Switch to base buffer when updating imenu

[dvzubarev]

When current buffer is indirect and the base buffer is visible, reuse imenu--index-alist from the base buffer.
Should fix #30

[joaotavora]

Let's continue here.

Yes. If a base buffer is visible then it will compute imenu-buffer-alist, that can be reused in an indirect buffer. On the other hand, if the base buffer is hidden, then the indirect buffer should request an update of imenu-buffer-alist by itself. Otherwise it won't be updated. But it occurred to me now that it won't help, if there are two indirect buffers and the base buffer is hidden.
Both indirect buffers will request an update and one of them will hang.

Right. I think for this to work we need to always do the work in the base buffer, regardless of whether it's visible or not. So if an indirect buffer was going to request it, it shouldn't. It should pretend the base buffer wants to (even if it doesn't), by using with-current-buffer base. Then when the result comes in, assign the to the indirect buffer. Something like that. Cna't think very well right now. Good luck!

[joaotavora]

Does this most recent version work already for you and fix #30? Because it looks very simple conceptually, which is good.

[dvzubarev]

Yes, it works for me. I've been using breadcrumb with this fix for a while. I haven't noticed any issues.