[libc++][test] Close LWG3018 and add tests (#93047)

Author: huixie90

libcxx/docs/Status/Cxx20Issues.csv

@@ -191,7 +191,7 @@
 "","","","","",""
 "`1203 <https://wg21.link/LWG1203>`__","More useful rvalue stream insertion","Prague","|Complete|","12.0"
 "`2859 <https://wg21.link/LWG2859>`__","Definition of *reachable* in [ptr.launder] misses pointer arithmetic from pointer-interconvertible object","Prague","",""
-"`3018 <https://wg21.link/LWG3018>`__","``shared_ptr``\  of function type","Prague","",""
+"`3018 <https://wg21.link/LWG3018>`__","``shared_ptr``\  of function type","Prague","|Nothing To Do|",""
 "`3050 <https://wg21.link/LWG3050>`__","Conversion specification problem in ``chrono::duration``\  constructor","Prague","|Complete|","19.0","|chrono|"
 "`3141 <https://wg21.link/LWG3141>`__","``CopyConstructible``\  doesn't preserve source values","Prague","|Nothing to do|",""
 "`3150 <https://wg21.link/LWG3150>`__","``UniformRandomBitGenerator``\  should validate ``min``\  and ``max``\ ","Prague","|Complete|","13.0","|ranges|"

libcxx/test/std/utilities/memory/util.smartptr/util.smartptr.shared/util.smartptr.shared.const/pointer_deleter.pass.cpp

@@ -48,6 +48,27 @@ static_assert(!std::is_constructible<std::shared_ptr<int[5]>, int*, bad_deleter>
 static_assert(!std::is_constructible<std::shared_ptr<int[5]>, int(*)[5], test_deleter<int> >::value, "");
 #endif
 
+int f() { return 5; }
+
+// https://cplusplus.github.io/LWG/issue3018
+// LWG 3018. shared_ptr of function type
+struct function_pointer_deleter {
+  function_pointer_deleter(bool& deleter_called) : deleter_called_(deleter_called) {}
+
+  void operator()(int (*)()) const { deleter_called_ = true; }
+
+  bool& deleter_called_;
+};
+
+void test_function_type() {
+  bool deleter_called = false;
+  {
+    std::shared_ptr<int()> p(&f, function_pointer_deleter(deleter_called));
+    assert((*p)() == 5);
+  }
+  assert(deleter_called);
+}
+
 int main(int, char**)
 {
     {
@@ -94,5 +115,6 @@ int main(int, char**)
     }
 #endif // TEST_STD_VER >= 11
 
+  test_function_type();
   return 0;
 }