Add update operation-specific variable with unmatch|match additional values

Note that the unmatch (match but do not update) and match (update during
match) values are only supported by certain rules (and potentially only for
certain prerequisite types).

Additionally:

- All operation-specific variables are now checked for false as an override
  for the prerequisite-specific include value. In particular, this can now be
  used to disable a prerequisite for update, for example:

  ./: exe{test}: update = false

- The cc::link_rule now supports the update=match value for headers and ad hoc
  prerequisites. In particular, this can be used to make sure all the library
  headers are updated before matching any of its (or dependent's) object
  files.

1 files changed, 9 insertions, 6 deletions

diff --git a/libbuild2/operation.hxx b/libbuild2/operation.hxx
index 2f88e88..ce3cd79 100644
--- a/libbuild2/operation.hxx
+++ b/libbuild2/operation.hxx
@@ -125,12 +125,14 @@ namespace build2
     void (*meta_operation_post) (context&, const values&);
 
     // Optional prerequisite exclusion override callback. See include() for
-    // details. Note that it's not called for include_type::normal;
+    // details. Note that it's not called for include_type::normal without
+    // operation-specific override.
     //
     include_type (*include) (action,
                              const target&,
                              const prerequisite_member&,
-                             include_type);
+                             include_type,
+                             lookup&);
   };
 
   // Built-in meta-operations.
@@ -194,6 +196,7 @@ namespace build2
     const operation_id id;
     const operation_id outer_id;
     const char* name;
+    const char* var_name; // Operation variable or NULL if not used.
 
     // Name derivatives for diagnostics. Note that unlike meta-operations,
     // these can only be empty for the default operation (id 1), And
@@ -309,10 +312,10 @@ namespace build2
   // are represented as NULL pointers. Also, lookup out of bounds
   // is treated as a hole.
   //
-  template <typename T>
+  template <typename T, size_t N>
   struct sparse_vector
   {
-    using base_type = vector<T*>;
+    using base_type = small_vector<T*, N>;
     using size_type = typename base_type::size_type;
 
     void
@@ -348,8 +351,8 @@ namespace build2
     base_type v_;
   };
 
-  using meta_operations = sparse_vector<const meta_operation_info>;
-  using operations = sparse_vector<const operation_info>;
+  using meta_operations = sparse_vector<const meta_operation_info, 8>;
+  using operations = sparse_vector<const operation_info, 10>;
 }
 
 namespace butl