From f9df228dbde7e9b85b13721d33054481d66f0488 Mon Sep 17 00:00:00 2001
From: Maxim Cournoyer <maxim@guixotic.coop>
Date: Thu, 26 Jun 2025 11:11:45 +0900
Subject: [PATCH] gnu: docbook2x: Fix invalid lt entity re-declaration.

This bug would cause multiple errors when building the documentation of Git,
for example, like:

   error : xmlAddEntity: invalid redeclaration of predefined entity

* gnu/packages/patches/docbook2x-entity-lt.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/docbook.scm (docbook2x) [source]: Apply it.

Change-Id: I8d2e694ff4b97a1016644d3525b2cddb1b85f12d
---
 gnu/local.mk                                  |  1 +
 gnu/packages/docbook.scm                      |  3 +-
 .../patches/docbook2x-entity-lt.patch         | 44 +++++++++++++++++++
 3 files changed, 47 insertions(+), 1 deletion(-)
 create mode 100644 gnu/packages/patches/docbook2x-entity-lt.patch

diff --git a/gnu/local.mk b/gnu/local.mk
index 150cb1474d996a1abc10bdca5f41e45bbb67c88c..2edcab36721da79c7a9bfbab03e46452fc79c0c6 100644
--- a/gnu/local.mk
+++ b/gnu/local.mk
@@ -1206,6 +1206,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/docbook-utils-respect-refentry-for-name.patch	\
   %D%/packages/patches/docbook-utils-source-date-epoch.patch	\
   %D%/packages/patches/docbook-utils-use-date-element.patch	\
+  %D%/packages/patches/docbook2x-entity-lt.patch                \
   %D%/packages/patches/docbook2x-filename-handling.patch	\
   %D%/packages/patches/docbook2x-fix-synopsis.patch		\
   %D%/packages/patches/docbook2x-manpage-typo.patch		\
diff --git a/gnu/packages/docbook.scm b/gnu/packages/docbook.scm
index 1e164f165a802fe784226e422251a6c195259452..49bea0daa13b959265ce48e9ee82cb54fef91597 100644
--- a/gnu/packages/docbook.scm
+++ b/gnu/packages/docbook.scm
@@ -909,7 +909,8 @@ Detect the differences in markup between two SGML files.
                                "docbook2x-fix-synopsis.patch"
                                "docbook2x-manpage-typo.patch"
                                "docbook2x-preprocessor-declaration.patch"
-                               "docbook2x-static-datadir-evaluation.patch"))
+                               "docbook2x-static-datadir-evaluation.patch"
+                               "docbook2x-entity-lt.patch"))
               (modules '((guix build utils)))
               (snippet
                ;; Fix a failing test (maybe it worked with old texinfo?)
diff --git a/gnu/packages/patches/docbook2x-entity-lt.patch b/gnu/packages/patches/docbook2x-entity-lt.patch
new file mode 100644
index 0000000000000000000000000000000000000000..74aa14a00ffe8eee7a190a71826fd3e4317353d7
--- /dev/null
+++ b/gnu/packages/patches/docbook2x-entity-lt.patch
@@ -0,0 +1,44 @@
+Upstream-status: https://sourceforge.net/p/docbook2x/bugs/25/
+
+From 040f468fcfae3fe67818023ebc54f3f48fc1bfd9 Mon Sep 17 00:00:00 2001
+From: Sebastian Pipping <sebastian@pipping.org>
+Date: Mon, 24 Feb 2025 23:25:40 +0100
+Subject: [PATCH] Fix invalid redeclaration of predefined XML entity "&lt;"
+
+Section "4.6 Predefined Entities" of XML 1.0r4 is clear that:
+
+> If the entities lt or amp are declared, they MUST be declared
+> as internal entities whose replacement text is a character reference
+> to the respective character (less-than sign or ampersand) being escaped[.]
+
+Source:
+https://www.w3.org/TR/2006/REC-xml-20060816/#sec-predefined-ent
+---
+ xslt/common/text/l10n-set.xml | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+diff --git a/xslt/common/text/l10n-set.xml b/xslt/common/text/l10n-set.xml
+index 0ed7454..b2c334b 100644
+--- a/xslt/common/text/l10n-set.xml
++++ b/xslt/common/text/l10n-set.xml
+@@ -21,7 +21,7 @@
+ <!ENTITY it SYSTEM "it.xml">
+ <!ENTITY ja SYSTEM "ja.xml">
+ <!ENTITY ko SYSTEM "ko.xml">
+-<!ENTITY lt SYSTEM "lt.xml">
++<!ENTITY lt_ SYSTEM "lt.xml">
+ <!ENTITY nl SYSTEM "nl.xml">
+ <!ENTITY nn SYSTEM "nn.xml">
+ <!ENTITY no SYSTEM "no.xml">
+@@ -65,7 +65,7 @@
+ &it;
+ &ja;
+ &ko;
+-&lt;
++&lt_;
+ &nl;
+ &nn;
+ &no;
+-- 
+2.48.1
+