IntraLineLoader: Add unit-tests

In order to reproduce issue #3423, add some unit-tests for the server-side
intra-line diff calculation.

The following test cases document the expected behavior and are
currently failing:

 * preferInsertAtLineBreak2,
 * preferDeleteAtLineBreak,
 * insertedWhitespaceIsRecognizedInIdenticalLines

They are annotated with @Test(expected = AssertionError) to mark them as
expected failure.

Bug: Issue 3423
Change-Id: Icbee1fb4cd14ee8981b0f6a4ec18f65b3bd141fa

gerrit-server/BUCK

@@ -193,6 +193,7 @@ java_test(
     ':testutil',
     '//gerrit-antlr:query_exception',
     '//gerrit-common:annotations',
+    '//gerrit-patch-jgit:server',
     '//gerrit-server/src/main/prolog:common',
     '//lib:args4j',
     '//lib:grappa',

gerrit-server/src/test/java/com/google/gerrit/server/patch/IntraLineLoaderTest.java

@@ -0,0 +1,226 @@
+// Copyright (C) 2016 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.server.patch;
+
+import static com.google.common.truth.Truth.assertThat;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import java.util.List;
+
+import org.eclipse.jgit.diff.Edit;
+import org.eclipse.jgit.diff.EditList;
+import org.eclipse.jgit.diff.ReplaceEdit;
+
+import org.junit.Test;
+
+public class IntraLineLoaderTest {
+
+  @Test
+  public void rewriteAtStartOfLineIsRecognized() throws Exception {
+    String a = "abc1\n";
+    String b = "def1\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .replace("abc", "def").common("1\n").edits
+    );
+  }
+
+  @Test
+  public void rewriteAtEndOfLineIsRecognized() throws Exception {
+    String a = "abc1\n";
+    String b = "abc2\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .common("abc").replace("1", "2").common("\n").edits
+    );
+  }
+
+  @Test
+  public void completeRewriteIncludesNewline() throws Exception {
+    String a = "abc1\n";
+    String b = "def2\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .replace("abc1\n", "def2\n").edits
+    );
+  }
+
+  @Test
+  public void closeEditsAreCombined() throws Exception {
+    String a = "ab1cdef2gh\n";
+    String b = "ab2cdef3gh\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .common("ab").replace("1cdef2", "2cdef3").common("gh\n").edits
+    );
+  }
+
+  @Test
+  public void preferInsertAfterCommonPart1() throws Exception {
+    String a = "start middle end\n";
+    String b = "start middlemiddle end\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .common("start middle").insert("middle").common(" end\n").edits
+    );
+  }
+
+  @Test
+  public void preferInsertAfterCommonPart2() throws Exception {
+    String a = "abc def\n";
+    String b = "abc  def\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .common("abc ").insert(" ").common("def\n").edits
+    );
+  }
+
+  @Test
+  public void preferInsertAtLineBreak1() throws Exception {
+    String a = "multi\nline\n";
+    String b = "multi\nlinemulti\nline\n";
+    assertThat(intraline(a, b)).isEqualTo(wordEdit(10, 10, 6, 16));
+    // better would be:
+    //assertThat(intraline(a, b)).isEqualTo(wordEdit(6, 6, 6, 16));
+    // or the equivalent:
+    //assertThat(intraline(a, b)).isEqualTo(ref()
+    //    .common("multi\n").insert("linemulti\n").common("line\n").edits
+    //);
+  }
+
+  //TODO: expected failure
+  // the current code does not work on the first line
+  // and the insert marker is in the wrong location
+  @Test(expected = AssertionError.class)
+  public void preferInsertAtLineBreak2() throws Exception {
+    String a = "  abc\n    def\n";
+    String b = "    abc\n      def\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .insert("  ").common("  abc\n")
