i18n: add infrastructure for translating Git with gettextab/enable-i18n

Change the skeleton implementation of i18n in Git to one that can show
localized strings to users for our C, Shell and Perl programs using
either GNU libintl or the Solaris gettext implementation.

This new internationalization support is enabled by default. If
gettext isn't available, or if Git is compiled with
NO_GETTEXT=YesPlease, Git falls back on its current behavior of
showing interface messages in English. When using the autoconf script
we'll auto-detect if the gettext libraries are installed and act
appropriately.

This change is somewhat large because as well as adding a C, Shell and
Perl i18n interface we're adding a lot of tests for them, and for
those tests to work we need a skeleton PO file to actually test
translations. A minimal Icelandic translation is included for this
purpose. Icelandic includes multi-byte characters which makes it easy
to test various edge cases, and it's a language I happen to
understand.

The rest of the commit message goes into detail about various
sub-parts of this commit.

= Installation

Gettext .mo files will be installed and looked for in the standard
$(prefix)/share/locale path. GIT_TEXTDOMAINDIR can also be set to
override that, but that's only intended to be used to test Git itself.

= Perl

Perl code that's to be localized should use the new Git::I18n
module. It imports a __ function into the caller's package by default.

Instead of using the high level Locale::TextDomain interface I've
opted to use the low-level (equivalent to the C interface)
Locale::Messages module, which Locale::TextDomain itself uses.

Locale::TextDomain does a lot of redundant work we don't need, and
some of it would potentially introduce bugs. It tries to set the
$TEXTDOMAIN based on package of the caller, and has its own
hardcoded paths where it'll search for messages.

I found it easier just to completely avoid it rather than try to
circumvent its behavior. In any case, this is an issue wholly
internal Git::I18N. Its guts can be changed later if that's deemed
necessary.

See <AANLkTilYD_NyIZMyj9dHtVk-ylVBfvyxpCC7982LWnVd@mail.gmail.com> for
a further elaboration on this topic.

= Shell

Shell code that's to be localized should use the git-sh-i18n
library. It's basically just a wrapper for the system's gettext.sh.

If gettext.sh isn't available we'll fall back on gettext(1) if it's
available. The latter is available without the former on Solaris,
which has its own non-GNU gettext implementation. We also need to
emulate eval_gettext() there.

If neither are present we'll use a dumb printf(1) fall-through
wrapper.

= About libcharset.h and langinfo.h

We use libcharset to query the character set of the current locale if
it's available. I.e. we'll use it instead of nl_langinfo if
HAVE_LIBCHARSET_H is set.

The GNU gettext manual recommends using langinfo.h's
nl_langinfo(CODESET) to acquire the current character set, but on
systems that have libcharset.h's locale_charset() using the latter is
either saner, or the only option on those systems.

GNU and Solaris have a nl_langinfo(CODESET), FreeBSD can use either,
but MinGW and some others need to use libcharset.h's locale_charset()
instead.

=Credits

This patch is based on work by Jeff Epler <jepler@unpythonic.net> who
did the initial Makefile / C work, and a lot of comments from the Git
mailing list, including Jonathan Nieder, Jakub Narebski, Johannes
Sixt, Erik Faye-Lund, Peter Krefting, Junio C Hamano, Thomas Rast and
others.

[jc: squashed a small Makefile fix from Ramsay]

