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, 24 insertions, 1 deletions

diff --git a/build2/dist/operation.cxx b/build2/dist/operation.cxx
index f980568..44cdfab 100644
--- a/build2/dist/operation.cxx
+++ b/build2/dist/operation.cxx
@@ -623,6 +623,28 @@ namespace build2
       out_rm.cancel ();
     }
 
+    static include_type
+    dist_include (action,
+                  const target&,
+                  const prerequisite_member& p,
+                  include_type i)
+    {
+      tracer trace ("dist_include");
+
+      // Override excluded to adhoc so that every source is included into the
+      // distribution. Note that this should be harmless to a custom rule
+      // given the prescribed semantics of adhoc (match/execute but otherwise
+      // ignore) is followed.
+      //
+      if (i == include_type::excluded)
+      {
+        l5 ([&]{trace << "overriding exclusion of " << p;});
+        i = include_type::adhoc;
+      }
+
+      return i;
+    }
+
     const meta_operation_info mo_dist {
       dist_id,
       "dist",
@@ -638,7 +660,8 @@ namespace build2
       nullptr, // no match (see execute()).
       &dist_execute,
       nullptr, // operation post
-      nullptr  // meta-operation post
+      nullptr, // meta-operation post
+      &dist_include
     };
   }
 }