Remove custom compressor wrappers when replacing or disabling compression

[OskarEichler]

Summary

Assigning nil to js_compressor or css_compressor disables the current compressor, including objects implementing compress. Assigning another compressor replaces the previous one.

Remember the actual registered processor separately from the existing public compressor reader value. A compress object is wrapped in a Proc, but removal previously used the reader symbol instead of that Proc. Existing reader values are preserved. Checks cover object-to-object, object-to-callable/class/symbol, nil, repeated nil, JS/CSS, processor counts and preservation of other processors. The reproduction clears the asset cache to isolate registration behavior; this does not solve arbitrary custom processor cache-key configuration.

Reproduction

With require "sprockets"; require "tmpdir":

Dir.mktmpdir do |dir|
  File.write(File.join(dir, "entry.js"), "var value=1;")
  env = Sprockets::Environment.new(dir); env.append_path(dir)
  compressor = Object.new
  def compressor.compress(data); data + "/*CUSTOM*/"; end
  env.js_compressor = compressor
  env.js_compressor = nil
  env.cache.clear
  p env["entry.js"].to_s.include?("CUSTOM")
  # false; previously true. CSS and replacing the compressor have the same defect.
end

Verification

• Isolated patch: unchanged bundle exec rake test and bundle exec rake test_isolated each pass 913 tests / 4,109 assertions / zero failures/errors / four skips, on Ruby 3.2.11 and 4.0.6 with Rack 3.2.7.
• 196 focused external checks pass on each Ruby. Baseline reproduces the defect. All Ruby commands used rbenv.
• Full RuboCop: 133 files, zero offenses. Changed Ruby files pass syntax checks on both Rubies; git diff --check passes.
• Gem build and content comparison preserve all 84 package paths, version 4.4.1, Ruby >=2.5 and dependency metadata. Only README, CHANGELOG and the relevant runtime files differ.

Compatibility and limitations

Breaking changes: no intended change to valid supported behavior; the incorrect behavior described above changes. No new dependencies or version upgrades. Nested configuration ownership, unrelated cache invalidation and HTTP behavior are outside this focused patch.

Based on installed release/current upstream main 49d9f20c00ac7d9a7ee57db058961edcccd86699. This is an upstream-only contribution; no personal fork is being adopted in the application. Older Ruby/Linux/JRuby verification is left to upstream CI, not claimed locally. No checked-in tests were added or edited under the requesting repository's no-test-edit policy; focused reproductions ran externally. Prepared with AI assistance. This does not claim exhaustive Sprockets coverage.