Parse override keyword

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

@@ -0,0 +1,7 @@
+contract X {
+	int public override override testvar;
+	function test() internal override override returns (uint256);
+}
+// ----
+// ParserError: (34-42): Override already specified.
+// ParserError: (87-95): Override already specified.

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

@@ -0,0 +1,5 @@
+contract X {
+	int public override testvar;
+	function test() internal override returns (uint256);
+}
+// ----

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

@@ -0,0 +1,10 @@
+contract A {
+	int public testvar;
+	function test() internal returns (uint256);
+}
+contract X is A {
+	int public override testvar;
+	function test() internal override() returns (uint256);
+}
+// ----
+// ParserError: (164-165): Expected identifier but got ')'

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

@@ -0,0 +1,9 @@
+contract A {
+	function foo() internal returns (uint256);
+}
+contract X {
+	int public override testvar;
+	function test() internal override returns (uint256);
+	function foo() internal override(X, A) returns (uint256);
+}
+// ----

test/libsolidity/syntaxTests/inheritance/override/override_multiple_fail1.sol

@@ -0,0 +1,8 @@
+contract A {
+	function foo() internal returns (uint256);
+}
+contract X {
+	int public override(A,) testvar;
+}
+// ----
+// ParserError: (95-96): Expected identifier but got ')'

test/libsolidity/syntaxTests/inheritance/override/override_multiple_fail2.sol

@@ -0,0 +1,8 @@
+contract A {
+	function foo() internal returns (uint256);
+}
+contract X {
+	function test() internal override(,) returns (uint256);
+}
+// ----
+// ParserError: (107-108): Expected identifier but got ','

test/libsolidity/syntaxTests/inheritance/override/override_multiple_fail3.sol

@@ -0,0 +1,8 @@
+contract A {
+	function foo() internal returns (uint256);
+}
+contract X {
+	function foo() internal override(X, address) returns (uint256);
+}
+// ----
+// ParserError: (109-116): Expected identifier but got 'address'

test/libsolidity/syntaxTests/inheritance/override/override_multiple_fail4.sol

@@ -0,0 +1,8 @@
+contract A {
+	function foo() internal returns (uint256);
+}
+contract X {
+	int public override() testvar;
+}
+// ----
+// ParserError: (93-94): Expected identifier but got ')'