fix(util): workaround MSVC bug for UFCS of 'F' in member 'F'

Author: JohelEGP

include/cpp2util.h

@@ -788,37 +788,61 @@ class out {
 #define CPP2_UFCS_REMPARENS(...) __VA_ARGS__
 
 // Ideally, the expression `CPP2_UFCS_IS_NOTHROW` expands to
-// is in the _noexcept-specifier_ of the UFCS lambda.
+// is in the _noexcept-specifier_ of the UFCS lambda, but without 'std::declval'.
 // To workaround [GCC bug 101043](https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101043),
 // we instead make it a template parameter of the UFCS lambda.
 // But using a template parameter, Clang also ICEs on an application.
 // So we use these `NOTHROW` macros to fall back to the ideal for when not using GCC.
 #define CPP2_UFCS_IS_NOTHROW(QUALID,TEMPKW,...) \
-   requires { requires requires { std::declval<Obj>().CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(std::declval<Params>()...); }; \
-              requires noexcept(std::declval<Obj>().CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(std::declval<Params>()...)); } \
+   requires { requires  requires { std::declval<Obj>().CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(std::declval<Params>()...); }; \
+              requires    noexcept(std::declval<Obj>().CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(std::declval<Params>()...)); } \
 || requires { requires !requires { std::declval<Obj>().CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(std::declval<Params>()...); }; \
               requires noexcept(CPP2_UFCS_REMPARENS QUALID __VA_ARGS__(std::declval<Obj>(), std::declval<Params>()...)); }
-#define CPP2_UFCS_IS_NOTHROW_PARAM(QUALID,TEMPKW,...) /*empty*/
-#define CPP2_UFCS_IS_NOTHROW_ARG(QUALID,TEMPKW,...) CPP2_UFCS_IS_NOTHROW(QUALID,TEMPKW,__VA_ARGS__)
+#define CPP2_UFCS_IS_NOTHROW_PARAM(...)               /*empty*/
+#define CPP2_UFCS_IS_NOTHROW_ARG(QUALID,TEMPKW,...)   CPP2_UFCS_IS_NOTHROW(QUALID,TEMPKW,__VA_ARGS__)
 #if defined(__GNUC__) && !defined(__clang__)
-    #undef CPP2_UFCS_IS_NOTHROW_PARAM
-    #undef CPP2_UFCS_IS_NOTHROW_ARG
+    #undef  CPP2_UFCS_IS_NOTHROW_PARAM
+    #undef  CPP2_UFCS_IS_NOTHROW_ARG
     #define CPP2_UFCS_IS_NOTHROW_PARAM(QUALID,TEMPKW,...) , bool IsNothrow = CPP2_UFCS_IS_NOTHROW(QUALID,TEMPKW,__VA_ARGS__)
-    #define CPP2_UFCS_IS_NOTHROW_ARG(QUALID,TEMPKW,...)   IsNothrow
+    #define CPP2_UFCS_IS_NOTHROW_ARG(...)                 IsNothrow
     #if __GNUC__ < 11
-        #undef CPP2_UFCS_IS_NOTHROW_PARAM
-        #undef CPP2_UFCS_IS_NOTHROW_ARG
+        #undef  CPP2_UFCS_IS_NOTHROW_PARAM
+        #undef  CPP2_UFCS_IS_NOTHROW_ARG
         #define CPP2_UFCS_IS_NOTHROW_PARAM(...)    /*empty*/
         #define CPP2_UFCS_IS_NOTHROW_ARG(...)      false // GCC 10 UFCS is always potentially-throwing.
     #endif
 #endif
 
