[Find/Replace]: Classic Dialog doesn't handle RegEx-Errors well

[fedejeanne]

(Taken from https://github.com/eclipse-platform/eclipse.platform.ui/issues/1204)

The problems

• The validation of the regular expression in the "old" search dialog (Ctrl + f in Windows) is not displayed correctly.

Goal

• The result of the validation should be shown in a decoration (ControlDecoration), with an error icon instead of the red text at the bottom.
• The text of the decoration should contain the details of the validation result e.g. "Unclosed character near..."
• The same should be used for the Search dialog (org.eclipse.search.internal.ui.SearchDialog) and for the new search overlay.
• The decoration should not interfere with the existing decoration that is used to hint the content assist (all 3 places have it) so the new validation decoration should be placed using SWT.CENTER as a style-bit.
• If possible, the new decoration should be used in all 3 places to avoid code duplication

Non-goals

• View to validate regular expressions mentioned in comment-1759158486

[fedejeanne]

Maybe @jakub-suliga and/or @jannisCode would like to chat about it with @Wittmaxi and support him/take over?

[Wittmaxi]

@fedejeanne the mentionned issue is a good first issue for new contributors. The main issue here is in finding an expected solution - we could not yet agree on an expected behavior (it might be helpful to create a few different prototypes ?)

Moreover, the Find/Replace overlay does not offer any feedback on RegEx-Errors (thus slightly losing functionality). Maybe we can find a solution for the Overlay as well?

I am not currently planning on fixing the above issue, I believe it is an excellent issue e.g. for @jannisCode so he can quickly see first results. Feel free to reach out :)

[fedejeanne]

Thank you for the details, @Wittmaxi! Then I'll refine this issue and set some goals and proposals in the coming days.

Moreover, the Find/Replace overlay does not offer any feedback on RegEx-Errors (thus slightly losing functionality). Maybe we can find a solution for the Overlay as well?

I'll keep that in mind 👍

[fedejeanne]

@jannisCode I changed the description of this issue to reflect what we discussed. I left it in this internal issue because I merely accepted the proposals that were made in the original issue (https://github.com/eclipse-platform/eclipse.platform.ui/issues/1204) so the PR can simply reference that issue.

@Wittmaxi I left out the part about the view to evaluate the expressions (see Non-goals). That one can be done in a separate PR/Issue.