Cherry-Pick: Fix memnew_placement with char * arguments (godotengine/godot#112033)

[morgothaufheroin88]

Cherry-pick of godotengine/godot#112033 (upstream commit 65bf51600652bddc8faea0f7f6a1ead0e28da81b, merged 2025-10-25), plus a regression test.

memnew_placement(ptr, T(...)) expands to ::new (ptr) T(...). When ptr is a char *, overload resolution prefers operator new(size_t, const char *p_description) (the "new with description" overload in core/os/memory.h) over the standard operator new(size_t, void *), because char * → const char * is a better conversion than char * → void *. The object is then constructed in a freshly allocated block and the intended storage is never written.

Concretely, LocalVector<char>::push_back(), insert(), resize_initialized() and memnew_arr_placement() on char storage silently produce garbage and leak. Nothing in the current tree hits this (all LocalVector<char> users go through resize() + memcpy), but I ran into it immediately while writing a follow-up FileAccess::get_line() PR, and upstream hit it as data loss (godotengine/godot#112022).

The upstream fix adds an operator new(size_t, char *) overload that forwards to placement new. It is applied verbatim with the original author and (cherry picked from ...) trailer; the test is a separate commit.

Testing

• New test [LocalVector] Push Back char. fails on master (CHECK( vector[0] == 'a' ) → 0 == 97) and passes with the fix.
• Full unit-test suite: 1343/1343 test cases pass on the fixed build.

Summary by CodeRabbit

• Bug Fixes

  • Fixed placement construction for character-buffer destinations, preventing incorrect overload selection.
  • Improved reliability when adding and inserting elements in local character vectors.

• Tests

  • Added regression coverage for character vector insertion, resizing, and zero-initialized elements.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Advanced

Run ID: 9246d8b8-31d6-4497-8e98-b87a7ae2ff2d

📥 Commits

Reviewing files that changed from the base of the PR and between 2ab24bc and 3e6231b.

📒 Files selected for processing (2)

• core/os/memory.h
• tests/core/templates/test_local_vector.h

Included review availability: Your plan provides up to 8 included reviews per hour; 7 remain after this review.

---

Walkthrough

The change adds a char * placement-new overload that forwards to the existing void * overload. A LocalVector<char> test covers insertion and initialized resizing.

Changes

Placement-new overload fix

Layer / File(s)	Summary
Add overload and validate LocalVector<char> behavior core/os/memory.h, tests/core/templates/test_local_vector.h	Adds operator new(size_t, char *) and forwards its destination to the existing placement-new overload. Adds a regression test for LocalVector<char> insertion, resizing, element order, and zero initialization.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: mcdubhghlas, generalprotectionfault

Merge Risk: ⚪ Minimal · up to 3e623

The placement-new fix has appropriate regression coverage and no remaining merge-blocking risk was identified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the cherry-pick and the main fix for memnew_placement calls with char * arguments.
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.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}

[JoltedJon]

Tested and see that it's fixed with this PR. Thanks for bringing this in!