gettext.c: remove/reword a mostly-useless comment

Mostly remove the comment I added 5e9637c629 (i18n: add
infrastructure for translating Git with gettext, 2011-11-18). Since
then we had a fix in 9c0495d23e (gettext.c: detect the vsnprintf bug
at runtime, 2013-12-01) so we're not running with the "set back to C
locale" hack on any modern system.

So having more than 1/4 of the file taken up by a digression about a
glibc bug that mostly doesn't happen to anyone anymore is just a
needless distraction. Shorten the comment to make a brief mention of
the bug, and where to find more info by looking at the git history for
this now-removed comment.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

gettext.c

@@ -87,88 +87,24 @@ static int test_vsnprintf(const char *fmt, ...)
 
 static void init_gettext_charset(const char *domain)
 {
-	/*
-	   This trick arranges for messages to be emitted in the user's
-	   requested encoding, but avoids setting LC_CTYPE from the
-	   environment for the whole program.
-
-	   This primarily done to avoid a bug in vsnprintf in the GNU C
-	   Library [1]. which triggered a "your vsnprintf is broken" error
-	   on Git's own repository when inspecting v0.99.6~1 under a UTF-8
-	   locale.
-
-	   That commit contains a ISO-8859-1 encoded author name, which
-	   the locale aware vsnprintf(3) won't interpolate in the format
-	   argument, due to mismatch between the data encoding and the
-	   locale.
-
-	   Even if it wasn't for that bug we wouldn't want to use LC_CTYPE at
-	   this point, because it'd require auditing all the code that uses C
-	   functions whose semantics are modified by LC_CTYPE.
-
-	   But only setting LC_MESSAGES as we do creates a problem, since
-	   we declare the encoding of our PO files[2] the gettext
-	   implementation will try to recode it to the user's locale, but
-	   without LC_CTYPE it'll emit something like this on 'git init'
-	   under the Icelandic locale:
-
-	       Bj? til t?ma Git lind ? /hlagh/.git/
-
-	   Gettext knows about the encoding of our PO file, but we haven't
-	   told it about the user's encoding, so all the non-US-ASCII
-	   characters get encoded to question marks.
-
-	   But we're in luck! We can set LC_CTYPE from the environment
-	   only while we call nl_langinfo and
-	   bind_textdomain_codeset. That suffices to tell gettext what
-	   encoding it should emit in, so it'll now say:
-
-	       Bjó til tóma Git lind í /hlagh/.git/
-
-	   And the equivalent ISO-8859-1 string will be emitted under a
-	   ISO-8859-1 locale.
-
-	   With this change way we get the advantages of setting LC_CTYPE
-	   (talk to the user in his language/encoding), without the major
-	   drawbacks (changed semantics for C functions we rely on).
-
-	   However foreign functions using other message catalogs that
-	   aren't using our neat trick will still have a problem, e.g. if
-	   we have to call perror(3):
-
-	   #include <stdio.h>
-	   #include <locale.h>
-	   #include <errno.h>
-
-	   int main(void)
-	   {
-		   setlocale(LC_MESSAGES, "");
-		   setlocale(LC_CTYPE, "C");
-		   errno = ENODEV;
-		   perror("test");
-		   return 0;
-	   }
-
-	   Running that will give you a message with question marks:
-
-	   $ LANGUAGE= LANG=de_DE.utf8 ./test
-	   test: Kein passendes Ger?t gefunden
-
-	   The vsnprintf bug has been fixed since glibc 2.17.
-
-	   Then we could simply set LC_CTYPE from the environment, which would
-	   make things like the external perror(3) messages work.
-
-	   See t/t0203-gettext-setlocale-sanity.sh's "gettext.c" tests for
-	   regression tests.
-
-	   1. http://sourceware.org/bugzilla/show_bug.cgi?id=6530
-	   2. E.g. "Content-Type: text/plain; charset=UTF-8\n" in po/is.po
-	*/
 	setlocale(LC_CTYPE, "");
 	charset = locale_charset();
 	bind_textdomain_codeset(domain, charset);
-	/* the string is taken from v0.99.6~1 */
+
+	/*
+	 * Work around an old bug fixed in glibc 2.17 (released on
+	 * 2012-12-24), at the cost of potentially making translated
+	 * messages from external functions like perror() emitted in
+	 * the wrong encoding.
+	 *
+	 * The bug affected e.g. git.git's own 7eb93c89651 ([PATCH]
+	 * Simplify git script, 2005-09-07), which is the origin of
+	 * the "David_K\345gedal" test string.
+	 *
+	 * See a much longer comment added to this file in 5e9637c6297
+	 * (i18n: add infrastructure for translating Git with gettext,
+	 * 2011-11-18) for more details.
+	 */
 	if (test_vsnprintf("%.*s", 13, "David_K\345gedal") < 0)
 		setlocale(LC_CTYPE, "C");
 }