On 11 August 2017 at 09:02, fengxia <fx...@lenovo.com> wrote:
> Hi Juju,
> I'm building a charm by including two layers in layer.yaml:
> includes:
>   - 'layer:basic'
>   - 'layer:pylxca'
> Pylxca is a library I packaged into a "layer" format for reuse.
> Both layers have a folder called "hooks", and each has a hook called
> "install". The curious result is that after `charm build`, the pylxca's
> install hook is the one in dist.

The pylxca layer should not be adding the hook stubs if the hooks/
directory. These are declared in layer:basic, and duplicating them in
the pylxca leads to the problem you describe.

> So my question now is, if I want to use layers, and each layer defines its
> own hooks so to help its implementation, how does `charm build` handle them?
> Are they merged? From this test, only the last one will survive. If so, does
> it mean only one layer can define hooks?

Only one layer should define the hook stubs. Layers can do it, as you
have found, and it can be useful in some debugging situations to
override and inject behaviour, but I don't think should ever go as far
as a release.

If multiple layers need hook specific code, they can all declare
handlers with the @hook decorator and they are all run in an arbitrary
order. Its best to avoid @hook completely though and just use normal
reactive states. So instead of using @hook('install'), use
@when_not('mycharm.installed') and have that handler set the
mycharm.installed state at the end.

Stuart Bishop <stuart.bis...@canonical.com>

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