preferences: fix merge method in PreferenceProvider

[AlexandraBuzila]

What it does

When merging preferences, in the PreferenceProvider, also merge properties of type array. Currently, properties of type object are merged, but for arrays only the value from the target JSON is used.

This fixes the first use case described in issue #8987, where launch configs defined in the workspace are not visible, if other launch configs exist in a launch.json file.

How to test

1. Create a workspace with a test folder and a .theia-workspace file, e.g.:

{
    "folders": [
        {
            "path": "test"
        }
    ],
    "settings": {
        "launch": {
            "configurations": [
                {
                    "name": "from .theia-workspace",
                    "request": "launch",
                    "type": "node",
                }
            ]
        }
    }
}

2. Go to the Debug view and check that the launch configs from the workspace file are present in the dropdown at the top of the view.
3. Add a .theia/launch.json file with at least one launch configuration, e.g.:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "from .theia",
            "request": "launch",
            "type": "node",
        }
    ]
}

4. Go to the Debug view and check that the launch configs from launch.json are visible in the dropdown, alongside the ones from the workspace file.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[paul-marechal]

Code LGTM and the changes work as described.

[tsmaeder]

@AlexandraBuzila can we close the related issue? It didn't auto-close, it seems.

[AlexandraBuzila]

I think the main problem that was reported in that ticket is solved by this PR, however there was a second issue mentioned in the ticket description: if there are launch configurations defined both in "someProject/.theia/launch.json" and "someProject/.vscode/launch.json", only the ones from the .theia folder are visible.

If the current behavior is expected and should not be changed, then the ticket can be closed from my point of view 👍

[tsmaeder]

If we're not sure it's completely fixed, you did the right thing leaving it open, IMO. I was just wondering.

[marcdumais-work]

Hi,

I believe that this PR introduced a bug. I've been working to improve the browser test suite and when I rebased to include it, over 100 tests from launch-preferences.spec.js started failing. This test file is a bit obscure, but I think that with this PR here, we end-up with duplicated launch configurations.

Please see: #12153

[AlexandraBuzila]

Hi @marcdumais-work! Thank you for catching this, I will have a look ASAP.