libstdc++: Reduce header dependencies for C++20 (PR 92546)

In C++20 <memory> depends on <bits/ranges_unitialized.h> which
depends on <bits/random.h> just for a single concept. Including
<bits/random.h> also requires including <cmath>, which is huge due to
the C++17 special functions.

This change moves the concept to the <bits/uniform_int_dist.h> internal
header that exists so that <bits/stl_algobase.h> doesn't need to include
<bits/random.h>.

	PR libstdc++/92546 (partial)
	* include/bits/random.h (uniform_random_bit_generator): Move definition
	to <bits/uniform_int_dist.h>.
	* include/bits/ranges_algo.h: Include <bits/uniform_int_dist.h> instead
	of <bits/random.h>.
	* include/bits/ranges_algobase.h: Do not include <cmath>.
	* include/bits/uniform_int_dist.h (uniform_random_bit_generator):
	Move here.
	* include/std/ranges: Do not include <limits>.
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error lineno.

libstdc++-v3/ChangeLog

 2020-02-17  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/92546 (partial)
+	* include/bits/random.h (uniform_random_bit_generator): Move definition
+	to <bits/uniform_int_dist.h>.
+	* include/bits/ranges_algo.h: Include <bits/uniform_int_dist.h> instead
+	of <bits/random.h>.
+	* include/bits/ranges_algobase.h: Do not include <cmath>.
+	* include/bits/uniform_int_dist.h (uniform_random_bit_generator):
+	Move here.
+	* include/std/ranges: Do not include <limits>.
+	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error lineno.
+
+	PR libstdc++/92546 (partial)
 	* include/Makefile.am: Add new header.
 	* include/Makefile.in: Regenerate.
 	* include/bits/int_limits.h: New header.

libstdc++-v3/include/bits/random.h

@@ -33,9 +33,6 @@
 
 #include <vector>
 #include <bits/uniform_int_dist.h>
-#if __cplusplus > 201703L
-# include <concepts>
-#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -51,18 +48,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    * @{
    */
 
-#ifdef __cpp_lib_concepts
-  /// Requirements for a uniform random bit generator.
-  template<typename _Gen>
-    concept uniform_random_bit_generator
-      = invocable<_Gen&> && unsigned_integral<invoke_result_t<_Gen&>>
-      && requires
-      {
-	{ _Gen::min() } -> same_as<invoke_result_t<_Gen&>>;
-	{ _Gen::max() } -> same_as<invoke_result_t<_Gen&>>;
-	requires bool_constant<(_Gen::min() < _Gen::max())>::value;
-      };
-#endif
+  // std::uniform_random_bit_generator is defined in <bits/uniform_int_dist.h>
 
   /**
    * @brief A function template for converting the output of a (integral)

libstdc++-v3/include/bits/ranges_algo.h

@@ -33,7 +33,7 @@
 #if __cplusplus > 201703L
 
 #include <bits/ranges_algobase.h>
-#include <bits/random.h> // concept uniform_random_bit_generator
+#include <bits/uniform_int_dist.h> // concept uniform_random_bit_generator
 
 #if __cpp_lib_concepts
 namespace std _GLIBCXX_VISIBILITY(default)

libstdc++-v3/include/bits/ranges_algobase.h

@@ -32,7 +32,6 @@
 
 #if __cplusplus > 201703L
 
-#include <cmath>
 #include <compare>
 #include <iterator>
 // #include <bits/range_concepts.h>

libstdc++-v3/include/bits/uniform_int_dist.h

@@ -33,11 +33,27 @@
 
 #include <type_traits>
 #include <limits>
+#if __cplusplus > 201703L
+# include <concepts>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
+#ifdef __cpp_lib_concepts
+  /// Requirements for a uniform random bit generator.
+  template<typename _Gen>
+    concept uniform_random_bit_generator
+      = invocable<_Gen&> && unsigned_integral<invoke_result_t<_Gen&>>
+      && requires
+      {
+	{ _Gen::min() } -> same_as<invoke_result_t<_Gen&>>;
+	{ _Gen::max() } -> same_as<invoke_result_t<_Gen&>>;
+	requires bool_constant<(_Gen::min() < _Gen::max())>::value;
+      };
+#endif
+
   namespace __detail
   {
     /* Determine whether number is a power of 2.  */

libstdc++-v3/include/std/ranges

@@ -42,7 +42,6 @@
 #include <compare>
 #include <initializer_list>
 #include <iterator>
-#include <limits>
 #include <optional>
 #include <tuple>
 

libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc

@@ -10,6 +10,6 @@ std::__detail::_Adaptor<std::mt19937, unsigned long> aurng(urng);
 auto x = std::generate_canonical<std::size_t,
 			std::numeric_limits<std::size_t>::digits>(urng);
 
-// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 172 }
+// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 158 }
 
 // { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 3281 }