On Thu, Sep 29, 2016 at 01:24:22PM -0300, Cleber Rosa wrote:
As detailed in the following card:
https://trello.com/c/oWzrV48E/837-execution-order-support-in-plugins
It should be possible to specify a custom order for plugins to be
executed by setting specific configuration.
The first observed approach would be to create a section
called `[plugins.<type>]` where the `<type>` conforms to the
description on fully qualified plugin names given here:
https://github.com/avocado-framework/avocado/pull/1495/commits/193a10ce98cb5747395eefcb485dd452696b4b11#diff-0f4f89ace79fa15278d9b283c2d9d9b2R84
Then, by creating a key named `order`, containing the short names as a
list. Enabled plugins not listed will be executed *after* plugins
listed, but in non-determined order.
The phrase "enabled plugins" implies that there can be disabled
plugins as well.
For instance, consider the following entry points::
'avocado.plugins.result' : [
'xunit = avocado.plugins.xunit:XUnitResult',
'json = avocado.plugins.jsonresult:JSONResult',
'archive = avocado.plugins.archive:Archive',
'mail = avocado.plugins.mail:Mail',
'html = avocado_result_html:HTMLResult'
]
We can say that:
* The plugin type, according to the fully qualified plugin name
definition here is `result`.
* The plugin fully qualified names are:
- result.xunit
- result.json
- result.archive
- result.mail
- result.html
* The short names for plugins of type "result" are:
- xunit
- json
- archive
- mail
- html
I like this use of examples. The illustrations are clear and easy to
understand.
To make sure that the mail plugin is run after (and thus includes)
the HTML result, the following configuration entry can be set::
[plugins.result]
order = html, archive
What does it mean for a plugin to "include" the results of an earlier
plugin?
The other result plugins, namely xunit, json and mail, will still
be run. It's guaranteed they'll be run *after* the other result
plugins. The order in which they'll run after the explicitly
ordered plugins is undefined.
Can a plugin determine what plugin(s) have run before it? (I don't
think it's necessary.)
Other possible approach
-----------------------
The other approach possible, would require a default order value
for plugins. This would still preferably be done in configuration
rather than in code. Then, the fully qualified name for a plugin could
be used as part of the configuration section. Example::
[plugin.result.archive]
order = 50
[plugin.result.html]
order = 30
Small typo: "plugins.result" not "plugin.result" (two lines).
This would make the `html` plugin run before the `archive` plugin.
While more verbose, it would allow for external plugins to ship with
stock configuration files that would set, by default, its ordering.
Order is here is used as a numerical value to indicate a relative
ordering, correct? I'm not sure I like the name "order"; how about
"sequence"?
A drawback to this approach is that you still have to come up with a
rule for what happens when two plugins have the same sequence number.
Feedback is highly appreciated!
Another way to specify the order is to use an attribute at the
[plugins] or [plugins.result] level with certain expected values:
[plugins]
execution-order = random | lexical | user-defined
where 'user-defined' would require yet another attribute
that defines the sequence. 'user-defined' would also have to
handle the 'unspecified' condition.
I think this is too complicated, but I offer it as a counter-example.
Finally, the typo got me to thinking: should it be "plugin" or
"plugins"? I don't care one way or the other. However, I do believe
that the attribute should be named consistent with the rest of
avocado. If there isn't a style guide for avocado proposals and naming
conventions, it would be good to have one. Consistency is going to be
hard to establish and maintain without it.
-Jeff
--
Cleber Rosa
[ Sr Software Engineer - Virtualization Team - Red Hat ]
[ Avocado Test Framework - avocado-framework.github.io ]
