Issue state mutability restriction for overriding and not for virtual functions.

test/libsolidity/syntaxTests/inheritance/interface/diamond/diamond_no_relist.sol

@@ -1,10 +1,10 @@
 interface Parent {
-    function test() external returns (uint256);
+    function test() external pure returns (uint256);
 }
 
 interface SubA is Parent {}
 interface SubB is Parent {}
 
 contract C is SubA, SubB {
-    function test() external override returns (uint256) { return 42; }
+    function test() external override pure returns (uint256) { return 42; }
 }

test/libsolidity/syntaxTests/inheritance/interface/diamond/diamond_with_relist.sol

@@ -1,15 +1,15 @@
 interface Parent {
-    function test() external returns (uint256);
+    function test() external pure returns (uint256);
 }
 
 interface SubA is Parent {
-    function test() external override returns (uint256);
+    function test() external pure override returns (uint256);
 }
 
 interface SubB is Parent {
-    function test() external override returns (uint256);
+    function test() external pure override returns (uint256);
 }
 
 contract C is SubA, SubB {
-    function test() external override(SubA, SubB) returns (uint256) { return 42; }
+    function test() external pure override(SubA, SubB) returns (uint256) { return 42; }
 }

test/libsolidity/syntaxTests/inheritance/interface/implementation/complete.sol

@@ -1,17 +1,17 @@
 interface ParentA {
-    function testA() external returns (uint256);
+    function testA() external pure returns (uint256);
 }
 
 interface ParentB {
-    function testB() external returns (uint256);
+    function testB() external pure returns (uint256);
 }
 
 interface Sub is ParentA, ParentB {
-    function testSub() external returns (uint256);
+    function testSub() external pure returns (uint256);
 }
 
 contract SubImpl is Sub {
-    function testA() external override returns (uint256) { return 12; }
-    function testB() external override(ParentB) returns (uint256) { return 42; }
-    function testSub() external override returns (uint256) { return 99; }
+    function testA() external pure override returns (uint256) { return 12; }
+    function testB() external pure override(ParentB) returns (uint256) { return 42; }
+    function testSub() external pure override returns (uint256) { return 99; }
 }

test/libsolidity/syntaxTests/inheritance/override/restrict_mutability_for_override_only.sol

@@ -0,0 +1,14 @@
+contract A {
+    // no "state mutability can be restricted"-warning here
+    function foo() external virtual returns (uint) { return 1; }
+}
+contract B is A {
+    // no "state mutability can be restricted"-warning here
+    function foo() external virtual override returns (uint) { return 2; }
+}
+contract C is B {
+    // warning is here
+    function foo() external override returns (uint) { return 3; }
+}
+// ----
+// Warning 2018: (339-400): Function state mutability can be restricted to pure

test/libsolidity/syntaxTests/nameAndTypeResolution/149_test_for_bug_override_function_with_bytearray_type.sol

@@ -5,4 +5,4 @@ contract Bike is Vehicle {
     function f(bytes calldata) override external returns (uint256 r) {r = 42;}
 }
 // ----
-// Warning 2018: (23-95): Function state mutability can be restricted to pure
+// Warning 2018: (129-203): Function state mutability can be restricted to pure