Allow back overriding variables specified in buildfiles

It is still not clear whether this is the right thing to allow, conceptually,
but with this disallowed it's hard to test this functionality. Perhaps we
should have an attribute [overridable]. The problem is one will also have to
set this variable to some value (e.g., [null]) which is not exactly the same
as undefined (especially when testing).

1 files changed, 10 insertions, 4 deletions

diff --git a/build2/variable.cxx b/build2/variable.cxx
index 78f7c04..48f3345 100644
--- a/build2/variable.cxx
+++ b/build2/variable.cxx
@@ -1003,7 +1003,14 @@ namespace build2
       if (o == nullptr)
         o = &*p.overridable;
       else if (p.match)
-        assert (*o == *p.overridable);
+      {
+        // Allow the pattern to restrict but not relax.
+        //
+        if (*o)
+          o = &*p.overridable;
+        else
+          assert (*o == *p.overridable);
+      }
     }
   }
 
@@ -1046,9 +1053,8 @@ namespace build2
     {
       if (t != nullptr || v != nullptr || o != nullptr)
         update (r, t, v, o); // Not changing the key.
-      else
-        if (r.override != nullptr)
-          fail << "variable " << r.name << " cannot be overridden";
+      else if (r.override != nullptr)
+        fail << "variable " << r.name << " cannot be overridden";
     }
 
     return r;