Allow file annotations (blame) in side-by-side diff

Using CodeMirror's lint addon on the UI to display the blame
annotations. It works on both sides of the side-by-side
diff and also supports the auto-merge commit. It requires manual
step to enable the annotations to avoid any unnecessary git
processing and network traffic between the server and client.

Introduces a new dependency on blame-cache in gerrit-server
to reuse BlameCache.

In a following change, the gutter showing the blame info will be
made clickable. Clicking on the gutter will open a new tab that
takes the user to the corresponding change in Gerrit.

The commit SHA-1 hashes are currently not selectable. Making it
so might require an upstream change in CodeMirror's lint addon.

Bug: Issue 1642
Change-Id: I6267d30cbee448f8137e11c7120959dc424eaeeb

Documentation/config-gerrit.txt

@@ -915,6 +915,12 @@ If 0 the update polling is disabled.
 +
 Default is 30 seconds.
 
+[[change.allowBlame]]change.allowBlame::
++
+Allow blame on side by side diff. If set to false, blame cannot be used.
++
+Default is true.
+
 [[change.allowDrafts]]change.allowDrafts::
 +
 Allow drafts workflow. If set to false, drafts cannot be created,

Documentation/rest-api-changes.txt

@@ -3753,6 +3753,66 @@ differences are reported in the result.  Valid values are `IGNORE_NONE`,
 The `context` parameter can be specified to control the number of lines of surrounding context
 in the diff.  Valid values are `ALL` or number of lines.
 
+[[get-blame]]
+=== Get Blame
+--
+'GET /changes/link:#change-id[\{change-id\}]/revisions/link:#revision-id[\{revision-id\}]/files/link:#file-id[\{file-id\}]/blame'
+--
+
+Gets the blame of a file from a certain revision.
+
+.Request
+----
+  GET /changes/myProject~master~I8473b95934b5732ac55d26311a706c9c2bde9940/revisions/674ac754f91e64a0efb8087e59a176484bd534d1/files/gerrit-server%2Fsrc%2Fmain%2Fjava%2Fcom%2Fgoogle%2Fgerrit%2Fserver%2Fproject%2FRefControl.java/blame HTTP/1.0
+----
+
+As response a link:#blame-info[BlameInfo] entity is returned that describes the
+blame.
+
+.Response
+----
+  HTTP/1.1 200 OK
+  Content-Disposition: attachment
+  Content-Type: application/json; charset=UTF-8
+
+  )]
+  {
+    [
+      {
+        "author": "Joe Daw",
+        "id": "64e140b4de5883a4dd74d06c2b62ccd7ffd224a7",
+        "time": 1421441349,
+        "commit_msg": "RST test\n\nChange-Id: I11e9e24bd122253f4bb10c36dce825ac2410d646\n",
+        "ranges": [
+          {
+            "start": 1,
+            "end": 10
+          },
+          {
+            "start": 16,
+            "end": 296
+          }
+        ]
+      },
+      {
+        "author": "Jane Daw",
+        "id": "8d52621a0e2ac6adec73bd3a49f2371cd53137a7",
+        "time": 1421825421,
+        "commit_msg": "add banner\n\nChange-Id: I2eced9b2691015ae3c5138f4d0c4ca2b8fb15be9\n",
+        "ranges": [
+          {
+            "start": 13,
+            "end": 13
+          }
+        ]
+      }
+    ]
+  }
+----
+
+The `base` parameter can be specified to control the base patch set from which
+the blame should be generated.
+
 [[set-reviewed]]
 === Set Reviewed
 --
@@ -3978,6 +4038,22 @@ NOTE: To apply different tags on on different votes/comments multiple
 invocations of the REST call are required.
 |===========================
 
