[PATCH/RFC 07/17] gettext.c: work around us not using setlocale(LC_CTYPE, "")

Change the gettext setup code to arrange for messages to be emitted in
the user's requested encoding, but avoid setting LC_CTYPE from the
environment for the whole program.

In 107880a I removed our use of setlocale(LC_CTYPE, "") because of a
bug in the GNU C Library [1]. 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'

    Bj? til t?ma Git lind ? /hl/agh/.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 /hl/agh/.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 drawbacks (changed
semantics for C functions we rely on).

In the long term we should probably see about getting that bug in
glibc fixed, and audit our code so it won't fall apart under a non-C
locale.

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

Suggested-by: Jonathan Nieder <redacted>
Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 gettext.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/gettext.c b/gettext.c
index db99742..8644098 100644
--- a/gettext.c
+++ b/gettext.c

@@ -1,11 +1,13 @@
 #include "exec_cmd.h"
 #include <locale.h>
 #include <libintl.h>
+#include <langinfo.h>
 #include <stdlib.h>
 
 extern void git_setup_gettext(void) {
 	char *podir;
 	char *envdir = getenv("GIT_TEXTDOMAINDIR");
+	char *charset;
 
 	if (envdir) {
 		(void)bindtextdomain("git", envdir);

@@ -17,5 +19,9 @@ extern void git_setup_gettext(void) {
 	}
 
 	(void)setlocale(LC_MESSAGES, "");
+	(void)setlocale(LC_CTYPE, "");
+	charset = nl_langinfo(CODESET);
+	(void)bind_textdomain_codeset("git", charset);
+	(void)setlocale(LC_CTYPE, "C");
 	(void)textdomain("git");
 }

-- 
1.7.2.2.536.g3f548