Does it cache --mount=type=cache?

[korobochkin]

I use a development/docker-compose-tests.yml file as a configuration. And relatively simple Dockerfile that uses --mount=type=cache for preserving Composer (PHP package manager) cache folder.

WORKDIR /home/php/app
RUN \
    --mount=type=bind,source=source,destination=./source \
    --mount=type=bind,source=tests,destination=./tests \
    --mount=type=bind,source=composer.json,destination=./composer.json \
    --mount=type=bind,source=composer.lock,destination=./composer.lock \
    --mount=type=bind,source=Makefile,destination=./Makefile \
    --mount=type=cache,id=composer,destination=/root/.composer \
    make vendor # This does "composer install"

Layers cache works good and I see all build steps as "CACHED" in the Workflow logs.

#12 [base 5/5] WORKDIR /home/php/app
#12 CACHED
#13 [dependencies 1/1] RUN     --mount=type=bind,source=source,destination=./source     --mount=type=bind,source=tests,destination=./tests     --mount=type=bind,source=composer.json,destination=./composer.json     --mount=type=bind,source=composer.lock,destination=./composer.lock     --mount=type=bind,source=Makefile,destination=./Makefile     --mount=type=cache,id=composer,destination=/root/.composer     make vendor
#13 CACHED

The issue

When Docker needs to rebuild a layer it seems that --mount=type=cache is empty and Composer downloads again all the packages from internet. I see a lot of "Downloading ..." records in Workflow logs and only then "Installing ...":

#16 0.058 composer install --no-scripts --no-interaction --no-progress --classmap-authoritative
#16 0.156 Installing dependencies from lock file (including require-dev)
#16 0.160 Verifying lock file contents can be installed on current platform.
#16 0.177 Package operations: 93 installs, 0 updates, 0 removals
#16 0.180   - Downloading revolt/event-loop (v1.0.8)
#16 0.181   - Downloading amphp/serialization (v1.1.0)
#16 0.182   - Downloading amphp/amp (v3.1.1)
...
#16 2.150   - Installing revolt/event-loop (v1.0.8): Extracting archive

Local build produces only "Installing ... Extracting archive":

composer install --no-scripts --no-interaction --no-progress --classmap-authoritative
...
- Installing staabm/side-effects-detector (1.0.5): Extracting archive`
...

Questions

1. Does this action cache --mount=type=cache? If not, then any ideas how to cache it?
2. Is there any difference with cache in docker/build-push-action?

[crazy-max]

Not yet, this is tracked in moby/buildkit#1512