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, 16 insertions, 24 deletions

diff --git a/include/gsl/gsl_util b/include/gsl/gsl_util
index ee61711..542bbaa 100644
--- a/include/gsl/gsl_util
+++ b/include/gsl/gsl_util
@@ -34,8 +34,8 @@
 #if _MSC_VER < 1910
 #pragma push_macro("constexpr")
 #define constexpr /*constexpr*/
-#endif                          // _MSC_VER < 1910
-#endif                          // _MSC_VER
+#endif            // _MSC_VER < 1910
+#endif            // _MSC_VER
 
 namespace gsl
 {
@@ -62,6 +62,7 @@ public:
     final_action& operator=(const final_action&) = delete;
     final_action& operator=(final_action&&) = delete;
 
+    GSL_SUPPRESS(f.6) // NO-FORMAT: attribute // terminate if throws
     ~final_action() noexcept
     {
         if (invoke_) f_();
@@ -69,12 +70,11 @@ public:
 
 private:
     F f_;
-    bool invoke_ {true};
+    bool invoke_{true};
 };
 
 // finally() - convenience function to generate a final_action
 template <class F>
-
 final_action<F> finally(const F& f) noexcept
 {
     return final_action<F>(f);
@@ -88,10 +88,7 @@ final_action<F> finally(F&& f) noexcept
 
 // narrow_cast(): a searchable way to do narrowing casts of values
 template <class T, class U>
-#if defined(__clang__) || defined(__GNUC__)
-#else
-[[gsl::suppress(type.1)]]
-#endif
+GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
 constexpr T narrow_cast(U&& u) noexcept
 {
     return static_cast<T>(std::forward<U>(u));
@@ -108,15 +105,13 @@ namespace details
         : public std::integral_constant<bool, std::is_signed<T>::value == std::is_signed<U>::value>
     {
     };
-}
+} // namespace details
 
 // narrow() : a checked version of narrow_cast() that throws if the cast changed the value
 template <class T, class U>
-#if defined(__clang__) || defined(__GNUC__)
-#else
-[[gsl::suppress(type.1)]]
-#endif
-T narrow(U u)
+GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
+GSL_SUPPRESS(f.6) // NO-FORMAT: attribute // TODO: MSVC /analyze does not recognise noexcept(false)
+T narrow(U u) noexcept(false)
 {
     T t = narrow_cast<T>(u);
     if (static_cast<U>(t) != u) gsl::details::throw_exception(narrowing_error());
@@ -129,29 +124,26 @@ T narrow(U u)
 // at() - Bounds-checked way of accessing builtin arrays, std::array, std::vector
 //
 template <class T, std::size_t N>
-#if defined(__clang__) || defined(__GNUC__)
-#else
-[[gsl::suppress(type.1,bounds.2,bounds.4)]]
-#endif
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
 constexpr T& at(T (&arr)[N], const index i)
 {
     Expects(i >= 0 && i < narrow_cast<index>(N));
-    return arr[static_cast<std::size_t>(i)];
+    return arr[narrow_cast<std::size_t>(i)];
 }
 
 template <class Cont>
-#if defined(__clang__) || defined(__GNUC__)
-#else
-[[gsl::suppress(type.1,bounds.4)]]
-#endif
+GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
+GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
 constexpr auto at(Cont& cont, const index i) -> decltype(cont[cont.size()])
 {
     Expects(i >= 0 && i < narrow_cast<index>(cont.size()));
     using size_type = decltype(cont.size());
-    return cont[static_cast<size_type>(i)];
+    return cont[narrow_cast<size_type>(i)];
 }
 
 template <class T>
+GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
 constexpr T at(const std::initializer_list<T> cont, const index i)
 {
     Expects(i >= 0 && i < narrow_cast<index>(cont.size()));