Add .selector member on function types

Changelog.md

@@ -1,6 +1,7 @@
 ### 0.4.17 (unreleased)
 
 Features:
+ * Code Generator: Added ``.selector`` member on external function types to retrieve their signature.
  * Optimizer: Add new optimization step to remove unused ``JUMPDEST``s.
  * Type Checker: Display helpful warning for unused function arguments/return parameters.
  * Type Checker: Do not show the same error multiple times for events.

docs/abi-spec.rst

@@ -17,6 +17,8 @@ We assume the interface functions of a contract are strongly typed, known at com
 
 This specification does not address contracts whose interface is dynamic or otherwise known only at run-time. Should these cases become important they can be adequately handled as facilities built within the Ethereum ecosystem.
 
+.. _abi_function_selector:
+
 Function Selector
 =================
 

docs/types.rst

@@ -400,6 +400,17 @@ Note that public functions of the current contract can be used both as an
 internal and as an external function. To use ``f`` as an internal function,
 just use ``f``, if you want to use its external form, use ``this.f``.
 
+Additionally, public (or external) functions also have a special member called ``selector``,
+which returns the :ref:`ABI function selector <abi_function_selector>`::
+
+    pragma solidity ^0.4.0;
+
+    contract Selector {
+      function f() returns (bytes4) {
+        return this.f.selector;
+      }
+    }
+
 Example that shows how to use internal function types::
 
     pragma solidity ^0.4.5;

libsolidity/ast/Types.cpp

@@ -2436,6 +2436,11 @@ MemberList::MemberMap FunctionType::nativeMembers(ContractDefinition const*) con
 	case Kind::BareDelegateCall:
 	{
 		MemberList::MemberMap members;
+		if (m_kind == Kind::External)
+			members.push_back(MemberList::Member(
+				"selector",
+				make_shared<FixedBytesType>(4)
+			));
 		if (m_kind != Kind::BareDelegateCall && m_kind != Kind::DelegateCall)
 		{
 			if (isPayable())

libsolidity/codegen/ExpressionCompiler.cpp

@@ -1068,7 +1068,14 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 			solAssert(false, "Invalid member access to integer");
 		break;
 	case Type::Category::Function:
-		solAssert(!!_memberAccess.expression().annotation().type->memberType(member),
+		if (member == "selector")
+		{
+			m_context << Instruction::SWAP1 << Instruction::POP;
+			/// need to store store it as bytes4
+			utils().leftShiftNumberOnStack(224);
+		}
+		else
+			solAssert(!!_memberAccess.expression().annotation().type->memberType(member),
 				 "Invalid member access to function.");
 		break;
 	case Type::Category::Magic:

test/libsolidity/SolidityEndToEndTest.cpp

@@ -10051,6 +10051,30 @@ BOOST_AUTO_TEST_CASE(delegatecall_return_value)
 	BOOST_CHECK(callContractFunction("get_delegated()") == encodeArgs(u256(1)));
 }
 
+BOOST_AUTO_TEST_CASE(function_types_sig)
+{
+	char const* sourceCode = R"(
+		contract C {
+			function f() returns (bytes4) {
+				return this.f.selector;
+			}
+			function g() returns (bytes4) {
+				function () external returns (bytes4) fun = this.f;
+				return fun.selector;
+			}
+			function h() returns (bytes4) {
+				function () external returns (bytes4) fun = this.f;
+				var funvar = fun;
+				return funvar.selector;
+			}
+		}
+	)";
+	compileAndRun(sourceCode, 0, "C");
+	BOOST_CHECK(callContractFunction("f()") == encodeArgs(asString(FixedHash<4>(dev::keccak256("f()")).asBytes())));
+	BOOST_CHECK(callContractFunction("g()") == encodeArgs(asString(FixedHash<4>(dev::keccak256("f()")).asBytes())));
+	BOOST_CHECK(callContractFunction("h()") == encodeArgs(asString(FixedHash<4>(dev::keccak256("f()")).asBytes())));
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 
 }

test/libsolidity/SolidityNameAndTypeResolution.cpp

@@ -6285,6 +6285,87 @@ BOOST_AUTO_TEST_CASE(modifiers_access_storage_pointer)
 	CHECK_SUCCESS_NO_WARNINGS(text);
 }
 
+BOOST_AUTO_TEST_CASE(function_types_sig)
+{
+	char const* text = R"(
+		contract C {
+			function f() returns (bytes4) {
+				return f.selector;
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Member \"selector\" not found");
+	text = R"(
+		contract C {
+			function g() internal {
+			}
+			function f() returns (bytes4) {
+				return g.selector;
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Member \"selector\" not found");
+	text = R"(
+		contract C {
+			function f() returns (bytes4) {
+				function () g;
+				return g.selector;
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Member \"selector\" not found");
+	text = R"(
+		contract C {
+			function f() returns (bytes4) {
+				return this.f.selector;
+			}
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+	text = R"(
+		contract C {
+			function f() external returns (bytes4) {
+				return this.f.selector;
+			}
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+	text = R"(
+		contract C {
+			function h() external {
+			}
+			function f() external returns (bytes4) {
+				var g = this.h;
+				return g.selector;
+			}
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+	text = R"(
+		contract C {
+			function h() external {
+			}
+			function f() external returns (bytes4) {
+				function () external g = this.h;
+				return g.selector;
+			}
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+	text = R"(
+		contract C {
+			function h() external {
+			}
+			function f() external returns (bytes4) {
+				function () external g = this.h;
+				var i = g;
+				return i.selector;
+			}
+		}
+	)";
+	CHECK_SUCCESS_NO_WARNINGS(text);
+}
+
 BOOST_AUTO_TEST_CASE(using_this_in_constructor)
 {
 	char const* text = R"(