From ee3b75027e7cc1cec6f4a3ed03cf55e331c37309 Mon Sep 17 00:00:00 2001
From: Will Robertson <wspr81@gmail.com>
Date: Mon, 14 Jan 2019 12:42:09 +0800
Subject: [PATCH] chk fp

because `\fp_use:N \undefined` eventually errors hard, this check needs to abort if it fails
---
 l3kernel/l3fp-convert.dtx | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/l3kernel/l3fp-convert.dtx b/l3kernel/l3fp-convert.dtx
index 78a2edd6db..79a9b14e73 100644
--- a/l3kernel/l3fp-convert.dtx
+++ b/l3kernel/l3fp-convert.dtx
@@ -542,7 +542,16 @@
 % \begin{macro}[EXP]{\fp_use:N, \fp_use:c, \fp_eval:n}
 %   Those public functions are simple copies of the decimal conversions.
 %    \begin{macrocode}
-\cs_new_eq:NN \fp_use:N \fp_to_decimal:N
+\__kernel_if_debug:TF
+  {
+    \cs_new:Npn \fp_use:N #1
+      {
+        \__kernel_chk_var_exist:NT #1 { \fp_to_decimal:N #1 }
+      }
+  }
+  {
+    \cs_new_eq:NN \fp_use:N \fp_to_decimal:N
+  }
 \cs_generate_variant:Nn \fp_use:N { c }
 \cs_new_eq:NN \fp_eval:n \fp_to_decimal:n
 %    \end{macrocode}