Support interactive variables in launch configurations

[weinand]

This is a feature required for #6569.

For details please see my prototype in the andre/pickervariables branch:

https://github.com/Microsoft/vscode/blob/andre/pickervariables/src/vs/workbench/parts/debug/electron-browser/debugService.ts#L564

[isidorn]

@weinand I checked out the branch and the code looks good. Though I have some things which I would change, would your prefer:

• I incorparate all that feedback and rewrite parts of your code on master
• You create a PR and I add comments on your PR

Both work equally fine for me 😊

[weinand]

@isidorn my code is not meant as a PR, it was just code that I wrote to unblock me. Since you are the owner of the launch config variable substitution you should implement this feature.

[isidorn]

Pushed a first version of this to master, check it out and let me know what you think.
Seems to work fine for the mock debug example - note that the variable name is case sensitive and in package.json of mock debug you contribute 'PickProcess'

[weinand]

@isidorn looks great! I've released "Attach to Process" support for node-debug to master.
One issue I saw: dismissing the process picker with ESC does not abort the launching of the debug session.

[isidorn]

I pushed the change that dimissing hte process picker silently aborts the debug session - let me know if we should show an info message in that case.

Also feedback on following wording is welcome. When extension writer hovers over variables in package.json we say 'Mapping from interactive variables (e.g ${action.pickProcess}) in launch.json to a command.'

When there is an interactive variable which is not contributed we say: 'Adapter {0} does not contribute variable {1} that is specified in launch configuration.'

[weinand]

@isidorn if an action variable is used multiple times in a launch config, the associated command should only be run once.

The reason behind this is as follows:
For a user the mental model of action variables should be that a variable has a value and that VS Code ensures that this value is initialised once, and not that every use of an action variable is a function call with a potentially different result.

[isidorn]

@weinand pushed a fix that should take care of this issue - so an action will get triggered only once even if it occurs multiple times in launch.json