fix(cpp1): handle known UFCS corner cases

Provide transparent SFINAE.
Forward `noexcept`.
Accept object with unparenthesized comma like `v<a, b>`.
Disable UFCS in `f := t().f();`.
Do not capture in signatures.

Incidentially, merge the UFCS macros.

Author: JohelEGP

include/cpp2util.h

@@ -191,7 +191,7 @@
         // in our -pure-cpp2 "import std;" simulation mode... if you need this,
         // use mixed mode (not -pure-cpp2) and #include all the headers you need
         // including this one
-        // 
+        //
         // #include <execution>
     #endif
 
@@ -480,7 +480,7 @@ template<typename T>
 auto Typeid() -> decltype(auto) {
 #ifdef CPP2_NO_RTTI
     Type.expects(
-        !"'any' dynamic casting is disabled with -fno-rtti", // more likely to appear on console 
+        !"'any' dynamic casting is disabled with -fno-rtti", // more likely to appear on console
          "'any' dynamic casting is disabled with -fno-rtti"  // make message available to hooked handlers
     );
 #else
@@ -670,12 +670,19 @@ class out {
 //-----------------------------------------------------------------------
 //
 #if defined(_MSC_VER) && !defined(__clang_major__)
-    #define CPP2_FORCE_INLINE        __forceinline
-    #define CPP2_FORCE_INLINE_LAMBDA [[msvc::forceinline]]
+    #define CPP2_FORCE_INLINE              __forceinline
+    #define CPP2_FORCE_INLINE_LAMBDA       [[msvc::forceinline]]
+    #define CPP2_FORCE_INLINE_LAMBDA_CLANG /* empty */
     #define CPP2_LAMBDA_NO_DISCARD
 #else
-    #define CPP2_FORCE_INLINE        __attribute__((always_inline))
-    #define CPP2_FORCE_INLINE_LAMBDA __attribute__((always_inline))
+    #define CPP2_FORCE_INLINE              __attribute__((always_inline))
+    #if defined(__clang__)
+        #define CPP2_FORCE_INLINE_LAMBDA       /* empty */
+        #define CPP2_FORCE_INLINE_LAMBDA_CLANG __attribute__((always_inline))
+    #else
+        #define CPP2_FORCE_INLINE_LAMBDA       __attribute__((always_inline))
+        #define CPP2_FORCE_INLINE_LAMBDA_CLANG /* empty */
+    #endif
 
     #if defined(__clang_major__)
         //  Also check __cplusplus, only to satisfy Clang -pedantic-errors
@@ -701,84 +708,40 @@ class out {
 #endif
 
 
-//  Note: [&] is because a nested UFCS might be viewed as trying to capture 'this'
-
-#define CPP2_UFCS(FUNCNAME,PARAM1,...) \
-[&] CPP2_LAMBDA_NO_DISCARD (auto&& obj, auto&& ...params) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).FUNCNAME(CPP2_FORWARD(params)...); }) { \
-        return CPP2_FORWARD(obj).FUNCNAME(CPP2_FORWARD(params)...); \
+#define CPP2_UFCS_(LAMBDADEFCAPT,TEMPKW,...) \
+[LAMBDADEFCAPT] CPP2_LAMBDA_NO_DISCARD (auto&& obj, auto&& ...params) CPP2_FORCE_INLINE_LAMBDA_CLANG \
+  noexcept(requires { requires requires { CPP2_FORWARD(obj).TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); }; \
+                      requires noexcept(CPP2_FORWARD(obj).TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...)); } \
+           || requires { requires !requires { CPP2_FORWARD(obj).TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); }; \
+                         requires noexcept(__VA_ARGS__(CPP2_FORWARD(obj), CPP2_FORWARD(params)...)); }) \
+    CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) \
+    requires requires { CPP2_FORWARD(obj).TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); } \
+             || requires { __VA_ARGS__(CPP2_FORWARD(obj), CPP2_FORWARD(params)...); } { \
+    if constexpr (requires{ CPP2_FORWARD(obj).TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); }) { \
+        return CPP2_FORWARD(obj).TEMPKW __VA_ARGS__(CPP2_FORWARD(params)...); \
     } else { \
-        return FUNCNAME(CPP2_FORWARD(obj), CPP2_FORWARD(params)...); \
+        return __VA_ARGS__(CPP2_FORWARD(obj), CPP2_FORWARD(params)...); \
     } \
-}(PARAM1, __VA_ARGS__)
-
-#define CPP2_UFCS_0(FUNCNAME,PARAM1) \
-[&] CPP2_LAMBDA_NO_DISCARD (auto&& obj) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).FUNCNAME(); }) { \
-        return CPP2_FORWARD(obj).FUNCNAME(); \
-    } else { \
-        return FUNCNAME(CPP2_FORWARD(obj)); \
-    } \
-}(PARAM1)
+}
 
