Add support for prepend/append in target type/pattern-specific vars

Semantically, these are similar to variable overrides and are essentially
treated as "templates" that are applied on lookup to the "stem" value that is
specific to the target type/name. For example:

x = [string] a
file{f*}: x =+ b

sub/:
{
  file{*}: x += c

  print $(file{foo}:x)  # abc
  print $(file{bar}:x)  # ac
}

1 files changed, 42 insertions, 24 deletions

diff --git a/build2/dump.cxx b/build2/dump.cxx
index 9310405..08700fc 100644
--- a/build2/dump.cxx
+++ b/build2/dump.cxx
@@ -53,35 +53,51 @@ namespace build2
     }
   }
 
+  enum class variable_kind {scope, tt_pat, target};
+
   static void
   dump_variable (ostream& os,
                  const variable& var,
                  const lookup& org,
                  const scope& s,
-                 bool target)
+                 variable_kind k)
   {
-    if (var.type != nullptr)
-      os << '[' << var.type->name << "] ";
-
-    os << var.name << " = ";
-
-    // If this variable is overriden, print both the override and the
-    // original values.
+    // Target type/pattern-specific prepends/appends are kept untyped and not
+    // overriden.
     //
-    if (var.override != nullptr &&
-        var.name.rfind (".__override") == string::npos &&
-        var.name.rfind (".__suffix") == string::npos &&
-        var.name.rfind (".__prefix") == string::npos)
+    if (k == variable_kind::tt_pat && org->extra != 0)
     {
-      // The original is always from this scope/target, so depth is 1.
+      // @@ Might be useful to dump the cache.
       //
-      lookup l (s.find_override (var, make_pair (org, 1), target).first);
-      assert (l.defined ()); // We at least have  the original.
+      os << var.name << (org->extra == 1 ? " =+ " : " += ");
+    }
+    else
+    {
+      if (var.type != nullptr)
+        os << '[' << var.type->name << "] ";
 
-      if (org != l)
+      os << var.name << " = ";
+
+      // If this variable is overriden, print both the override and the
+      // original values.
+      //
+      if (var.override != nullptr &&
+          var.name.rfind (".__override") == string::npos &&
+          var.name.rfind (".__suffix") == string::npos &&
+          var.name.rfind (".__prefix") == string::npos)
       {
-        dump_value (os, *l, l->type != var.type);
-        os << " # original: ";
+        // The original is always from this scope/target, so depth is 1.
+        //
+        lookup l (
+          s.find_override (
+            var, make_pair (org, 1), k == variable_kind::target).first);
+        assert (l.defined ()); // We at least have the original.
+
+        if (org != l)
+        {
+          dump_value (os, *l, l->type != var.type);
+          os << " # original: ";
+        }
       }
     }
 
@@ -93,17 +109,19 @@ namespace build2
                   string& ind,
                   const variable_map& vars,
                   const scope& s,
-                  bool target)
+                  variable_kind k)
   {
     for (const auto& e: vars)
     {
       os << endl
          << ind;
 
-      dump_variable (os, e.first, lookup (&e.second, &vars), s, target);
+      dump_variable (os, e.first, lookup (&e.second, &vars), s, k);
     }
   }
 
+  // Dump target type/pattern-specific variables.
+  //
   static void
   dump_variables (ostream& os,
                   string& ind,
@@ -140,14 +158,14 @@ namespace build2
                          vars.begin ()->first,
                          lookup (&vars.begin ()->second, &vars),
                          s,
-                         false);
+                         variable_kind::tt_pat);
         }
         else
         {
           os << endl
              << ind << '{';
           ind += "  ";
-          dump_variables (os, ind, vars, s, false);
+          dump_variables (os, ind, vars, s, variable_kind::tt_pat);
           ind.resize (ind.size () - 2);
           os << endl
              << ind << '}';
@@ -216,7 +234,7 @@ namespace build2
       os << endl
          << ind << '{';
       ind += "  ";
-      dump_variables (os, ind, t.vars, s, true);
+      dump_variables (os, ind, t.vars, s, variable_kind::target);
       ind.resize (ind.size () - 2);
       os << endl
          << ind << '}';
@@ -262,7 +280,7 @@ namespace build2
       if (vb)
         os << endl;
 
-      dump_variables (os, ind, p.vars, p, false);
+      dump_variables (os, ind, p.vars, p, variable_kind::scope);
       vb = true;
     }