Implement support for scope operation callbacks

An entity (module, core) can register a function that will be called when an
action is executed on the dir{} target that corresponds to the scope. The pre
callback is called just before the recipe and the post -- immediately after.

1 files changed, 44 insertions, 0 deletions

diff --git a/build2/target-state.hxx b/build2/target-state.hxx
new file mode 100644
index 0000000..2913abb
--- /dev/null
+++ b/build2/target-state.hxx
@@ -0,0 +1,44 @@
+// file      : build2/target-state.hxx -*- C++ -*-
+// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#ifndef BUILD2_TARGET_STATE_HXX
+#define BUILD2_TARGET_STATE_HXX
+
+#include <build2/types.hxx>
+#include <build2/utility.hxx>
+
+namespace build2
+{
+  // The order of the enumerators is arranged so that their integral values
+  // indicate whether one "overrides" the other in the "merge" operator|
+  // (see below).
+  //
+  // Note that postponed is "greater" than unchanged since it may result in
+  // the changed state.
+  //
+  enum class target_state: uint8_t
+  {
+    unknown,
+    unchanged,
+    postponed,
+    busy,
+    changed,
+    failed,
+    group       // Target's state is the group's state.
+  };
+
+  inline target_state&
+  operator |= (target_state& l, target_state r)
+  {
+    if (static_cast<uint8_t> (r) > static_cast<uint8_t> (l))
+      l = r;
+
+    return l;
+  }
+
+  ostream&
+  operator<< (ostream&, target_state); // target.cxx
+}
+
+#endif // BUILD2_TARGET_STATE_HXX