+#if 1 // When not rebasing, enable this branch.
+#define CPP2_UFCS(...)                   CPP2_UFCS_(&,,__VA_ARGS__)
+#define CPP2_UFCS_TEMPLATE(...)          CPP2_UFCS_(&,template,__VA_ARGS__)
+#define CPP2_UFCS_NONLOCAL(...)          CPP2_UFCS_(,,__VA_ARGS__)
+#define CPP2_UFCS_TEMPLATE_NONLOCAL(...) CPP2_UFCS_(,template,__VA_ARGS__)
+#else // When rebasing, enable this branch.
+// `git restore --staged` and `git restore` conflicting sources.
+// Compile `cppfront`. Regenerate conflicting sources. Disable this branch. Complete rebase.
 #define CPP2_UFCS_REMPARENS(...) __VA_ARGS__
-
-#define CPP2_UFCS_TEMPLATE(FUNCNAME,TEMPARGS,PARAM1,...) \
-[&] CPP2_LAMBDA_NO_DISCARD (auto&& obj, auto&& ...params) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(params)...); }) { \
-        return CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(params)...); \
-    } else { \
-        return FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(obj), CPP2_FORWARD(params)...); \
-    } \
-}(PARAM1, __VA_ARGS__)
-
-#define CPP2_UFCS_TEMPLATE_0(FUNCNAME,TEMPARGS,PARAM1) \
-[&] CPP2_LAMBDA_NO_DISCARD (auto&& obj) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (); }) { \
-        return CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (); \
-    } else { \
-        return FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(obj)); \
-    } \
-}(PARAM1)
-
-
-//  But for non-local lambdas [&] is not allowed
-
-#define CPP2_UFCS_NONLOCAL(FUNCNAME,PARAM1,...) \
-[] CPP2_LAMBDA_NO_DISCARD (auto&& obj, auto&& ...params) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).FUNCNAME(CPP2_FORWARD(params)...); }) { \
-        return CPP2_FORWARD(obj).FUNCNAME(CPP2_FORWARD(params)...); \
-    } else { \
-        return FUNCNAME(CPP2_FORWARD(obj), CPP2_FORWARD(params)...); \
-    } \
-}(PARAM1, __VA_ARGS__)
-
-#define CPP2_UFCS_0_NONLOCAL(FUNCNAME,PARAM1) \
-[] CPP2_LAMBDA_NO_DISCARD (auto&& obj) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).FUNCNAME(); }) { \
-        return CPP2_FORWARD(obj).FUNCNAME(); \
-    } else { \
-        return FUNCNAME(CPP2_FORWARD(obj)); \
-    } \
-}(PARAM1)
-
-#define CPP2_UFCS_TEMPLATE_NONLOCAL(FUNCNAME,TEMPARGS,PARAM1,...) \
-[] CPP2_LAMBDA_NO_DISCARD (auto&& obj, auto&& ...params) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(params)...); }) { \
-        return CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(params)...); \
-    } else { \
-        return FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(obj), CPP2_FORWARD(params)...); \
-    } \
-}(PARAM1, __VA_ARGS__)
-
-#define CPP2_UFCS_TEMPLATE_0_NONLOCAL(FUNCNAME,TEMPARGS,PARAM1) \
-[] CPP2_LAMBDA_NO_DISCARD (auto&& obj) CPP2_FORCE_INLINE_LAMBDA -> decltype(auto) { \
-    if constexpr (requires{ CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (); }) { \
-        return CPP2_FORWARD(obj).template FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (); \
-    } else { \
-        return FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS (CPP2_FORWARD(obj)); \
-    } \
-}(PARAM1)
+#define CPP2_UFCS(FUNCNAME,PARAM1,...) CPP2_UFCS_(&,,FUNCNAME)(PARAM1,__VA_ARGS__)
+#define CPP2_UFCS_0(FUNCNAME,PARAM1) CPP2_UFCS_(&,,FUNCNAME)(PARAM1)
+#define CPP2_UFCS_TEMPLATE(FUNCNAME,TEMPARGS,PARAM1,...) CPP2_UFCS_(&,template,FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS)(PARAM1,__VA_ARGS__)
+#define CPP2_UFCS_TEMPLATE_0(FUNCNAME,TEMPARGS,PARAM1) CPP2_UFCS_(&,template,FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS)(PARAM1)
+#define CPP2_UFCS_NONLOCAL(FUNCNAME,PARAM1,...) CPP2_UFCS_(,,FUNCNAME)(PARAM1,__VA_ARGS__)
+#define CPP2_UFCS_0_NONLOCAL(FUNCNAME,PARAM1) CPP2_UFCS_(,,FUNCNAME)(PARAM1)
+#define CPP2_UFCS_TEMPLATE_NONLOCAL(FUNCNAME,TEMPARGS,PARAM1,...) CPP2_UFCS_(,template,FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS)(PARAM1,__VA_ARGS__)
+#define CPP2_UFCS_TEMPLATE_0_NONLOCAL(FUNCNAME,TEMPARGS,PARAM1) CPP2_UFCS_(,template,FUNCNAME CPP2_UFCS_REMPARENS TEMPARGS)(PARAM1)
+#endif
 
