documentation: update CodingStyle tips for Emacs users

Documentation/CodingStyle make a good program). · line 491

Quoted 6 lines · On Fri, 04 Jul 2008 19:52:16 +0200 Johannes Weiner <[email protected]> wrote:

Documentation/CodingStyle +6 -0

+(add-hook 'c-mode-hook
+          (lambda ()
+            (let ((filename (buffer-file-name)))
+              ;; Enable kernel mode for the appropriate files
+              (when (and file
+                         (string-match "/usr/src/linux" filename))

Shouldn't that be "(and filename ..." rather than "file"?

A test for /usr/src/linux seems misplaced, though; I don't think a whole lot of people keep their kernel trees there anymore. There must be a better heuristic one can use to figure out whether a kernel source file is being edited.

A heuristics seems overkill as this snippet is not distributed code that needs to be portable but it is just a tip for ones .emacs.

Quoted 2 lines · On Sat, 05 Jul 2008 11:36:44 +0000 Johannes Weiner <[email protected]> wrote:

A heuristics seems overkill as this snippet is not distributed code that needs to be portable but it is just a tip for ones .emacs.

You're right, it's fine the way it is.

Describe a setup that integrates better with Emacs' cc-mode and also fixes up the alignment of continuation lines to really only use tabs.

Documentation/CodingStyle +10 -0

+(defun c-lineup-arglist-tabs-only (ignored)
+  "Line up argument lists by tabs, not spaces"
+  (let* ((anchor (c-langelem-pos c-syntactic-element))
+	 (column (c-langelem-2nd-pos c-syntactic-element))
+	 (offset (- (1+ column) anchor))
+	 (steps (floor offset c-basic-offset)))
+    (* (max steps 1)
+       c-basic-offset)))
+
+(add-hook 'c-mode-hook

Quoted 2 lines · Johannes Weiner

Describe a setup that integrates better with Emacs' cc-mode and also fixes up the alignment of continuation lines to really only use tabs.

[...]

Quoted 10 lines

Documentation/CodingStyle +10 -0

+(defun c-lineup-arglist-tabs-only (ignored)
+  "Line up argument lists by tabs, not spaces"
+  (let* ((anchor (c-langelem-pos c-syntactic-element))
+	 (column (c-langelem-2nd-pos c-syntactic-element))
+	 (offset (- (1+ column) anchor))
+	 (steps (floor offset c-basic-offset)))
+    (* (max steps 1)
+       c-basic-offset)))
+
+(add-hook 'c-mode-hook

Documentation/CodingStyle make a good program). · line 496

Quoted 10 lines

Documentation/CodingStyle +10 -0

+          (lambda ()
+            (let ((filename (buffer-file-name)))
+              ;; Enable kernel mode for the appropriate files
+              (when (and file
+                         (string-match "/usr/src/linux" filename))
+                (setq indent-tabs-mode t)
+                (c-set-style "linux")
+                (c-set-offset 'arglist-cont-nonempty
+                              '(c-lineup-gcc-asm-reg
+                                c-lineup-arglist-tabs-only))))))

When starting writing kernel source code last year (the hardware time stamping patch) I used this macro to format it. I very much liked the possibility to only switch on Linux style when editing Linux code (because I work on a variety of code bases with different formatting).

But the macro above did not produce the result expected by some patch reviewers (John Stultz, Dave Miller). I had to redo the formatting manually.

The sticky point is continuation after splitting a long parameter list - in other words, exactly what the "arglist-cont-nonempty" setting above changes. The macro formats it so that the continuation is aligned at the tab that is closest to the initial argument in the previous line:

int a_very_long_function_name(int arg1, char *arg2,

			double arg3);

The expected style was tab plus spaces to align with the first argument:

int a_very_long_function_name(int arg1, char *arg2,

			        double arg3);

Is this a bug in the macro? I'm using emacs 22.1.1, in case that matters. Or are there different opinions in the Linux developer community about the right formatting?

Unfortunately, this seems to depend on the maintainer. Both styles are used all over the kernel but Documentation/CodingStyle and scripts/checkpatch.pl prefer what the above emacs configuration does.

I doubt that people do tab tab tab space space space space space by hand, so I strongly suspect that the tab-only zealots don't use emacs which does this adjustment automatically.

You should probably add linux-davem to the above or something. Or name the coding style after the text-editor the target maintainer uses :-)

On Wed, 2009-02-18 at 09:59 +0000, Johannes Weiner wrote:
[formatting of line continuation in argument list]

Quoted 3 lines

Unfortunately, this seems to depend on the maintainer. Both styles are used all over the kernel but Documentation/CodingStyle and scripts/checkpatch.pl prefer what the above emacs configuration does.

checkpatch.pl didn't seem to mind either way. I haven't seen this particular aspect mentioned in the CodingStyle either.

Quoted 7 lines

I doubt that people do tab tab tab space space space space space by hand, so I strongly suspect that the tab-only zealots don't use emacs which does this adjustment automatically.

You should probably add linux-davem to the above or something. Or name the coding style after the text-editor the target maintainer uses :-)

One could also get really fancy and extend the path matching to pick the right style depending on the subdirectory ;-)

Thanks for the clarification. In the future I'll pay closer attention to existing code and turn the macro on or off accordingly.