,"fullyImplemented":true,"id":6,"linearizedBaseContracts":[6],"name":"C","nodeType":"ContractDefinition","nodes":[{"body":{"id":4,"nodeType":"Block","src":"61:2:0","statements":[]},"documentation":null,"id":5,"implemented":true,"kind":"function","modifiers":[],"name":"f","nodeType":"FunctionDefinition","overrides":null,"parameters":{"id":2,"nodeType":"ParameterList","parameters":[],"src":"46:2:0"},"returnParameters":{"id":3,"nodeType":"ParameterList","parameters":[],"src":"61:0:0"},"scope":6,"src":"36:27:0","stateMutability":"pure","superFunction":null,"visibility":"public"}],"scope":7,"src":"23:42:0"}],"src":"0:65:0"},"id":0}}}
+{"sources":{"A":{"ast":{"absolutePath":"A","exportedSymbols":{"C":[6]},"id":7,"nodeType":"SourceUnit","nodes":[{"id":1,"literals":["solidity",">=","0.0"],"nodeType":"PragmaDirective","src":"0:22:0"},{"abstract":false,"baseContracts":[],"contractDependencies":[],"contractKind":"contract","documentation":null,"fullyImplemented":true,"id":6,"linearizedBaseContracts":[6],"name":"C","nodeType":"ContractDefinition","nodes":[{"body":{"id":4,"nodeType":"Block","src":"61:2:0","statements":[]},"documentation":null,"id":5,"implemented":true,"kind":"function","modifiers":[],"name":"f","nodeType":"FunctionDefinition","overrides":null,"parameters":{"id":2,"nodeType":"ParameterList","parameters":[],"src":"46:2:0"},"returnParameters":{"id":3,"nodeType":"ParameterList","parameters":[],"src":"61:0:0"},"scope":6,"src":"36:27:0","stateMutability":"pure","superFunction":null,"visibility":"public"}],"scope":7,"src":"23:42:0"}],"src":"0:65:0"},"id":0}}}

test/compilationTests/gnosis/Events/Event.sol

@@ -6,7 +6,7 @@ import "../Oracles/Oracle.sol";
 
 /// @title Event contract - Provide basic functionality required by different event types
 /// @author Stefan George - <stefan@gnosis.pm>
-contract Event {
+abstract contract Event {
 
     /*
      *  Events

test/compilationTests/gnosis/MarketMakers/MarketMaker.sol

@@ -3,7 +3,7 @@ import "../Markets/Market.sol";
 
 
 /// @title Abstract market maker contract - Functions to be implemented by market maker contracts
-contract MarketMaker {
+abstract contract MarketMaker {
 
     /*
      *  Public functions

test/compilationTests/gnosis/Markets/Market.sol

@@ -4,7 +4,7 @@ import "../MarketMakers/MarketMaker.sol";
 
 
 /// @title Abstract market contract - Functions to be implemented by market contracts
-contract Market {
+abstract contract Market {
 
     /*
      *  Events

test/compilationTests/gnosis/Markets/MarketFactory.sol

@@ -5,7 +5,7 @@ import "../Markets/Market.sol";
 
 
 /// @title Abstract market factory contract - Functions to be implemented by market factories
-contract MarketFactory {
+abstract contract MarketFactory {
 
     /*
      *  Events

test/compilationTests/gnosis/Oracles/Oracle.sol

@@ -2,7 +2,7 @@ pragma solidity >=0.0;
 
 
 /// @title Abstract oracle contract - Functions to be implemented by oracles
-contract Oracle {
+abstract contract Oracle {
 
     function isOutcomeSet() public view returns (bool);
     function getOutcome() public view returns (int);

test/compilationTests/gnosis/Tokens/Token.sol

@@ -3,7 +3,7 @@ pragma solidity >=0.0;
 
 
 /// @title Abstract token contract - Functions to be implemented by token contracts
-contract Token {
+abstract contract Token {
 
     /*
      *  Events

test/contracts/AuctionRegistrar.cpp

@@ -45,12 +45,12 @@ namespace
 static char const* registrarCode = R"DELIMITER(
 pragma solidity >=0.4.0 <0.7.0;
 
