Merge branch 'stable-3.0' into stable-3.1

* stable-3.0:
  Switch off intraline diffs for some cases (invalid cache key sharing)
  Fix an internal server error when diffing patch sets (non-merge commit)
  Set HTTP thread name to describe the request it is processing

Change-Id: I2ec9d44bc7a9dd372e074a4030a7dd6b6d2ab657

java/com/google/gerrit/httpd/SetThreadNameFilter.java

@@ -0,0 +1,91 @@
+// Copyright (C) 2020 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.httpd;
+
+import com.google.gerrit.server.CurrentUser;
+import com.google.inject.Inject;
+import com.google.inject.Module;
+import com.google.inject.Provider;
+import com.google.inject.Singleton;
+import com.google.inject.servlet.ServletModule;
+import java.io.IOException;
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+
+@Singleton
+public class SetThreadNameFilter implements Filter {
+  private static final int MAX_PATH_LENGTH = 120;
+
+  public static Module module() {
+    return new ServletModule() {
+      @Override
+      protected void configureServlets() {
+        filter("/*").through(SetThreadNameFilter.class);
+      }
+    };
+  }
+
+  private final Provider<CurrentUser> user;
+
+  @Inject
+  public SetThreadNameFilter(Provider<CurrentUser> user) {
+    this.user = user;
+  }
+
+  @Override
+  public void init(FilterConfig filterConfig) {}
+
+  @Override
+  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
+      throws IOException, ServletException {
+    Thread current = Thread.currentThread();
+    String old = current.getName();
+    try {
+      current.setName(computeName((HttpServletRequest) request));
+      chain.doFilter(request, response);
+    } finally {
+      current.setName(old);
+    }
+  }
+
+  private String computeName(HttpServletRequest req) {
+    StringBuilder s = new StringBuilder();
+    s.append("HTTP ");
+    s.append(req.getMethod());
+    s.append(" ");
+    s.append(req.getRequestURI());
+    String query = req.getQueryString();
+    if (query != null) {
+      s.append("?").append(query);
+    }
+    if (s.length() > MAX_PATH_LENGTH) {
+      s.delete(MAX_PATH_LENGTH, s.length());
+    }
+    s.append(" (");
+    s.append(user.get().getUserName().orElse("N/A"));
+    s.append(" from ");
+    s.append(req.getRemoteAddr());
+    s.append(")");
+    return s.toString();
+  }
+
+  @Override
+  public void destroy() {}
+}

java/com/google/gerrit/httpd/init/WebAppInitializer.java

@@ -31,6 +31,7 @@ import com.google.gerrit.httpd.RequestCleanupFilter;
 import com.google.gerrit.httpd.RequestContextFilter;
 import com.google.gerrit.httpd.RequestMetricsFilter;
 import com.google.gerrit.httpd.RequireSslFilter;
+import com.google.gerrit.httpd.SetThreadNameFilter;
 import com.google.gerrit.httpd.WebModule;
 import com.google.gerrit.httpd.WebSshGlueModule;
 import com.google.gerrit.httpd.auth.oauth.OAuthModule;
@@ -383,6 +384,7 @@ public class WebAppInitializer extends GuiceServletContextListener implements Fi
     modules.add(sysInjector.getInstance(GerritAuthModule.class));
     modules.add(sysInjector.getInstance(GitOverHttpModule.class));
     modules.add(RequestCleanupFilter.module());
+    modules.add(SetThreadNameFilter.module());
     modules.add(AllRequestFilter.module());
     modules.add(sysInjector.getInstance(WebModule.class));
     modules.add(sysInjector.getInstance(RequireSslFilter.Module.class));