+[[blame-info]]
+=== BlameInfo
+The `BlameInfo` entity stores the commit metadata with the row coordinates where
+it applies.
+
+[options="header",cols="1,6"]
+|===========================
+|Field Name | Description
+|`author`     | The author of the commit.
+|`id`         | The id of the commit.
+|`time`       | Commit time.
+|`commit_msg` | The commit message.
+|`ranges`     |
+The blame row coordinates as link:#range-info[RangeInfo] entities.
+|===========================
+
 [[change-edit-input]]
 === ChangeEditInput
 The `ChangeEditInput` entity contains information for restoring a
@@ -4637,6 +4713,17 @@ found while checking the signature or the key itself, as a
 link:rest-api-accounts.html#gpg-key-info[GpgKeyInfo] entity.
 |===========================
 
+[[range-info]]
+=== RangeInfo
+The `RangeInfo` entity stores the coordinates of a range.
+
+[options="header",cols="1,6"]
+|===========================
+|Field Name   | Description
+|`start`      | First index.
+|`end`        | Last index.
+|===========================
+
 [[rebase-input]]
 === RebaseInput
 The `RebaseInput` entity contains information for changing parent when rebasing.

Documentation/rest-api-config.txt

@@ -1076,6 +1076,9 @@ section.
 [options="header",cols="1,^1,5"]
 |=============================
 |Field Name           ||Description
+|`allow_blame`        |not set if `false`|
+link:config-gerrit.html#change.allowBlame[Whether blame on side by side diff is
+allowed].
 |`allow_drafts`       |not set if `false`|
 link:config-gerrit.html#change.allowDrafts[Whether draft workflow is
 allowed].

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/BlameInfo.java

@@ -0,0 +1,43 @@
+// Copyright (C) 2015 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.extensions.common;
+
+import java.util.List;
+
+public class BlameInfo {
+  public String author;
+  public String id;
+  public int time;
+  public String commitMsg;
+  public List<RangeInfo> ranges;
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (o == null || getClass() != o.getClass()) {
+      return false;
+    }
+    BlameInfo blameInfo = (BlameInfo) o;
+
+    return id.equals(blameInfo.id);
+  }
+
+  @Override
+  public int hashCode() {
+    return id.hashCode();
+  }
+}

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/RangeInfo.java

@@ -0,0 +1,25 @@
+// 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.extensions.common;
+
+public class RangeInfo {
+  public int start;
+  public int end;
+
+  public RangeInfo(int start, int end) {
+    this.start = start;
+    this.end = end;
+  }
+}

gerrit-gwtui-common/src/main/java/com/google/gerrit/client/Resources.java

@@ -42,6 +42,9 @@ public interface Resources extends ClientBundle {
   @Source("resultset_up_gray.png")
   ImageResource arrowUp();
 
+  @Source("lightbulb.png")
+  ImageResource blame();
+
   @Source("page_white_put.png")
   ImageResource downloadIcon();
 

gerrit-gwtui-common/src/main/java/com/google/gerrit/client/info/ServerInfo.java

@@ -56,6 +56,7 @@ public class ServerInfo extends JavaScriptObject {
 
   public static class ChangeConfigInfo extends JavaScriptObject {
     public final native boolean allowDrafts() /*-{ return this.allow_drafts || false; }-*/;
+    public final native boolean allowBlame() /*-{ return this.allow_blame || false; }-*/;
     public final native int largeChange() /*-{ return this.large_change || 0; }-*/;
     public final native String replyLabel() /*-{ return this.reply_label; }-*/;
     public final native String replyTooltip() /*-{ return this.reply_tooltip; }-*/;

gerrit-gwtui/src/main/java/com/google/gerrit/client/RangeInfo.java

@@ -0,0 +1,26 @@
+// 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.client;
+
+import com.google.gwt.core.client.JavaScriptObject;
+
+public class RangeInfo extends JavaScriptObject {
+  public final native int start() /*-{ return this.start; }-*/;
+
+  public final native int end() /*-{ return this.end; }-*/;
+
+  protected RangeInfo() {
+  }
+}