-contract NameRegister {
+abstract contract NameRegister {
 	function addr(string memory _name) public view returns (address o_owner);
 	function name(address _owner) public view returns (string memory o_name);
 }
 
-contract Registrar is NameRegister {
+abstract contract Registrar is NameRegister {
 	event Changed(string indexed name);
 	event PrimaryChanged(string indexed name, address indexed addr);
 
@@ -62,7 +62,7 @@ contract Registrar is NameRegister {
 	function name(address _owner) public override view returns (string memory o_name);
 }
 
-contract AuctionSystem {
+abstract contract AuctionSystem {
 	event AuctionEnded(string indexed _name, address _winner);
 	event NewBid(string indexed _name, address _bidder, uint _value);
 

test/contracts/FixedFeeRegistrar.cpp

@@ -55,7 +55,7 @@ static char const* registrarCode = R"DELIMITER(
 
 pragma solidity >=0.4.0 <0.7.0;
 
-contract Registrar {
+abstract contract Registrar {
 	event Changed(string indexed name);
 
 	function owner(string memory _name) public view returns (address o_owner);

test/contracts/Wallet.cpp

@@ -276,7 +276,7 @@ contract multiowned {
 // inheritable "property" contract that enables methods to be protected by placing a linear limit (specifiable)
 // on a particular resource per calendar day. is multiowned to allow the limit to be altered. resource that method
 // uses is specified in the modifier.
-contract daylimit is multiowned {
+abstract contract daylimit is multiowned {
 
 	// MODIFIERS
 
@@ -330,7 +330,7 @@ contract daylimit is multiowned {
 }
 
 // interface contract for multisig proxy contracts; see below for docs.
-contract multisig {
+abstract contract multisig {
 
 	// EVENTS
 

test/externalTests/solc-js/DAO/DAO.sol

@@ -24,7 +24,7 @@ to automate organizational governance and decision-making.
 import "./TokenCreation.sol";
 import "./ManagedAccount.sol";
 
-contract DAOInterface {
+abstract contract DAOInterface {
 
     // The amount of days for which people who try to participate in the
     // creation by calling the fallback function will still get their ether back

test/externalTests/solc-js/DAO/ManagedAccount.sol

@@ -21,7 +21,7 @@ Basic account, used by the DAO contract to separately manage both the rewards
 and the extraBalance accounts.
 */
 
-contract ManagedAccountInterface {
+abstract contract ManagedAccountInterface {
     // The only address with permission to withdraw from this account
     address public owner;
     // If true, only the owner of the account can receive ether from it

test/externalTests/solc-js/DAO/Token.sol

@@ -30,7 +30,7 @@ https://github.com/ethereum/wiki/wiki/Standardized_Contract_APIs
 
 /// @title Standard Token Contract.
 
-contract TokenInterface {
+abstract contract TokenInterface {
     mapping (address => uint256) balances;
     mapping (address => mapping (address => uint256)) allowed;
 
@@ -85,7 +85,7 @@ contract TokenInterface {
     );
 }
 
-contract tokenRecipient {
+abstract contract tokenRecipient {
     function receiveApproval(address _from, uint256 _value, address _token, bytes memory _extraData) public;
 }
 

test/externalTests/solc-js/DAO/TokenCreation.sol

@@ -25,7 +25,7 @@ along with the DAO.  If not, see <http://www.gnu.org/licenses/>.
 import "./Token.sol";
 import "./ManagedAccount.sol";
 
