Implement support for excluded and ad hoc prerequisites

The inclusion/exclusion is controlled via the 'include' prerequisite-specific
variable. Valid values are:

false  - exclude
true   - include
adhoc  - include but treat as an ad hoc input

For example:

lib{foo}: cxx{win32-utility}: include = ($cxx.targe.class == 'windows')
exe{bar}: libs{plugin}: include = adhoc

1 files changed, 13 insertions, 3 deletions

diff --git a/build2/target.hxx b/build2/target.hxx
index 761cb4e..515a082 100644
--- a/build2/target.hxx
+++ b/build2/target.hxx
@@ -15,8 +15,8 @@
 #include <build2/utility.hxx>
 
 #include <build2/scope.hxx>
+#include <build2/action.hxx>
 #include <build2/variable.hxx>
-#include <build2/operation.hxx>
 #include <build2/target-key.hxx>
 #include <build2/target-type.hxx>
 #include <build2/target-state.hxx>
@@ -92,14 +92,18 @@ namespace build2
   {
     using target_type = build2::target;
 
-    prerequisite_target (const target_type* t, uintptr_t d = 0)
-        : target (t), data (d) {}
+    prerequisite_target (const target_type* t, bool a = false, uintptr_t d = 0)
+        : target (t), adhoc (a), data (d) {}
+
+    prerequisite_target (const target_type* t, include_type a, uintptr_t d = 0)
+        : prerequisite_target (t, a == include_type::adhoc, d) {}
 
     operator const target_type*&  ()       {return target;}
     operator const target_type*   () const {return target;}
     const target_type* operator-> () const {return target;}
 
     const target_type* target;
+    bool               adhoc;  // True if include=adhoc.
     uintptr_t          data;
   };
   using prerequisite_targets = vector<prerequisite_target>;
@@ -932,6 +936,12 @@ namespace build2
     return os << pm.key ();
   }
 
+  inline include_type
+  include (action a, const target& t, const prerequisite_member& pm)
+  {
+    return include (a, t, pm.prerequisite, pm.member);
+  }
+
   // A "range" that presents a sequence of prerequisites (e.g., from
   // group_prerequisites()) as a sequence of prerequisite_member's. For each
   // group prerequisite you will "see" either the prerequisite itself or all