java/com/google/gerrit/pgm/Daemon.java

@@ -35,6 +35,7 @@ import com.google.gerrit.httpd.RequestCleanupFilter;
 import com.google.gerrit.httpd.RequestContextFilter;
 import com.google.gerrit.httpd.RequestMetricsFilter;
 import com.google.gerrit.httpd.RequireSslFilter;
+import com.google.gerrit.httpd.SetThreadNameFilter;
 import com.google.gerrit.httpd.WebModule;
 import com.google.gerrit.httpd.WebSshGlueModule;
 import com.google.gerrit.httpd.auth.oauth.OAuthModule;
@@ -547,6 +548,7 @@ public class Daemon extends SiteProgram {
     }
     modules.add(RequestCleanupFilter.module());
     modules.add(AllRequestFilter.module());
+    modules.add(SetThreadNameFilter.module());
     modules.add(sysInjector.getInstance(WebModule.class));
     modules.add(sysInjector.getInstance(RequireSslFilter.Module.class));
     modules.add(new HttpPluginModule());

java/com/google/gerrit/server/patch/PatchScriptBuilder.java

@@ -133,7 +133,7 @@ class PatchScriptBuilder {
     edits = new ArrayList<>(content.getEdits());
     ImmutableSet<Edit> editsDueToRebase = content.getEditsDueToRebase();
 
-    if (isModify(content) && diffPrefs.intralineDifference) {
+    if (isModify(content) && diffPrefs.intralineDifference && isIntralineModeAllowed(b)) {
       IntraLineDiff d =
           patchListCache.getIntraLineDiff(
               IntraLineDiffKey.create(a.id, b.id, diffPrefs.ignoreWhitespace),
@@ -267,6 +267,16 @@ class PatchScriptBuilder {
     }
   }
 
+  private static boolean isIntralineModeAllowed(Side side) {
+    // The intraline diff cache keys are the same for these cases. It's better to not show
+    // intraline results than showing completely wrong diffs or to run into a server error.
+    return !Patch.isMagic(side.path) && !isSubmoduleCommit(side.mode);
+  }
+
+  private static boolean isSubmoduleCommit(FileMode mode) {
+    return mode.getObjectType() == Constants.OBJ_COMMIT;
+  }
+
   private void correctForDifferencesInNewlineAtEnd() {
     // a.src.size() is the size ignoring a newline at the end whereas a.size() considers it.
     int aSize = a.src.size();
@@ -279,6 +289,12 @@ class PatchScriptBuilder {
       return;
     }
 
+    if (edits.isEmpty() && (aSize != bSize)) {
+      // Only edits due to rebase were present. If we now added the edits for the newlines, the
+      // code which later assembles the file contents would fail.
+      return;
+    }
+
     Optional<Edit> lastEdit = getLast(edits);
     if (isNewlineAtEndDeleted()) {
       Optional<Edit> lastLineEdit = lastEdit.filter(edit -> edit.getEndA() == aSize);

javatests/com/google/gerrit/acceptance/api/revision/RevisionDiffIT.java

@@ -17,6 +17,7 @@ package com.google.gerrit.acceptance.api.revision;
 import static com.google.common.truth.Truth.assertThat;
 import static com.google.common.truth.TruthJUnit.assume;
 import static com.google.gerrit.entities.Patch.COMMIT_MSG;
+import static com.google.gerrit.entities.Patch.MERGE_LIST;
 import static com.google.gerrit.extensions.common.testing.DiffInfoSubject.assertThat;
 import static com.google.gerrit.extensions.common.testing.FileInfoSubject.assertThat;
 import static com.google.gerrit.git.ObjectIds.abbreviateName;
@@ -41,6 +42,7 @@ import com.google.gerrit.extensions.common.ChangeType;
 import com.google.gerrit.extensions.common.DiffInfo;
 import com.google.gerrit.extensions.common.FileInfo;
 import com.google.gerrit.extensions.restapi.BinaryResult;
+import com.google.gerrit.extensions.restapi.RestApiException;
 import com.google.gerrit.testing.ConfigSuite;
 import java.awt.image.BufferedImage;
 import java.io.ByteArrayOutputStream;
@@ -400,6 +402,24 @@ public class RevisionDiffIT extends AbstractDaemonTest {
     assertThat(diff.metaB.lines).isEqualTo(1);
   }
 
