7 files changed, 85 insertions, 1 deletions
diff --git a/Changelog.md b/Changelog.md
index be0e8329..c1098bdf 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,5 +1,8 @@
 ### 0.4.10 (unreleased)
 
+Features:
+ * Type system: Support explicit conversion of external function to address.
+
 ### 0.4.9 (2017-01-31)
 
 Features:
diff --git a/libsolidity/ast/Types.cpp b/libsolidity/ast/Types.cpp
index dbabc8db..4a64b4c8 100644
--- a/libsolidity/ast/Types.cpp
+++ b/libsolidity/ast/Types.cpp
@@ -2158,6 +2158,17 @@ bool FunctionType::operator==(Type const& _other) const
 	return true;
 }
 
+bool FunctionType::isExplicitlyConvertibleTo(Type const& _convertTo) const
+{
+	if (m_location == Location::External && _convertTo.category() == Category::Integer)
+	{
+		IntegerType const& convertTo = dynamic_cast<IntegerType const&>(_convertTo);
+		if (convertTo.isAddress())
+			return true;
+	}
+	return _convertTo.category() == category();
+}
+
 TypePointer FunctionType::unaryOperatorResult(Token::Value _operator) const
 {
 	if (_operator == Token::Value::Delete)
diff --git a/libsolidity/ast/Types.h b/libsolidity/ast/Types.h
index a5147f17..3917dca2 100644
--- a/libsolidity/ast/Types.h
+++ b/libsolidity/ast/Types.h
@@ -922,6 +922,7 @@ public:
 
 	virtual std::string identifier() const override;
 	virtual bool operator==(Type const& _other) const override;
+	virtual bool isExplicitlyConvertibleTo(Type const& _convertTo) const override;
 	virtual TypePointer unaryOperatorResult(Token::Value _operator) const override;
 	virtual std::string canonicalName(bool /*_addDataLocation*/) const override;
 	virtual std::string toString(bool _short) const override;
diff --git a/libsolidity/codegen/CompilerUtils.cpp b/libsolidity/codegen/CompilerUtils.cpp
index 477f021a..9f019d27 100644
--- a/libsolidity/codegen/CompilerUtils.cpp
+++ b/libsolidity/codegen/CompilerUtils.cpp
@@ -787,6 +787,20 @@ void CompilerUtils::convertType(Type const& _typeOnStack, Type const& _targetTyp
 		if (_cleanupNeeded)
 			m_context << Instruction::ISZERO << Instruction::ISZERO;
 		break;
+	case Type::Category::Function:
+	{
+		if (targetTypeCategory == Type::Category::Integer)
+		{
+			IntegerType const& targetType = dynamic_cast<IntegerType const&>(_targetType);
+			solAssert(targetType.isAddress(), "Function type can only be converted to address.");
+			FunctionType const& typeOnStack = dynamic_cast<FunctionType const&>(_typeOnStack);
+			solAssert(typeOnStack.location() == FunctionType::Location::External, "Only external function type can be converted.");
+
+			// stack: <address> <function_id>
+			m_context << Instruction::POP;
+			break;
+		}
+	}
 	default:
 		// All other types should not be convertible to non-equal types.
 		solAssert(_typeOnStack == _targetType, "Invalid type conversion requested.");
diff --git a/libsolidity/codegen/ContractCompiler.cpp b/libsolidity/codegen/ContractCompiler.cpp
index 4d33927d..9d6129a3 100644
--- a/libsolidity/codegen/ContractCompiler.cpp
+++ b/libsolidity/codegen/ContractCompiler.cpp
@@ -42,7 +42,7 @@ class StackHeightChecker
 public:
 	StackHeightChecker(CompilerContext const& _context):
 		m_context(_context), stackHeight(m_context.stackHeight()) {}
-	void check() { solAssert(m_context.stackHeight() == stackHeight, "I sense a disturbance in the stack."); }
+	void check() { solAssert(m_context.stackHeight() == stackHeight, std::string("I sense a disturbance in the stack: ") + std::to_string(m_context.stackHeight()) + " vs " + std::to_string(stackHeight)); }
 private:
 	CompilerContext const& m_context;
 	unsigned stackHeight;
diff --git a/test/libsolidity/SolidityEndToEndTest.cpp b/test/libsolidity/SolidityEndToEndTest.cpp
index 4075a016..4924b55d 100644
--- a/test/libsolidity/SolidityEndToEndTest.cpp
+++ b/test/libsolidity/SolidityEndToEndTest.cpp
@@ -8462,6 +8462,25 @@ BOOST_AUTO_TEST_CASE(function_array_cross_calls)
 	BOOST_CHECK(callContractFunction("test()") == encodeArgs(u256(5), u256(6), u256(7)));
 }
 
+BOOST_AUTO_TEST_CASE(external_function_to_address)
+{
+	char const* sourceCode = R"(
+		contract C {
+			function f() returns (bool) {
+				return address(this.f) == address(this);
+			}
+			function g(function() external cb) returns (address) {
+				return address(cb);
+			}
+		}
+	)";
+
+	compileAndRun(sourceCode, 0, "C");
+	BOOST_CHECK(callContractFunction("f()") == encodeArgs(true));
+	BOOST_CHECK(callContractFunction("g(function)", fromHex("00000000000000000000000000000000000004226121ff00000000000000000")) == encodeArgs(u160(0x42)));
+}
+
+
 BOOST_AUTO_TEST_CASE(copy_internal_function_array_to_storage)
 {
 	char const* sourceCode = R"(
diff --git a/test/libsolidity/SolidityNameAndTypeResolution.cpp b/test/libsolidity/SolidityNameAndTypeResolution.cpp
index 472067ec..f5768022 100644
--- a/test/libsolidity/SolidityNameAndTypeResolution.cpp
+++ b/test/libsolidity/SolidityNameAndTypeResolution.cpp
@@ -4725,6 +4725,42 @@ BOOST_AUTO_TEST_CASE(delete_external_function_type_invalid)
 	CHECK_ERROR(text, TypeError, "");
 }
 
+BOOST_AUTO_TEST_CASE(external_function_type_to_address)
+{
+	char const* text = R"(
+		contract C {
+			function f() returns (address) {
+				return address(this.f);
+			}
+		}
+	)";
+	CHECK_SUCCESS(text);
+}
+
+BOOST_AUTO_TEST_CASE(internal_function_type_to_address)
+{
+	char const* text = R"(
+		contract C {
+			function f() returns (address) {
+				return address(f);
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Explicit type conversion not allowed");
+}
+
+BOOST_AUTO_TEST_CASE(external_function_type_to_uint)
+{
+	char const* text = R"(
+		contract C {
+			function f() returns (uint) {
+				return uint(this.f);
+			}
+		}
+	)";
+	CHECK_ERROR(text, TypeError, "Explicit type conversion not allowed");
+}
+
 BOOST_AUTO_TEST_CASE(invalid_fixed_point_literal)
 {
 	char const* text = R"(