Fixed #787 - the results of const reference return values need to be copied as the holder object may go out of scope

src/db/unit_tests/dbLayoutQueryTests.cc

@@ -1488,3 +1488,24 @@ TEST(63)
 
   EXPECT_EQ (g.under_construction (), false);
 }
+
+//  issue-787
+TEST(64)
+{
+  db::Layout g;
+  init_layout (g);
+
+  {
+    db::LayoutQuery q ("select inst.dtrans from instances of .*.*");
+    db::LayoutQueryIterator iq (q, &g);
+    std::string s = q2s_var (iq, "data");
+    EXPECT_EQ (s, "r0 0.01,-0.02,m45 -0.01,0.02,m45 -0.01,0.02,m45 -0.01,0.02,r0 0.01,-0.02,m45 -0.01,0.02");
+  }
+
+  {
+    db::LayoutQuery q ("select inst.dtrans.disp.x,inst.dtrans.disp.y from instances of .*.*");
+    db::LayoutQueryIterator iq (q, &g);
+    std::string s = q2s_var (iq, "data");
+    EXPECT_EQ (s, "0.01,-0.02,-0.01,0.02,-0.01,0.02,-0.01,0.02,0.01,-0.02,-0.01,0.02");
+  }
+}

src/gsi/gsi/gsiExpression.cc

@@ -901,6 +901,13 @@ struct reader<ObjectType>
 
       tl_assert (cls != 0);
       *out = tl::Variant ();
+
+      //  consider prefer_copy
+      if (! owner && atype.prefer_copy () && !clsact->is_managed () && clsact->can_copy ()) {
+        obj = clsact->clone (obj);
+        owner = true;
+      }
+
       out->set_user (obj, cls, owner);
 
     }

src/tl/unit_tests/tlExpression.cc

@@ -1189,3 +1189,24 @@ TEST(19)
   v = e.parse ("# A comment\nvar i=CellInstArray.new(17,tr,a,b,100,200); i.to_s(); # A final comment").execute ();
   EXPECT_EQ (v.to_string (), std::string ("#17 r90 10,20 [1,2*100;11,22*200]"));
 }
+
+// issue-787
+TEST(20)
+{
+  tl::Eval e;
+  e.parse ("var ly=Layout.new(true)").execute ();
+  e.parse ("var top=ly.create_cell('TOP')").execute ();
+  e.parse ("var cell=ly.create_cell('CHILD')").execute ();
+  e.parse ("var i1 = top.insert(CellInstArray.new(cell.cell_index,Trans.new(Vector.new(100,200))))").execute ();
+  e.parse ("var i2 = top.insert(CellInstArray.new(cell.cell_index,Trans.new(Vector.new(-100,300))))").execute ();
+
+  tl::Variant v;
+  v = e.parse ("i1.dtrans.disp.x").execute ();
+  EXPECT_EQ (v.to_string (), std::string ("0.1"));
+  v = e.parse ("i1.dtrans.disp.y").execute ();
+  EXPECT_EQ (v.to_string (), std::string ("0.2"));
+  v = e.parse ("i2.dtrans.disp.x").execute ();
+  EXPECT_EQ (v.to_string (), std::string ("-0.1"));
+  v = e.parse ("i2.dtrans.disp.y").execute ();
+  EXPECT_EQ (v.to_string (), std::string ("0.3"));
+}