+  @Test
+  public void diffBetweenPatchSetsOfMergeCommitCanBeRetrievedForCommitMessageAndMergeList()
+      throws Exception {
+    PushOneCommit.Result result = createMergeCommitChange("refs/for/master", "my_file.txt");
+    String changeId = result.getChangeId();
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    addModifiedPatchSet(changeId, "my_file.txt", content -> content.concat("Line I\nLine II\n"));
+
+    // Call both of them in succession to ensure that they don't share the same cache keys.
+    DiffInfo commitMessageDiffInfo =
+        getDiffRequest(changeId, CURRENT, COMMIT_MSG).withBase(previousPatchSetId).get();
+    DiffInfo mergeListDiffInfo =
+        getDiffRequest(changeId, CURRENT, MERGE_LIST).withBase(previousPatchSetId).get();
+
+    assertThat(commitMessageDiffInfo).content().hasSize(3);
+    assertThat(mergeListDiffInfo).content().hasSize(1);
+  }
+
   @Test
   public void diffOfUnmodifiedFileMarksAllLinesAsCommon() throws Exception {
     String filePath = "a_new_file.txt";
@@ -577,6 +597,109 @@ public class RevisionDiffIT extends AbstractDaemonTest {
     assertThat(changedFiles.get(FILE_NAME)).linesDeleted().isEqualTo(1);
   }
 
+  @Test
+  public void addedNewlineAtEndOfFileIsMarkedInDiffWhenOtherwiseOnlyEditsDueToRebaseExist()
+      throws Exception {
+    addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("Line 101"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = FILE_CONTENT.replace("Line 70\n", "Line seventy\n");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("\n"));
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_NONE)
+            .withBase(previousPatchSetId)
+            .get();
+    assertThat(diffInfo).content().element(0).commonLines().isNotEmpty();
+    assertThat(diffInfo).content().element(1).isNotNull(); // Line 70 modification
+    assertThat(diffInfo).content().element(2).commonLines().isNotEmpty();
+    assertThat(diffInfo).content().element(3).linesOfA().containsExactly("Line 101");
+    assertThat(diffInfo).content().element(3).linesOfB().containsExactly("Line 101", "");
+
+    assertThat(diffInfo).metaA().totalLineCount().isEqualTo(101);
+    assertThat(diffInfo).metaB().totalLineCount().isEqualTo(102);
+  }
+
+  @Test
+  // TODO: Fix this issue. This test documents the current behavior and ensures that we at least
+  //  don't run into an internal server error.
+  public void addedNewlineAtEndOfFileIsNotIdentifiedAsDueToRebaseEvenThoughItShould()
+      throws Exception {
+    String baseFileContent = FILE_CONTENT.concat("Line 101");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, baseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    // Add a comment so that file contents are not 'skipped'. To be able to add a comment, touch
+    // (= modify) the file in the change.
+    addModifiedPatchSet(
+        changeId, FILE_NAME, fileContent -> fileContent.replace("Line 2\n", "Line two\n"));
+    CommentInput comment = createCommentInput(3, 0, 4, 0, "Comment to not skip file content.");
+    addCommentTo(changeId, CURRENT, FILE_NAME, comment);
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = baseFileContent.concat("\n");
+    ObjectId commit3 = addCommit(commit2, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit3);
