Use a BufferedReader to parse diff trees

By using `BufferedReader`s all the platform dependent line endings are
handled automatically. This also reduces space usage if the input is
read from a file, because not all lines are duplicated in memory at the
same time.

Call sites which generate a `String` and have to use `StringReader` are
subject to future refactoring.

Author: ibbem

src/main/java/org/variantsync/diffdetective/diff/difftree/DiffTree.java

@@ -8,9 +8,10 @@
 import org.variantsync.diffdetective.diff.difftree.traverse.DiffTreeVisitor;
 import org.variantsync.diffdetective.diff.result.DiffResult;
 import org.variantsync.diffdetective.util.Assert;
-import org.variantsync.diffdetective.util.IO;
 
+import java.io.BufferedReader;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -48,10 +49,11 @@ public static DiffResult<DiffTree> fromDiff(final String diff, boolean collapseM
     }
 
     public static DiffResult<DiffTree> fromFile(final Path p, boolean collapseMultipleCodeLines, boolean ignoreEmptyLines, final DiffNodeParser annotationParser) throws IOException {
-        final String fullDiff = IO.readAsString(p);
-        final DiffResult<DiffTree> tree = DiffTreeParser.createDiffTree(fullDiff, collapseMultipleCodeLines, ignoreEmptyLines, annotationParser);
-        tree.unwrap().ifSuccess(t -> t.setSource(new PatchFile(p)));
-        return tree;
+        try (BufferedReader file = Files.newBufferedReader(p)) {
+            final DiffResult<DiffTree> tree = DiffTreeParser.createDiffTree(file, collapseMultipleCodeLines, ignoreEmptyLines, annotationParser);
+            tree.unwrap().ifSuccess(t -> t.setSource(new PatchFile(p)));
+            return tree;
+        }
     }
 
     public static DiffResult<DiffTree> fromDiff(final String diff, boolean collapseMultipleCodeLines, boolean ignoreEmptyLines, final DiffNodeParser annotationParser) {

src/main/java/org/variantsync/diffdetective/diff/difftree/parse/DiffTreeParser.java

@@ -17,7 +17,9 @@
 import org.variantsync.diffdetective.util.Assert;
 import org.variantsync.diffdetective.util.StringUtils;
 
+import java.io.BufferedReader;
 import java.io.IOException;
+import java.io.StringReader;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Stack;
@@ -46,8 +48,19 @@ public static DiffResult<DiffTree> createDiffTree(
             boolean ignoreEmptyLines,
             DiffNodeParser nodeParser)
     {
-        final String[] fullDiffLines = fullDiff.split(LINEBREAK_REGEX);
+        try {
+            return createDiffTree(new BufferedReader(new StringReader(fullDiff)), collapseMultipleCodeLines, ignoreEmptyLines, nodeParser);
+        } catch (IOException e) {
+            throw new AssertionError("No actual IO should be performed, because only a StringReader is used");
+        }
+    }
 
+    public static DiffResult<DiffTree> createDiffTree(
+            BufferedReader fullDiff,
+            boolean collapseMultipleCodeLines,
+            boolean ignoreEmptyLines,
+            DiffNodeParser nodeParser) throws IOException
+    {
         final List<DiffNode> nodes = new ArrayList<>();
         final Stack<DiffNode> beforeStack = new Stack<>();
         final Stack<DiffNode> afterStack = new Stack<>();
@@ -68,8 +81,9 @@ public static DiffResult<DiffTree> createDiffTree(
         beforeStack.push(root);
         afterStack.push(root);
 
-        for (int i = 0; i < fullDiffLines.length; i++) {
-            final String currentLine = fullDiffLines[i];
+        String line;
+        for (int i = 0; (line = fullDiff.readLine()) != null; i++) {
+            final String currentLine = line; // Has to be final, because it's used in a lambda.
             final DiffType diffType = DiffType.ofDiffLine(currentLine);
 
             // count line numbers

src/test/java/TestMultiLineMacros.java

@@ -15,20 +15,23 @@
 import org.variantsync.diffdetective.util.StringUtils;
 import org.variantsync.functjonal.Pair;
 
+import java.io.BufferedReader;
 import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
 
 public class TestMultiLineMacros {
     private static final Path resDir = Constants.RESOURCE_DIR.resolve("multilinemacros");
 
     public void diffToDiffTree(DiffTreeLineGraphExportOptions exportOptions, Path p) throws IOException {
-        final String fullDiff = IO.readAsString(p);
-
-        final DiffTree tree = DiffTreeParser.createDiffTree(
-                fullDiff,
-                true,
-                true,
-                DiffNodeParser.Default).unwrap().getSuccess();
+        DiffTree tree;
+        try (BufferedReader fullDiff = Files.newBufferedReader(p)) {
+            tree = DiffTreeParser.createDiffTree(
+                    fullDiff,
+                    true,
+                    true,
+                    DiffNodeParser.Default).unwrap().getSuccess();
+        }
 
         final Pair<DiffTreeSerializeDebugData, String> result = LineGraphExport.toLineGraphFormat(tree, exportOptions);
         Assert.assertNotNull(result);