 
 //-----------------------------------------------------------------------
@@ -847,17 +810,17 @@ auto is( X const& ) -> bool {
 
 template< typename C, typename X >
     requires (
-        ( std::is_base_of_v<X, C> || 
-          ( std::is_polymorphic_v<C> && std::is_polymorphic_v<X>) 
+        ( std::is_base_of_v<X, C> ||
+          ( std::is_polymorphic_v<C> && std::is_polymorphic_v<X>)
         ) && !std::is_same_v<C,X>)
 auto is( X const& x ) -> bool {
     return Dynamic_cast<C const*>(&x) != nullptr;
 }
 
 template< typename C, typename X >
     requires (
-        ( std::is_base_of_v<X, C> || 
-          ( std::is_polymorphic_v<C> && std::is_polymorphic_v<X>) 
+        ( std::is_base_of_v<X, C> ||
+          ( std::is_polymorphic_v<C> && std::is_polymorphic_v<X>)
         ) && !std::is_same_v<C,X>)
 auto is( X const* x ) -> bool {
     return Dynamic_cast<C const*>(x) != nullptr;
@@ -1462,7 +1425,7 @@ inline auto to_string(std::string const& s) -> std::string const&
 
 template<typename T>
 inline auto to_string(T const& sv) -> std::string
-    requires (std::is_convertible_v<T, std::string_view> 
+    requires (std::is_convertible_v<T, std::string_view>
               && !std::is_convertible_v<T, const char*>)
 {
     return std::string{sv};

regression-tests/mixed-bugfix-for-ufcs-non-local.cpp2

@@ -0,0 +1,35 @@
+template<bool> struct t { };
+constexpr bool f(const t<true>&) { return true; }
+constexpr t<true> o{};
+
+// Variables.
+
+// _: <V: t<o.f()>> bool = (); // Blocked on #389, [GCC109781][].
+
+// _: t<o.f()> = (); // Blocked on Clang 12 (lambda in unevaluated context).
+
+_: bool = o.f();
+
+// Functions.
+
+// g: <V: t<o.f()>> () = { } // Blocked on [GCC109781][].
+
+// g: (x: t<o.f()>) = { } // Blocked on Clang 12 (lambda in unevaluated context).
+
+g: () [[pre: o.f()]] = { }
+
+// h: () -> t<o.f()> = o; // Blocked on Clang 12 (lambda in unevaluated context).
+
+// Aliases.
+
+// a: <V: t<o.f()>> type == bool; // Blocked on [GCC109781][].
+
+// b: <V: t<o.f()>> _ == false; // Blocked on [GCC109781][].
+
+// c: type == t<o.f()>; // Blocked on Clang 12 (lambda in unevaluated context).
+
+// d: _ == t<o.f()>(); // Blocked on Clang 12 (lambda in unevaluated context).
+
+main: () = { }
+
+// [GCC109781]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109781