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_ALL)
+            .withBase(previousPatchSetId)
+            .get();
+    assertThat(diffInfo).content().element(0).commonLines().isNotEmpty();
+    assertThat(diffInfo).content().element(1).linesOfA().isNull();
+    assertThat(diffInfo).content().element(1).linesOfB().containsExactly("");
+    // This should actually be isDueToRebase().
+    assertThat(diffInfo).content().element(1).isNotDueToRebase();
+  }
+
+  @Test
+  public void
+      addedNewlineAtEndOfFileIsMarkedWhenEditDueToRebaseIncreasedLineCountAndWhitespaceConsidered()
+          throws Exception {
+    addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("Line 101"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = FILE_CONTENT.replace("Line 70\n", "Line 70\nLine 70.5\n");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("\n"));
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_NONE)
+            .withBase(previousPatchSetId)
+            .get();
+    assertThat(diffInfo).content().element(0).commonLines().isNotEmpty();
+    assertThat(diffInfo).content().element(1).isNotNull(); // Line 70.5 insertion
+    assertThat(diffInfo).content().element(2).commonLines().isNotEmpty();
+    assertThat(diffInfo).content().element(3).linesOfA().containsExactly("Line 101");
+    assertThat(diffInfo).content().element(3).linesOfB().containsExactly("Line 101", "");
+
+    assertThat(diffInfo).metaA().totalLineCount().isEqualTo(101);
+    assertThat(diffInfo).metaB().totalLineCount().isEqualTo(103);
+  }
+
+  @Test
+  // TODO: Fix this issue. This test documents the current behavior and ensures that we at least
+  //  don't run into an internal server error.
+  public void
+      addedNewlineAtEndOfFileIsNotMarkedWhenEditDueToRebaseIncreasedLineCountAndWhitespaceIgnoredEvenThoughItShould()
+          throws Exception {
+    addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("Line 101"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = FILE_CONTENT.replace("Line 70\n", "Line 70\nLine 70.5\n");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("\n"));
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_ALL)
+            .withBase(previousPatchSetId)
+            .get();
+    assertThat(diffInfo).content().element(0).numberOfSkippedLines().isGreaterThan(0);
+  }
+
   @Test
   public void addedLastLineWithoutNewlineBeforeAndAfterwardsIsMarkedInDiff() throws Exception {
     addModifiedPatchSet(changeId, FILE_NAME, fileContent -> fileContent.concat("Line 101"));
@@ -2374,9 +2497,7 @@ public class RevisionDiffIT extends AbstractDaemonTest {
     addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
     String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
     CommentInput comment = createCommentInput(2, 0, 3, 0, "Should be 'Line 2'.");
-    ReviewInput reviewInput = new ReviewInput();
-    reviewInput.comments = ImmutableMap.of(FILE_NAME, ImmutableList.of(comment));
-    gApi.changes().id(changeId).revision(previousPatchSetId).review(reviewInput);
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
     addModifiedPatchSet(
         changeId, FILE_NAME2, content -> content.replace("2nd line\n", "Second line\n"));
 
