Multi-line diagnostics

[ccapndave]

Some error messages (e.g. from Elm) are quite verbose, and are very hard to read properly without line breaks.

Therefore it would be nice if the vscode.Diagnostic message could contain line breaks (these could be stripped out in the Errors and warnings selector to keep the UI sensible). It would be even nicer still if error messages could contain colors and styles.

This is an example of the kind of thing it would be nice to have in a diagnostic popup:

[jrieken]

Wd do support this with the hover. I'll add support for the F8 feature, unsure what to do with the new error list.

[sandy081]

With regards to error-lists, showing long error messages completely would occupy space. So, I am thinking to provide an expand/collapse option for the error-entry to show or hide the complete description.

[jrieken]

Also, a mono-space font should be used. Otherwise whitespace based formatting won't work

[jrieken]

Like the hover, the message part of the in-editor error display now uses the editor font.

[jrieken]

cc @stevencl for how to handle multiline diagnostics in the error list view

[sandy081]

Supporting multiline or long descriptions is not trivial with current infrastructure. Firstly, I will be showing them with ellipsis.

@joaomoreno mentioned different ideas on how we can support this in trees.. Will look into them.