[EPIC] Deprecations for CCCL 2.8 and breaking changes for CCCL 3.0

[jrhemstad]

This issue is to keep track of breaking changes we'd like to make in the next major version release.

Removals

• Drop deprecated CUB macros #3821
• Drop thrust::optional (dropped by Drop thrust::future|event|async::* #3730, but reinstated by Reinstate thrust::optional #3759 to give users more time to migrate, @miscco is responsible to determine when we can drop)
• Drop/internalize some macros #3936
• Drop deprecated features from CUB util_ptx.cuh #3935
• Drop public access to RegBoundScaling/MemBoundScaling #3934
• Drop CUB thread operators #3918
• Drop deprecated iterators from Thrust cuda utils #3905
• Remove pre-C++17 code paths #3595
• Error when users specialize BaseTraits but not numeric_limits #3836
• Drop deprecated CUB iterators #3831
• Drop/Internalize cub::PolicyWrapper, cub::KernelConfig, triple_chevron, thrust logical meta functions, thrust macros from type_deduction.h, thrust::cuda_cub::terminate, thrust::numeric_limits, cub::IterateThreadStore,cub::Swap Drop small deprecated entites #3748
• Drop cub::GridBarrier #3745
• Drop Thrust's cpp_compatibility.h #3746
• Drop thrust::future|event|async::* #3730
• Drop thrust::identity #3747
• CUB CUB_IS_INT128_ENABLED, Int2Type, BinaryOpHasIdxParam::HAS_PARAM, FpLimits: Drop deprecated entities from CUB util_type #3743
• Remove Agent* alias templates for the respective detail::<algorithm name>::Agent* #3467
• Drop Thrust's global workaround #3692
• Remove cub::ArrayWrapper #3665
• Drop support for VS 2017 in code #3375
• Drop CTK 11.x support in code #3284
• Remove any LEGACY_PTX_ARCH parameters #3552
• Dropcub::DeviceSpmv in favor of cuSPARSE #3070
• Internalize cuda/detail/core/* #3505
• Remove all code paths and policies below SM50 #3431
• Drop thrust::null_type #3508
• Move CUB kernel entry points to a detail namespace #3407
• Drop thrust universal iterator categories #3474
• Require C++17 for compiling libcu++
• Drop deprecated features from CUB util_ptx #3430
• Remove CDPv1 Support #3341
• Drop deprecated ::result_type etc. from Thrust function objects (and alias them to the libcu++ ones) #3271
• Drop cub::DivideAndRoundUp #3347
• Drop thrust::void_t #3362
• Drop cub::ValueCache #3346
• Drop all deprecated CUB APIs accepting a debug_synchronous parameter #3329
• Drop CI runs for CTK 11.x #3249
• Remove clang <14 from CI #3184
• Require C++17 for compiling Thrust and CUB #3252
• Drop Thrust's deprecated compiler macros #3301
• Drop CUB's util_compiler.cuh #3302
• Drop CUB's util_compiler.cuh for real #3340
• Drop CUB_RUNTIME_ENABLED and __THRUST_HAS_CUDART__ #3305
• Drop Thrust's compiler_fence.h #3300
• Drop Thrust legacy arch macros #3298
• Drop support for Intel ICC in code #3278
• Drop VS 2017 from CI #3286
• Drop CUB legacy macros in util_arch.cuh #3256
• Drop cub::Mutex #3250
• Drop Intel ICC from CI #3276
• Drop thrust::[unary|binary]_function #3273
• Drop thrust unary_traits and binary_traits #3259
• Drop thrust not1 and not2 #3263
• Drop support for GCC6 #3267
• Remove deprecated cub::min and thrust::remove_cvref #3450
• Remove cub::max

Deprecations with backports to 2.8

Moved to #3700

Planned deprecations for which we ran out of time

Moved to #3701

API breaking changes

• Assert offset type in DispatchScan to be unsigned
• Extended <cuda/bit> operations: bitfield_insert, bitfield_extract, bit_reverse, bitmask #3941 as a replacement of removed CUB bit functions
• CUB histogram API signatures are misleading #1765
• Evaluate unification of how Thrust execution policies are passed around #3862
• Iterators should be iterators #3767
• Make thrust::discard_iterator's value_type void #3399
• Move all CUB dispatchers into internal namespaces #3094
• Thrust universal_host_pinned_memory_resource's pointer type should probably be a universal_ptr #2659
• Minimize usage of cub::Traits #3863
• Define is_floating_point_v in terms of is_floating_point #3923
• [FEA]: libcu++ iterator_traits should pick up std iterator_traits specializations #1930
• Move Dispatcher policy hub parameters to the back #3740
• Move ForceInclusive parameter of DispatchScan before policy #3739
• Replace boolean parameters of CUB dispatchers by enumerations #3352
• Fixes value type of thrust::tabulate_output_iterator #3573
• [FEA]: ceil_div should return the resulting type of its operation #2845
• [BUG]: thrust::transform_iterator<F, ...> is broken if F is not copy_assignable #2393

ABI breaking changes

• Deprecate and drop old libcu++ ABI namespaces #3424

Behavioral changes

• Unify accumulator type handling across CUB/Thrust
• Unify initial value handling across CUB/Thrust
• Fix reduce to match the documentation and use numeric limits #920
• Remove multiplication and division nan handling <complex> Enable users to disable normalization for division too. libcudacxx#474 (review)

Cleanup

• Replace implementations in thrust/thrust/system/detail/sequential/* by libcu++ <algorithm>
• Replace THRUST_UNUSED_VAR by some CCCL macro
• Refactor and simplify Thrust iterators #3824
• [FEA]: Refactor user-facing Thrust types to use libcu++  #34
• Replace mdspan implementation with one derived from the newer LLVM implementation #3353
• Fix transform_iterator<identity> and drop result_of_adaptable_function #3652

[bernhardmgruber]

I reviewed the list of deprecated entites for CCCL 2.8 #3700 and updated the list of stuff to be removed for CCCL 3.0.