gerrit-gwtui/src/main/java/com/google/gerrit/client/blame/BlameInfo.java

@@ -0,0 +1,31 @@
+// Copyright (C) 2015 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.client.blame;
+
+import com.google.gerrit.client.RangeInfo;
+import com.google.gwt.core.client.JavaScriptObject;
+import com.google.gwt.core.client.JsArray;
+
+public class BlameInfo extends JavaScriptObject {
+  public final native String author() /*-{ return this.author; }-*/;
+  public final native String id() /*-{ return this.id; }-*/;
+  public final native String commitMsg() /*-{ return this.commit_msg; }-*/;
+  public final native int time() /*-{ return this.time; }-*/;
+  public final native JsArray<RangeInfo> ranges() /*-{ return this.ranges; }-*/;
+
+  protected BlameInfo() {
+  }
+
+}

gerrit-gwtui/src/main/java/com/google/gerrit/client/changes/ChangeApi.java

@@ -97,6 +97,14 @@ public class ChangeApi {
     return call(id, "detail");
   }
 
+  public static RestApi blame(PatchSet.Id id, String path, boolean base) {
+    return revision(id)
+        .view("files")
+        .id(path)
+        .view("blame")
+        .addParameter("base", base);
+  }
+
   public static RestApi actions(int id, String revision) {
     if (revision == null || revision.equals("")) {
       revision = "current";

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DiffTable.java

@@ -98,6 +98,16 @@ abstract class DiffTable extends Composite {
     return changeType;
   }
 
+  void setUpBlameIconA(CodeMirror cm, boolean isBase, PatchSet.Id rev,
+      String path) {
+    patchSetSelectBoxA.setUpBlame(cm, isBase, rev, path);
+  }
+
+  void setUpBlameIconB(CodeMirror cm, PatchSet.Id rev,
+      String path) {
+    patchSetSelectBoxB.setUpBlame(cm, false, rev, path);
+  }
+
   void set(DiffPreferences prefs, JsArray<RevisionInfo> list, DiffInfo info,
       boolean editExists, boolean current, boolean open, boolean binary) {
     this.changeType = info.changeType();

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PatchSetSelectBox.java

@@ -16,9 +16,12 @@ package com.google.gerrit.client.diff;
 
 import com.google.gerrit.client.Dispatcher;
 import com.google.gerrit.client.Gerrit;
+import com.google.gerrit.client.blame.BlameInfo;
+import com.google.gerrit.client.changes.ChangeApi;
 import com.google.gerrit.client.info.ChangeInfo.RevisionInfo;
 import com.google.gerrit.client.info.WebLinkInfo;
 import com.google.gerrit.client.patches.PatchUtil;
+import com.google.gerrit.client.rpc.GerritCallback;
 import com.google.gerrit.client.rpc.Natives;
 import com.google.gerrit.client.ui.InlineHyperlink;
 import com.google.gerrit.reviewdb.client.Change;
@@ -27,6 +30,7 @@ import com.google.gerrit.reviewdb.client.PatchSet;
 import com.google.gwt.core.client.GWT;
 import com.google.gwt.core.client.JsArray;
 import com.google.gwt.event.dom.client.ClickEvent;
+import com.google.gwt.event.dom.client.ClickHandler;
 import com.google.gwt.resources.client.CssResource;
 import com.google.gwt.uibinder.client.UiBinder;
 import com.google.gwt.uibinder.client.UiField;
@@ -38,6 +42,7 @@ import com.google.gwt.user.client.ui.Image;
 import com.google.gwt.user.client.ui.ImageResourceRenderer;
 import com.google.gwt.user.client.ui.Widget;
 import com.google.gwtorm.client.KeyUtil;
+import net.codemirror.lib.CodeMirror;
 
 import java.util.List;
 