+// Ideally, the expression `CPP2_UFCS_CONSTRAINT_ARG` expands to
+// is in the _requires-clause_ of the UFCS lambda.
+// To workaround an MSVC bug within a member function 'F' where UFCS is also for 'F'
+// (<https://github.com/hsutter/cppfront/pull/506#issuecomment-1826086952>),
+// we instead make it a template parameter of the UFCS lambda.
+// But using a template parameter, Clang also ICEs and GCC rejects a local 'F'.
+// Also, Clang rejects the SFINAE test case when using 'std::declval'.
+// So we use these `CONSTRAINT` macros to fall back to the ideal for when not using MSVC.
+#define CPP2_UFCS_CONSTRAINT_PARAM(...)               /*empty*/
+#define CPP2_UFCS_CONSTRAINT_ARG(QUALID,TEMPKW,...) \
+   requires { CPP2_FORWARD(obj).CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); } \
+|| requires { CPP2_UFCS_REMPARENS QUALID __VA_ARGS__(CPP2_FORWARD(obj), CPP2_FORWARD(params)...); }
+#if defined(_MSC_VER)
+    #undef  CPP2_UFCS_CONSTRAINT_PARAM
+    #undef  CPP2_UFCS_CONSTRAINT_ARG
+    #define CPP2_UFCS_CONSTRAINT_PARAM(QUALID,TEMPKW,...) , bool IsViable = \
+   requires { std::declval<Obj>().CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(std::declval<Params>()...); } \
+|| requires { CPP2_UFCS_REMPARENS QUALID __VA_ARGS__(std::declval<Obj>(), std::declval<Params>()...); }
+    #define CPP2_UFCS_CONSTRAINT_ARG(...)                 IsViable
+#endif
+
 #define CPP2_UFCS_(LAMBDADEFCAPT,QUALID,TEMPKW,...) \
-[LAMBDADEFCAPT]<typename Obj, typename... Params CPP2_UFCS_IS_NOTHROW_PARAM(QUALID,TEMPKW,__VA_ARGS__)> \
+[LAMBDADEFCAPT]< \
+    typename Obj, typename... Params \
+    CPP2_UFCS_IS_NOTHROW_PARAM(QUALID,TEMPKW,__VA_ARGS__) \
+    CPP2_UFCS_CONSTRAINT_PARAM(QUALID,TEMPKW,__VA_ARGS__) \
+  > \
   CPP2_LAMBDA_NO_DISCARD (Obj&& obj, Params&& ...params) CPP2_FORCE_INLINE_LAMBDA_CLANG \
   noexcept(CPP2_UFCS_IS_NOTHROW_ARG(QUALID,TEMPKW,__VA_ARGS__)) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) \
-    requires requires { CPP2_FORWARD(obj).CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); } \
-             || requires { CPP2_UFCS_REMPARENS QUALID __VA_ARGS__(CPP2_FORWARD(obj), CPP2_FORWARD(params)...); } { \
+    requires CPP2_UFCS_CONSTRAINT_ARG(QUALID,TEMPKW,__VA_ARGS__) { \
     if constexpr (requires{ CPP2_FORWARD(obj).CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); }) { \
         return CPP2_FORWARD(obj).CPP2_UFCS_REMPARENS QUALID TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); \
     } else { \

regression-tests/pure2-bugfix-for-ufcs-arguments.cpp2

@@ -60,3 +60,12 @@ t: @struct <T: int, U: int> type = {
   f: <V: int> (_: int) -> i32 = 0;
 }
 } // namespace ns
+
+A: @struct type = {
+  f: (this) = { }
+}
+
+B: @struct type = {
+  m: A;
+  f: (this) = m.f();
+}

regression-tests/test-results/pure2-bugfix-for-ufcs-arguments.cpp

@@ -19,6 +19,12 @@ template<int T, int U> class t;
 
 }
 
+class A;
+  
+
+#line 68 "pure2-bugfix-for-ufcs-arguments.cpp2"
+class B;
+  
 
 //=== Cpp2 type definitions and function declarations ===========================
 
@@ -68,6 +74,15 @@ template<int T, int U> class t {
 };
 } // namespace ns
 
+class A {
+  public: auto f() const& -> void;
+};
+
+class B {
+  public: A m; 
+  public: auto f() const& -> void;
+};
+
 
 //=== Cpp2 function definitions =================================================
 
@@ -136,3 +151,9 @@ namespace ns {
 
 }
 
+#line 65 "pure2-bugfix-for-ufcs-arguments.cpp2"
+  auto A::f() const& -> void{}
+
+#line 70 "pure2-bugfix-for-ufcs-arguments.cpp2"
+  auto B::f() const& -> void { CPP2_UFCS(f)(m);  }
+