bug#35286: 26.2; indent-sexp broken

[Noam Postavsky]

tags 35286 + patch
quit

Leo Liu <sdl.web@gmail.com> writes:

> The bug is caused by the following unsafe part of indent-sexp introduced
> in 26.2:
>
>   (save-excursion
>     (let ((eol (line-end-position)))
>       (forward-sexp 1)
>       (condition-case ()
>           (while (and (< (point) eol) (not (eobp)))
>             (forward-sexp 1))
>         (scan-error nil)))
>     (point))
>
> which can easily include two or more sexps after point. This looks like
> a major breakage.

I put that code there because Emacs 25 and earlier also indents more
than one sexps after point in some cases.  The regression is that the
Emacs 26 code gets confused by comments at the end of line.  Here's a
patch for emacs-26 to fix this:

>From 7678458e5431e3b5a365343ec172cc75cc41ffb7 Mon Sep 17 00:00:00 2001
From: Noam Postavsky <npostavs@gmail.com>
Date: Mon, 15 Apr 2019 18:49:57 -0400
Subject: [PATCH] Fix indent-sexp confusion over eol comments (Bug#35286)

* lisp/emacs-lisp/lisp-mode.el (indent-sexp): Skip over comments
before checking for end of line.
---
 lisp/emacs-lisp/lisp-mode.el            |  6 +++++-
 test/lisp/emacs-lisp/lisp-mode-tests.el | 12 ++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/lisp-mode.el b/lisp/emacs-lisp/lisp-mode.el
index 57f57175c5..a0caaf7475 100644
--- a/lisp/emacs-lisp/lisp-mode.el
+++ b/lisp/emacs-lisp/lisp-mode.el
@@ -1212,7 +1212,11 @@ (defun indent-sexp (&optional endpos)
                         ;; indent things like #s(...).  This might not
                         ;; be needed if Bug#15998 is fixed.
                         (condition-case ()
-                            (while (and (< (point) eol) (not (eobp)))
+                            (while (progn (while (and (forward-comment 1)
+                                                      (if (< (point) eol) t
+                                                        (goto-char eol)
+                                                        nil)))
+                                          (and (< (point) eol) (not (eobp))))
                               (forward-sexp 1))
                           ;; But don't signal an error for incomplete
                           ;; sexps following the first complete sexp
diff --git a/test/lisp/emacs-lisp/lisp-mode-tests.el 
b/test/lisp/emacs-lisp/lisp-mode-tests.el
index a6370742ab..3782bad315 100644
--- a/test/lisp/emacs-lisp/lisp-mode-tests.el
+++ b/test/lisp/emacs-lisp/lisp-mode-tests.el
@@ -136,6 +136,18 @@ (ert-deftest indent-sexp-cant-go ()
     (indent-sexp)
     (should (equal (buffer-string) "(())"))))
 
+(ert-deftest indent-sexp-stop-before-eol-comment ()
+  "`indent-sexp' shouldn't look for more sexps after an eol comment."
+  ;; See https://debbugs.gnu.org/cgi/bugreport.cgi?bug=35286.
+  (with-temp-buffer
+    (emacs-lisp-mode)
+    (let ((str "() ;;\n  x"))
+      (insert str)
+      (goto-char (point-min))
+      (indent-sexp)
+      ;; The "x" is in the next sexp, so it shouldn't get indented.
+      (should (equal (buffer-string) str)))))
+
 (ert-deftest lisp-indent-region ()
   "Test basics of `lisp-indent-region'."
   (with-temp-buffer
-- 
2.11.0