Make non-payable default for conversion to address.

libsolidity/analysis/TypeChecker.cpp

@@ -1778,9 +1778,7 @@ bool TypeChecker::visit(FunctionCall const& _functionCall)
 			}
 			if (resultType->category() == Type::Category::Address)
 			{
-				bool payable = true;
-				if (auto const* contractType = dynamic_cast<ContractType const*>(argType.get()))
-					payable = contractType->isPayable();
+				bool payable = argType->isExplicitlyConvertibleTo(AddressType::addressPayable());
 				resultType = make_shared<AddressType>(payable ? StateMutability::Payable : StateMutability::NonPayable);
 			}
 		}

libsolidity/ast/Types.cpp

@@ -2641,8 +2641,8 @@ bool FunctionType::operator==(Type const& _other) const
 
 bool FunctionType::isExplicitlyConvertibleTo(Type const& _convertTo) const
 {
-	if (m_kind == Kind::External && _convertTo.category() == Category::Address)
-			return true;
+	if (m_kind == Kind::External && _convertTo == AddressType::address())
+		return true;
 	return _convertTo.category() == category();
 }
 

test/libsolidity/syntaxTests/functionTypes/external_function_type_to_address_payable.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f() public view returns (address payable) {
+        return address(this.f);
+    }
+}
+// ----
+// TypeError: (85-100): Return argument type address is not implicitly convertible to expected type (type of first return variable) address payable.

test/libsolidity/syntaxTests/types/address/address_to_payable_address_double.sol

@@ -0,0 +1,7 @@
+contract C {
+    function f(address a) public pure returns (address payable) {
+        return address(address(a));
+    }
+}
+// ----
+// TypeError: (94-113): Return argument type address is not implicitly convertible to expected type (type of first return variable) address payable.

test/libsolidity/syntaxTests/types/address/bytes_long_to_payable_address.sol

@@ -0,0 +1,8 @@
+contract C {
+    function f(bytes32 x) public pure returns (address payable) {
+        return address(x);
+    }
+}
+// ----
+// TypeError: (94-104): Explicit type conversion not allowed from "bytes32" to "address".
+// TypeError: (94-104): Return argument type address is not implicitly convertible to expected type (type of first return variable) address payable.

test/libsolidity/syntaxTests/types/address/bytes_short_to_payable_address.sol

@@ -0,0 +1,8 @@
+contract C {
+    function f(bytes10 x) public pure returns (address payable) {
+        return address(x);
+    }
+}
+// ----
+// TypeError: (94-104): Explicit type conversion not allowed from "bytes10" to "address".
+// TypeError: (94-104): Return argument type address is not implicitly convertible to expected type (type of first return variable) address payable.

test/libsolidity/syntaxTests/types/address/bytes_to_payable_address.sol

@@ -0,0 +1,5 @@
+contract C {
+    function f(bytes20 x) public pure returns (address payable) {
+        return address(x);
+    }
+}

test/libsolidity/syntaxTests/types/address/uint_to_payable_address.sol

@@ -0,0 +1,5 @@
+contract C {
+    function f(uint x) public pure returns (address payable) {
+        return address(x);
+    }
+}