Jsonrpc: avoid redisplay_internal calls from jsonrpc-request

The 'jsonrpc-request' function, when called with non-nil CANCEL-ON-INPUT,
relies on 'sit-for' to stop immediately when the user inputs something into
Emacs.  Although this behavior is working well, it has the hitherto
undiscovered side effect of invoking 'redisplay_internal', which triggers
expensive operations such as fontification.

This bug was noticied when using the 'breadcrumb' package in conjunction
with Eglot and a narrowed buffer.  To provide breadcrumbs for the current
context, breadcrumb.el invokes 'imenu--make-index-alist' on a timer.  That
function temporarily widens the buffer and then eventually calls
'redisplay_internal' (through 'eglot-imenu', 'jsonrpc-request', and
'sit-for').  This has the effect that the temporarily widened buffer is
re-rendered and displayed to the user until the LSP server answers the
request and 'imenu--make-index-alist' restores the restriction, an effect
that lasts between 0.5 and 2 seconds usually and is annoying and confusing.

To fix this, using a non-nil NODISP argument in the 'sit-for' is not enough
(though it's arguable it should be and maybe that's a separate bug).
Binding 'inhibit-redisplay' to 't' around 'sit-for' seems to fix the issue
robustly.

* lisp/jsonrpc.el (jsonrpc-request): Bind inhibit-redisplay to t and pass
  NODISP to sit-for.

0 files changed, 0 insertions, 0 deletions