Reset value::extra on variable_map value change/version increment

The reset on each modification semantics is used to implement the default
value distinction as currently done in the config module but later probably
will be done for ?= and $origin().

5 files changed, 25 insertions, 7 deletions

diff --git a/libbuild2/config/utility.txx b/libbuild2/config/utility.txx
index b88f76c..0362d6a 100644
--- a/libbuild2/config/utility.txx
+++ b/libbuild2/config/utility.txx
@@ -58,7 +58,7 @@ namespace build2
       if (!l.defined () || (def_ovr && !l.belongs (rs)))
       {
         value& v (rs.assign (var) = std::forward<T> (def_val)); // VC14
-        v.extra = true; // Default value flag.
+        v.extra = 1; // Default value flag.
 
         n = (sflags & save_default_commented) == 0; // Absence means default.
         l = lookup (v, var, rs);
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index 19c1751..cc3fba7 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -4532,7 +4532,7 @@ namespace build2
       // Note that the pattern is preserved if insert fails with regex_error.
       //
       p = scope_->target_vars[ptt].insert (pt, move (pat)).insert (
-        var, kind == type::assign);
+        var, kind == type::assign, false /* reset_extra */);
     }
     catch (const regex_error& e)
     {
diff --git a/libbuild2/variable.cxx b/libbuild2/variable.cxx
index 0f2a3de..74fad14 100644
--- a/libbuild2/variable.cxx
+++ b/libbuild2/variable.cxx
@@ -1761,13 +1761,16 @@ namespace build2
     auto* r (const_cast<value_data*> (p.first));
 
     if (r != nullptr)
+    {
+      r->extra = 0;
       r->version++;
+    }
 
     return pair<value_data*, const variable&> (r, p.second);
   }
 
   pair<value&, bool> variable_map::
-  insert (const variable& var, bool typed)
+  insert (const variable& var, bool typed, bool reset_extra)
   {
     assert (!global_ || ctx->phase == run_phase::load);
 
@@ -1776,6 +1779,9 @@ namespace build2
 
     if (!p.second)
     {
+      if (reset_extra)
+        r.extra = 0;
+
       // Check if this is the first access after being assigned a type.
       //
       // Note: we still need atomic in case this is not a global state.
diff --git a/libbuild2/variable.hxx b/libbuild2/variable.hxx
index d00243e..9c1e02c 100644
--- a/libbuild2/variable.hxx
+++ b/libbuild2/variable.hxx
@@ -276,7 +276,13 @@ namespace build2
     // Extra data that is associated with the value that can be used to store
     // flags, etc. It is initialized to 0 and copied (but not assigned) from
     // one value to another but is otherwise untouched (not even when the
-    // value is reset to NULL).
+    // value is reset to NULL) unless it is part of variable_map::value_data,
+    // in which case it is reset to 0 on each modification (version
+    // increment; however, see reset_extra flag in variable_map::insert()).
+    //
+    // (The reset on each modification semantics is used to implement the
+    // default value distinction as currently done in the config module but
+    // later probably will be done for ?= and $origin()).
     //
     // Note: if deciding to use for something make sure it is not overlapping
     // with an existing usage.
@@ -1506,7 +1512,10 @@ namespace build2
       using value::value;
       using value::operator=;
 
-      size_t version = 0; // Incremented on each modification (variable_cache).
+      // Incremented on each modification, at which point we also reset
+      // value::extra to 0.
+      //
+      size_t version = 0;
     };
 
     // Note that we guarantee ascending iteration order (e.g., for predictable
@@ -1606,6 +1615,7 @@ namespace build2
     {
       assert (l.vars == this);
       value& r (const_cast<value&> (*l.value));
+      r.extra = 0;
       static_cast<value_data&> (r).version++;
       return r;
     }
@@ -1629,10 +1639,11 @@ namespace build2
 
     // As above but also return an indication of whether the new value (which
     // will be NULL) was actually inserted. Similar to find(), if typed is
-    // false, leave the value untyped even if the variable is.
+    // false, leave the value untyped even if the variable is. If reset_extra
+    // is false, then don't reset the existing value's value::extra.
     //
     pair<value&, bool>
-    insert (const variable&, bool typed = true);
+    insert (const variable&, bool typed = true, bool reset_extra = true);
 
     // Note: does not deal with aliases.
     //
diff --git a/libbuild2/variable.txx b/libbuild2/variable.txx
index b1c4112..d75befb 100644
--- a/libbuild2/variable.txx
+++ b/libbuild2/variable.txx
@@ -1070,6 +1070,7 @@ namespace build2
 
       e.stem_version = sver;
 
+      e.value.extra = 0; // For consistency (we don't really use it).
       e.value.version++; // Value changed.
     }
     else