Give better diagnostic for invalid comparisons, closes #817

Author: hsutter

include/cpp2util.h

@@ -862,11 +862,23 @@ class out {
 //
 //-----------------------------------------------------------------------
 //
+//  For use when returning "no such thing", such as
+//  when customizing "as" for std::variant
+struct nonesuch_ {
+    auto operator==(auto const&) -> bool { return false; }
+};
+constexpr inline nonesuch_ nonesuch;
+
 inline auto to_string(...) -> std::string
 {
     return "(customize me - no cpp2::to_string overload exists for this type)";
 }
 
+inline auto to_string(nonesuch_) -> std::string
+{
+    return "(invalid type)";
+}
+
 inline auto to_string(std::same_as<std::any> auto const&) -> std::string
 {
     return "std::any";
@@ -1093,13 +1105,6 @@ inline constexpr auto is( auto const& x, auto const& value ) -> bool
 //  Built-in as
 //
 
-//  For use when returning "no such thing", such as
-//  when customizing "as" for std::variant
-struct nonesuch_ {
-    auto operator==(auto const&) -> bool { return false; }
-};
-constexpr inline nonesuch_ nonesuch;
-
 //  The 'as' cast functions are <To, From> so use that order here
 //  If it's confusing, we can switch this to <From, To>
 template< typename To, typename From >
@@ -1786,34 +1791,80 @@ CPP2_FORCE_INLINE constexpr auto cmp_mixed_signedness_check() -> void
         //  static_assert to reject the comparison is the right way to go.
         static_assert(
             program_violates_type_safety_guarantee<T, U>,
-            "mixed signed/unsigned comparison is unsafe - prefer using .ssize() instead of .size(), consider using std::cmp_less instead, or consider explicitly casting one of the values to change signedness by using 'as' or 'cpp2::unsafe_narrow'");
+            "mixed signed/unsigned comparison is unsafe - prefer using .ssize() instead of .size(), consider using std::cmp_less instead, or consider explicitly casting one of the values to change signedness by using 'as' or 'cpp2::unsafe_narrow'"
+            );
     }
 }
 
+
 CPP2_FORCE_INLINE constexpr auto cmp_less(auto&& t, auto&& u) -> decltype(auto)
+    requires requires {CPP2_FORWARD(t) < CPP2_FORWARD(u);}
 {
     cmp_mixed_signedness_check<CPP2_TYPEOF(t), CPP2_TYPEOF(u)>();
     return CPP2_FORWARD(t) < CPP2_FORWARD(u);
 }
 
+CPP2_FORCE_INLINE constexpr auto cmp_less(auto&& t, auto&& u) -> decltype(auto)
+{
+    static_assert(
+        program_violates_type_safety_guarantee<decltype(t), decltype(u)>,
+        "attempted to compare '<' for incompatible types"
+        );
+    return nonesuch;
+}
+
+
 CPP2_FORCE_INLINE constexpr auto cmp_less_eq(auto&& t, auto&& u) -> decltype(auto)
+    requires requires {CPP2_FORWARD(t) <= CPP2_FORWARD(u);}
 {
     cmp_mixed_signedness_check<CPP2_TYPEOF(t), CPP2_TYPEOF(u)>();
     return CPP2_FORWARD(t) <= CPP2_FORWARD(u);
 }
 
+CPP2_FORCE_INLINE constexpr auto cmp_less_eq(auto&& t, auto&& u) -> decltype(auto)
+{
+    static_assert(
+        program_violates_type_safety_guarantee<decltype(t), decltype(u)>,
+        "attempted to compare '<=' for incompatible types"
+        );
+    return nonesuch;
+}
+
+
 CPP2_FORCE_INLINE constexpr auto cmp_greater(auto&& t, auto&& u) -> decltype(auto)
+    requires requires {CPP2_FORWARD(t) > CPP2_FORWARD(u);}
 {
     cmp_mixed_signedness_check<CPP2_TYPEOF(t), CPP2_TYPEOF(u)>();
     return CPP2_FORWARD(t) > CPP2_FORWARD(u);
 }
 
+CPP2_FORCE_INLINE constexpr auto cmp_greater(auto&& t, auto&& u) -> decltype(auto)
+{
+    static_assert(
+        program_violates_type_safety_guarantee<decltype(t), decltype(u)>,
+        "attempted to compare '>' for incompatible types"
+        );
+    return nonesuch;
+}
+
+
 CPP2_FORCE_INLINE constexpr auto cmp_greater_eq(auto&& t, auto&& u) -> decltype(auto)
+    requires requires {CPP2_FORWARD(t) >= CPP2_FORWARD(u);}
 {
     cmp_mixed_signedness_check<CPP2_TYPEOF(t), CPP2_TYPEOF(u)>();
     return CPP2_FORWARD(t) >= CPP2_FORWARD(u);
 }
 