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

@@ -0,0 +1,46 @@
+print_res: (x: i32) -> i32 = {
+  std::cout << x;
+  if (x == 9) { std::cout << '\n'; }
+  return x;
+}
+t: @struct type = {
+  f: (inout this) -> i32 = print_res(0);
+  f: (inout this, x) -> i32 = print_res(1);
+  f: <T> (inout this) -> i32 = print_res(2);
+  f: <T> (inout this, x) -> i32 = print_res(3);
+  f: <T, U> (inout this, x, y) -> i32 = print_res(4);
+}
+f: (o: t) -> i32 = print_res(5);
+f: (o: t, x) -> i32 = print_res(6);
+f: <T> (o: t) -> i32 = print_res(7);
+f: <T> (o: t, x) -> i32 = print_res(8);
+f: <T, U> (o: t, x, y) -> i32 = print_res(9);
+m: t       = ();
+n: const t = ();
+a: <T, U> _ == n;
+_: i32   = m.f();
+_: i32   = m.f(0);
+_: i32   = m.f<t>();
+_: i32   = m.f<t>(0);
+_: i32   = m.f<t, t>(0, 0);
+_: i32   = n.f();
+_: i32   = n.f(0);
+_: i32   = n.f<t>();
+_: i32   = n.f<t>(0);
+_: i32   = n.f<t, t>(0, 0);
+_: i32   = a<t, t>.f<t, t>(0, 0);
+main: () = {
+  _: i32 = m.f();
+  _: i32 = m.f(0);
+  _: i32 = m.f<t>();
+  _: i32 = m.f<t>(0);
+  _: i32 = m.f<t, t>(0, 0);
+  _: i32 = n.f();
+  _: i32 = n.f(0);
+  _: i32 = n.f<t>();
+  _: i32 = n.f<t>(0);
+  _: i32 = n.f<t, t>(0, 0);
+  _: i32 = a<t, t>.f<t, t>(0, 0);
+
+  _ = :(a, f) = { _ = a.f(a).f(); };
+}

regression-tests/pure2-bugfix-for-ufcs-name-lookup.cpp2

@@ -0,0 +1,6 @@
+t: type = {
+  f: (this) -> i32 = 0;
+}
+main: () = {
+  f := t().f();
+}

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

@@ -0,0 +1,6 @@
+t: type = {
+  // swap: (inout this, that) = { } // Blocked on #508.
+}
+main: () = {
+  // static_assert(noexcept(t().swap(t()))); // Blocked on Clang 12 (lambda in unevaluated context).
+}

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

@@ -0,0 +1,5 @@
+// f: <T> () -> std::type_identity_t<decltype(T().a())> = { } // Blocked on Clang 12 (lambda in unevaluated context).
+B: type                                              = { }
+main: ()                                             = {
+  // static_assert(!std::invocable<decltype(:<T> (x: T) -> std::void_t<decltype(f<T>())> = {}), B>); // Blocked on Clang 12 (lambda in unevaluated context).
+}

regression-tests/test-results/clang-18/clang-version.output

@@ -1,4 +1,4 @@
-clang version 18.0.0 (https://git.uplinklabs.net/mirrors/llvm-project.git c0abd3814564a568dfc607c216e6407eaa314f46)
+clang version 18.0.0 (https://github.com/llvm/llvm-project.git 3723ede3cf5324827f8fbbe7f484c2ee4d7a7204)
 Target: x86_64-pc-linux-gnu
 Thread model: posix
 InstalledDir: /home/johel/root/clang-main/bin

regression-tests/test-results/clang-18/mixed-bugfix-for-ufcs-non-local.cpp.execution

@@ -0,0 +1,4 @@
+0123456789
+9
+0123456789
+9

regression-tests/test-results/clang-18/mixed-bugfix-for-ufcs-non-local.cpp.output

@@ -0,0 +1,4 @@
+0123456789
+9
+0123456789
+9

regression-tests/test-results/clang-18/pure2-bugfix-for-ufcs-arguments.cpp.execution

