master 224aeb2877: Fix yank-media utf-16 detection

[Lars Ingebrigtsen]

branch: master
commit 224aeb2877fffc894e9d1b31f7f44db0e55160c3
Author: Lars Ingebrigtsen <larsi@gnus.org>
Commit: Lars Ingebrigtsen <larsi@gnus.org>

    Fix yank-media utf-16 detection
    
    * lisp/yank-media.el (yank-media--utf-16-p): Factor out into its
    own function for easier testing and fix the code.
---
 lisp/yank-media.el            | 47 ++++++++++++++++++-------------------------
 test/lisp/yank-media-tests.el | 38 ++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 27 deletions(-)

diff --git a/lisp/yank-media.el b/lisp/yank-media.el
index 8c75877724..5cd75eb318 100644
--- a/lisp/yank-media.el
+++ b/lisp/yank-media.el
@@ -155,33 +155,7 @@ non-supported selection data types."
     (format "%s" data))
    ((string-match-p "\\`text/" (symbol-name data-type))
     ;; We may have utf-16, which Emacs won't detect automatically.
-    (let ((coding-system
-           (and (zerop (mod (length data) 2))
-                (let ((stats (vector 0 0)))
-                  (dotimes (i (length data))
-                    (when (zerop (elt data i))
-                      (setf (aref stats (mod i 2))
-                            (1+ (aref stats (mod i 2))))))
-                  ;; We have some nuls...
-                  (and (not (and (zerop (elt stats 0))
-                                 (zerop (elt stats 1))))
-                       ;; If we have more than 90% every-other nul, then it's
-                       ;; pretty likely to be utf-16.
-                       (cond
-                        ((> (if (zerop (elt stats 1))
-                                1
-                              (/ (float (elt stats 0))
-                                 (float (elt stats 1))))
-                            0.9)
-                         ;; Big endian.
-                         'utf-16-be)
-                        ((> (if (zerop (elt stats 0))
-                                1
-                              (/ (float (elt stats 1))
-                                 (float (elt stats 0))))
-                            0.9)
-                         ;; Little endian.
-                         'utf-16-le)))))))
+    (let ((coding-system (yank-media--utf-16-p data)))
       (if coding-system
           (decode-coding-string data coding-system)
         ;; Some programs add a nul character at the end of text/*
@@ -192,6 +166,25 @@ non-supported selection data types."
    (t
     data)))
 
+(defun yank-media--utf-16-p (data)
+  (and (zerop (mod (length data) 2))
+       (let ((stats (vector 0 0)))
+         (dotimes (i (length data))
+           (when (zerop (elt data i))
+             (setf (aref stats (mod i 2))
+                   (1+ (aref stats (mod i 2))))))
+         ;; If we have more than 90% every-other nul, then it's
+         ;; pretty likely to be utf-16.
+         (cond
+          ((> (/ (float (elt stats 0)) (/ (length data) 2))
+              0.9)
+           ;; Big endian.
+           'utf-16-be)
+          ((> (/ (float (elt stats 1)) (/ (length data) 2))
+              0.9)
+           ;; Little endian.
+           'utf-16-le)))))
+
 (provide 'yank-media)
 
 ;;; yank-media.el ends here
diff --git a/test/lisp/yank-media-tests.el b/test/lisp/yank-media-tests.el
new file mode 100644
index 0000000000..4487ae150d
--- /dev/null
+++ b/test/lisp/yank-media-tests.el
@@ -0,0 +1,38 @@
+;;; yank-media-tests.el --- Tests for yank-media.el  -*- lexical-binding: t; 
-*-
+
+;; Copyright (C) 2022 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;;
+
+;;; Code:
+
+(require 'yank-media)
+(require 'ert)
+(require 'ert-x)
+
+(ert-deftest test-utf-16 ()
+  (should-not (yank-media--utf-16-p "f"))
+  (should-not (yank-media--utf-16-p "fo"))
+  (should-not (yank-media--utf-16-p "\000ofo"))
+  (should (eq (yank-media--utf-16-p "\000o\000o") 'utf-16-be))
+  (should (eq (yank-media--utf-16-p "o\000o\000") 'utf-16-le))
+  (should-not (yank-media--utf-16-p "o\000\000o")))
+
+;;; yank-media-tests.el ends here