bug#24627: 24.5; (thing-at-point 'list) may return a non-empty string without a list

[Tino Calancha <tino.calancha@gmail.com>]

Andreas Röhler <andreas.roehler@easy-emacs.de> writes:

> beg still needs a check like
>
> (not (nth 8 (parse-partial-sexp (point-min) (point))))
>
> otherwise it could match inside a string or comment

I have the feeling that this should return the local list
at point, even if inside a string or comment.  Then, if
point is inside a comment/string and there is no list there,
the function might look for a list around (i.e., outside) that
comment/string region.  See patch below.

Anyway, neither the doc string of `thing-at-point' nor
`thing-at-point-bounds-of-list-at-point' mention what expect
when point is inside a comment/string.  That's why i believe it
might be better to request that in a different bug report.
Writting additional tests also might be helpful to find a robust implementation.

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From bfc9b7fb739dfeab09c2ffd064a6ebe65a28b686 Mon Sep 17 00:00:00 2001
From: Tino Calancha <tino.calancha@gmail.com>
Date: Thu, 13 Oct 2016 16:34:35 +0900
Subject: [PATCH] (thing-at-point 'list) return nil if no list at point

* lisp/thingatpt.el (thing-at-point-bounds-of-list-at-point):
Check first if we are at the beginning of a top-level sexp (Bug#24627).
If found a list inside a comment or string return it.  Otherwise, look
for a list around the comment/string.
Escape '[' in doc string.
---
 lisp/thingatpt.el | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/lisp/thingatpt.el b/lisp/thingatpt.el
index 6d1014b..656d2c7 100644
--- a/lisp/thingatpt.el
+++ b/lisp/thingatpt.el
@@ -219,22 +219,26 @@ 'beginning-of-sexp
 
 (defun thing-at-point-bounds-of-list-at-point ()
   "Return the bounds of the list at point.
-[Internal function used by `bounds-of-thing-at-point'.]"
+\[Internal function used by `bounds-of-thing-at-point'.]"
   (save-excursion
-    (let ((opoint (point))
-	  (beg (ignore-errors
-		 (up-list -1)
-		 (point))))
+    (let* ((opoint (point))
+	   (st (syntax-ppss))
+	   (find-list-fn (lambda ()
+                           (ignore-errors
+                             (up-list -1)
+                             (point))))
+	   (beg (if (eq 4 (car (syntax-after (point))))
+		    (point)
+		  (funcall find-list-fn))))
+      ;; If inside a string or comment and there is no list
+      ;; at point, check for a list surrounding the string/comment region.
+      (when (and (nth 8 st) (= opoint (point)))
+	(goto-char (nth 8 st))
+	(setq beg (funcall find-list-fn)))
       (ignore-errors
-	(if beg
-	    (progn (forward-sexp)
-		   (cons beg (point)))
-	  ;; Are we are at the beginning of a top-level sexp?
-	  (forward-sexp)
-	  (let ((end (point)))
-	    (backward-sexp)
-	    (if (>= opoint (point))
-		(cons opoint end))))))))
+        (when beg
+          (forward-sexp)
+          (cons beg (point)))))))
 
 ;; Defuns
 
-- 
2.9.3

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In GNU Emacs 26.0.50.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.1)
 of 2016-10-13
Repository revision: 1dd54e3eef7543720eff161457677a35fae2435c