Add override exception for interface functions.

test/libsolidity/syntaxTests/inheritance/interface/overrides_multiple.sol

@@ -23,8 +23,6 @@ interface Sub is SuperA, SuperB {
 }
 
 // ----
-// TypeError 9456: (572-616): Overriding function is missing "override" specifier.
-// TypeError 9456: (572-616): Overriding function is missing "override" specifier.
 // TypeError 4327: (572-616): Function needs to specify overridden contracts "SuperA" and "SuperB".
 // TypeError 4327: (647-655): Function needs to specify overridden contracts "SuperA" and "SuperB".
 // TypeError 4327: (705-721): Function needs to specify overridden contract "SuperB".

test/libsolidity/syntaxTests/inheritance/interface/overrides_single.sol

@@ -11,4 +11,3 @@ interface Sub is Super {
 }
 
 // ----
-// TypeError 9456: (197-241): Overriding function is missing "override" specifier.

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

@@ -6,9 +6,9 @@ interface I {
 }
 contract C is I {
     uint dummy;
-    function f(uint[] memory) public override pure {}
-    function g(uint[] memory) public override view { dummy; }
-    function h(uint[] memory) public override { dummy = 42; }
-    function i(uint[] memory) public override payable {}
+    function f(uint[] memory) public pure {}
+    function g(uint[] memory) public view { dummy; }
+    function h(uint[] memory) public { dummy = 42; }
+    function i(uint[] memory) public payable {}
 }
 // ----

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

@@ -2,7 +2,7 @@ interface I {
     function f(uint[] calldata) external pure;
 }
 contract A is I {
-    function f(uint[] memory) public override pure {}
+    function f(uint[] memory) public pure {}
 }
 contract C {
     function f() public {

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

@@ -9,8 +9,8 @@ interface I {
 contract C is I {
     uint dummy;
     function f(S memory) public override pure {}
-    function g(S memory) public override view { dummy; }
+    function g(S memory) public view { dummy; }
     function h(S memory) public override { dummy = 42; }
-    function i(S memory) public override payable {}
+    function i(S memory) public payable {}
 }
 // ----

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

@@ -7,5 +7,4 @@ contract B is I {
   function f() public pure returns (uint, uint) {}
 }
 // ----
-// TypeError 9456: (182-230): Overriding function is missing "override" specifier.
 // TypeError 4822: (182-230): Overriding function return types differ.

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

@@ -3,15 +3,15 @@ interface I {
     function g() external;
 }
 abstract contract A is I {
-    function f() external override {}
-    function g() external override virtual;
+    function f() external {}
+    function g() external virtual;
 }
 abstract contract B is I {
-    function g() external override {}
-    function f() external override virtual;
+    function g() external {}
+    function f() external virtual;
 }
 contract C is A, B {
 }
 // ----
-// TypeError 6480: (292-314): Derived contract must override function "f". Two or more base classes define function with same name and parameter types.
-// TypeError 6480: (292-314): Derived contract must override function "g". Two or more base classes define function with same name and parameter types.
+// TypeError 6480: (256-278): Derived contract must override function "f". Two or more base classes define function with same name and parameter types.
+// TypeError 6480: (256-278): Derived contract must override function "g". Two or more base classes define function with same name and parameter types.

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

@@ -3,10 +3,10 @@ interface I {
     function g() external;
 }
 abstract contract A is I {
-    function f() external override {}
+    function f() external {}
 }
 abstract contract B is I {
-    function g() external override {}
+    function g() external {}
 }
 contract C is A, B {
 }

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

@@ -3,7 +3,7 @@ interface I {
 }
 abstract contract A is I
 {
-	uint public override f;
+	uint public f;
 }
 abstract contract B is I
 {

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

@@ -3,12 +3,12 @@ interface I {
 }
 contract A is I
 {
-	uint public override f;
+	uint public f;
 }
 abstract contract B is I
 {
-	function f() external virtual override returns (uint);
+	function f() external virtual returns (uint);
 }
 abstract contract C is A, B {}
 // ----
-// TypeError 6480: (185-215): Derived contract must override function "f". Two or more base classes define function with same name and parameter types. Since one of the bases defines a public state variable which cannot be overridden, you have to change the inheritance layout or the names of the functions.
+// TypeError 6480: (167-197): Derived contract must override function "f". Two or more base classes define function with same name and parameter types. Since one of the bases defines a public state variable which cannot be overridden, you have to change the inheritance layout or the names of the functions.

