GNU bug report logs - #22169
25.0.50; File name compiletion doesn't work with non-ASCII characters on OS X

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Anders Lindgren <andlind <at> gmail.com>
Cc: random832 <at> fastmail.com, 22169 <at> debbugs.gnu.org
Subject: bug#22169: 25.0.50; File name compiletion doesn't work with non-ASCII characters on OS X
Date: Mon, 21 Dec 2015 18:09:18 +0200

> Date: Mon, 21 Dec 2015 07:52:53 +0100
> From: Anders Lindgren <andlind <at> gmail.com>
> Cc: random832 <at> fastmail.com, 22169 <at> debbugs.gnu.org
> 
> I did some simple measurements with and without this patch. I ran
> `(file-name-all-completions "x" "src")' on the Emacs src directory. The timing
> values were almost identical (varying between 0.001012 and 0.001080).

You should try it on a larger directory, preferably one that has many
files with non-ASCII file names.

> The way I see it, the patch doesn't do any harm in any coding system, and it is
> fast. Hence, I don't really see that it's worth the effort to make this code
> conditional.

I'm surprised to hear that.  Did you look at the implementation of
Fcompare_strings?  It's highly non-trivial.  What's more, if the user
sets completion-ignore-case non-nil, Fcompare_strings will call
Fupcase on each character, which is another non-trivial function; if
you are particularly unlucky, Fupcase can even GC (if it needs to set
up the case-table), which will definitely take several hundreds of
milliseconds if not longer.

And that's today; what if tomorrow someone comes and adds to
Fcompare_strings something that makes it even more complex and slow?

I've learned long ago not to call any non-trivial API unless I really
need it.  You can never know what complexity hides in there.  Besides,
it simply looks bad in the code to do processing that is unnecessary.

> However, please write a patch for this if you still thinks it's necessary. I
> can test it here to make sure it works under OS X.

Attached (relative to the current emacs-25 branch).

Please note that the patch below attempts to solve a couple of
additional subtle aspects of this:

  . it doesn't force the extra comparison for unibyte strings (which
    include ASCII strings and unibyte non-ASCII strings), since the
    issue doesn't exist then, and ENCODE_FILE/DECODE_FILE are no-ops

  . it forces the FILE argument to have all of its characters
    precomposed, since if the caller passes us a file name with
    decomposed characters, we risk rejecting them in the code we are
    adding

Please see that these indeed o their job correctly, as I could only
test the code very superficially.

Thanks.

diff --git a/lisp/international/ucs-normalize.el b/lisp/international/ucs-normalize.el
index 8839b00..6f2fb28 100644
--- a/lisp/international/ucs-normalize.el
+++ b/lisp/international/ucs-normalize.el
@@ -627,6 +627,10 @@ 'utf-8-hfs
   :pre-write-conversion 'ucs-normalize-hfs-nfd-pre-write-conversion
   )
 
+;; This is tested in dired.c:file_name_completion in order to reject
+;; false positives due to comparison of encoded file names.
+(coding-system-put 'utf-8-hfs 'decomposed-characters 't)
+
 (provide 'ucs-normalize)
 
 ;; Local Variables:
diff --git a/src/dired.c b/src/dired.c
index 84bf247..d5628d5 100644
--- a/src/dired.c
+++ b/src/dired.c
@@ -467,6 +467,7 @@ file_name_completion (Lisp_Object file, Lisp_Object dirname, bool all_flag,
      well as "." and "..".  Until shown otherwise, assume we can't exclude
      anything.  */
   bool includeall = 1;
+  bool check_decoded = false;
   ptrdiff_t count = SPECPDL_INDEX ();
 
   elt = Qnil;
@@ -485,6 +486,28 @@ file_name_completion (Lisp_Object file, Lisp_Object dirname, bool all_flag,
      on the encoded file name.  */
   encoded_file = ENCODE_FILE (file);
   encoded_dir = ENCODE_FILE (Fdirectory_file_name (dirname));
+  if (STRING_MULTIBYTE (file))
+    {
+      Lisp_Object file_encoding = Vfile_name_coding_system;
+
+      if (NILP (Vfile_name_coding_system))
+	file_encoding = Vdefault_file_name_coding_system;
+      /* If the file-name encoding decomposes characters, as we do for
+	 HFS+ filesystems, we need to make an additional comparison of
+	 decoded names in order to filter false positives, such as "a"
+	 falsely matching "a-ring".  */
+      if (!NILP (file_encoding)
+	  && !NILP (Fplist_get (Fcoding_system_plist (file_encoding),
+				Qdecomposed_characters)))
+	{
+	  check_decoded = true;
+	  /* Recompute FILE to make sure any decomposed characters in
+	     it are re-composed by the post-read-conversion.
+	     Otherwise, any decomposed characters will be rejected by
+	     the additional check below.  */
+	  file = DECODE_FILE (encoded_file);
+	}
+    }
   int fd;
   DIR *d = open_directory (encoded_dir, &fd);
   record_unwind_protect_ptr (directory_files_internal_unwind, d);
@@ -637,6 +660,21 @@ file_name_completion (Lisp_Object file, Lisp_Object dirname, bool all_flag,
       if (!NILP (predicate) && NILP (call1 (predicate, name)))
 	continue;
 
+      /* Reject entries where the encoded strings match, but the
+         decoded don't.  For example, "a" should not match "a-ring" on
+         file systems that store decomposed characters. */
+      Lisp_Object zero = make_number (0);
+      Lisp_Object compare;
+      Lisp_Object cmp;
+      if (check_decoded && SCHARS (file) <= SCHARS (name))
+	{
+	  compare = make_number (SCHARS (file));
+ 	  cmp = Fcompare_strings (name, zero, compare, file, zero, compare,
+				  completion_ignore_case ? Qt : Qnil);
+	  if (!EQ (cmp, Qt))
+	    continue;
+	}
+
       /* Suitably record this match.  */
 
       matchcount += matchcount <= 1;
@@ -650,15 +688,13 @@ file_name_completion (Lisp_Object file, Lisp_Object dirname, bool all_flag,
 	}
       else
 	{
-	  Lisp_Object zero = make_number (0);
 	  /* FIXME: This is a copy of the code in Ftry_completion.  */
-	  ptrdiff_t compare = min (bestmatchsize, SCHARS (name));
-	  Lisp_Object cmp
-	    = Fcompare_strings (bestmatch, zero,
-				make_number (compare),
-				name, zero,
-				make_number (compare),
-				completion_ignore_case ? Qt : Qnil);
+	  compare = min (bestmatchsize, SCHARS (name));
+	  cmp = Fcompare_strings (bestmatch, zero,
+				  make_number (compare),
+				  name, zero,
+				  make_number (compare),
+				  completion_ignore_case ? Qt : Qnil);
 	  ptrdiff_t matchsize = EQ (cmp, Qt) ? compare : eabs (XINT (cmp)) - 1;
 
 	  if (completion_ignore_case)
@@ -1007,6 +1043,7 @@ syms_of_dired (void)
   DEFSYM (Qfile_attributes, "file-attributes");
   DEFSYM (Qfile_attributes_lessp, "file-attributes-lessp");
   DEFSYM (Qdefault_directory, "default-directory");
+  DEFSYM (Qdecomposed_characters, "decomposed-characters");
 
   defsubr (&Sdirectory_files);
   defsubr (&Sdirectory_files_and_attributes);

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