Fix plugin install detection when update info unavailable

[swissspidy]

What

wp plugin install <slug> could try to install a plugin that is already installed, failing with Warning: Destination folder already exists. instead of reporting Warning: <slug>: Plugin already installed.

Why

Plugin_Command::install_from_repo() relied solely on install_plugin_install_status(). That function only recognizes an installed plugin when it has update data to compare against:

} else {
	// If the above update check failed, then that probably means that the update checker has out-of-date information, force a refresh.
	if ( ! $loop ) {
		delete_site_transient( 'update_plugins' );
		wp_update_plugins();
		return install_plugin_install_status( $api, true );
	}
}

If plugins_api() reports a version newer than the installed one and the refreshed update_plugins transient still holds no entry for that slug, there is no fallback: the status stays install for a plugin that is sitting on disk. WP-CLI then downloads the package and the installation fails on the existing folder.

This broke the Install dependencies with activation scenario in the nightly run of 2026-08-18 (run 32089579364) — in every job, WP latest and trunk, PHP 7.4 through nightly:

Installing Akismet Anti-spam: Spam Protection (5.7.1)
Downloading installation package from https://downloads.wordpress.org/plugin/akismet.5.7.1.zip...
Unpacking the package...
Installing the plugin...
Plugin installation failed.
[...]
Warning: Destination folder already exists. "{WORKING_DIR}/wp-content/plugins/akismet/"
Error: Only installed 1 of 2 plugins.

Nothing changed on our side; the same commit passed the day before. What is certain is that during that run plugins_api() offered Akismet 5.7.1 (and downloads.wordpress.org served the ZIP), while the update_plugins transient held no update entry for the Akismet version bundled with WordPress.

A plausible explanation is the staged distribution of new plugin releases announced in Protect The Shire: Akismet 5.7.1 was released around midnight UTC, and the failing run started at 01:49 UTC. This is not confirmed — the announcement frames the hold in terms of auto-updates, and people have reported seeing such updates offered in wp-admin during the hold — but the timing matches, and re-running the very same workflow later that day passed with no changes.

Either way the fall-through in install_plugin_install_status() is real, and it is not Akismet-specific: any plugin installed from WordPress.org can hit it in the window after a release. The same applies outside WP-CLI, where the Add Plugins screen offers "Install Now" for an already installed plugin and fails the same way on click.

How

Check the file system in addition to the reported status, similar to what Theme_Command::install_from_repo() already does via wp_get_theme( $slug )->exists(). The new is_plugin_installed() helper requires both the directory and a valid plugin file (get_plugins( '/' . $slug )), so the existing Paths aren't backslashed when destination folder already exists scenario — which deletes akismet.php first — keeps working unchanged.

The added scenario reproduces the state deterministically, without depending on WordPress.org timing: an mu-plugin empties site_transient_update_plugins, and a stub debug-bar 0.1 stands in for the outdated install.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NeGydmXhxbx34V4UV6M3L6

Summary by CodeRabbit

• New Features

  • Plugin installation now recognizes plugins that are already installed, even when update information is unavailable.
  • Added a --force option path to allow installation to proceed when needed.

• Bug Fixes

  • Prevented unnecessary downloads and destination-folder warnings for already-installed plugins.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

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Plan: Pro Plus

Run ID: 12d50a66-6bd3-4013-acc8-1c6e05445ac7

📥 Commits

Reviewing files that changed from the base of the PR and between 3d4ea50 and 471b95f.

📒 Files selected for processing (2)

• features/plugin-install.feature
• src/Plugin_Command.php

Included review availability: Your plan includes up to 1 review per rolling hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

Plugin installation now checks plugin status and filesystem contents before downloading. A feature scenario verifies that an outdated Debug Bar installation is reported as already installed when update data is unavailable.

Changes

Plugin installation detection

Layer / File(s)	Summary
Existing plugin detection and validation src/Plugin_Command.php, features/plugin-install.feature	install_from_repo() detects installed plugins from status data and plugin files, while preserving --force behavior. The feature scenario validates the already_installed result and successful exit status without a destination-folder warning.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 471b9

This is a localized plugin-install detection fix with a regression scenario; no actionable merge-blocking risk remains after the normal validation checks pass.

Suggested reviewers: schlessera, brianhenryie

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main fix for plugin installation detection when update information is unavailable.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/akismet-test-failure-gq0g7i

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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