FunctionDefinition.resolveVirtual(): Skip unimplemented functions when lookup happens via super

test/libsolidity/syntaxTests/functionCalls/call_unimplemented_base_via_super.sol

@@ -0,0 +1,18 @@
+abstract contract I {
+    function a() internal view virtual returns(uint256);
+}
+
+abstract contract C is I {
+    function f() public view returns(uint256) {
+        return I.a();
+    }
+}
+
+abstract contract D is I {
+    function f() public view returns(uint256) {
+        return super.a();
+    }
+}
+// ----
+// TypeError 7501: (172-177): Cannot call unimplemented base function.
+// TypeError 9582: (278-285): Member "a" not found or not visible after argument-dependent lookup in type(contract super D).

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

@@ -0,0 +1,13 @@
+contract A {
+    function f() public virtual {}
+}
+abstract contract B {
+    function f() public virtual;
+}
+contract C is A, B {
+    function f() public virtual override(A, B) {
+        B.f(); // Should not skip over to A.f() just because B.f() has no implementation.
+    }
+}
+// ----
+// TypeError 7501: (185-190): Cannot call unimplemented base function.

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

@@ -0,0 +1,12 @@
+contract A {
+    function f() public virtual {}
+}
+abstract contract B {
+    function f() public virtual;
+}
+contract C is A, B {
+    function f() public override(A, B) {
+        super.f(); // super should skip the unimplemented B.f() and call A.f() instead.
+    }
+}
+// ----

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

@@ -0,0 +1,12 @@
+contract A {
+    function f() public virtual {}
+}
+abstract contract B {
+    function f() public virtual;
+}
+contract C is A, B {
+    function f() public override(A, B) {
+        // This is fine. The unimplemented B.f() is not used.
+    }
+}
+// ----

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

@@ -0,0 +1,13 @@
+contract A {
+    function f() public virtual {}
+}
+abstract contract B {
+    function f() public virtual;
+}
+abstract contract C is A, B {
+    function g() public {
+        f(); // Would call B.f() if we did not require an override in C.
+    }
+}
+// ----
+// TypeError 6480: (107-243): Derived contract must override function "f". Two or more base classes define function with same name and parameter types.

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

@@ -0,0 +1,11 @@
+contract A {
+    function f() public virtual {}
+}
+abstract contract B is A {
+    function f() public virtual override;
+}
+contract C is B {
+    function f() public virtual override {}
+}
+// ----
+// TypeError 4593: (81-118): Overriding an implemented function with an unimplemented function is not allowed.