[PATCH v4 i18n 1/1] add pgettext() and npgettext() support for context-aware translations

[Kefu Chai <k.chai@proxmox.com>]

Context-aware translations (msgctxt in gettext) distinguish identical
msgids that mean different things in different parts of the UI, for
example "Monitor" for Ceph versus QEMU.

To keep msgid+msgctxt pairs distinct in the generated JS catalog,
po2js.pl now hashes the two together with the standard gettext EOT
separator ("\x04") between them. Messages without a context fall
through to the existing fnv31a(msgid). Locale::PO::load_file_ashash()
conflates rows that share the same msgid, so switch to
load_file_asarray() to preserve the distinct entries. The generated
catalog gains JS pgettext() and npgettext() helpers that perform the
same lookup at runtime.

The Makefile change adds --keyword=npgettext:1c,2,3 to xgettext.
pgettext is in xgettext's default JavaScript keyword list, but
npgettext is not: it was omitted from the defaults in gettext 0.18.3
(2013) when JavaScript support first landed, and never added since.
Without the explicit flag, xgettext silently drops npgettext() calls
during 'make update_pot'.

See "xgettext Invocation" in the GNU gettext manual:
https://www.gnu.org/software/gettext/manual/html_node/xgettext-Invocation.html

Signed-off-by: Kefu Chai <k.chai@proxmox.com>
---
 Makefile |  1 +
 po2js.pl | 69 ++++++++++++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 61 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index 16aab32..e1d9633 100644
--- a/Makefile
+++ b/Makefile
@@ -155,6 +155,7 @@ define potupdate
 	  --package-version="$(shell cd $(2);git rev-parse HEAD)" \
 	  --msgid-bugs-address="<support@proxmox.com>" \
 	  --copyright-holder="Copyright (C) Proxmox Server Solutions GmbH <support@proxmox.com> & the translation contributors." \
+	  --keyword=npgettext:1c,2,3 \
 	  --output="$(1)".pot
 endef
 
diff --git a/po2js.pl b/po2js.pl
index 316c0bd..4b7b044 100755
--- a/po2js.pl
+++ b/po2js.pl
@@ -8,10 +8,6 @@ use Getopt::Long;
 use JSON;
 use Locale::PO;
 
-# current limits:
-# - we do not support plural. forms
-# - no message content support
-
 my $options = {};
 GetOptions($options, 't=s', 'o=s', 'v=s') or die "unable to parse options\n";
 
@@ -34,6 +30,15 @@ sub fnv31a {
     return $hval & 0x7fffffff;
 }
 
+# Hash function for messages with context
+sub fnv31a_ctxt {
+    my ($msgctxt, $msgid) = @_;
+    return fnv31a($msgid) if !length($msgctxt);  # Empty context = no context
+    # Use EOT character (0x04) as separator, standard in gettext
+    my $combined = $msgctxt . "\x04" . $msgid;
+    return fnv31a($combined);
+}
+
 my $catalog = {};
 my $plurals_catalog = {};
 
@@ -41,11 +46,20 @@ my $nplurals = 2;
 my $plural_forms = "n!=1";
 
 foreach my $filename (@ARGV) {
-    my $href = Locale::PO->load_file_ashash($filename)
+    my $aref = Locale::PO->load_file_asarray($filename)
         || die "unable to load '$filename'\n";
 
     my $charset;
-    my $hpo = $href->{'""'} || die "no header";
+    # Find header entry (msgid "")
+    my $hpo;
+    foreach my $po (@$aref) {
+        if ($po->msgid eq '""') {
+            $hpo = $po;
+            last;
+        }
+    }
+    die "no header" if !$hpo;
+
     my $header = $hpo->dequote($hpo->msgstr);
     if ($header =~ m|^Content-Type:\s+text/plain;\s+charset=(\S+)$|im) {
         $charset = $1;
@@ -58,8 +72,7 @@ foreach my $filename (@ARGV) {
 	$plural_forms = $2;
     }
 
-    foreach my $k (keys %$href) {
-        my $po = $href->{$k};
+    foreach my $po (@$aref) {
         next if $po->fuzzy(); # skip fuzzy entries
         my $ref = $po->reference();
 
@@ -76,9 +89,18 @@ foreach my $filename (@ARGV) {
         my $qmsgid_plural = decode($charset, $po->msgid_plural);
         my $msgid_plural = $po->dequote($qmsgid_plural);
 
+        # Extract message context if present
+        my $msgctxt = '';
+        if (defined($po->msgctxt)) {
+            my $qmsgctxt = decode($charset, $po->msgctxt);
+            $msgctxt = $po->dequote($qmsgctxt);
+        }
+
         next if !length($msgid) && !length($msgid_plural); # skip header
 
-        my $digest = fnv31a($msgid);
+        my $digest = length($msgctxt) > 0
+            ? fnv31a_ctxt($msgctxt, $msgid)
+            : fnv31a($msgid);
 
         die "duplicate digest" if $catalog->{$digest};
 
@@ -150,6 +172,35 @@ function ngettext(singular, plural, n) {
     }
     return translation[msg_idx];
 }
+
+function fnv31a_ctxt(context, text) {
+    // Use EOT character (0x04) as separator
+    var combined = context + "\\x04" + text;
+    return fnv31a(combined);
+}
+
+function pgettext(context, msgid) {
+    var digest = fnv31a_ctxt(context, msgid);
+    var data = __proxmox_i18n_msgcat__[digest];
+    if (!data) {
+        return msgid;  // Return msgid (not context) as fallback
+    }
+    return data[0] || msgid;
+}
+
+function npgettext(context, singular, plural, n) {
+    const msg_idx = Number($plural_forms);
+    const digest = fnv31a_ctxt(context, singular);
+    const translation = __proxmox_i18n_plurals_msgcat__[digest];
+    if (!translation || msg_idx >= translation.length) {
+        if (n === 1) {
+            return singular;
+        } else {
+            return plural;
+        }
+    }
+    return translation[msg_idx];
+}
 __EOD
 
 if ($outfile) {
-- 
2.47.3