@@ -2394,6 +2515,112 @@ public class RevisionDiffIT extends AbstractDaemonTest {
         .inOrder();
   }
 
+  @Test
+  public void
+      diffOfFileWithOnlyRebaseHunksAndWithCommentAndConsideringWhitespaceReturnsFileContents()
+          throws Exception {
+    addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = FILE_CONTENT.replace("Line 70\n", "Line seventy\n");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    CommentInput comment = createCommentInput(2, 0, 3, 0, "Should be 'Line 2'.");
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withBase(previousPatchSetId)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_NONE)
+            .get();
+    // We don't list the full file contents here as that is not the focus of this test.
+    assertThat(diffInfo)
+        .content()
+        .element(0)
+        .commonLines()
+        .containsAtLeast("Line 1", "Line two", "Line 3", "Line 4", "Line 5")
+        .inOrder();
+  }
+
+  @Test
+  public void diffOfFileWithOnlyRebaseHunksAndWithCommentAndIgnoringWhitespaceReturnsFileContents()
+      throws Exception {
+    addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = FILE_CONTENT.replace("Line 70\n", "Line seventy\n");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    CommentInput comment = createCommentInput(2, 0, 3, 0, "Should be 'Line 2'.");
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withBase(previousPatchSetId)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_ALL)
+            .get();
+    // We don't list the full file contents here as that is not the focus of this test.
+    assertThat(diffInfo)
+        .content()
+        .element(0)
+        .commonLines()
+        .containsAtLeast("Line 1", "Line two", "Line 3", "Line 4", "Line 5")
+        .inOrder();
+  }
+
+  @Test
+  public void
+      diffOfFileWithMultilineRebaseHunkAddingNewlineAtEndOfFileAndWithCommentReturnsFileContents()
+          throws Exception {
+    String baseFileContent = FILE_CONTENT.concat("Line 101");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, baseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = baseFileContent.concat("\nLine 102\nLine 103\n");
+    ObjectId commit3 = addCommit(commit2, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit3);
+    CommentInput comment = createCommentInput(2, 0, 3, 0, "Should be 'Line 2'.");
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withBase(previousPatchSetId)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_NONE)
+            .get();
+    // We don't list the full file contents here as that is not the focus of this test.
+    assertThat(diffInfo)
+        .content()
+        .element(0)
+        .commonLines()
+        .containsAtLeast("Line 1", "Line two", "Line 3", "Line 4", "Line 5")
+        .inOrder();
+  }
+
+  @Test
+  public void
+      diffOfFileWithMultilineRebaseHunkRemovingNewlineAtEndOfFileAndWithCommentReturnsFileContents()
+          throws Exception {
+    addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
+    String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
+    String newBaseFileContent = FILE_CONTENT.concat("Line 101\nLine 103\nLine 104");
+    ObjectId commit2 = addCommit(commit1, FILE_NAME, newBaseFileContent);
+    rebaseChangeOn(changeId, commit2);
+    CommentInput comment = createCommentInput(2, 0, 3, 0, "Should be 'Line 2'.");
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
+
+    DiffInfo diffInfo =
+        getDiffRequest(changeId, CURRENT, FILE_NAME)
+            .withBase(previousPatchSetId)
+            .withWhitespace(DiffPreferencesInfo.Whitespace.IGNORE_NONE)
+            .get();
+    // We don't list the full file contents here as that is not the focus of this test.
+    assertThat(diffInfo)
+        .content()
+        .element(0)
+        .commonLines()
+        .containsAtLeast("Line 1", "Line two", "Line 3", "Line 4", "Line 5")
+        .inOrder();
+  }
+
   @Test
   public void diffOfNonExistentFileIsAnEmptyDiffResult() throws Exception {
     addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
@@ -2432,9 +2659,7 @@ public class RevisionDiffIT extends AbstractDaemonTest {
         changeId, FILE_NAME, content -> content.replace("Line 20\n", "Line twenty\n"));
     String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
     CommentInput comment = createCommentInput(20, 0, 21, 0, "Should be 'Line 20'.");
-    ReviewInput reviewInput = new ReviewInput();
-    reviewInput.comments = ImmutableMap.of(FILE_NAME, ImmutableList.of(comment));
-    gApi.changes().id(changeId).revision(previousPatchSetId).review(reviewInput);
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
     addModifiedPatchSet(
         changeId, FILE_NAME2, content -> content.replace("2nd line\n", "Second line\n"));
 
@@ -2476,9 +2701,7 @@ public class RevisionDiffIT extends AbstractDaemonTest {
     addModifiedPatchSet(changeId, FILE_NAME, content -> content.replace("Line 2\n", "Line two\n"));
     String previousPatchSetId = gApi.changes().id(changeId).get().currentRevision;
     CommentInput comment = createCommentInput(2, 0, 3, 0, "Should be 'Line 2'.");
-    ReviewInput reviewInput = new ReviewInput();
-    reviewInput.comments = ImmutableMap.of(FILE_NAME, ImmutableList.of(comment));
-    gApi.changes().id(changeId).revision(previousPatchSetId).review(reviewInput);
+    addCommentTo(changeId, previousPatchSetId, FILE_NAME, comment);
     String newFilePath = "a_new_file.txt";
     gApi.changes().id(changeId).edit().renameFile(FILE_NAME, newFilePath);
     gApi.changes().id(changeId).edit().publish();
@@ -2507,6 +2730,14 @@ public class RevisionDiffIT extends AbstractDaemonTest {
     return comment;
   }
 
+  private void addCommentTo(
+      String changeId, String previousPatchSetId, String fileName, CommentInput comment)
+      throws RestApiException {
+    ReviewInput reviewInput = new ReviewInput();
+    reviewInput.comments = ImmutableMap.of(fileName, ImmutableList.of(comment));
+    gApi.changes().id(changeId).revision(previousPatchSetId).review(reviewInput);
+  }
+
   private void assertDiffForNewFile(
       PushOneCommit.Result pushResult, String path, String expectedContentSideB) throws Exception {
     DiffInfo diff =