New --dump-generators option to list all generators.

[SVN r55711]

src/build-system.jam

@@ -25,7 +25,7 @@ import toolset ;
 import utility ;
 import version ;
 import virtual-target ;
-
+import generators ;
 
 ################################################################################
 #
@@ -686,8 +686,12 @@ local rule should-clean-project ( project )
     {
         targets += [ project.target [ project.module-name "." ] ] ;
     }
-
-
+    
+    if [ option.get dump-generators : : true ] 
+    {
+        generators.dump ;
+    }
+    
     # Now that we have a set of targets to build and a set of property sets to
     # build the targets with, we can start the main build process by using each
     # property set to generate virtual targets from all of our listed targets

src/build/generators.jam

@@ -722,6 +722,8 @@ class generator
 #
 rule register ( g )
 {
+    .all-generators += $(g) ;
+        
     # A generator can produce several targets of the same type. We want unique
     # occurrence of that generator in .generators.$(t) in that case, otherwise,
     # it will be tried twice and we will get a false ambiguity.
@@ -1393,3 +1395,12 @@ rule add-usage-requirements ( result * : raw-properties * )
         }
     }
 }
+
+rule dump ( )
+{
+    for local g in $(.all-generators)
+    {
+        ECHO [ $(g).id ] ":" [ $(g).source-types ] -> [ $(g).target-types ] ;            
+    }    
+}
+