Mark function selector accesses as pure for pure expressions and mark function accesses via contract name as pure.

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.