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 72 insertions, 28 deletions

diff --git a/git-sh-i18n.sh b/git-sh-i18n.sh
index e672366f0c..b4575fb3a1 100644
--- a/git-sh-i18n.sh
+++ b/git-sh-i18n.sh
@@ -2,47 +2,91 @@
 #
 # Copyright (c) 2010 Ævar Arnfjörð Bjarmason
 #
-# This is a skeleton no-op implementation of gettext for Git. It'll be
-# replaced by something that uses gettext.sh in a future patch series.
+# This is Git's interface to gettext.sh. See po/README for usage
+# instructions.
+
+# Export the TEXTDOMAIN* data that we need for Git
+TEXTDOMAIN=git
+export TEXTDOMAIN
+if test -z "$GIT_TEXTDOMAINDIR"
+then
+	TEXTDOMAINDIR="@@LOCALEDIR@@"
+else
+	TEXTDOMAINDIR="$GIT_TEXTDOMAINDIR"
+fi
+export TEXTDOMAINDIR
 
 if test -z "$GIT_GETTEXT_POISON"
 then
-	gettext () {
-		printf "%s" "$1"
-	}
+	if test -z "$GIT_INTERNAL_GETTEXT_TEST_FALLBACKS" && type gettext.sh >/dev/null 2>&1
+	then
+		# This is GNU libintl's gettext.sh, we don't need to do anything
+		# else than setting up the environment and loading gettext.sh
+		GIT_INTERNAL_GETTEXT_SH_SCHEME=gnu
+		export GIT_INTERNAL_GETTEXT_SH_SCHEME
 
-	gettextln() {
-		printf "%s\n" "$1"
-	}
+		# Try to use libintl's gettext.sh, or fall back to English if we
+		# can't.
+		. gettext.sh
 
-	eval_gettext () {
-		printf "%s" "$1" | (
-			export PATH $(git sh-i18n--envsubst --variables "$1");
-			git sh-i18n--envsubst "$1"
-		)
-	}
+	elif test -z "$GIT_INTERNAL_GETTEXT_TEST_FALLBACKS" && test "$(gettext -h 2>&1)" = "-h"
+	then
+		# We don't have gettext.sh, but there's a gettext binary in our
+		# path. This is probably Solaris or something like it which has a
+		# gettext implementation that isn't GNU libintl.
+		GIT_INTERNAL_GETTEXT_SH_SCHEME=solaris
+		export GIT_INTERNAL_GETTEXT_SH_SCHEME
 
-	eval_gettextln () {
-		printf "%s\n" "$1" | (
-			export PATH $(git sh-i18n--envsubst --variables "$1");
-			git sh-i18n--envsubst "$1"
-		)
-	}
+		# Solaris has a gettext(1) but no eval_gettext(1)
+		eval_gettext () {
+			gettext "$1" | (
+				export PATH $(git sh-i18n--envsubst --variables "$1");
+				git sh-i18n--envsubst "$1"
+			)
+		}
+
+	else
+		# Since gettext.sh isn't available we'll have to define our own
+		# dummy pass-through functions.
+
+		# Tell our tests that we don't have the real gettext.sh
+		GIT_INTERNAL_GETTEXT_SH_SCHEME=fallthrough
+		export GIT_INTERNAL_GETTEXT_SH_SCHEME
+
+		gettext () {
+			printf "%s" "$1"
+		}
+
+		eval_gettext () {
+			printf "%s" "$1" | (
+				export PATH $(git sh-i18n--envsubst --variables "$1");
+				git sh-i18n--envsubst "$1"
+			)
+		}
+	fi
 else
+	# Emit garbage under GETTEXT_POISON=YesPlease. Unlike the C tests
+	# this relies on an environment variable
+
+	GIT_INTERNAL_GETTEXT_SH_SCHEME=poison
+	export GIT_INTERNAL_GETTEXT_SH_SCHEME
+
 	gettext () {
 		printf "%s" "# GETTEXT POISON #"
 	}
 
-	gettextln () {
-		printf "%s\n" "# GETTEXT POISON #"
-	}
-
 	eval_gettext () {
 		printf "%s" "# GETTEXT POISON #"
 	}
-
-	eval_gettextln () {
-		printf "%s\n" "# GETTEXT POISON #"
-	}
 fi
 
+# Git-specific wrapper functions
+gettextln () {
+	gettext "$1"
+	echo
+}
+
+eval_gettextln () {
+	eval_gettext "$1"
+	echo
+}