Merge pull request #8263 from ethereum/functionSelectorPure

Mark function selectors accessed via declaration as pure.

libsolidity/analysis/TypeChecker.cpp

@@ -2527,7 +2527,15 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
 	else if (TypeType const* typeType = dynamic_cast<decltype(typeType)>(exprType))
 	{
 		if (ContractType const* contractType = dynamic_cast<decltype(contractType)>(typeType->actualType()))
+		{
 			annotation.isLValue = annotation.referencedDeclaration->isLValue();
+			if (
+				auto const* functionType = dynamic_cast<FunctionType const*>(annotation.type);
+				functionType &&
+				functionType->kind() == FunctionType::Kind::Declaration
+			)
+				annotation.isPure = _memberAccess.expression().annotation().isPure;
+		}
 	}
 
 	// TODO some members might be pure, but for example `address(0x123).balance` is not pure
@@ -2535,6 +2543,20 @@ bool TypeChecker::visit(MemberAccess const& _memberAccess)
 	if (auto tt = dynamic_cast<TypeType const*>(exprType))
 		if (tt->actualType()->category() == Type::Category::Enum)
 			annotation.isPure = true;
+	if (
+		auto const* functionType = dynamic_cast<FunctionType const*>(exprType);
+		functionType &&
+		functionType->hasDeclaration() &&
+		dynamic_cast<FunctionDefinition const*>(&functionType->declaration()) &&
+		memberName == "selector"
+	)
+		if (auto const* parentAccess = dynamic_cast<MemberAccess const*>(&_memberAccess.expression()))
+		{
+			annotation.isPure = parentAccess->expression().annotation().isPure;
+			if (auto const* exprInt = dynamic_cast<Identifier const*>(&parentAccess->expression()))
+				if (exprInt->name() == "this" || exprInt->name() == "super")
+					annotation.isPure = true;
+		}
 	if (auto magicType = dynamic_cast<MagicType const*>(exprType))
 	{
 		if (magicType->kind() == MagicType::Kind::ABI)

libsolidity/codegen/ExpressionCompiler.cpp

@@ -1303,6 +1303,8 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 			{
 				switch (funType->kind())
 				{
+				case FunctionType::Kind::Declaration:
+					break;
 				case FunctionType::Kind::Internal:
 					// We do not visit the expression here on purpose, because in the case of an
 					// internal library function call, this would push the library address forcing

test/libsolidity/syntaxTests/types/contractTypeType/members/base_contract.sol

@@ -3,9 +3,9 @@ contract B {
     function g() public {}
 }
 contract C is B {
-    function h() public {
-        B.f.selector;
-        B.g.selector;
+    function h() public returns (bytes4 fs, bytes4 gs) {
+        fs = B.f.selector;
+        gs = B.g.selector;
         B.g();
     }
 }

test/libsolidity/syntaxTests/types/contractTypeType/members/function_selector_via_contract_name.sol

@@ -3,7 +3,7 @@ contract A {
 }
 
 contract B {
-    function g() external pure {
-        A.f.selector;
+    function g() external pure returns(bytes4) {
+        return A.f.selector;
     }
 }

test/libsolidity/syntaxTests/types/contractTypeType/members/function_selector_via_interface_name.sol

@@ -3,7 +3,7 @@ interface I {
 }
 
 contract B {
-    function g() external pure {
-        I.f.selector;
+    function g() external pure returns(bytes4) {
+        return I.f.selector;
     }
 }

test/libsolidity/syntaxTests/types/contractTypeType/members/function_via_contract_name_public.sol

@@ -3,7 +3,7 @@ contract A {
 }
 
 contract B {
-    function g() external pure {
-        A.f.selector;
+    function g() external pure returns(bytes4) {
+        return A.f.selector;
     }
 }

test/libsolidity/syntaxTests/types/function_types/function_definition_expression.sol

@@ -0,0 +1,11 @@
+interface Banana {
+    function transfer(address,uint256) external returns(bool);
+}
+
+contract Apple {
+    function f() public pure {
+        Banana.transfer;
+    }
+}
+// ----
+// Warning: (141-156): Statement has no effect.

test/libsolidity/syntaxTests/types/function_types/selector/function_selector_pure.sol

@@ -0,0 +1,14 @@
+interface A {
+    function f() external;
+}
+contract B {
+    function g() public {}
+}
+
+contract C is B {
+    function h() external {}
+    bytes4 constant s1 = A.f.selector;
+    bytes4 constant s2 = B.g.selector;
+    bytes4 constant s3 = this.h.selector;
+    bytes4 constant s4 = super.g.selector;
+}

test/libsolidity/syntaxTests/types/function_types/selector/local_variable_selector_not_pure.sol

@@ -0,0 +1,8 @@
+contract C {
+    function f() public pure returns (bytes4) {
+        function() external g;
+        // Make sure g.selector is not considered pure:
+        // If it was considered pure, this would emit a warning "Statement has no effect".
+        g.selector;
+    }
+}

test/libsolidity/syntaxTests/types/function_types/selector/state_variable_selector_contract_name.sol

@@ -0,0 +1,9 @@
+contract A {
+    function() external public f;
+}
+
+contract C {
+    bytes4 constant s4 = A.f.selector;
+}
+// ----
+// TypeError: (88-91): Member "f" not found or not visible after argument-dependent lookup in type(contract A).

test/libsolidity/syntaxTests/types/function_types/selector/state_variable_selector_not_pure.sol

@@ -0,0 +1,17 @@
+contract A {
+    function() external public f;
+}
+contract B {
+    function() external public g;
+}
+
+contract C is B {
+    function() external public h;
+    bytes4 constant s1 = h.selector;
+    bytes4 constant s2 = B.g.selector;
+    bytes4 constant s3 = this.h.selector;
+}
+// ----
+// TypeError: (176-186): Initial value for constant variable has to be compile-time constant.
+// TypeError: (213-225): Initial value for constant variable has to be compile-time constant.
+// TypeError: (252-267): Initial value for constant variable has to be compile-time constant.

test/libsolidity/syntaxTests/types/function_types/selector/state_variable_selector_super.sol

@@ -0,0 +1,9 @@
+contract B {
+    function() external public g;
+}
+
+contract C is B {
+    bytes4 constant s4 = super.g.selector;
+}
+// ----
+// TypeError: (93-100): Member "g" not found or not visible after argument-dependent lookup in contract super C.