From 9cb8ee086f40b1a85d454b068d98cef1ee10d04f Mon Sep 17 00:00:00 2001
From: Rene Rivera <grafikrobot@gmail.com>
Date: Wed, 18 Oct 2017 18:43:56 -0500
Subject: [PATCH] Guard against redef of asciidoctor in common b2.

---
 doc/asciidoctor.jam | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/doc/asciidoctor.jam b/doc/asciidoctor.jam
index 488670d..56362be 100644
--- a/doc/asciidoctor.jam
+++ b/doc/asciidoctor.jam
@@ -9,23 +9,26 @@ import scanner ;
 import generators ;
 import boostbook ;
 
-# File type
-
-type.register ASCIIDOC : asciidoc adoc ;
-
-# Define dependency scanner
-
-class asciidoc-scanner : common-scanner
+if ! [ type.registered ASCIIDOC ]
 {
-    rule pattern ( )
+    # File type
+    
+    type.register ASCIIDOC : asciidoc adoc ;
+    
+    # Define dependency scanner
+    
+    class asciidoc-scanner : common-scanner
     {
-        return "include::([^[]+)\\[" ;
+        rule pattern ( )
+        {
+            return "include::([^[]+)\\[" ;
+        }
     }
+    
+    scanner.register asciidoc-scanner : include ;
+    type.set-scanner ASCIIDOC : asciidoc-scanner ;
 }
 
-scanner.register asciidoc-scanner : include ;
-type.set-scanner ASCIIDOC : asciidoc-scanner ;
-
 # Define generators
 
 generators.register-standard asciidoctor.asciidoc-to-html : ASCIIDOC : HTML ;