[PATCH v1 1/1] libstdc++: Improve diagnostic message for `cmp_*` and `in_range`.

[Luc Grosheintz]

Without the message, the compiler output can be very short, e.g.
as short as a `required from here`. If the output includes the
line of code that trigges the static_assert, the user might
interpret it as "must be a standard integer", which is incorrect,
because that term doesn't cover extended integers.

This commit adds a diagnostic message that states that the template
argument must be a signed or unsigned integer.

libstdc++-v3/ChangeLog:

	* include/std/utility (cmp_equal): Add message to the
	static_assert.
	(cmp_less): Ditto.
	(in_range): Ditto.
---
 libstdc++-v3/include/std/utility | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/libstdc++-v3/include/std/utility b/libstdc++-v3/include/std/utility
index 8a85ccfd09b..8a79ee9cc21 100644
--- a/libstdc++-v3/include/std/utility
+++ b/libstdc++-v3/include/std/utility
@@ -133,8 +133,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr bool
     cmp_equal(_Tp __t, _Up __u) noexcept
     {
-      static_assert(__is_standard_integer<_Tp>::value);
-      static_assert(__is_standard_integer<_Up>::value);
+      static_assert(__is_standard_integer<_Tp>::value,
+	"T must be a signed or unsigned integer");
+      static_assert(__is_standard_integer<_Up>::value,
+	"U must be a signed or unsigned integer");
 
       if constexpr (is_signed_v<_Tp> == is_signed_v<_Up>)
 	return __t == __u;
@@ -153,8 +155,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr bool
     cmp_less(_Tp __t, _Up __u) noexcept
     {
-      static_assert(__is_standard_integer<_Tp>::value);
-      static_assert(__is_standard_integer<_Up>::value);
+      static_assert(__is_standard_integer<_Tp>::value,
+	"T must be a signed or unsigned integer");
+      static_assert(__is_standard_integer<_Up>::value,
+	"U must be a signed or unsigned integer");
 
       if constexpr (is_signed_v<_Tp> == is_signed_v<_Up>)
 	return __t < __u;
@@ -183,8 +187,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     constexpr bool
     in_range(_Tp __t) noexcept
     {
-      static_assert(__is_standard_integer<_Res>::value);
-      static_assert(__is_standard_integer<_Tp>::value);
+      static_assert(__is_standard_integer<_Res>::value,
+	"R must be a signed or unsigned integer");
+      static_assert(__is_standard_integer<_Tp>::value,
+	"T must be a signed or unsigned integer");
       using __gnu_cxx::__int_traits;
 
       if constexpr (is_signed_v<_Tp> == is_signed_v<_Res>)
-- 
2.49.0