flet vs cl-flet vs compilation-start

[Stephen Leake]

I'm using compilation-mode to show results from running an external
program; it produces output that looks like compilation errors (it's
actually cross-reference info).

Some users would like to preserve output from several calls to the
external program.

compilation-start does not provide an option for this; it calls
(erase-buffer) unconditionally.

So someone suggested this hack:

(require 'cl)
(flet ((erase-buffer nil (goto-char (point-max))))
    (compilation-start ... ))

That works, but produces byte-compiler warnings about cl and flet.

So I tried:

(require 'cl-lib)
(cl-flet ((erase-buffer nil (goto-char (point-max))))
    (compilation-start ... ))

This does _not_ work. Apparently in the "flet" case, the local
definition of 'erase-buffer' overrides the global one, but in the
'cl-flet' case it does not.

I'm running emacs-25 compiled from the branch with mingw64.

This is consistent with the doc strings:

cl-flet says:

Make local function definitions.

flet says:

Make temporary overriding function definitions.

and goes on to say "use cl-flet".

Perhaps the doc string of flet should be improved to point out that
cl-flet does not produce _overriding_ function definitions, and suggest
workarounds.


I could try applying and removing advice on erase-buffer, but a simpler
workaround is to copy the buffer content into a local string var, then
paste it back.

Is there any support for introducing a parameter to compilation-start
that says "don't erase the buffer"?

-- 
-- Stephe