Neat features in Eclipse editor

[Richard Stallman]

I just got a demo of the Eclipse editor and saw these features
which we should have in Emacs.

* Having tabs above a window to switch buffers in it.

* "Perspectives" are named persistent window configurations.  We have
had the window configuration mechanism in GNU Emacs since the
beginning but we have never developed a good user interface to take
advantage of them.  Eclipse's user interface seems to be good.

* Perspectives work well even if you do the equivalent of C-x 4 C-f
because of the distinction between view windows vs file windows.  In
Emacs this is more or less the "dedicated window" feature, but we have
never really made it work for this.

* Perspectives also need to interact with the tabs.

* Imenu could be extended into a file-structure browsing mechanism
using code like that of customize-groups.

* Flymake's customization mechanism needs to be both simpler (fewer
levels of indirection) and better documented, so it is easier to
understand.  I find it quite hard to figure out what compilation
command it will use.

I suggest totally rewriting that part of Flymake, using the simplest
mechanism that sufficies for the specific needs.  That will be easy
for users to customize.

* Display something in the margin on lines that have compilation
errors.

* Compilation error navigation bar, parallel to the scroll bar,
indicating where in the buffer there are compilation errors.
Perhaps we could arrange to display these error indications on top
of the scroll bar itself.  That depends on to what extent toolkit
scroll bars are extensible.