-contract TokenCreationInterface {
+abstract contract TokenCreationInterface {
 
     // End of token creation, in Unix time
     uint public closingTime;

test/libsolidity/ASTJSON/abstract_contract.json

@@ -0,0 +1,72 @@
+{
+  "absolutePath": "a",
+  "exportedSymbols":
+  {
+    "C":
+    [
+      5
+    ]
+  },
+  "id": 6,
+  "nodeType": "SourceUnit",
+  "nodes":
+  [
+    {
+      "abstract": true,
+      "baseContracts": [],
+      "contractDependencies": [],
+      "contractKind": "contract",
+      "documentation": null,
+      "fullyImplemented": true,
+      "id": 5,
+      "linearizedBaseContracts":
+      [
+        5
+      ],
+      "name": "C",
+      "nodeType": "ContractDefinition",
+      "nodes":
+      [
+        {
+          "body":
+          {
+            "id": 3,
+            "nodeType": "Block",
+            "src": "44:4:1",
+            "statements": []
+          },
+          "documentation": null,
+          "id": 4,
+          "implemented": true,
+          "kind": "constructor",
+          "modifiers": [],
+          "name": "",
+          "nodeType": "FunctionDefinition",
+          "overrides": null,
+          "parameters":
+          {
+            "id": 1,
+            "nodeType": "ParameterList",
+            "parameters": [],
+            "src": "34:2:1"
+          },
+          "returnParameters":
+          {
+            "id": 2,
+            "nodeType": "ParameterList",
+            "parameters": [],
+            "src": "44:0:1"
+          },
+          "scope": 5,
+          "src": "23:25:1",
+          "stateMutability": "nonpayable",
+          "superFunction": null,
+          "visibility": "public"
+        }
+      ],
+      "scope": 6,
+      "src": "0:50:1"
+    }
+  ],
+  "src": "0:51:1"
+}

test/libsolidity/ASTJSON/abstract_contract.sol

@@ -0,0 +1,6 @@
+abstract contract C {
+	constructor() public {
+	}
+}
+
+// ----

test/libsolidity/ASTJSON/abstract_contract_legacy.json

@@ -0,0 +1,112 @@
+{
+  "attributes":
+  {
+    "absolutePath": "a",
+    "exportedSymbols":
+    {
+      "C":
+      [
+        5
+      ]
+    }
+  },
+  "children":
+  [
+    {
+      "attributes":
+      {
+        "abstract": true,
+        "baseContracts":
+        [
+          null
+        ],
+        "contractDependencies":
+        [
+          null
+        ],
+        "contractKind": "contract",
+        "documentation": null,
+        "fullyImplemented": true,
+        "linearizedBaseContracts":
+        [
+          5
+        ],
+        "name": "C",
+        "scope": 6
+      },
+      "children":
+      [
+        {
+          "attributes":
+          {
+            "documentation": null,
+            "implemented": true,
+            "isConstructor": true,
+            "kind": "constructor",
+            "modifiers":
+            [
+              null
+            ],
+            "name": "",
+            "overrides": null,
+            "scope": 5,
+            "stateMutability": "nonpayable",
+            "superFunction": null,
+            "visibility": "public"
+          },
+          "children":
+          [
+            {
+              "attributes":
+              {
+                "parameters":
+                [
+                  null
+                ]
+              },
+              "children": [],
+              "id": 1,
+              "name": "ParameterList",
+              "src": "34:2:1"
+            },
+            {
+              "attributes":
+              {
+                "parameters":
+                [
+                  null
+                ]
+              },
+              "children": [],
+              "id": 2,
+              "name": "ParameterList",
+              "src": "44:0:1"
+            },
+            {
+              "attributes":
+              {
+                "statements":
+                [
+                  null
+                ]
+              },
+              "children": [],
+              "id": 3,
+              "name": "Block",
+              "src": "44:4:1"
+            }
+          ],
+          "id": 4,
+          "name": "FunctionDefinition",
+          "src": "23:25:1"
+        }
+      ],
+      "id": 5,
+      "name": "ContractDefinition",
+      "src": "0:50:1"
+    }
+  ],
+  "id": 6,
+  "name": "SourceUnit",
+  "src": "0:51:1"
+}

test/libsolidity/ASTJSON/address_payable.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/address_payable_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/array_type_name.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/array_type_name_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/constructor.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/constructor_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/contract_dep_order.json