+CPP2_FORCE_INLINE constexpr auto cmp_greater_eq(auto&& t, auto&& u) -> decltype(auto)
+{
+    static_assert(
+        program_violates_type_safety_guarantee<decltype(t), decltype(u)>,
+        "attempted to compare '>=' for incompatible types"
+        );
+    return nonesuch;
+}
+
+
 
 //-----------------------------------------------------------------------
 //

regression-tests/test-results/gcc-10/pure2-bugfix-for-requires-clause-in-forward-declaration.cpp.output

@@ -11,18 +11,18 @@ pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:46: error: expect
 In file included from pure2-bugfix-for-requires-clause-in-forward-declaration.cpp:7:
 ../../../include/cpp2util.h:10005:47: error: static assertion failed: GCC 11 or higher is required to support variables and type-scope functions that have a 'requires' clause. This includes a type-scope 'forward' parameter of non-wildcard type, such as 'func: (this, forward s: std::string)', which relies on being able to add a 'requires' clause - in that case, use 'forward s: _' instead if you need the result to compile with GCC 10.
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:4:1: note: in expansion of macro ‘CPP2_REQUIRES_’
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:3: error: no declaration matches ‘element::element(auto:82&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::__ct ::n)>::type>::type, std::__cxx11::string>’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:3: error: no declaration matches ‘element::element(auto:90&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::__ct ::n)>::type>::type, std::__cxx11::string>’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:5:11: note: candidates are: ‘element::element(const element&)’
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp:16:20: note:                 ‘template<class auto:80> element::element(auto:80&&)’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp:16:20: note:                 ‘template<class auto:88> element::element(auto:88&&)’
    16 |   public: explicit element(auto&& n)
       |                    ^~~~~~~
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp:14:7: note: ‘class element’ defined here
    14 | class element {
       |       ^~~~~~~
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:3: error: expected unqualified-id before ‘{’ token
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:8: error: no declaration matches ‘element& element::operator=(auto:83&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::operator=::n)>::type>::type, std::__cxx11::string>’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:8: error: no declaration matches ‘element& element::operator=(auto:91&&) requires  is_same_v<typename std::remove_cv<typename std::remove_reference<decltype(element::operator=::n)>::type>::type, std::__cxx11::string>’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:6:16: note: candidates are: ‘void element::operator=(const element&)’
-pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:16: note:                 ‘template<class auto:81> element& element::operator=(auto:81&&)’
+pure2-bugfix-for-requires-clause-in-forward-declaration.cpp2:3:16: note:                 ‘template<class auto:89> element& element::operator=(auto:89&&)’
 pure2-bugfix-for-requires-clause-in-forward-declaration.cpp:14:7: note: ‘class element’ defined here
    14 | class element {
       |       ^~~~~~~

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

@@ -9,8 +9,8 @@ pure2-print.cpp2:66:1: note: in expansion of macro ‘CPP2_REQUIRES_’
 pure2-print.cpp2:94:1: note: in expansion of macro ‘CPP2_REQUIRES_’
 pure2-print.cpp2:6:29: error: ‘constexpr const T outer::object_alias’ is not a static data member of ‘class outer’
 pure2-print.cpp2:6:36: error: template definition of non-template ‘constexpr const T outer::object_alias’
-pure2-print.cpp2:65:14: error: no declaration matches ‘void outer::mytype::variadic(const auto:89& ...) requires (is_convertible_v<typename std::remove_cv<typename std::remove_reference<decltype(outer::mytype::variadic::x)>::type>::type, int> && ...)’
-pure2-print.cpp2:65:29: note: candidate is: ‘template<class ... auto:80> static void outer::mytype::variadic(const auto:80& ...)’
+pure2-print.cpp2:65:14: error: no declaration matches ‘void outer::mytype::variadic(const auto:97& ...) requires (is_convertible_v<typename std::remove_cv<typename std::remove_reference<decltype(outer::mytype::variadic::x)>::type>::type, int> && ...)’
+pure2-print.cpp2:65:29: note: candidate is: ‘template<class ... auto:88> static void outer::mytype::variadic(const auto:88& ...)’
 pure2-print.cpp2:8:19: note: ‘class outer::mytype’ defined here
 pure2-print.cpp2:93:37: error: no declaration matches ‘void outer::print(std::ostream&, const Args& ...) requires  cpp2::cmp_greater_eq(sizeof (Args)..., 0)’
 pure2-print.cpp2:93:37: note: no functions named ‘void outer::print(std::ostream&, const Args& ...) requires  cpp2::cmp_greater_eq(sizeof (Args)..., 0)’

regression-tests/test-results/version

@@ -1,5 +1,5 @@
 
-cppfront compiler v0.3.0   Build 8B09:1419
+cppfront compiler v0.3.0   Build 8B10:1325
 Copyright(c) Herb Sutter   All rights reserved
 
 SPDX-License-Identifier: CC-BY-NC-ND-4.0

source/build.info

@@ -1 +1 @@
-"8B09:1419"
+"8B10:1325"