bug#47050: 28.0.50; [PATCH] `next-error-find-buffer' does things in the wrong order

[Nick Dokos]

The doc for `next-error' says:

<quote>
C-x ` normally uses the most recently started
compilation, grep, or occur buffer.  It can also operate on any
buffer with output from the M-x compile, M-x grep commands, or,
more generally, on any buffer in Compilation mode or with
Compilation Minor mode enabled, or any buffer in which
‘next-error-function’ is bound to an appropriate function.
To specify use of a particular buffer for error messages, type
C-x ` in that buffer.  You can also use the command
‘next-error-select-buffer’ to select the buffer to use for the subsequent
invocation of ‘next-error’.
</quote>

I interpreted that to mean that if I create e.g. two `grep' buffers and
rename them uniquely to `*grep*<2>' and `*grep<3>', then switching
to one or the other of them and calling `next-error' would use the hits
from that buffer. However it always uses the hits from the last-used grep
buffer and I have to change that explicitly, by calling
`next-error-select-buffer', instead of letting the current buffer
determine it.

The problem is caused by `next-error-find-buffer' which does things in
the (IMO) wrong order: it first checks for next-error-last-buffer and
then it checks for the current buffer.

Here is a patch to reverse the order:

--8<---------------cut here---------------start------------->8---
diff --git a/lisp/simple.el b/lisp/simple.el
index f8050091d5..8796b612cc 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -298,15 +298,15 @@ next-error-find-buffer
    (funcall next-error-find-buffer-function avoid-current
                                             extra-test-inclusive
                                             extra-test-exclusive)
-   ;; 2. If next-error-last-buffer is an acceptable buffer, use that.
+   ;; 2. If the current buffer is acceptable, choose it.
+   (if (next-error-buffer-p (current-buffer) avoid-current
+                           extra-test-inclusive extra-test-exclusive)
+       (current-buffer))
+   ;; 3. If next-error-last-buffer is an acceptable buffer, use that.
    (if (and next-error-last-buffer
             (next-error-buffer-p next-error-last-buffer avoid-current
                                  extra-test-inclusive extra-test-exclusive))
        next-error-last-buffer)
-   ;; 3. If the current buffer is acceptable, choose it.
-   (if (next-error-buffer-p (current-buffer) avoid-current
-                           extra-test-inclusive extra-test-exclusive)
-       (current-buffer))
    ;; 4. Look for any acceptable buffer.
    (let ((buffers (buffer-list)))
      (while (and buffers
--8<---------------cut here---------------end--------------->8---


This arose in a question on the Emacs SE:

https://emacs.stackexchange.com/questions/63807/is-there-a-way-to-get-two-separate-next-error-lists-so-i-can-bind-them-to-two-di

---------------------------------------------------------------------------


In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.25, cairo 
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 of 2021-03-07 built on pierrot.dokosmarshall.org
Repository revision: 997142a4ddc98158cb71bdcef58df5a24f9a9a5c
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-- 
Nick



-- 
Nick