@@ -28,6 +28,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",
@@ -45,6 +46,7 @@
       "src": "0:14:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {
@@ -88,6 +90,7 @@
       "src": "15:19:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {
@@ -133,6 +136,7 @@
       "src": "35:19:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {
@@ -180,6 +184,7 @@
       "src": "55:19:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {

test/libsolidity/ASTJSON/contract_dep_order_legacy.json

@@ -31,6 +31,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null
@@ -60,6 +61,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           1
@@ -113,6 +115,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           1,
@@ -168,6 +171,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           1,
@@ -225,6 +229,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           1,

test/libsolidity/ASTJSON/documentation.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",
@@ -45,6 +46,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",
@@ -78,6 +80,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/documentation_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/enum_value.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/enum_value_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/event_definition.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/event_definition_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/fallback.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/fallback_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/fallback_payable.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/fallback_payable_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/function_type.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/function_type_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/inheritance_specifier.json

@@ -16,6 +16,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",
@@ -33,6 +34,7 @@
       "src": "0:14:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {

test/libsolidity/ASTJSON/inheritance_specifier_legacy.json

@@ -19,6 +19,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null
@@ -48,6 +49,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           1

test/libsolidity/ASTJSON/long_type_name_binary_operation.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/long_type_name_binary_operation_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/long_type_name_identifier.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/long_type_name_identifier_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/modifier_definition.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/modifier_definition_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/modifier_invocation.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/modifier_invocation_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/non_utf8.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/non_utf8_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/override.json

@@ -20,6 +20,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",
@@ -75,6 +76,7 @@
       "src": "0:40:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {
@@ -186,6 +188,7 @@
       "src": "41:78:1"
     },
     {
+      "abstract": false,
       "baseContracts":
       [
         {

test/libsolidity/ASTJSON/override_legacy.json

@@ -23,6 +23,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null
@@ -115,6 +116,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           5
@@ -283,6 +285,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "contractDependencies":
         [
           5,

test/libsolidity/ASTJSON/placeholder_statement.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/placeholder_statement_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/short_type_name.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/short_type_name_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/short_type_name_ref.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/short_type_name_ref_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/smoke.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/smoke_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/source_location.json

@@ -12,6 +12,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/source_location_legacy.json

@@ -15,6 +15,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/ASTJSON/using_for_directive.json

@@ -16,6 +16,7 @@
   "nodes":
   [
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "library",
@@ -33,6 +34,7 @@
       "src": "0:12:1"
     },
     {
+      "abstract": false,
       "baseContracts": [],
       "contractDependencies": [],
       "contractKind": "contract",

test/libsolidity/ASTJSON/using_for_directive_legacy.json

@@ -19,6 +19,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null
@@ -48,6 +49,7 @@
     {
       "attributes":
       {
+        "abstract": false,
         "baseContracts":
         [
           null

test/libsolidity/SolidityEndToEndTest.cpp

@@ -5446,7 +5446,7 @@ BOOST_AUTO_TEST_CASE(pass_dynamic_arguments_to_the_base_base_with_gap)
 			}
 			uint public m_i;
 		}
-		contract Base1 is Base {
+		abstract contract Base1 is Base {
 			constructor(uint k) public {}
 		}
 		contract Derived is Base, Base1 {
@@ -10483,7 +10483,7 @@ BOOST_AUTO_TEST_CASE(mutex)
 BOOST_AUTO_TEST_CASE(calling_nonexisting_contract_throws)
 {
 	char const* sourceCode = R"YY(
-		contract D { function g() public; }
+		abstract contract D { function g() public; }
 		contract C {
 			D d = D(0x1212);
 			function f() public returns (uint) {

