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, 14 insertions, 0 deletions

diff --git a/libbuild2/algorithm.hxx b/libbuild2/algorithm.hxx
index 8a6eb65..c30680a 100644
--- a/libbuild2/algorithm.hxx
+++ b/libbuild2/algorithm.hxx
@@ -595,6 +595,20 @@ namespace build2
   LIBBUILD2_SYMEXPORT target_state
   execute_direct (action, const target&);
 
+  // Update the target during the match phase (by switching the phase and
+  // calling execute_direct()). Return true if the target has changed or, if
+  // the passed timestamp is not timestamp_unknown, it is older than the
+  // target.
+  //
+  // Note that such a target must still be updated normally during the execute
+  // phase in order to keep the dependency counts straight (at which point the
+  // target state/timestamp will be re-incorporated into the result).
+  //
+  LIBBUILD2_SYMEXPORT bool
+  update_during_match (tracer&,
+                       action, const target&,
+                       timestamp = timestamp_unknown);
+
   // The default prerequisite execute implementation. Call execute_async() on
   // each non-ignored (non-NULL) prerequisite target in a loop and then wait
   // for their completion. Return target_state::changed if any of them were