cxa-throw: Don't auto-detect

[edolstra]

Motivation

This speeds up running meson (re)configuration from 16.6s to 2.9s.

More importantly though, it's better to just specify that we expect this to work rather than try to compile something, since that can silently mask errors and disable this feature.

Context

Summary by CodeRabbit

• Refactor
  • Simplified build configuration by removing runtime capability probes and replacing them with deterministic platform-based wiring.
  • On Linux, exception handling support is enabled unconditionally; static-library builds configure wrap-based support, while non-static builds always include the interpose variant.
  • Reduced conditional checks and removed probe-related build variables, lowering maintenance complexity with no change to end-user behavior.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7ca49eb6-ef74-4e3f-9675-36353494cf41

📥 Commits

Reviewing files that changed from the base of the PR and between 84a8cbe and 2e8c23b.

📒 Files selected for processing (1)

• nix-meson-build-support/common/cxa-throw/meson.build

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📝 Walkthrough

Walkthrough

On Linux the Meson build now sets have_cxa_throw = true; for static builds it defines wrap_cxa_throw_args. For non-static builds it always builds interpose-cxa-throw and exposes cxa_throw_dep via link_whole. Runtime cxx.run probes were removed.

Changes

Linux CXA throw wiring

Layer / File(s)	Summary
Enable on Linux & static wrap args nix-meson-build-support/common/cxa-throw/meson.build	When host_machine.system() == 'linux', have_cxa_throw is set to true. If get_option('default_library') == 'static', wrap_cxa_throw_args is defined for the existing wrap-cxa-throw static-library wiring; probe variables were removed.
Interpose static lib and cxa_throw_dep nix-meson-build-support/common/cxa-throw/meson.build	In the non-static branch the build now unconditionally builds interpose-cxa-throw (static) and declares cxa_throw_dep via link_whole to that library; prior probe-driven conditionals are removed.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Poem

🐇 I hopped into Meson, tidy and quick,
Removed the probes that made it stick,
On Linux now the flags are set,
One steady link, no more regret,
A cleaner build — that's my trick.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'cxa-throw: Don't auto-detect' directly and concisely captures the main change: removing auto-detection of cxa-throw capability in favor of deterministic wiring, which is the primary objective and focus of the entire changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch unconditional-cxa-throw

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[github-actions]

🚀 Deployed on https://6a06f2644cd18d61f6705991--determinate-nix.netlify.app

[cole-h]

I was really proud of this autodetection 😭

But I do like speed, so 🚀