Add warning log for 3rd party legacy plugins

[joshdover]

Regardless of if we remove legacy plugin support in 7.x or 8.0 (#56205) we should start logging warnings for any 3rd party legacy plugins that are found during the legacy discovering process.

This should include a note to documentation about the upcoming breaking change and how to migrate the plugin.

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[joshdover]

We need to make sure we can reliably identify 3rd party plugins + should probably only do this in development mode since users don't have any recourse to fix legacy plugins.

[pgayvallet]

Legacy plugins are currently discovered using two config properties: plugins.paths and plugins.scanDirs

kibana/src/legacy/plugin_discovery/find_plugin_specs.js

Lines 111 to 121 in 8e9a8a8

	// find plugin packs in configured paths/dirs
	const packageJson$ = config$.pipe(
	mergeMap(config =>
	Rx.merge(
	...config.get('plugins.paths').map(createPackageJsonAtPath$),
	...config.get('plugins.scanDirs').map(createPackageJsonsInDirectory$)
	)
	),
	distinct(getDistinctKeyForFindResult),
	share()
	);

Default values being:

plugins.paths [ '/x-pack' ]
plugins.scanDirs [ '/plugins', '/src/legacy/core_plugins' ]

Also in legacy, xpack is technically only a single 'plugin' registering all the 'real' plugins at once:

kibana/x-pack/index.js

Lines 38 to 46 in 2a8a7d7

	module.exports = function(kibana) {
	return [
	xpackMain(kibana),
	graph(kibana),
	monitoring(kibana),
	reporting(kibana),
	spaces(kibana),
	security(kibana),
	tilemap(kibana),

As there is no metadata-related approach to 'detect' 3rd party plugins, my guess is that our only option is going to be to detect them depending on their actual path ?

The only info we currently have is the folder the plugin's package.json is inside:

kibana/src/legacy/plugin_discovery/plugin_pack/create_pack.js

Lines 24 to 34 in 8e9a8a8

	function createPack(packageJson) {
	let provider = require(packageJson.directoryPath); // eslint-disable-line import/no-dynamic-require
	if (provider.__esModule) {
	provider = provider.default;
	}
	if (typeof provider !== 'function') {
	throw createInvalidPackError(packageJson.directoryPath, 'must export a function');
	}
	return new PluginPack({ path: packageJson.directoryPath, pkg: packageJson.contents, provider });
	}

Should we assume than anyPluginPack with a path/directoryPath outside of [./x-pack, ./src/legacy/core_plugins] is a 3rd party plugin?

WDYT? Does anyone see any alternative to that detection approach?

[mshustov]

Should we assume than anyPluginPack with a path/directoryPath outside of [./x-pack, ./src/legacy/core_plugins] is a 3rd party plugin?

Sounds reasonable. I have nothing to add.

Default values being:

I thought we scan kibana-extra as well. Don't we?

[pgayvallet]

I thought we scan kibana-extra as well. Don't we?

We do for NP plugins, but it doesn't seem to be the case for legacy plugins. Env.pluginSearchPaths is only used for NP plugins and that's the only reference outside of the optimizer I could find.

kibana/src/core/server/config/env.ts

Lines 108 to 114 in 4e8ab56

	this.pluginSearchPaths = [
	resolve(this.homeDir, 'src', 'plugins'),
	...(options.cliArgs.oss ? [] : [resolve(this.homeDir, 'x-pack', 'plugins')]),
	resolve(this.homeDir, 'plugins'),
	...(options.cliArgs.runExamples ? [resolve(this.homeDir, 'examples')] : []),
	resolve(this.homeDir, '..', 'kibana-extra'),
	];

@joshdover could you confirm that?

[pgayvallet]

This should include a note to documentation about the upcoming breaking change and how to migrate the plugin.

Do we have any persistent url to such documentation? Or should we just point to the source MIGRATION.md file?

[mshustov]

I know about https://github.com/elastic/kibana/blob/master/docs/migration/migrate_8_0.asciidoc link to the all NP migration docs are valuable as well.