fix: EliminateEmptyAlt. making inconsistent labels

Author: pmbittner

src/main/java/org/variantsync/diffdetective/variation/diff/transform/EliminateEmptyAlternatives.java

@@ -1,8 +1,11 @@
-
 package org.variantsync.diffdetective.variation.diff.transform;
 
 import org.prop4j.Node;
-import org.variantsync.diffdetective.variation.Label;
+import org.prop4j.NodeWriter;
+import org.variantsync.diffdetective.util.Assert;
+import org.variantsync.diffdetective.util.StringUtils;
+import org.variantsync.diffdetective.variation.DiffLinesLabel;
+import static org.variantsync.diffdetective.variation.DiffLinesLabel.Line;
 import org.variantsync.diffdetective.variation.tree.VariationTree;
 import org.variantsync.diffdetective.variation.tree.VariationTreeNode;
 
@@ -35,20 +38,52 @@
  *
  * @author Paul Bittner
  */
-public class EliminateEmptyAlternatives<L extends Label> implements Transformer<VariationTree<L>> {
-    private void elim(VariationTreeNode<L> subtree) {
+public class EliminateEmptyAlternatives implements Transformer<VariationTree<DiffLinesLabel>> {
+    /**
+     * Creates a copy of the given label but where the formula is set to the given formula.
+     * This method also updates the text in the DiffLinesLabel accordingly so that the text is
+     * consistent with the formula.
+     * This method assumes that the label has at least one line of text, otherwise the given label
+     * could not have a formula.
+     */
+    private static DiffLinesLabel updatedLabel(DiffLinesLabel l, Node formula) {
+        final List<Line> lines = l.getDiffLines();
+        Assert.assertFalse(lines.isEmpty());
+
+        // Assumption:
+        // The only case in which there is more than one line of text is, when we parsed a multiline macro.
+        //
+        // We hence may safely ignore any subsequent lines from our existing label because these correspond
+        // only to lines of a multiline macro, which we ought to replace anyway.
+        final Line head = lines.get(0);
+        Assert.assertTrue(head.content().contains("if"));
+        final String indent = StringUtils.getLeadingWhitespace(head.content());
+
+        final String newText = indent + "#if " + formula.toString(NodeWriter.javaSymbols);
+
+        // We might have replaced multiple lines by a single line here.
+        // In this case, some line numbers got lost and any variation tree using this updated label somewhere might not
+        // have consecutive line numbering anymore. We could consider inserting empty lines to retain
+        // consecutive line numbers but that might be a more artifical change than inconsecutive line numbers.
+        return new DiffLinesLabel(
+            List.of(new Line(newText, head.lineNumber())),
+            l.getDiffTrailingLines()
+        );
+    }
+
+    private static void elim(VariationTreeNode<DiffLinesLabel> subtree) {
         // We simplify only annotations.
         if (!subtree.isAnnotation()) return;
 
-        final List<VariationTreeNode<L>> children = subtree.getChildren();
+        final List<VariationTreeNode<DiffLinesLabel>> children = subtree.getChildren();
 
         // When there are no children, 'subtree' is an empty annotation that can be eliminated.
         if (children.isEmpty()) {
             subtree.drop();
         }
         // When there is exactly one child and that child is an 'else' or 'elif' we can simplify that nesting.
         else if (children.size() == 1) {
-            final VariationTreeNode<L> child = children.getFirst();
+            final VariationTreeNode<DiffLinesLabel> child = children.getFirst();
 
             if ((subtree.isIf() || subtree.isElif()) && (child.isElif() || child.isElse())) {
                 // determine new feaure mapping
@@ -57,6 +92,7 @@ else if (children.size() == 1) {
                     newFormula = and(newFormula, child.getFormula());
                 }
                 subtree.setFormula(newFormula);
+                subtree.setLabel(updatedLabel(subtree.getLabel(), newFormula));
 
                 // simplify tree
                 child.drop();
@@ -66,7 +102,7 @@ else if (children.size() == 1) {
     }
 
     @Override
-    public void transform(VariationTree<L> tree) {
-        tree.forAllPostorder(this::elim);
+    public void transform(VariationTree<DiffLinesLabel> tree) {
+        tree.forAllPostorder(EliminateEmptyAlternatives::elim);
     }
 }