async_mpi: harden transform_mpi callback helpers with static_asserts on receiver shape

[guptapratykshh]

Proposed Changes

• Add static_assert guards to the two transform_mpi callback helpers in transform_mpi.hpp (set_value_request_callback_void and set_value_request_callback_non_void) that check the receiver-shape contract at the helper boundary: the void path asserts the receiver is invocable as set_value(rcv), the non-void path asserts both that InvokeResult is non-void and that the receiver is invocable as set_value(rcv, res).
• Add a contract comment on each helper documenting the single-move invariant on Ts... and the fact that the captured lambda fires on the polling thread (not the receiver's preferred completion scheduler).
• Pure additive hardening: no API change, no removed code, ~44 LOC of static_asserts + comments in a single file.

Any background context you want to provide?

Checklist

Not all points below apply to all pull requests.

• I have added a new feature and have added tests to go along with it.
• I have fixed a bug and have added a regression test.
• I have added a test using random numbers; I have made sure it uses a seed, and that random numbers generated are valid inputs for the tests.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

View in Codacy

_{NEW Get contextual insights on your PRs based on Codacy's metrics, along with PR and Jira context, without leaving GitHub. Enable AI reviewer
TIP This summary will be updated as you push new changes.}

[StellarBot]

Can one of the admins verify this patch?

[hkaiser]

Could you please add compile-time only tests that make the asserts fire? You can do that using the HPX testing build system infrastructure. Please look around in other modules to see examples.

[Copilot]

Pull request overview

Adds defensive static_asserts at the boundary of the two transform_mpi completion-callback helpers (set_value_request_callback_void / set_value_request_callback_non_void) so receiver-shape misuse fails with a clear diagnostic at the helper rather than deep inside the captured lambda, and documents the single-move and polling-thread invariants. Two FAILURE_EXPECTED compile-only tests are added to lock in the new diagnostics.

Changes:

• Add receiver-shape (and non-void result) static_asserts plus contract comments to both callback helpers in transform_mpi.hpp.
• Add two negative compile-only tests that pass mismatched receivers and are expected to fail compilation.
• Wire the new tests through libs/core/async_mpi/tests/unit/CMakeLists.txt behind HPX_WITH_COMPILE_ONLY_TESTS / HPX_WITH_FAIL_COMPILE_TESTS.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
libs/core/async_mpi/include/hpx/async_mpi/transform_mpi.hpp	Adds static_asserts and contract comments to the two callback helpers.
libs/core/async_mpi/tests/unit/fail_compile_set_value_request_callback_void.cpp	New negative compile test for the void-return path's receiver-shape assert.
libs/core/async_mpi/tests/unit/fail_compile_set_value_request_callback_non_void.cpp	New negative compile test for the non-void path's receiver-shape assert.
libs/core/async_mpi/tests/unit/CMakeLists.txt	Registers the two FAILURE_EXPECTED compile-only tests, gated on the standard HPX compile-test options.

[hkaiser]

LGTM, thanks!