+        .insert("  ").common("  def\n").edits
+    );
+  }
+
+  //TODO: expected failure
+  // the current code does not work on the first line
+  @Test(expected = AssertionError.class)
+  public void preferDeleteAtLineBreak() throws Exception {
+    String a = "    abc\n      def\n";
+    String b = "  abc\n    def\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .remove("  ").common("  abc\n")
+        .remove("  ").common("  def\n").edits
+    );
+  }
+
+  @Test
+  public void insertedWhitespaceIsRecognized() throws Exception {
+    String a = " int *foobar\n";
+    String b = " int * foobar\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .common(" int *").insert(" ").common("foobar\n").edits
+    );
+  }
+
+  //TODO: expected failure, issue #3423
+  // The current code wrongly marks the first space of the second line,
+  // instead of the one inserted after the '*'.
+  @Test(expected = AssertionError.class)
+  public void insertedWhitespaceIsRecognizedInMultipleLines() throws Exception {
+    //         |0    5   10  |  5   20    5   30
+    String a = " int *foobar\n int *foobar\n";
+    String b = " int * foobar\n int * foobar\n";
+    assertThat(intraline(a, b)).isEqualTo(ref()
+        .common(" int *").insert(" ").common("foobar\n")
+        .common(" int *").insert(" ").common("foobar\n").edits
+    );
+  }
+
+  // helper functions to call IntraLineLoader.compute
+
+  private static int countLines(String s) {
+    int count = 0;
+    for (int i = 0; i < s.length(); i++) {
+      if (s.charAt(i) == '\n') {
+        count++;
+      }
+    }
+    return count;
+  }
+
+  private static List<Edit> intraline(String a, String b) throws Exception {
+    return intraline(a, b, new Edit(0, countLines(a), 0, countLines(b)));
+  }
+
+  private static List<Edit> intraline(String a, String b, Edit lines)
+      throws Exception {
+    Text aText = new Text(a.getBytes(UTF_8));
+    Text bText = new Text(b.getBytes(UTF_8));
+
+    IntraLineDiff diff;
+    diff = IntraLineLoader.compute(aText, bText, EditList.singleton(lines));
+
+    assertThat(diff.getStatus()).isEqualTo(IntraLineDiff.Status.EDIT_LIST);
+    List<Edit> actualEdits = diff.getEdits();
+    assertThat(actualEdits).hasSize(1);
+    Edit actualEdit = actualEdits.get(0);
+    assertThat(actualEdit.getBeginA()).isEqualTo(lines.getBeginA());
+    assertThat(actualEdit.getEndA()).isEqualTo(lines.getEndA());
+    assertThat(actualEdit.getBeginB()).isEqualTo(lines.getBeginB());
+    assertThat(actualEdit.getEndB()).isEqualTo(lines.getEndB());
+    assertThat(actualEdit).isInstanceOf(ReplaceEdit.class);
+
+    return ((ReplaceEdit) actualEdit).getInternalEdits();
+  }
+
+  // helpers to compute reference values
+
+  private static List<Edit> wordEdit(int as, int ae, int bs, int be) {
+    return EditList.singleton(new Edit(as, ae, bs, be));
+  }
+
+  private static Reference ref() {
+    return new Reference();
+  }
+
+  private static class Reference {
+    List<Edit> edits;
+    private int posA;
+    private int posB;
+
+    Reference() {
+      edits = new EditList();
+      posA = posB = 0;
+    }
+
+    Reference common(String s) {
+      int len = s.length();
+      posA += len;
+      posB += len;
+      return this;
+    }
+
+    Reference insert(String s) {
+      return replace("", s);
+    }
+
+    Reference remove(String s) {
+      return replace(s, "");
+    }
+
+    Reference replace(String a, String b) {
+      int lenA = a.length();
+      int lenB = b.length();
+      edits.add(new Edit(posA, posA + lenA, posB, posB + lenB));
+      posA += lenA;
+      posB += lenB;
+      return this;
+    }
+  }
+}