Limits of Grunt's File Expansion Caching Across Tasks

Direct Answers

Question 1: No. When a task modifies files matching a cached glob pattern, grunt.file.cached does not automatically update. Subsequent expand calls with the same pattern and working directory return the stale cached array until grunt.file.cached.clear() is called.

Question 2: Yes. The cache key includes process.cwd() at call time. Changing the working directory between tasks (via grunt.file.setBase or process.chdir) creates a separate cache entry for identical glob patterns.

Question 3: No documented strategy exists. The only supported invalidation method is grunt.file.cached.clear(), which wipes the entire cache. Grunt's source (lib/grunt/file.js) shows a simple Map with no granular purge API.

Confirmed Behavior

• Cache lives only for the duration of a single Grunt process; it does not persist across separate Grunt invocations.
• Child processes (e.g., grunt-shell, grunt-exec) do not share the parent's in-memory cache. File changes made in a child are invisible to the parent's cached expands unless the parent re-expands after the child exits.
• The cache key is the exact glob string plus the current working directory. Relying on this undocumented key structure is fragile; Grunt could change it in a minor release.

Practical Patterns for Repeatable CI

1. Clear at task boundaries: Call grunt.file.cached.clear() at the start of any task that depends on up-to-date file lists.
2. Avoid cached expands for volatile patterns: Use plain grunt.file.expand for globs that may change during the build.
3. Isolate by cwd deliberately: If you need separate caches for the same pattern, change process.cwd() before expanding—but treat this as an implementation detail, not a guaranteed contract.

Minimal Verification Script

// Gruntfile.js
module.exports = function(grunt) {
  grunt.initConfig({});

  grunt.registerTask('write', 'Create a new .txt file', function() {
    grunt.file.write('new.txt', 'hello');
  });

  grunt.registerTask('readCached', 'Expand with cache', function() {
    const files = grunt.file.cached.expand('*.txt');
    grunt.log.writeln('Cached expand found:', files);
  });

  grunt.registerTask('readFresh', 'Expand without cache', function() {
    const files = grunt.file.expand('*.txt');
    grunt.log.writeln('Fresh expand found:', files);
  });

  grunt.registerTask('clear', 'Clear cache', function() {
    grunt.file.cached.clear();
    grunt.log.writeln('Cache cleared');
  });

  // Run: grunt write readCached readFresh clear readCached
};

Run the task sequence above. readCached after write will miss new.txt; readFresh will include it. After clear, the next readCached picks up the new file.

One Diagnostic to Request

If you observe different behavior, confirm the Grunt version (grunt --version) and whether any plugin monkey-patches grunt.file.cached. The cache implementation has been stable since Grunt 0.4, but plugins can replace it.