algorithms/containers: annotate sort, stable_sort, and partitioned_vector with preconditions

Add HPX_PRE(first <= last) to hpx::sort and hpx::stable_sort (both
sequential and parallel overloads). Both algorithms already enforce
std::random_access_iterator via static_assert, so <= is always valid.

Add HPX_PRE(pos < size()) to partitioned_vector::operator[] (const and
non-const). Mirrors the existing small_vector annotation.

Signed-off-by: Sanchit2662 <sanchit2662@gmail.com>

Author: Sanchit2662

components/containers/partitioned_vector/include/hpx/components/containers/partitioned_vector/partitioned_vector_decl.hpp

@@ -11,6 +11,7 @@
 
 #include <hpx/config.hpp>
 #include <hpx/assert.hpp>
+#include <hpx/contracts.hpp>
 #include <hpx/components/client_base.hpp>
 #include <hpx/distribution_policies/container_distribution_policy.hpp>
 #include <hpx/distribution_policies/explicit_container_distribution_policy.hpp>
@@ -506,6 +507,7 @@ namespace hpx {
         ///         this proxy instance is used.
         ///
         segmented::detail::vector_value_proxy<T, Data> operator[](size_type pos)
+            HPX_PRE(pos < size())
         {
             return segmented::detail::vector_value_proxy<T, Data>(*this, pos);
         }
@@ -521,7 +523,7 @@ namespace hpx {
         /// \note This function does not return a reference to the actual
         ///       element but a copy of its value.
         ///
-        T operator[](size_type pos) const
+        T operator[](size_type pos) const HPX_PRE(pos < size())
         {
             return get_value(launch::sync, pos);
         }

libs/core/algorithms/CMakeLists.txt

@@ -279,6 +279,7 @@ add_hpx_module(
     hpx_concepts
     hpx_concurrency
     hpx_config
+    hpx_contracts
     hpx_coroutines
     hpx_datastructures
     hpx_errors

libs/core/algorithms/include/hpx/parallel/algorithms/sort.hpp

@@ -152,6 +152,7 @@ namespace hpx {
 #include <hpx/config.hpp>
 #include <hpx/algorithms/traits/projected.hpp>
 #include <hpx/assert.hpp>
+#include <hpx/contracts.hpp>
 #include <hpx/modules/async_local.hpp>
 #include <hpx/modules/concepts.hpp>
 #include <hpx/modules/execution.hpp>
@@ -394,6 +395,7 @@ namespace hpx {
         // clang-format on
         friend void tag_fallback_invoke(
             hpx::sort_t, RandomIt first, RandomIt last, Comp comp = Comp())
+            HPX_PRE(first <= last)
         {
             static_assert(std::random_access_iterator<RandomIt>,
                 "Requires a random access iterator.");
@@ -416,7 +418,7 @@ namespace hpx {
         // clang-format on
         friend parallel::util::detail::algorithm_result_t<ExPolicy>
         tag_fallback_invoke(hpx::sort_t, ExPolicy&& policy, RandomIt first,
-            RandomIt last, Comp comp = Comp())
+            RandomIt last, Comp comp = Comp()) HPX_PRE(first <= last)
         {
             static_assert(std::random_access_iterator<RandomIt>,
                 "Requires a random access iterator.");

libs/core/algorithms/include/hpx/parallel/algorithms/stable_sort.hpp

@@ -150,6 +150,7 @@ namespace hpx {
 
 #include <hpx/config.hpp>
 #include <hpx/algorithms/traits/projected.hpp>
+#include <hpx/contracts.hpp>
 #include <hpx/modules/concepts.hpp>
 #include <hpx/modules/execution.hpp>
 #include <hpx/modules/executors.hpp>
@@ -285,7 +286,7 @@ namespace hpx {
             )
         // clang-format on
         friend void tag_fallback_invoke(hpx::stable_sort_t, RandomIt first,
-            RandomIt last, Comp comp = Comp())
+            RandomIt last, Comp comp = Comp()) HPX_PRE(first <= last)
         {
             static_assert(std::random_access_iterator<RandomIt>,
                 "Requires a random access iterator.");
@@ -310,6 +311,7 @@ namespace hpx {
         friend hpx::parallel::util::detail::algorithm_result_t<ExPolicy>
         tag_fallback_invoke(hpx::stable_sort_t, ExPolicy&& policy,
             RandomIt first, RandomIt last, Comp comp = Comp())
+            HPX_PRE(first <= last)
         {
             static_assert(std::random_access_iterator<RandomIt>,
                 "Requires a random access iterator.");