Validate CodeMirror as alternative blob view implementation

Created by: fkling

This issues keeps track of the work that needs to be done for a baseline implementation of the blob view with CodeMirror.

The feature flag is enableCodeMirrorFileView.

• Add minimal implementation behind feature flag #37922 (closed)
  • Sync line selection to/from URL
• Enable syntax highlighting with SCIP data
  • POC: #39116
  • Client side: #39386
  • Syntax highlight server #39264
  • Syntax highlight server #2 https://github.com/sourcegraph/sourcegraph/pull/39850
  • GraphQL/Go glue https://github.com/sourcegraph/sourcegraph/pull/40166
• Code intel popovers
  • https://github.com/sourcegraph/sourcegraph/pull/39482
  • https://github.com/sourcegraph/sourcegraph/pull/39650
  • https://github.com/sourcegraph/sourcegraph/pull/39881
• Search with meta+F https://github.com/sourcegraph/sourcegraph/pull/39884
• Basic telemetry
• Jump to definition
  • https://github.com/sourcegraph/sourcegraph/pull/39881
• Click to jump to definition
  • From @fkling: As long as we have a real text cursor it would be surprising if we implemented this exact behavior. Apparently IDEs support this if a modifier key is pressed, so we should consider to do the same.
  • Implementation without modifier: https://github.com/sourcegraph/sourcegraph/pull/40232
• Find references
  • https://github.com/sourcegraph/sourcegraph/pull/39881
• Git blame
  • https://github.com/sourcegraph/sourcegraph/pull/39650
• Highlight symbol references on hover
  • https://github.com/sourcegraph/sourcegraph/pull/39482
  • https://github.com/sourcegraph/sourcegraph/pull/39650
• Support status bar (including extensions)
  • https://github.com/sourcegraph/sourcegraph/pull/39650
• Support extension API as far as possible and document what isn't supported (if any)
  • https://github.com/sourcegraph/sourcegraph/pull/39650

Known issues to be fixed/discussed:

• Selected line is not synced with cursor position and therefore not sent to extensions
  • Handled in https://github.com/sourcegraph/sourcegraph/pull/40131 by sending the information about selected lines to the extensions instead.
• File content is visible under line numbers (looks like line number background is transparent?)
  • https://github.com/sourcegraph/sourcegraph/pull/40131
• Dismissing the hovercard info box causes the hovercard to shrink upwards, "detaching" it from the line/token it was shown for.
  • We either need to call CodeMirror's repositioning logic
    • this was also done in https://github.com/sourcegraph/sourcegraph/pull/39881
  • Or change the style so that the the dimensions of the hovercard don't change.
• Hovercards are disabled in reference panel blob view (see https://github.com/sourcegraph/sourcegraph/pull/40131 for more information)
  • From @fkling: Issue was something different. See PR If replacing <Router /> with <MemoryRouter /> would fix the navigation issue (which I don't know), then we could introduce a special flag/config option to instruct the React wrapper to use MemoryRouter instead of Router. It's not pretty but doable. But if simply using <MemoryRouter /> would not solve the issue then I don't think there is anything we can do about that (except refactoring the ref panel and hover cards to work differently). So whether or not to fix/change this is up for debate.
  • https://github.com/sourcegraph/sourcegraph/pull/40249
• Close button is not functional in un-pinned hovercards
  • From @fkling: Planned solution, as discussed below: Hide close button if hovercard is not pinned
  • Hide close button: https://github.com/sourcegraph/sourcegraph/pull/40232