[cli] Allow plugins to extend CLI

[brillout]

This would require changes in https://github.com/brillout/reframe/blob/master/core/utils/processReframeConfig.js

This would be super cool though.

@tdfranklin up for it?

[tdfranklin]

Happy to take a stab at it! Might need you to point me in the right direction of what you're looking for, if you don't mind?

[brillout]

A plugin can currently do something like that:

function myPlugin() {
    return {
        webpackBrowserConfig: ({config}) => {
            // change webpack config
            return config;
        },
    };
}

We could extend a plugin to be able to do

function myPlugin() {
    return {
        commands: [
            {
                name: 'my-new-command',
                description: 'This is an awesome command',
                handler: function (cliArgs) {
                    console.log('something cool happened');
                },
            },
        ],
    };
}

For that

1.

processReframeConfig needs to be changed.

See comments in the https://github.com/brillout/reframe/blob/master/core/utils/processReframeConfig.js file

2.

The reframe config needs to be loaded and processReframeConfig needs to be called before the whole commander thingy: https://github.com/brillout/reframe/blob/c75f2a5de272b18523186e50d94848c62e88aee4/core/cli/cli.js#L15-L39

Currently the reframe config is loaded here: https://github.com/brillout/reframe/blob/c75f2a5de272b18523186e50d94848c62e88aee4/core/cli/cli.js#L53-L55.
We would move that before the commander stuff.

[brillout]

@tdfranklin

What could also help is to look at current plugins such as https://github.com/brillout/reframe/blob/master/plugins/postcss/index.js

[brillout]

@tdfranklin

You're right, after

 const {pagesDirPath, reframeConfigPath, appDirPath} = find_files(cwd); 
 const reframeConfig = reframeConfigPath && require(reframeConfigPath); 

we need to process the reframe config:

const {processReframeConfig} = require('@reframe/utils/processReframeConfig');
processReframeConfig(reframeConfig); 
// we now have access to the processed stuff
console.log(reframeConfig._processed);
// We could change `processReframeConfig` to add something like
// `reframeConfig._processed.cli_commands`

At that point, everything we do in processReframeConfig will be availble to cli.js

[brillout]

Done
Good job @tdfranklin