bug#51380: 29.0.50; The annotated example of a complete working Flymake backend leaves process buffers around

[Rudolf Adamkovič]

I noticed that the "annotated example of a complete working Flymake backend" at

<https://www.gnu.org/software/emacs/manual/html_mono/flymake.html#Backend-functions>

leaves zombie buffers around. I traced the problem down to

┌────
│ (when (eq 'exit (process-status proc)) …
└────

The backend kills the process buffer on `'exit' but not on `'signal', which 
happens when Flymake kills an obsolete in-progress check. I fixed the problem 
locally by checking for both `(or (eq status 'exit) (eq status 'signal)'. 
Below, I include a macro that includes the fix.

┌────
│ (defmacro my-define-flymake-backend (name cmd regexp warning-p)
│   "Define a new Flymake backend named NAME.
│ 
│ CMD takes a buffer file name and returns a system command
│ to run to check the buffer. REGEXP matches the output of the system
│ command in three capture groups: (1) line, (2) column, and (3)
│ message. WARNING-P takes the message matched by REGEXP and decides if
│ the issue represents a warning or an error.
│ 
│ The macro defines a function called NAME representing the Flymake
│ backend and a variable called NAME that stores the current process."
│   `(defun ,name (report-fn &rest _args)
│      (defvar-local ,name nil)
│      (when (process-live-p ,name) (kill-process ,name))
│      (let ((src (current-buffer)))
│        (save-restriction
│          (widen)
│          (setq
│           ,name
│           (make-process
│            :name (symbol-name ',name)
│            :noquery t
│            :connection-type 'pipe
│            :buffer (generate-new-buffer
│                     (concat "*" (symbol-name ',name) "*"))
│            :command (with-current-buffer src
│                       (funcall ,cmd buffer-file-name))
│            :sentinel
│            (lambda (proc _event)
│              (let ((status (process-status proc)))
│                (when (or (eq status 'exit)
│                          (eq status 'signal))
│                  (unwind-protect
│                      (when (and (with-current-buffer src (eq proc ,name))
│                                 (eq status 'exit))
│                        (with-current-buffer (process-buffer proc)
│                          (goto-char (point-min))
│                          (cl-loop
│                           while (search-forward-regexp ,regexp nil t)
│                           for msg = (match-string 3)
│                           for line = (string-to-number (match-string 1))
│                           for col = (string-to-number (match-string 2))
│                           for (beg . end) = (flymake-diag-region src line col)
│                           for type = (if (funcall ,warning-p msg) :warning 
:error)
│                           collect (flymake-make-diagnostic src beg end type 
msg)
│                           into diags
│                           finally (funcall report-fn diags))))
│                    (kill-buffer (process-buffer proc))))))))
│          (process-send-region ,name (point-min) (point-max))
│          (process-send-eof ,name)))))
└────

For completeness, I call the macro above as follows:

┌────
│ (my-define-flymake-backend
│  my-flymake-vale
│  (lambda (source) (list "vale" "--output" "line" "--ext" ".md", "--no-wrap"))
│  "^stdin.md:\\([0-9]+\\):\\([0-9]+\\):\\(.*\\)$"
│  (lambda (msg) t))
└────

Rudy


In GNU Emacs 29.0.50 (build 6, x86_64-apple-darwin20.6.0, NS appkit-2022.60 
Version 11.5.1 (Build 20G80))
 of 2021-10-24 built on Workstation.local
Repository revision: aea4af5119fdf130f1df7190478a23c6777f92a2
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2022
System Description:  macOS 11.5.1

Configured using:
 'configure --with-json
 
PKG_CONFIG_PATH=/usr/local/Cellar/zlib/1.2.11/lib/pkgconfig:/usr/local/lib/pkgconfig:/opt/X11/lib/pkgconfig'

Configured features:
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KQUEUE NS PDUMPER PNG RSVG THREADS TIFF TOOLKIT_SCROLL_BARS WEBP XIM
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Important settings:
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Major mode: Text

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Load-path shadows:
/Users/salutis/.emacs.d/elpa/transient-20211023.2151/transient hides 
/Users/salutis/src/emacs/nextstep/Emacs.app/Contents/Resources/lisp/transient

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Memory information:
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-- 
"I love deadlines. I love the whooshing noise they make as they go by." -- 
Douglas Adams, The Salmon of Doubt

Rudolf Adamkovič <salutis@me.com>
Studenohorská 25
84103 Bratislava
Slovakia

[he/him]