Package: emacs;
Reported by: Michal Nazarewicz <mina86 <at> mina86.com>
Date: Sun, 3 May 2020 20:32:01 UTC
Severity: wishlist
Tags: patch
Done: Michał Nazarewicz <mina86 <at> mina86.com>
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Michal Nazarewicz <mina86 <at> mina86.com> To: 41061 <at> debbugs.gnu.org Subject: bug#41061: [PATCH] cc-mode: add ‘c-lineup-ternary-bodies’ Date: Sun, 3 May 2020 21:30:47 +0100
Introduce ‘c-lineup-ternary-bodies’ function which, when used as
a c lineup function, aligns question mark and colon of a ternary
operator. For example:
return arg % 2 == 0 ? arg / 2
: (3 * arg + 1);
* lisp/progmodes/cc-align.el (c-lineup-ternary-bodies): New function.
* doc/misc/cc-mode.texi (Operator Line-Up Functions): Document the
new function.
* test/lisp/progmodes/cc-mode-tests.el (c-lineup-ternary-bodies): New
test case.
---
It’s not perfectly clear to me whether there is a better
implementation of this. Some sort of function that cc-mode provides
which parses an expression into a syntax tree of some kind perhaps.
The approach I’ve taken does seem to work well enough though.
If there isn’t any opposition to this, I’m gonna push it in a week or
so.
doc/misc/cc-mode.texi | 20 +++++++++++++++++
etc/NEWS | 18 ++++++++++++++++
lisp/progmodes/cc-align.el | 32 ++++++++++++++++++++++++++++
test/lisp/progmodes/cc-mode-tests.el | 20 +++++++++++++++++
4 files changed, 90 insertions(+)
diff --git a/doc/misc/cc-mode.texi b/doc/misc/cc-mode.texi
index f9c9f5e1830..16eac4828c7 100644
--- a/doc/misc/cc-mode.texi
+++ b/doc/misc/cc-mode.texi
@@ -6395,6 +6395,26 @@ Operator Line-Up
@comment ------------------------------------------------------------
+@defun c-lineup-ternary-bodies
+@findex lineup-ternary-bodies @r{(c-)}
+Line up true and false branches of a ternary operator
+(i.e. @code{?:}). More precisely, if the line starts with a colon
+which is a part of a said operator it with corresponding question
+mark. For example:
+
+@example
+@group
+return arg % 2 == 0 ? arg / 2
+ : (3 * arg + 1); @hereFn{c-lineup-ternary-bodies}
+@end group
+@end example
+
+@workswith @code{arglist-cont}, @code{arglist-cont-nonempty} and
+@code{statement-cont}.
+@end defun
+
+@comment ------------------------------------------------------------
+
@defun c-lineup-cascaded-calls
@findex lineup-cascaded-calls @r{(c-)}
Line up ``cascaded calls'' under each other. If the line begins with
diff --git a/etc/NEWS b/etc/NEWS
index 753b7a7fd36..1b805784338 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -302,6 +302,24 @@ use ‘doxygen’ by default one might evaluate:
(c++-mode . doxygen)))
or use it in a custom ‘c-style’.
+
+*** Added support to line up ‘?’ and ‘:’ of a ternary operator.
+The new ‘c-lineup-ternary-bodies’ function can be used as a lineup
+function to align question mark and colon which are part of a ternary
+operator (‘?:’). For example:
+
+ return arg % 2 == 0 ? arg / 2
+ : (3 * arg + 1);
+
+To enable, add it to appropriate entries in ‘c-offsets-alist’, e.g.:
+
+ (c-set-offset 'arglist-cont '(c-lineup-ternary-bodies
+ c-lineup-gcc-asm-reg))
+ (c-set-offset 'arglist-cont-nonempty '(c-lineup-ternary-bodies
+ c-lineup-gcc-asm-reg
+ c-lineup-arglist))
+ (c-set-offset 'statement-cont '(c-lineup-ternary-bodies +))
+
* New Modes and Packages in Emacs 28.1
diff --git a/lisp/progmodes/cc-align.el b/lisp/progmodes/cc-align.el
index f30477dc787..a6f3f1f8024 100644
--- a/lisp/progmodes/cc-align.el
+++ b/lisp/progmodes/cc-align.el
@@ -790,6 +790,38 @@ c-lineup-math
(or (c-lineup-assignments langelem)
c-basic-offset))
+(defun c-lineup-ternary-bodies (langelem)
+ "Line up true and false branches of a ternary operator (i.e. ‘?:’).
+More precisely, if the line starts with a colon which is a part of
+a said operator it with corresponding question mark; otherwise return
+nil. For example:
+
+ return arg % 2 == 0 ? arg / 2
+ : (3 * arg + 1); <- c-lineup-ternary-bodies
+
+Works with: arglist-cont, arglist-cont-nonempty and statement-cont.
+"
+ (save-excursion
+ (back-to-indentation)
+ (when (and (eq ?: (char-after))
+ (not (eq ?: (char-after (1+ (point))))))
+ (let ((limit (c-langelem-pos langelem)) (depth 1))
+ (catch 'done
+ (while (c-syntactic-skip-backward "^?:" limit t)
+ (goto-char (1- (point)))
+ (cond ((eq (char-after) ??)
+ ;; If we’ve found a question mark, decrease depth. If we’re
+ ;; reached zero, we’ve found the one we were looking for.
+ (when (zerop (setq depth (1- depth)))
+ (throw 'done (vector (current-column)))))
+ ((or (eq ?: (char-before)) (eq ?? (char-before)))
+ ;; Step over ‘::’ and ‘?:’ operators. We don’t have to
+ ;; handle ‘?:’ here but doing so saves an iteration.
+ (if (eq (point) limit)
+ (throw 'done)
+ (goto-char (1- (point)))))
+ ((setq depth (1+ depth)))))))))) ; Otherwise increase depth.
+
(defun c-lineup-cascaded-calls (langelem)
"Line up \"cascaded calls\" under each other.
If the line begins with \"->\" or \".\" and the preceding line ends
diff --git a/test/lisp/progmodes/cc-mode-tests.el b/test/lisp/progmodes/cc-mode-tests.el
index 0729841ce6f..cd461f55181 100644
--- a/test/lisp/progmodes/cc-mode-tests.el
+++ b/test/lisp/progmodes/cc-mode-tests.el
@@ -78,4 +78,24 @@ c-mode-macro-comment
(insert macro-string)
(c-mode))))
+(ert-deftest c-lineup-ternary-bodies ()
+ "Test for c-lineup-ternary-bodies function"
+ (with-temp-buffer
+ (c-mode)
+ (let* ((common-prefix "int value = condition ? ")
+ (expected-column (- (length common-prefix) 2)))
+ (dolist (test '(("a : \n b" . nil)
+ ("a \n ::b" . nil)
+ ("a \n : b" . t)
+ ("::a \n : b" . t)
+ ("(p ? q : r) \n : b" . t)
+ ("p ?: q \n : b" . t)
+ ("p ? : q \n : b" . t)
+ ("p ? q : r \n : b" . t)))
+ (delete-region (point-min) (point-max))
+ (insert common-prefix (car test))
+ (should (equal
+ (and (cdr test) (vector expected-column))
+ (c-lineup-ternary-bodies '(statement-cont . 1))))))))
+
;;; cc-mode-tests.el ends here
--
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