Enhance APCu include detection for in-tree builds

[henderkes]

see kjdev/php-ext-zstd#100

Summary by CodeRabbit

• Bug Fixes
  • Improved APCu detection during setup so it more accurately finds support when available.
  • Reduced unnecessary setup failures by treating missing APCu support as a non-fatal result in automatic detection mode.
  • Installation now better handles custom source layouts when checking for APCu compatibility.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 8d1a6020-97f6-4366-9b3f-073aacee3877

📥 Commits

Reviewing files that changed from the base of the PR and between 531a5b3 and afdd345.

📒 Files selected for processing (1)

• config.m4

📝 Walkthrough

Walkthrough

config.m4 now checks APCu support only when PHP_APCU is enabled, can fall back to $abs_srcdir for the serializer header, defines HAVE_APCU_SUPPORT when found, and distinguishes missing-header handling for auto versus non-auto settings.

Changes

APCu detection

Layer / File(s)	Summary
Conditional APCu header probe config.m4	config.m4 now gates the APCu header check on PHP_APCU != no, can redirect phpincludedir to $abs_srcdir, defines HAVE_APCU_SUPPORT when ext/apcu/apc_serializer.h is found, and errors only when the header is still missing and PHP_APCU is not auto.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

A bunny peeks at config.m4,
Sniffs for the header, then hops once more.
If found, a happy thump-thump rings,
If not, the build chooses gentler things.
Hop hop, the APCu path now sings 🐇

🚥 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 accurately summarizes the main change: improving APCu include detection for in-tree builds.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[henderkes]

Previously it would always silently fail using apcu in in-tree compilation, now it properly detects it.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@config.m4`:
- Around line 69-80: Default or declare PHP_APCU before the configure probe in
config.m4 so the feature can correctly behave as auto/no instead of always
entering the APCu check. Update the logic around the existing PHP_APCU
conditional to initialize it to a safe default and, if this is
user-configurable, add the matching PHP_ARG_* declaration so the branch in the
APCu include check and the AC_MSG_ERROR path only run when intended.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7b785e97-e85f-45d9-85f1-6efbaeb826ef

📥 Commits

Reviewing files that changed from the base of the PR and between bf27b2c and 531a5b3.

📒 Files selected for processing (1)

• config.m4