[search-in-workspace] Show diff editor only when replacement term is provided

[gbodeen]

Signed-off-by: Gabriel Bodeen gabriel.bodeen@ericsson.com

What it does

Aligns Theia's search-in-workspace replacement behavior more closely with VS Code's. The latter switches from search mode to search-and-replace mode only when the replacement field is visible and nonempty; currently Theia goes into search-and-replace mode whether the replacement field is filled or not. This behavior was reported by some of our users as confusing.

I'll note that there is one potential advantage to Theia's current behavior, which is making it obvious that the search-and-replace mode has the ability to easily search a term and replace it with nothing (i.e. just remove it). It can still do that in this branch via the replace-all button, but this option is no longer obvious. I think it's an acceptable cost.

How to test

This branch:

1. Open the search-in-workspace widget. Enter search text. Observe the styling.
2. Toggle to show the replace field & buttons. Observe the styling has not changed. If you click one of the lines, it will open a normal editor.
3. Enter a replacement term. Observe the styling changes and now displays the search and replace terms. If you click one of the lines, it will open a diff editor.

Current master:

1. Open the search-in-workspace widget. Enter search text. Observe the styling. If you click one of the lines, it will open a normal editor.
2. Toggle to show the replace field & buttons. Observe the styling changes and now displays the search and replace terms. If you click one of the lines, it will open a diff editor.

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

[vince-fugnitto]

The changes look good to me and work well 👍
I'm fine with the behavior present on master but this way has the advantage of aligning the behavior with vscode.