Initial basic support for namespaces and user-defined types

Added initial basic support.

Includes:
- access-specifiers: public, protected, private
- defaults: in type scope (aka members), types and functions are public by default, objects (data members) are private by default
- this-specifiers: implicit, virtual, override, final (but can't use them much since we don't have inheritance syntax yet, see next list)
- explicit `this` parameters (where the this-specifiers go)

NOT included yet:
- special member functions (`operator=`)
- inheritance / base classes
- metaclass functions to apply checks, defaults, and generated code (that'll be last...)

This checkin also changes the null/subscript/comparison checking opt-out command-line option from `/xxx-checks-` (which was only because the initial default was to opt into the checks) to `/no-xxx-checks`

Author: hsutter

include/cpp2util.h

@@ -491,10 +491,14 @@ template<typename T>
 //
 //-----------------------------------------------------------------------
 //
+template<typename T>
+constexpr bool prefer_pass_by_value =
+    sizeof(T) < 2*sizeof(void*) && std::is_trivially_copy_constructible_v<T>;
+
 template<typename T>
 using in =
     std::conditional_t <
-        sizeof(T) < 2*sizeof(void*) && std::is_trivially_copy_constructible_v<T>,
+        prefer_pass_by_value<T>,
         T const,
         T const&
     >;

regression-tests/pure2-deducing-pointers-error.cpp2

@@ -6,7 +6,7 @@ fun2: (inout i:int) -> (result : *int) = {
     result = i&;
 }
 
-main: (argc : int, argv : **char) -> int = {
+main: () -> int = {
     a:     int = 2;
     pa:   *int = a&;
     ppa: **int = pa&;

regression-tests/pure2-types-basics.cpp2

@@ -0,0 +1,33 @@
+
+N: namespace = {
+
+myclass : type = {
+
+    f: (virtual this, x: int) = {
+        std::cout << "N::myclass::f with (x)$\n";
+    }
+
+    data: int;
+
+    nested : type = {
+        g: () = std::cout << "N::myclass::nested::g\n";
+    }
+
+    f1: <T     , U     > (t:T, u:U) -> _ = t+u;
+    f2: <T:type, U:type> (t:T, u:U) -> _ = t+u;
+    f3: <T:_   , U:_   > ()         -> _ = T+U;
+    f4: <T:i8  , U:i16 > ()         -> _ = T+U;
+
+}
+
+}
+
+main: () = {
+    x: N::myclass = ();
+    x.f(53);
+    N::myclass::nested::g();
+    std::cout << "f1: (x.f1(1,1))$\n";
+    std::cout << "f2: (x.f2(2,2))$\n";
+    std::cout << "f3: (x.f3<3,3>())$\n";
+    std::cout << "f4: (x.f4<4,4>())$\n";
+}

regression-tests/test-results/clang-12/pure2-types-basics.cpp.execution

@@ -0,0 +1,6 @@
+N::myclass::f with 53
+N::myclass::nested::g
+f1: 2
+f2: 4
+f3: 6
+f4: 8

regression-tests/test-results/clang-12/pure2-types-basics.cpp.output

@@ -0,0 +1,6 @@
+N::myclass::f with 53
+N::myclass::nested::g
+f1: 2
+f2: 4
+f3: 6
+f4: 8

regression-tests/test-results/gcc-10/pure2-types-basics.cpp.execution

@@ -0,0 +1,6 @@
+N::myclass::f with 53
+N::myclass::nested::g
+f1: 2
+f2: 4
+f3: 6
+f4: 8

regression-tests/test-results/gcc-10/pure2-types-basics.cpp.output

@@ -0,0 +1 @@
+pure2-types-basics.cpp

regression-tests/test-results/msvc-2022/pure2-types-basics.cpp.execution

@@ -0,0 +1,50 @@
+
+#define CPP2_USE_MODULES         Yes
+
+#include "cpp2util.h"
+
+
+#line 2 "pure2-types-basics.cpp2"
+namespace N   {
+class myclass;
+};
+#line 25 "pure2-types-basics.cpp2"
+auto main() -> int;
+
+//=== Cpp2 definitions ==========================================================
+
+#line 1 "pure2-types-basics.cpp2"
+
+namespace N   {
+
+class myclass   {
+
+    public: virtual auto f(cpp2::in<int> x) const -> void{
+        std::cout << "N::myclass::f with " + cpp2::to_string(x) + "\n";
+    }
+
+    private: int data; 
+
+    public: class nested {
+        public: static auto g() -> void { std::cout << "N::myclass::nested::g\n"; }
+    };
+
+    public: template<typename T, typename U> [[nodiscard]] static auto f1(T const& t, U const& u) -> auto { return t + u; }
+    public: template<typename T, typename U> [[nodiscard]] static auto f2(T const& t, U const& u) -> auto { return t + u; }
+    public: template<auto T, auto U> [[nodiscard]] static auto f3() -> auto { return T + U; }
+    public: template<cpp2::i8 T, cpp2::i16 U> [[nodiscard]] static auto f4() -> auto { return T + U; }
+
+};
+
+};
+
+auto main() -> int{
+    N::myclass x {}; 
+    CPP2_UFCS(f, x, 53);
+    N::myclass::nested::g();
+    std::cout << "f1: " + cpp2::to_string(CPP2_UFCS(f1, x, 1, 1)) + "\n";
+    std::cout << "f2: " + cpp2::to_string(CPP2_UFCS(f2, x, 2, 2)) + "\n";
+    std::cout << "f3: " + cpp2::to_string(CPP2_UFCS_TEMPLATE_0(f3, (<3,3>), x)) + "\n";
+    std::cout << "f4: " + cpp2::to_string(CPP2_UFCS_TEMPLATE_0(f4, (<4,4>), std::move(x))) + "\n";
+}
+