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

@@ -3,12 +3,12 @@ interface I {
 }
 contract A is I
 {
-	uint public override f;
+	uint public f;
 }
 abstract contract B is I
 {
-	function f() external virtual override returns (uint) { return 2; }
+	function f() external virtual returns (uint) { return 2; }
 }
 abstract contract C is A, B {}
 // ----
-// TypeError 6480: (198-228): Derived contract must override function "f". Two or more base classes define function with same name and parameter types. Since one of the bases defines a public state variable which cannot be overridden, you have to change the inheritance layout or the names of the functions.
+// TypeError 6480: (180-210): Derived contract must override function "f". Two or more base classes define function with same name and parameter types. Since one of the bases defines a public state variable which cannot be overridden, you have to change the inheritance layout or the names of the functions.

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

@@ -1,3 +1,3 @@
 interface ERC20 { function x() external returns (uint); }
-contract C is ERC20 { uint public override x; }
+contract C is ERC20 { uint public x; }
 // ----

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

@@ -1,6 +1,6 @@
 interface X { function test() external returns (uint256); }
 contract Y is X {
-    uint256 public override test = 42;
+    uint256 public test = 42;
 }
 contract T {
     constructor() { new Y(); }

test/libsolidity/syntaxTests/inheritance/override/interface_exception/abstract_needed.sol

@@ -0,0 +1,8 @@
+abstract contract I {
+	function f() external virtual;
+}
+contract C is I {
+	function f() external {}
+}
+// ----
+// TypeError 9456: (75-99): Overriding function is missing "override" specifier.

test/libsolidity/syntaxTests/inheritance/override/interface_exception/diamond_needed.sol

@@ -0,0 +1,19 @@
+interface I {
+	function f() external;
+	function g() external;
+	function h() external;
+}
+interface J {
+	function f() external;
+	function g() external;
+	function h() external;
+}
+contract C is I, J {
+	function f() external {}
+	function g() external override {}
+	function h() external override(I) {}
+}
+// ----
+// TypeError 4327: (198-222): Function needs to specify overridden contracts "I" and "J".
+// TypeError 4327: (246-254): Function needs to specify overridden contracts "I" and "J".
+// TypeError 4327: (281-292): Function needs to specify overridden contract "J".

test/libsolidity/syntaxTests/inheritance/override/interface_exception/regular_optional.sol

@@ -0,0 +1,11 @@
+interface I {
+	function f() external;
+	function g() external;
+	function h() external;
+}
+contract C is I {
+	function f() external {}
+	function g() external override {}
+	function h() external override(I) {}
+}
+// ----

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

@@ -1,9 +1,11 @@
 interface A {
 	function test() external returns (uint256);
 	function test2() external returns (uint256);
+	function test3() external returns (uint256);
 }
 contract X is A {
 	function test() external override returns (uint256) {}
 	function test2() external override(A) returns (uint256) {}
+	function test3() external returns (uint256) {}
 }
 // ----

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

@@ -11,11 +11,11 @@ contract X is A, B {
     function goo() external virtual override(A, B) returns (uint) {}
 }
 abstract contract T is A {
-    function foo() external virtual override returns (uint);
-    function goo() external virtual override returns (uint);
+    function foo() external virtual returns (uint);
+    function goo() external virtual returns (uint);
 }
 contract Y is X, T {
 }
 // ----
-// TypeError 6480: (484-506): Derived contract must override function "foo". Two or more base classes define function with same name and parameter types. Since one of the bases defines a public state variable which cannot be overridden, you have to change the inheritance layout or the names of the functions.
-// TypeError 6480: (484-506): Derived contract must override function "goo". Two or more base classes define function with same name and parameter types.
+// TypeError 6480: (466-488): Derived contract must override function "foo". Two or more base classes define function with same name and parameter types. Since one of the bases defines a public state variable which cannot be overridden, you have to change the inheritance layout or the names of the functions.
+// TypeError 6480: (466-488): Derived contract must override function "goo". Two or more base classes define function with same name and parameter types.