Fix plugin reinstall failure after deletion in Sandbox runtime - #4044
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In the Sandbox (PHP WASM) runtime, PHP runs as a persistent process whose internal stat/realpath caches persist across HTTP requests. After a plugin is deleted via wp-admin, WordPress calls rmdir() which clears the stat-cache for that exact path. However on the next request (reinstalling the same plugin) the path may resolve differently (e.g. with/without trailing slash, via realpath) and the stale cache entry causes is_dir() to return true for a directory that no longer exists. WordPress then tries to delete it before installing, gets an ENOENT-equivalent failure from the VFS, and returns the error "The destination directory already exists and could not be removed." Add a mu-plugin that hooks into upgrader_pre_install and calls clearstatcache(true) to flush both the stat cache and the realpath cache before any upgrade/install operation. This ensures WordPress gets an accurate filesystem view and can proceed with the installation. Co-authored-by: wojtekn <wojtek.naruniec@automattic.com>
wojtekn
marked this pull request as ready for review
July 8, 2026 10:20
wojtekn
approved these changes
Jul 8, 2026
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📊 Performance Test ResultsComparing 270b16e vs trunk app-size
site-editor
site-startup
Results are median values from multiple test runs. Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff) |
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Related issues
Closes https://linear.app/a8c/issue/STU-1931
How AI was used in this PR
AI was used to investigate the root cause, design the fix, and write the code.
Proposed Changes
Fixes a bug where manually reinstalling a plugin (via zip upload) after deleting it through the WordPress Plugins admin screen would fail with:
The workaround was to restart the Studio site before reinstalling.
Root cause: In the Sandbox (PHP WASM) runtime, PHP runs as a persistent process whose internal stat/realpath caches persist across HTTP requests (unlike native PHP, where each request forks a fresh PHP process). After deleting a plugin in one request, PHP's cache can retain a stale "directory exists" result for the plugin path. On the next request (reinstalling the same plugin), WordPress calls
is_dir()on the destination — the stale cache says it exists — then tries to delete it and gets an ENOENT-equivalent failure from the VFS layer, producing the error.Fix: A new mu-plugin (
0-clear-stat-cache-before-upgrade.php) hooks into WordPress'supgrader_pre_installfilter and callsclearstatcache(true). This flushes both PHP's stat cache and its realpath cache immediately before any upgrade or install operation, ensuringis_dir()gets a fresh result from the real filesystem.This is a no-op for the native PHP runtime (each request already starts with a clean process and empty caches).
Testing Instructions
Pre-merge Checklist
Linear: STU-1931
Co-authored-by: wojtekn wojtek.naruniec@automattic.com