Revert "<ranges>: Temporarily disable join_view for non-forward_ranges, pending resolution of LWG-3698 (microsoft#2727)"

This reverts commit 2966813.

Author: cpplearner

stl/inc/ranges

@@ -3566,19 +3566,6 @@ namespace ranges {
     _EXPORT_STD template <input_range _Vw>
         requires view<_Vw> && input_range<range_reference_t<_Vw>>
     class join_view : public _Join_view_base<_Vw> {
-
-#ifndef _USE_JOIN_VIEW_INPUT_RANGE
-        static_assert(forward_range<_Vw>,
-            "Due to a design flaw, join_view can misbehave "
-            "with some input-only ranges (see https://wg21.link/lwg3698). "
-            "We believe that WG21 will be unable to fix this problem without breaking ABI. "
-            "To minimize breakage when a fix is implemented, "
-            "we are temporarily disabling potentially problematic cases. "
-            "You can define _USE_JOIN_VIEW_INPUT_RANGE to suppress this error, "
-            "but be aware that you will almost certainly need to recompile "
-            "when we release a fix.");
-#endif // _USE_JOIN_VIEW_INPUT_RANGE
-
     private:
         template <bool _Const>
         using _InnerRng = range_reference_t<_Maybe_const<_Const, _Vw>>;

tests/libcxx/usual_matrix.lst

@@ -3,7 +3,7 @@
 
 RUNALL_INCLUDE ..\universal_prefix.lst
 RUNALL_CROSSLIST
-PM_CL="/EHsc /MTd /std:c++latest /permissive- /utf-8 /FImsvc_stdlib_force_include.h /wd4643 /D_STL_CALL_ABORT_INSTEAD_OF_INVALID_PARAMETER /D_USE_JOIN_VIEW_INPUT_RANGE"
+PM_CL="/EHsc /MTd /std:c++latest /permissive- /utf-8 /FImsvc_stdlib_force_include.h /wd4643 /D_STL_CALL_ABORT_INSTEAD_OF_INVALID_PARAMETER"
 RUNALL_CROSSLIST
 PM_CL="/analyze:autolog- /Zc:preprocessor /wd6262"
 PM_COMPILER="clang-cl" PM_CL="-fno-ms-compatibility -fno-delayed-template-parsing -Wno-unqualified-std-cast-call"

tests/std/tests/P0896R4_views_join/test.cpp

@@ -1,8 +1,6 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-#define _USE_JOIN_VIEW_INPUT_RANGE
-
 #include <algorithm>
 #include <array>
 #include <cassert>