core20: part is not rebuilt even if source file has changed

[paddor]

Expected behaviour

Part should be rebuilt if the content of its source .tar.gz or .tar file has changed.

Steps to reproduce the problem

Create a bundle.tar like this: tar -c Gemfile Gemfile.lock vendor/cache > bundle.tar

Have a part like this:

  bundle:
    after:
      - ruby
    plugin: dump
    source: bundle.tar
    build-packages:
      - ccache
      - autoconf
      - automake
      - libxml2-dev
      - git
    build-environment:
      - CC: "ccache cc"
      - CXX: "ccache c++"
      - CFLAGS: "-Os"
    stage-packages:
      - libczmq-dev
      - libxml2
      - less
    override-build: |
      mkdir -p $SNAPCRAFT_PART_INSTALL/app
      cd $SNAPCRAFT_PART_INSTALL/app
      cp $SNAPCRAFT_PART_SRC/Gemfile .
      cp $SNAPCRAFT_PART_SRC/Gemfile.lock .
      bundle config set --local deployment true
      bundle config set --local cache_path $SNAPCRAFT_PART_SRC/vendor/cache
      bundle config set --local silence_root_warning true
      bundle config set --local jobs $SNAPCRAFT_PARALLEL_BUILD_COUNT
      bundle env

      if bundle check
      then
        echo "Bundle is already installed."
      else
        echo "Installing bundle ..."
        bundle install --local
        bundle check
      fi

      bundle clean --force

Build a snap: snapcraft --use-lxd --debug

Update the bundle.tar (e.g. add a gem to the Gemfile and bundle && bundle pack && tar -c Gemfile Gemfile.lock vendor/cache > bundle.tar

Try to build another snap:

snapcraft --use-lxd --debug
Launching a container.
Waiting for container to be ready
Waiting for network to be ready...
snap "snapd" has no updates available
Skipping pull app (already ran)
Skipping pull openssl (already ran)
Skipping pull ruby-install (already ran)
Skipping pull ruby (already ran)
Skipping pull bundle (already ran) # <---- wrong
Skipping pull webui (already ran)
Skipping build app (already ran)
Skipping build openssl (already ran)
Skipping build ruby-install (already ran)
Skipping build ruby (already ran)
Skipping build bundle (already ran)
Skipping build webui (already ran)
Skipping stage app (already ran)
Skipping stage openssl (already ran)
Skipping stage ruby-install (already ran)
Skipping stage ruby (already ran)
Skipping stage bundle (already ran) # <---- wrong
Skipping stage webui (already ran)
Skipping prime app (already ran)
Skipping prime openssl (already ran)
Skipping prime ruby-install (already ran)
Skipping prime ruby (already ran)
Skipping prime bundle (already ran)
Skipping prime webui (already ran)
The requested action has already been taken. Consider  # <---- does not make sense. I didn't request a specific action.
specifying parts, or clean the steps you want to run again.
Snapping |

Specs

• Operating system: Ubuntu 20.04

[cosmic-zip]

Post or link the snap file as a hole, it's difficult to help without it.

[paddor]

Since this is so fundamental, could you just tell me if this is something that's supposed to work or not? If the content of a source file of a part is changes (would result in a different checksum), shouldn't the whole part be rebuilt?