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -48,7 +48,7 @@ BOOST_AUTO_TEST_CASE(function_no_implementation)
 {
 	SourceUnit const* sourceUnit = nullptr;
 	char const* text = R"(
-		contract test {
+		abstract contract test {
 			function functionName(bytes32 input) public returns (bytes32 out);
 		}
 	)";
@@ -64,7 +64,7 @@ BOOST_AUTO_TEST_CASE(abstract_contract)
 {
 	SourceUnit const* sourceUnit = nullptr;
 	char const* text = R"(
-		contract base { function foo() public; }
+		abstract contract base { function foo() public; }
 		contract derived is base { function foo() public override {} }
 	)";
 	sourceUnit = parseAndAnalyse(text);
@@ -83,8 +83,8 @@ BOOST_AUTO_TEST_CASE(abstract_contract_with_overload)
 {
 	SourceUnit const* sourceUnit = nullptr;
 	char const* text = R"(
-		contract base { function foo(bool) public; }
+		abstract contract base { function foo(bool) public; }
-		contract derived is base { function foo(uint) public {} }
+		abstract contract derived is base { function foo(uint) public {} }
 	)";
 	sourceUnit = parseAndAnalyse(text);
 	std::vector<ASTPointer<ASTNode>> nodes = sourceUnit->nodes();
@@ -100,8 +100,8 @@ BOOST_AUTO_TEST_CASE(implement_abstract_via_constructor)
 {
 	SourceUnit const* sourceUnit = nullptr;
 	char const* text = R"(
-		contract base { function foo() public; }
+		abstract contract base { function foo() public; }
-		contract foo is base { constructor() public {} }
+		abstract contract foo is base { constructor() public {} }
 	)";
 	sourceUnit = parseAndAnalyse(text);
 	std::vector<ASTPointer<ASTNode>> nodes = sourceUnit->nodes();
@@ -356,7 +356,7 @@ BOOST_AUTO_TEST_CASE(string)
 BOOST_AUTO_TEST_CASE(dynamic_return_types_not_possible)
 {
 	char const* sourceCode = R"(
-		contract C {
+		abstract contract C {
 			function f(uint) public returns (string memory);
 			function g() public {
 				string memory x = this.f(2);

test/libsolidity/StandardCompiler.cpp

@@ -427,7 +427,7 @@ BOOST_AUTO_TEST_CASE(basic_compilation)
 	BOOST_CHECK_EQUAL(
 		dev::jsonCompactPrint(result["sources"]["fileA"]["legacyAST"]),
 		"{\"attributes\":{\"absolutePath\":\"fileA\",\"exportedSymbols\":{\"A\":[1]}},\"children\":"
-		"[{\"attributes\":{\"baseContracts\":[null],\"contractDependencies\":[null],\"contractKind\":\"contract\","
+		"[{\"attributes\":{\"abstract\":false,\"baseContracts\":[null],\"contractDependencies\":[null],\"contractKind\":\"contract\","
 		"\"documentation\":null,\"fullyImplemented\":true,\"linearizedBaseContracts\":[1],\"name\":\"A\",\"nodes\":[null],\"scope\":2},"
 		"\"id\":1,\"name\":\"ContractDefinition\",\"src\":\"0:14:0\"}],\"id\":2,\"name\":\"SourceUnit\",\"src\":\"0:14:0\"}"
 	);

test/libsolidity/smtCheckerTests/functions/functions_external_1.sol

@@ -17,4 +17,4 @@ contract C
 	}
 }
 // ----
-// Warning: (240-254): Assertion violation happens here
+// TypeError: (33-75): Contract "D" should be marked as abstract.

test/libsolidity/smtCheckerTests/functions/functions_external_2.sol

@@ -17,4 +17,4 @@ contract C
 	}
 }
 // ----
-// Warning: (280-304): Assertion violation happens here
+// TypeError: (33-75): Contract "D" should be marked as abstract.

test/libsolidity/smtCheckerTests/functions/functions_external_3.sol

@@ -18,4 +18,4 @@ contract C
 	}
 }
 // ----
-// Warning: (338-362): Assertion violation happens here
+// TypeError: (33-75): Contract "D" should be marked as abstract.

test/libsolidity/syntaxTests/abstract/abstract_contract_because_of_interface.sol

@@ -0,0 +1,7 @@
+interface A {
+    function utterance() external returns (bytes32);
+}
+contract B is A {
+}
+// ----
+// TypeError: (69-88): Contract "B" should be marked as abstract.

test/libsolidity/syntaxTests/abstract/abstract_contract_instantiation.sol

@@ -0,0 +1,12 @@
+abstract contract AbstractContract {
+    constructor() public { }
+    function utterance() public returns (bytes32) { return "miaow"; }
+}
+
+contract Test {
+    function create() public {
+       AbstractContract ac = new AbstractContract();
+    }
+}
+// ----
+// TypeError: (215-235): Cannot instantiate an abstract contract.

