From 41f33bc48d910d4af1d9c8702a1a17144449bc28 Mon Sep 17 00:00:00 2001
From: Joseph Wright <joseph.wright@morningstar2.co.uk>
Date: Thu, 15 Feb 2024 13:39:16 +0000
Subject: [PATCH] Re-introduce \IfInstanceExist(TF)

This reverts commit 10a330e5013d41f9d209a2f2ebaac91ffa18a62d.
---
 base/changes.txt                              |  4 +++
 base/lttemplates.dtx                          | 15 ++++++++++-
 base/testfiles-lttemplates/lttemplates003.lvt | 26 +++++++++++++++++++
 base/testfiles-lttemplates/lttemplates003.tlg | 14 +++++++---
 4 files changed, 55 insertions(+), 4 deletions(-)

diff --git a/base/changes.txt b/base/changes.txt
index dec230e89..1e76ddf9e 100644
--- a/base/changes.txt
+++ b/base/changes.txt
@@ -6,6 +6,10 @@ to completeness or accuracy and it contains some references to files that are
 not part of the distribution.
 ================================================================================
 
+2024-02-15 Joseph Wright  <Joseph.Wright@latex-project.org>
+	* lttemplates.dtx
+	Re-introduce \IfInstanceExist(TF)
+
 2024-01-30  David Carlisle  <David.Carlisle@latex-project.org>
 	* ltclass.dtx: check that \RequirePackage, \documentclass, \usepackage
 	  and related commands are at top level (gh/1185)
diff --git a/base/lttemplates.dtx b/base/lttemplates.dtx
index 844fb6fd3..d27c232fe 100644
--- a/base/lttemplates.dtx
+++ b/base/lttemplates.dtx
@@ -36,7 +36,7 @@
 %<*driver>
 % \fi
 \ProvidesFile{lttemplates.dtx}
-  [2024-02-11 v1.0a LaTeX Kernel (Prototype document functions)]
+  [2024-02-15 v1.0b LaTeX Kernel (Prototype document functions)]
 % \iffalse
 \documentclass{l3doc}
 \GetFileInfo{lttemplates.dtx}
@@ -2653,6 +2653,19 @@
 % \end{macro}
 % \end{macro}
 %
+% \begin{macro}{\IfInstanceExistT, \IfInstanceExistF, \IfInstanceExistTF}
+% \changes{2024-02-15}{v1.0b}{New macros}
+%   More direct translation.
+%    \begin{macrocode}
+\cs_new:Npn \IfInstanceExistTF #1#2
+  { \@@_if_instance_exist:nnTF {#1} {#2} }
+\cs_new:Npn \IfInstanceExistT #1#2
+  { \@@_if_instance_exist:nnT {#1} {#2} }
+\cs_new:Npn \IfInstanceExistF #1#2
+  { \@@_if_instance_exist:nnF {#1} {#2} }
+%    \end{macrocode}
+% \end{macro}
+%
 % \begin{macro}{\KeyValue}
 %   Simply dump the argument when executed: this should not happen.
 %    \begin{macrocode}
diff --git a/base/testfiles-lttemplates/lttemplates003.lvt b/base/testfiles-lttemplates/lttemplates003.lvt
index d16b95eaa..9c3c2d21d 100644
--- a/base/testfiles-lttemplates/lttemplates003.lvt
+++ b/base/testfiles-lttemplates/lttemplates003.lvt
@@ -317,6 +317,32 @@
 }
 
 
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% 17
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\TEST{Testing~instances:~existance~check}{
+
+   \IfInstanceExistTF {test} {nono}                      % instance unknwon, ok
+        {\typeout{Yes}} {\typeout{No}}
+
+   \IfInstanceExistTF {missingobjecttype} {nono}         % objecttype unknown, ok
+        {\typeout{Yes}} {\typeout{No}}
+
+   \group_begin:
+
+     \DeclareInstance {test} {myinstance} {tname2} {}
+
+     \IfInstanceExistTF {test} {myinstance}              % test inside group, ok
+	  {\typeout{Yes}} {\typeout{No}}
+
+   \group_end:
+
+     \IfInstanceExistTF {test} {myinstance}              % test outside group
+	  {\typeout{Yes}} {\typeout{No}}                 % no longer defined, ok
+
+}
+
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % 18
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
diff --git a/base/testfiles-lttemplates/lttemplates003.tlg b/base/testfiles-lttemplates/lttemplates003.tlg
index a7bed2004..33cdf6ceb 100644
--- a/base/testfiles-lttemplates/lttemplates003.tlg
+++ b/base/testfiles-lttemplates/lttemplates003.tlg
@@ -302,7 +302,15 @@ The template 'tname16' of type 'test' has variable mapping:
 l. ...}
 ============================================================
 ============================================================
-TEST 17: Testing instances: declare instance
+TEST 17: Testing instances: existance check
+============================================================
+No
+No
+Yes
+No
+============================================================
+============================================================
+TEST 18: Testing instances: declare instance
 ============================================================
 ! LaTeX template Error: The template 'never-defined' of type 'test' is unknown
 (template)              or has no implementation.
@@ -317,7 +325,7 @@ huh
 (Y-99)
 ============================================================
 ============================================================
-TEST 18: Edit template defaults
+TEST 19: Edit template defaults
 ============================================================
 Defining key template/test/tname17/key on line ...
 Defining key template/test/tname17/key/unknown on line ...
@@ -368,7 +376,7 @@ l. ...}
 The key 'wrong' was not declared in the interface for the current template.
 ============================================================
 ============================================================
-TEST 19: Edit instance values
+TEST 20: Edit instance values
 ============================================================
 The instance 'myinstance' of type 'test' has values:
 >  key  =>  A