1 files changed, 66 insertions, 0 deletions
diff --git a/libbuild2/config/utility.txx b/libbuild2/config/utility.txx
new file mode 100644
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+++ b/libbuild2/config/utility.txx
@@ -0,0 +1,66 @@
+// file      : libbuild2/config/utility.txx -*- C++ -*-
+// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
+// license   : MIT; see accompanying LICENSE file
+
+#include <libbuild2/scope.hxx>
+#include <libbuild2/context.hxx>
+
+namespace build2
+{
+  namespace config
+  {
+    template <typename T>
+    pair<lookup, bool>
+    required (scope& root,
+              const variable& var,
+              const T& def_val,
+              bool def_ovr,
+              uint64_t save_flags)
+    {
+      // Note: see also omitted() if changing anything here.
+
+      if (current_mif->id == configure_id)
+        save_variable (root, var, save_flags);
+
+      pair<lookup, size_t> org (root.find_original (var));
+
+      bool n (false); // New flag.
+      lookup l (org.first);
+
+      // The interaction with command line overrides can get tricky. For
+      // example, the override to defaul value could make (non-recursive)
+      // command line override in the outer scope no longer apply. So what we
+      // are going to do is first ignore overrides and perform the normal
+      // logic on the original. Then we apply the overrides on the result.
+      //
+      if (!l.defined () || (def_ovr && !l.belongs (root)))
+      {
+        value& v (root.assign (var) = def_val);
+        v.extra = true; // Default value flag.
+
+        n = (save_flags & save_commented) == 0; // Absence means default.
+        l = lookup (v, var, root);
+        org = make_pair (l, 1); // Lookup depth is 1 since it's in root.vars.
+      }
+      // Treat an inherited value that was set to default as new.
+      //
+      else if (l->extra)
+        n = (save_flags & save_commented) == 0; // Absence means default.
+
+      if (var.overrides != nullptr)
+      {
+        pair<lookup, size_t> ovr (root.find_override (var, move (org)));
+
+        if (l != ovr.first) // Overriden?
+        {
+          // Override is always treated as new.
+          //
+          n = true;
+          l = move (ovr.first);
+        }
+      }
+
+      return pair<lookup, bool> (l, n);
+    }
+  }
+}