Feat/compile time wrap check

[shivansh023023]

Fixes #

Proposed Changes

• Add INTERFACE compile definition HPX_HAVE_WRAP_MAIN_CONFIGURED to both hpx_wrap and hpx_auto_wrap targets in wrap/CMakeLists.txt (inside the existing HPX_WITH_DYNAMIC_HPX_MAIN + Linux guard). This injects the define automatically into any downstream CMake consumer, ensuring zero noise for CMake users.
• Add a #warning in wrap/include/hpx/hpx_main.hpp that fires when all of these are true: __linux__, HPX_HAVE_DYNAMIC_HPX_MAIN, HPX_HAVE_STATIC_LINKING, and HPX_HAVE_WRAP_MAIN_CONFIGURED is not defined. This catches the missing -Wl,-wrap=main linker flag at compile time instead of letting it become a runtime crash.
• The warning message is actionable: it tells the user exactly which flag to add and how to suppress the warning if they've already handled it.

Any background context you want to provide?

This is the compile-time component of a safety net for the UX gap where -Wl,-wrap=main does not propagate to non-CMake consumers (Godbolt / Compiler Explorer, Makefiles, raw g++ invocations). It complements:

• PR cmake: remove HPX_WITH_CXX20_STD_EXECUTION_POLICES feature test #7068 — godbolt-minimal CMake preset (build-system level)
• PR Add segmented is_sorted_until , is_sorted #7072 — hpx/local.hpp convenience header (usability level)

Design trade-off: Non-CMake users who have already added -Wl,-wrap=main manually will still see the #warning (since they lack the define). They can silence it with -DHPX_HAVE_WRAP_MAIN_CONFIGURED. A suppressible compile-time warning is far better than a silent compilation followed by a cryptic runtime crash.

This work is part of the GSoC 2026 effort to integrate HPX into Compiler Explorer.

Checklist

• I have added a new feature and have added tests to go along with it.
  • Verified with 6 preprocessor logic tests covering all define combinations (Linux/macOS, static/shared, dynamic-main on/off, suppress define present/absent). Warning fires in exactly one case: Linux + static + dynamic-main + no suppress define.
• I have fixed a bug and have added a regression test. (N/A — this is a new diagnostic, not a bugfix)
• I have added a test using random numbers (N/A)

[StellarBot]

Can one of the admins verify this patch?

[hkaiser]

Have you seen the existing HPX_HAVE_DYNAMIC_HPX_MAIN? Would that be sufficient for what you're trying to achieve?

[shivansh023023]

Have you seen the existing HPX_HAVE_DYNAMIC_HPX_MAIN? Would that be sufficient for what you're trying to achieve?

That's a good point, @hkaiser . I did consider HPX_HAVE_DYNAMIC_HPX_MAIN, but that macro indicates that the feature is enabled in the HPX build configuration.

The reason for the new HPX_HAVE_WRAP_MAIN_CONFIGURED (injected via INTERFACE compile definitions) is to distinguish between:

CMake users: Who get the linker flag automatically and should not see the warning.

Non-CMake users: Who have the feature enabled in their HPX installation but haven't necessarily passed the -Wl,-wrap=main flag to their manual link command.

Without the new definition, hpx_main.hpp wouldn't be able to tell if the user linking manually has actually applied the flag or not. Does that make sense, or is there a way to leverage the existing macro to detect the linker-state that I might have missed?

[hkaiser]

@shivansh023023 Could you please have a look at the compilation failure generated?

[hkaiser]

The CIs still report that one of the translation units can't find the header <hpx/config/static_linker_check.hpp>. Did you miss adding the file to this PR?

[hkaiser]

@shivansh023023 ping?

[hkaiser]

@shivansh023023 Are you still interested in moving tis forward? Otherwise I'll go ahead and close this without merging.

[codacy-production]

Up to standards ✅

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[hkaiser]

@shivansh023023 Please have an eye on the CIs yourself. Many issues are still being reported.