@@ -24,7 +24,7 @@
     std::set_terminate(std::abort);
 
     std::vector v {1, 2, 3, 4, 5, -999}; 
-    CPP2_UFCS_0(pop_back, v);
+    CPP2_UFCS(pop_back)(v);
     std::cout << cpp2::assert_in_bounds(std::move(v), 5) << "\n";
 }
 

regression-tests/test-results/clang-18/pure2-bugfix-for-ufcs-arguments.cpp.output

@@ -38,7 +38,7 @@ auto add_42_to_subrange(auto& rng, cpp2::in<int> start, cpp2::in<int> end) -> vo
 auto add_42_to_subrange(auto& rng, cpp2::in<int> start, cpp2::in<int> end) -> void
 {
     cpp2::Bounds.expects(cpp2::cmp_less_eq(0,start), "");
-    cpp2::Bounds.expects(cpp2::cmp_less_eq(end,CPP2_UFCS_0(ssize, rng)), "");
+    cpp2::Bounds.expects(cpp2::cmp_less_eq(end,CPP2_UFCS(ssize)(rng)), "");
 
     auto count {0}; 
     for ( 

regression-tests/test-results/clang-18/pure2-bugfix-for-ufcs-name-lookup.cpp.execution

@@ -37,7 +37,7 @@ auto print_subrange(auto const& rng, cpp2::in<int> start, cpp2::in<int> end) ->
 
 auto print_subrange(auto const& rng, cpp2::in<int> start, cpp2::in<int> end) -> void{
     cpp2::Bounds.expects(cpp2::cmp_less_eq(0,start), "");
-    cpp2::Bounds.expects(cpp2::cmp_less_eq(end,CPP2_UFCS_0(ssize, rng)), "");
+    cpp2::Bounds.expects(cpp2::cmp_less_eq(end,CPP2_UFCS(ssize)(rng)), "");
 
     auto count {0}; 
     for ( 

regression-tests/test-results/clang-18/pure2-bugfix-for-ufcs-name-lookup.cpp.output

@@ -0,0 +1,64 @@
+
+
+//=== Cpp2 type declarations ====================================================
+
+
+#include "cpp2util.h"
+
+
+
+//=== Cpp2 type definitions and function declarations ===========================
+
+template<bool> struct t { };
+constexpr bool f(const t<true>&) { return true; }
+constexpr t<true> o{};
+
+// Variables.
+
+// _: <V: t<o.f()>> bool = (); // Blocked on #389, [GCC109781][].
+
+// _: t<o.f()> = (); // Blocked on Clang 12 (lambda in unevaluated context).
+
+#line 11 "mixed-bugfix-for-ufcs-non-local.cpp2"
+extern bool auto_11_1;
+
+// Functions.
+
+// g: <V: t<o.f()>> () = { } // Blocked on [GCC109781][].
+
+// g: (x: t<o.f()>) = { } // Blocked on Clang 12 (lambda in unevaluated context).
+
+auto g() -> void;
+
+// h: () -> t<o.f()> = o; // Blocked on Clang 12 (lambda in unevaluated context).
+
+// Aliases.
+
+// a: <V: t<o.f()>> type == bool; // Blocked on [GCC109781][].
+
+// b: <V: t<o.f()>> _ == false; // Blocked on [GCC109781][].
+
+// c: type == t<o.f()>; // Blocked on Clang 12 (lambda in unevaluated context).
+
+// d: _ == t<o.f()>(); // Blocked on Clang 12 (lambda in unevaluated context).
+
+auto main() -> int;
+
+// [GCC109781]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109781
+
+
+//=== Cpp2 function definitions =================================================
+
+
+#line 11 "mixed-bugfix-for-ufcs-non-local.cpp2"
+bool auto_11_1 {CPP2_UFCS_NONLOCAL(f)(o)}; 
+
+#line 19 "mixed-bugfix-for-ufcs-non-local.cpp2"
+auto g() -> void{
+                         cpp2::Default.expects(CPP2_UFCS(f)(o), "");
+#line 19 "mixed-bugfix-for-ufcs-non-local.cpp2"
+}
+
+#line 33 "mixed-bugfix-for-ufcs-non-local.cpp2"
+auto main() -> int{}
+