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

3 files changed, 31 insertions, 3 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
     };
   }
 }
diff --git a/build2/dist/rule.cxx b/build2/dist/rule.cxx
index 5ae1f66..d5f42f0 100644
--- a/build2/dist/rule.cxx
+++ b/build2/dist/rule.cxx
@@ -31,6 +31,9 @@ namespace build2
       for (prerequisite_member p:
              group_prerequisite_members (a, t, members_mode::maybe))
       {
+        // Note: no exclusion tests, we want all of them (and see also the
+        // dist_include() override).
+
         // Skip prerequisites imported from other projects.
         //
         if (p.proj ())
@@ -49,6 +52,8 @@ namespace build2
         // is mentioned as a target, then it is in out (we don't do the same
         // target in both src/out).
         //
+        // @@ Note that this is still an issue in a custom dist rule.
+        //
         const target* pt (nullptr);
         if (p.is_a<file> ())
         {
diff --git a/build2/dist/rule.hxx b/build2/dist/rule.hxx
index 2050a5b..d384b32 100644
--- a/build2/dist/rule.hxx
+++ b/build2/dist/rule.hxx
@@ -9,8 +9,8 @@
 #include <build2/utility.hxx>
 
 #include <build2/rule.hxx>
+#include <build2/action.hxx>
 #include <build2/target.hxx>
-#include <build2/operation.hxx>
 
 namespace build2
 {
@@ -19,7 +19,7 @@ namespace build2
     // This is the default rule that simply matches all the prerequisites.
     //
     // A custom rule (usually the same as perform_update) may be necessary to
-    // establishing group links (so that we see the dist variable set on a
+    // establish group links (so that we see the dist variable set on a
     // group).
     //
     class rule: public build2::rule