Supporting capistrano's clean task

[denzelem]

In

precompiled_assets/lib/precompiled_assets/tasks/assets.rake

Line 15 in d2a0fc5

PrecompiledAssets::Tasks.remove_unused

we are deleting all assets, that are not part of the manifest.js anymore.

IMHO we should support something like https://github.com/rails/propshaft/blob/e7cdbcd4aa9c9a390dade263bbd7c7cedc0c6442/lib/propshaft/railties/assets.rake#L17 && https://github.com/rails/propshaft/blob/e7cdbcd4aa9c9a390dade263bbd7c7cedc0c6442/lib/propshaft/processor.rb#L24 in propshaft. Then set :keep_assets, 2 in capistrano would work as expected again, and rolling release will keep older assets available.

Wdyt?

[makmic]

Do you have any ideas on how to fix it? We currently don't have any information about previous assets in our manifests file, so we technically cannot keep X asset versions.

We could though warn if the user defines :keep_assets with any number except for 1 (which works as excpected)

[makmic]

one attempt would be to use something like log-rotate.

• The gem would create a SHA of the last manifest file and rename it using the SHA (rotate)
• a new manifest is only created if assets have changed
• based on the modified timestamp of those hashed manifest files we can keep only X of them
• the contents of these manifests are kept, the rest is discarded

[denzelem]

In case the digest format is unknown within the manifest.json, I agree it is difficult to solve. Otherwise something similar to https://github.com/rails/propshaft/blob/e7cdbcd4aa9c9a390dade263bbd7c7cedc0c6442/lib/propshaft/output_path.rb#L10-L23C6 might work:

Example (I will use the names logical_path for the left part without digest and digested_path for the right part with digest):

{
  "backend.js": "backend-5dd524a6b187583cacd52e36.js",
  "cover.jpg": "cover-2b884c2c70ef803b307518e5.jpg"
}

1. For each logical_path in the manifest find all digested_paths in the output e.g. public/assets

backend-1d69660cb9975aa76e6f4b0e.js
backend-042c8c36f345ffa238995e82.js
backend-cf4ff9f60349dfd08cb73c2b.js
...

2. Sort them by mtime
3. Keep the newest n assets according to keep_assets
4. (Optional) Drop all other assets that are not part of the manifest anymore and are older than the nth oldest known asset

This might not work good with chunked assets (the have the same logical path but different digests). But it seems it is not supported by precompiled_assets in the current version.

[foobear]

The whole idea behind precompiled_assets is to not make any assumptions about how assets are built.
As long as a manifest is included, precompiled_assets works independently of the assets' build process.

Because of that, I believe we cannot follow the outlined approach:

• We can not know if and how digests are injected into filenames. There are lots of different ways to do it.
• Ordering assets by mtime might not always be correct. This gem has no knowledge about how and when assets were actually built.

Propshaft does not have these issues as it also controls asset generation.

The manifest is our only source of truth which is why our suggestion is to keep backups of previous manifests. (We would assume that at least manifest files can be sorted reliably by mtime.)

[denzelem]

Then I'm fine with @makmic suggestion + short documentation.

We could though warn if the user defines :keep_assets with any number except for 1 (which works as excpected)

[foobear]

Agreed, :keep_assets > 1 should raise an error, possibly before any deployment starts.

I believe we could still implement some kind of manifest rotation to support values above 1 as a next step.