Make the diff algorithm handle within in new code

The code assumed that we would not be moving the code where it is
diffed, so the within sort of had to match. Now we add the within
in the source text and it won't show up in the diff but the white-
space should be properly preserved.

Belonging to [master]:
  - OpenModelica/OMCompiler#2998
  - OpenModelica/OpenModelica-testsuite#1147

Compiler/Parsers/SimpleModelicaParser.mo

@@ -47,6 +47,8 @@ import StringUtil;
 import MetaModelica.Dangerous.listReverseInPlace;
 import DoubleEndedList;
 
+constant Token newlineToken = Token.TOKEN("", TokenId.NEWLINE, "\n", 1, 1, 1, 1, 1, 1);
+
 public
 
 uniontype ParseTree
@@ -87,19 +89,20 @@ function treeDiff
 protected
   list<tuple<Diff,list<ParseTree>>> res1, res2;
   ParseTree within1, within2;
-  list<ParseTree> t2_updated;
+  list<ParseTree> t1_updated, t2_updated;
 algorithm
   within1 := findWithin(t1);
   within2 := findWithin(t2);
   // If the new file lacks a within that was in the first file, pretend it is there
   // The other option is to preserve within in OMEdit...
-  t2_updated := match (within1,within2)
-    case (EMPTY(), EMPTY()) then t2;
-    case (_, EMPTY()) then within1::t2;
-    else t2;
+  (t1_updated, t2_updated) := match (within1,within2)
+    case (EMPTY(), EMPTY()) then (t1,t2);
+    case (_, EMPTY()) then (t1, within1::t2);
+    case (EMPTY(), _) then (within2::LEAF(newlineToken)::LEAF(newlineToken)::t1, t2);
+    else (t1,t2);
   end match;
-  t2_updated := moveComments(t1, t2_updated);
-  res := treeDiffWork1(t1, t2_updated, nTokens);
+  t2_updated := moveComments(t1_updated, t2_updated);
+  res := treeDiffWork1(t1_updated, t2_updated, nTokens);
   res := moveCommentsAfterDiff(res);
 end treeDiff;