test/libsolidity/syntaxTests/abstract/contract.sol

@@ -0,0 +1 @@
+abstract contract A { constructor() public {} }

test/libsolidity/syntaxTests/abstract/interface.sol

@@ -0,0 +1,3 @@
+abstract interface A { }
+// ----
+// TypeError: (0-24): Only contracts can be abstract.

test/libsolidity/syntaxTests/abstract/library.sol

@@ -0,0 +1,3 @@
+abstract library A { }
+// ----
+// TypeError: (0-22): Only contracts can be abstract.

test/libsolidity/syntaxTests/abstract/unimplemented_functions.sol

@@ -0,0 +1,5 @@
+contract A {
+    function a() public;
+}
+// ----
+// TypeError: (0-39): Contract "A" should be marked as abstract.

test/libsolidity/syntaxTests/abstract/unimplemented_functions_inherited.sol

@@ -0,0 +1,7 @@
+abstract contract A {
+    function a() public;
+}
+contract B is A {
+}
+// ----
+// TypeError: (49-68): Contract "B" should be marked as abstract.

test/libsolidity/syntaxTests/constructor/abstract_creation_forward_reference.sol

@@ -12,4 +12,4 @@ contract Parent {
 contract Child is Parent {
 }
 // ----
-// TypeError: (146-155): Trying to create an instance of an abstract contract.
+// TypeError: (146-155): Cannot instantiate an abstract contract.

test/libsolidity/syntaxTests/controlFlow/storageReturn/unimplemented_internal.sol

@@ -2,3 +2,5 @@ contract C {
     function f() internal returns(uint[] storage);
     function g() internal returns(uint[] storage s);
 }
+// ----
+// TypeError: (0-118): Contract "C" should be marked as abstract.

test/libsolidity/syntaxTests/dataLocations/externalFunction/function_argument_location_specifier_test_external_calldata.sol

@@ -2,3 +2,4 @@ contract test {
     function f(bytes calldata) external;
 }
 // ----
+// TypeError: (0-58): Contract "test" should be marked as abstract.

test/libsolidity/syntaxTests/dataLocations/internalFunction/function_argument_location_specifier_test_internal_memory.sol

@@ -2,3 +2,4 @@ contract test {
     function f(bytes memory) internal;
 }
 // ----
+// TypeError: (0-56): Contract "test" should be marked as abstract.

test/libsolidity/syntaxTests/dataLocations/internalFunction/function_argument_location_specifier_test_internal_storage.sol

@@ -2,3 +2,4 @@ contract test {
     function f(bytes storage) internal;
 }
 // ----
+// TypeError: (0-57): Contract "test" should be marked as abstract.

test/libsolidity/syntaxTests/dataLocations/publicFunction/function_argument_location_specifier_test_public_memory.sol

@@ -2,3 +2,4 @@ contract test {
     function f(bytes memory) public;
 }
 // ----
+// TypeError: (0-54): Contract "test" should be marked as abstract.

test/libsolidity/syntaxTests/inheritance/override/implement_internal_function_by_public_variable.sol

@@ -7,3 +7,4 @@ contract T {
 }
 // ----
 // DeclarationError: (81-105): Identifier already declared.
+// TypeError: (0-58): Contract "X" should be marked as abstract.

test/libsolidity/syntaxTests/inheritance/override/implement_private_function_by_public_variable.sol

@@ -5,3 +5,5 @@ contract Y is X {
 contract T {
     constructor() public { new Y(); }
 }
+// ----
+// TypeError: (0-57): Contract "X" should be marked as abstract.

test/libsolidity/syntaxTests/inheritance/override/implement_public_function_by_public_variable.sol

@@ -7,3 +7,4 @@ contract T {
 }
 // ----
 // DeclarationError: (79-103): Identifier already declared.
+// TypeError: (0-56): Contract "X" should be marked as abstract.