Remove check for 'unused sources'. The check causes bogus warnings in at least

a couple of cases.

1. On Windows, DLLs are never directly linked to, so they are considered
   unused and cause a warning. There used to be special code in
   exe-target-class and lib-target-class to supress that warning, but this
   failed for unit-test, for example, since main target class for unit test
   is not related with exe-target-class. And making yet another main target
   class looks ugly.
2. A target specified via project-wide <source> or <library> property is
   added to sources for all targets, and cause a warning when it's not used.
   However, there are valid cases to ignore such sources. For example

       obj a : a.cpp : <optimization>off ;

   need to comsume any libraries.

It was not clear how to fix both problems. Further, the only case when I found
the warning to be usefull is when declaring new toolsets, and it that case it
does not add much information compared to --debug-generators output. So, let's
just kill the feature for now.


[SVN r22927]

src/build/alias.jam

@@ -50,12 +50,7 @@ class alias-target-class : basic-target
     rule check-for-link-compatibility ( * : * )
     {
     }
-    
-    rule check-for-unused-sources ( * : * )
-    {
-    }
-    
-        
+            
     rule compute-usage-requirements ( subvariant ) 
     {
         local base = [ basic-target.compute-usage-requirements $(subvariant) ] ;

src/build/targets.jam

@@ -972,8 +972,6 @@ class basic-target : abstract-target
                 
                 local result = 
                   [ construct $(source-targets) : $(rproperties) ] ;
-                check-for-unused-sources 
-                  $(result) : $(source-targets) ;
 
                 local s = [ create-subvariant $(result) : $(property-set) : $(source-targets)
                   : $(rproperties) : $(usage-requirements) ] ;
@@ -1038,49 +1036,7 @@ class basic-target : abstract-target
         }                        
         return $(s) ;
     }
-    
-        
-    # Check that each source virtual target which is not marked as intermediate
-    # is present dependency graph of 'result'. 
-    # If this is not the case, issues a warning.
-    # Sources which are directly presentin result are not considered used, and 
-    # a warning will be issued for them as well.
-    #
-    # Note that 'result' *can* be empty. For
-    # example, in this use case:
-    #    alias platform-sources ;
-    #    alias platform-sources : a.cpp : <os>NT ;
-    # result will be empty in the first case.
-    local rule check-for-unused-sources ( result * : sources * )
-    {
-        local isources ;
-        for local i in $(sources)
-        {
-            if ! [ $(i).intermediate ] 
-            {
-                isources += $(i) ;
-            }
-        }
-        sources = $(isources) ;
-        
-        local used-sources ;
-        for local r in $(result)
-        {
-            used-sources += [ virtual-target.traverse $(r) : include-roots : 1 ] ;
-        }
-        # Consider sources which are bypassed as unused
-        used-sources = [ set.difference $(used-sources) : $(result) ] ;
-        
-        local unused = [ set.difference $(sources) : $(used-sources) ] ;
-        if $(unused)
-        {
-            for local u in $(unused)
-            {               
-                errors.warning "Unused source" [ $(u).str ] "in main target" [ full-name ] ;
-            }                            
-        }                                                       
-    }
-    
+               
     # Checks if 'targets' are link-compatible with 'build-request' and
     # issues a warning if that's not the case.
     local rule check-for-link-compatibility ( targets * : build-request )

src/tools/builtin.jam

@@ -428,25 +428,7 @@ class lib-target-class : basic-target
         }
                                         
         return $(result) ;
-    }
-    
-    rule check-for-unused-sources ( result * : sources * )
-    {
-        # For library targets, it's okay to bypass input sources of
-        # type LIB: with <link>static we can't consume library.
-        
-        local sources-to-check ;
-        for local s in $(sources)
-        {
-            if ! [ type.is-derived [ $(s).type ] LIB ]
-            {
-                sources-to-check += $(s) ;
-            }            
-        }
-        basic-target.check-for-unused-sources $(result) : $(sources-to-check) ;
-    }
-    
-    
+    }            
 }
 
 rule lib ( name : sources * : requirements * : default-build * 

src/tools/gettext.jam

@@ -169,11 +169,7 @@ class update-translations-class : basic-target
             }            
         }
         return $(.constructed) ;                
-    }    
-    
-    rule check-for-unused-sources ( result * : sources * )
-    {        
-    }
+    }        
 }
 
 flags gettext.extract KEYWORD <gettext.keyword> ;

src/tools/stage.jam

@@ -224,11 +224,6 @@ class stage-target-class : basic-target
         result = [ sequence.unique $(result) ] ;        
     }
         
-    # Don't do nothing.
-    rule check-for-unused-sources ( result * : sources * )
-    {        
-    }
-    
     rule check-for-link-compatibility ( * : * )
     {
     }

test/test_all.py

@@ -92,7 +92,6 @@ tests = [ "project_test1",
           "make_rule",
           "alias",
           "alternatives",
-          "unused",
           "default_features",
           "print",
           "ndebug",