charm build overwrites files silently

[rgildein]

Checklist

• Confirmed this is an issue with charm-tools, not charmstore-client
• Provide versions of tools used
• Described the feature or ways to replicate the issue

What version am I running?

I ran the following command: charm version and got the following output:

charmstore-client 2.5.1
charm-tools 2.8.1

I am using: Ubuntu Focal

Issue/Feature

Charm build should not overwrite files silently, but should raise an error when file already exist and comes from another layer.

I expect/expected the following

While building charm-openstack-integrator:

charm-build --log-level DEBUG -o ~/canonical/charm-build/ .
charm-build: error: An attempt was made to overwrite a file "lib/charms/layer/__init__.py" with a layer "snap". The file has already been created by a layer "basic"

What I got

Because the merge layer: snap contains the file __init __.py, __init__.py from the layer: basic will be overwritten.

While building charm-openstack-integrator:

charm-build --log-level DEBUG -o ~/canonical/charm-build/ .
cat ~/canonical/charm-build/builds/openstack-integrator/.build.manifest | grep -A 3 'layer/__init__.py'
    "lib/charms/layer/__init__.py": [
      "layer:snap",
      "static",
      "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"

[auria]

The layer:snap commit that caused this overlap has been reverted [1].

1. https://code.launchpad.net/~canonical-is-bootstack/layer-snap/+git/layer-snap/+merge/397254