Suboptimal maintenance of parser cache files using touch()

[dvz]

The modification time of files in the parser cache directory (ParserCacheProvider::PARSER_CACHE_DIRECTORY, php-parser) may be changed multiple times during a single run:

• in ProjectAnalyzer::check() (on full, diff run):
  

  psalm/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php

  Line 681 in 14dcbc9

  $this->parser_cache_provider->touchParserCaches($this->getAllFiles($this->config), $start_checks);

  by calling ParserCacheProvider::touchParserCaches() with the results of ProjectAnalyzer::getAllFiles(), which may be particularly expensive, as the latter iterates recursively over all project directories, including unrelated files (see also: Suboptimal discovery of project files #7057)

• in IssueBuffer::finish() (on full run):
  

  psalm/src/Psalm/IssueBuffer.php

  Line 732 in 14dcbc9

  $codebase->statements_provider->parser_cache_provider->processSuccessfulRun();

  by calling ParserCacheProvider::processSuccessfulRun() which uses a simple loop over scandir($cache_directory)

Given that the only non-maintenance usage of modification time appears to be the comparison with source files at:

psalm/src/Psalm/Internal/Provider/ParserCacheProvider.php

Line 100 in 14dcbc9

&& filemtime($cache_location) > $file_modified_time

the apparent reason is to allow purging of old cache files in ProjectAnalyzer::check() at:

psalm/src/Psalm/Internal/Analyzer/ProjectAnalyzer.php

Lines 672 to 674 in 14dcbc9

	$removed_parser_files = $this->parser_cache_provider->deleteOldParserCaches(
	$is_diff ? $this->project_cache_provider->getLastRun(\PSALM_VERSION) : $start_checks
	);

by calling ParserCacheProvider::deleteOldParserCaches(), which seems to be non-functional:

psalm/src/Psalm/Internal/Provider/ParserCacheProvider.php

Lines 322 to 324 in b359847

	if ($cache_directory) {
	return 0;
	}

The mechanism that relies on touch() (likely introduced via e9b4eb6) could be replaced completely with one that deletes all cache files before a full run, or one that relies on a list of processed files for which a cache should be kept.