fix cppcorecheck warnings (#703)

* Added c++17 test configurations for clang5.0 and clang6.0

* Fixed CppCoreCheck warnings in GSL and tests

- Added CMakeSettings.json for VS Open Folder configuration
	- So we can easily run CppCoreCheck in VS
- Fixed CppCorecheck warnings where it made sense
- Suppressed the rest
	- Some suppression does not work due to compiler/tool bugs,
          so replaced by #pragma disable
	- CppCoreCheck has noise, suppressed those with comments
	- Catch produces many warnings, blanket-supressed them all
- Had to fix clang formatting to keep attributes in place
	- clang-format does not support attributes, so I am using
        - "CommentPragmas: '^ NO-FORMAT:'" to skip formatiting on them
- Removed GSL_NOEXCEPT macro, removed incorred noexcepts

* Ignore unknown attributes

* ignore unknown attributes in noexception mode tests

* fixed C26472 in at()

* created GSL_SUPPRESS macro to allow all compilers to parse suppression attributes

* try to fix gcc compilation problems with attributes

* ignore gsl::suppress for gcc

* move suppression to function level on return statements

clang5.0 and up does not allow attributes on return statemets in constexpr functions

* move suppression to function level on return statements

* use GSL_SUPPRESS in algorithm_tests

* Addressed PR comments

1 files changed, 34 insertions, 5 deletions

diff --git a/tests/notnull_tests.cpp b/tests/notnull_tests.cpp
index 1cb9c10..e522fb5 100644
--- a/tests/notnull_tests.cpp
+++ b/tests/notnull_tests.cpp
@@ -14,6 +14,13 @@
 //
 ///////////////////////////////////////////////////////////////////////////////
 
+#ifdef _MSC_VER
+// blanket turn off warnings from CppCoreCheck from catch
+// so people aren't annoyed by them when running the tool.
+#pragma warning(disable : 26440 26426) // from catch
+
+#endif
+
 #include <catch/catch.hpp> // for AssertionHandler, StringRef, CHECK, TEST_...
 
 #include <gsl/pointers> // for not_null, operator<, operator<=, operator>
@@ -63,6 +70,7 @@ struct CustomPtr
 template <typename T, typename U>
 std::string operator==(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
     return reinterpret_cast<const void*>(lhs.p_) == reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -70,6 +78,7 @@ std::string operator==(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator!=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
     return reinterpret_cast<const void*>(lhs.p_) != reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -77,6 +86,7 @@ std::string operator!=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator<(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
     return reinterpret_cast<const void*>(lhs.p_) < reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                          : "false";
 }
@@ -84,6 +94,7 @@ std::string operator<(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator>(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
     return reinterpret_cast<const void*>(lhs.p_) > reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                          : "false";
 }
@@ -91,6 +102,7 @@ std::string operator>(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator<=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
     return reinterpret_cast<const void*>(lhs.p_) <= reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -98,6 +110,7 @@ std::string operator<=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 template <typename T, typename U>
 std::string operator>=(CustomPtr<T> const& lhs, CustomPtr<U> const& rhs)
 {
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
     return reinterpret_cast<const void*>(lhs.p_) >= reinterpret_cast<const void*>(rhs.p_) ? "true"
                                                                                           : "false";
 }
@@ -111,9 +124,19 @@ struct NonCopyableNonMovable
     NonCopyableNonMovable& operator=(NonCopyableNonMovable&&) = delete;
 };
 
-bool helper(not_null<int*> p) { return *p == 12; }
-bool helper_const(not_null<const int*> p) { return *p == 12; }
+GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
+bool helper(not_null<int*> p)
+{
+    return *p == 12;
+}
+
+GSL_SUPPRESS(f.4) // NO-FORMAT: attribute
+bool helper_const(not_null<const int*> p)
+{
+    return *p == 12;
+}
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("TestNotNullConstructors")
 {
 #ifdef CONFIRM_COMPILATION_ERRORS
@@ -143,6 +166,7 @@ TEST_CASE("TestNotNullConstructors")
 }
 
 template<typename T>
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 void ostream_helper(T v)
 {
     not_null<T*> p(&v);
@@ -173,7 +197,8 @@ TEST_CASE("TestNotNullostream")
     ostream_helper<std::string>("string");
 }
 
-
+GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("TestNotNullCasting")
 {
     MyBase base;
@@ -236,6 +261,7 @@ TEST_CASE("TestNotNullRawPointerComparison")
 
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("TestNotNullDereferenceOperator")
 {
     {
@@ -297,6 +323,7 @@ TEST_CASE("TestNotNullSharedPtrComparison")
     CHECK((NotNullSp2(sp2) >= NotNullSp1(sp1)) == (sp2 >= sp1));
 }
 
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("TestNotNullCustomPtrComparison")
 {
     int ints[2] = {42, 43};
@@ -331,6 +358,8 @@ TEST_CASE("TestNotNullCustomPtrComparison")
 
 
 #if defined(__cplusplus) && (__cplusplus >= 201703L)
+
+GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
 TEST_CASE("TestNotNullConstructorTypeDeduction")
 {
     {
@@ -357,7 +386,7 @@ TEST_CASE("TestNotNullConstructorTypeDeduction")
     {
         auto workaround_macro = []() {
             int* p1 = nullptr;
-            not_null x{p1};
+            const not_null x{p1};
         };
         CHECK_THROWS_AS(workaround_macro(), fail_fast);
     }
@@ -365,7 +394,7 @@ TEST_CASE("TestNotNullConstructorTypeDeduction")
     {
         auto workaround_macro = []() {
             const int* p1 = nullptr;
-            not_null x{p1};
+            const not_null x{p1};
         };
         CHECK_THROWS_AS(workaround_macro(), fail_fast);
     }