@@ -124,6 +129,32 @@ class PatchSetSelectBox extends Composite {
     }
   }
 
+  void setUpBlame(final CodeMirror cm, final boolean isBase,
+      final PatchSet.Id rev, final String path) {
+    if (!Patch.COMMIT_MSG.equals(path) && Gerrit.isSignedIn()
+        && Gerrit.info().change().allowBlame()) {
+      Anchor blameIcon = createBlameIcon();
+      blameIcon.addClickHandler(new ClickHandler() {
+        @Override
+        public void onClick(ClickEvent clickEvent) {
+          if (cm.extras().getBlameInfo() != null) {
+            cm.extras().toggleAnnotation();
+          } else {
+            ChangeApi.blame(rev, path, isBase)
+              .get(new GerritCallback<JsArray<BlameInfo>>() {
+
+                @Override
+                public void onSuccess(JsArray<BlameInfo> lines) {
+                  cm.extras().toggleAnnotation(lines);
+                }
+              });
+          }
+        }
+      });
+      linkPanel.add(blameIcon);
+    }
+  }
+
   private Widget createEditIcon() {
     PatchSet.Id id = (idActive == null) ? other.idActive : idActive;
     Anchor anchor = new Anchor(
@@ -133,6 +164,13 @@ class PatchSetSelectBox extends Composite {
     return anchor;
   }
 
+  private Anchor createBlameIcon() {
+    Anchor anchor = new Anchor(
+        new ImageResourceRenderer().render(Gerrit.RESOURCES.blame()));
+    anchor.setTitle(PatchUtil.C.blame());
+    return anchor;
+  }
+
   static void link(PatchSetSelectBox a, PatchSetSelectBox b) {
     a.other = b;
     b.other = a;

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/SideBySide.java

@@ -192,6 +192,11 @@ public class SideBySide extends DiffScreen {
     cmA = newCm(diff.metaA(), diff.textA(), diffTable.cmA);
     cmB = newCm(diff.metaB(), diff.textB(), diffTable.cmB);
 
+    boolean reviewingBase = base == null;
+    getDiffTable().setUpBlameIconA(cmA, reviewingBase,
+        reviewingBase ? revision : base, path);
+    getDiffTable().setUpBlameIconB(cmB, revision, path);
+
     cmA.extras().side(DisplaySide.A);
     cmB.extras().side(DisplaySide.B);
     setShowTabs(prefs.showTabs());

gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchConstants.java

@@ -54,6 +54,7 @@ public interface PatchConstants extends Constants {
 
   String download();
   String edit();
+  String blame();
   String addFileCommentToolTip();
 
   String cannedReplyDone();

gerrit-gwtui/src/main/java/com/google/gerrit/client/patches/PatchConstants.properties

@@ -37,6 +37,7 @@ nextFileHelp = Next file
 
 download = Download
 edit = Edit
+blame = Blame
 addFileCommentToolTip = Click to add file comment
 
 sideBySideDiff = Side-by-side diff

gerrit-gwtui/src/main/java/net/codemirror/lib/BlameConfig.java

@@ -0,0 +1,23 @@
+// 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 net.codemirror.lib;
+
+import com.google.gwt.i18n.client.Messages;
+
+public interface BlameConfig extends Messages {
+  String shortBlameMsg(String commitId, String date, String author);
+  String detailedBlameMsg(String commitId, String author, String time,
+      String msg);
+}

gerrit-gwtui/src/main/java/net/codemirror/lib/BlameConfig.properties

@@ -0,0 +1,2 @@
+shortBlameMsg={0} {1} {2}
+detailedBlameMsg=commit {0}\nAuthor: {1}\nDate: {2}\n\n{3}

gerrit-gwtui/src/main/java/net/codemirror/lib/Extras.java

@@ -19,16 +19,30 @@ import static com.google.gwt.dom.client.Style.Unit.PX;
 import static net.codemirror.lib.CodeMirror.style;
 import static net.codemirror.lib.CodeMirror.LineClassWhere.WRAP;
 
+import com.google.gerrit.client.FormatUtil;
+import com.google.gerrit.client.RangeInfo;
+import com.google.gerrit.client.blame.BlameInfo;
 import com.google.gerrit.client.diff.DisplaySide;
+import com.google.gerrit.client.rpc.Natives;
+import com.google.gwt.core.client.GWT;
+import com.google.gwt.core.client.JavaScriptObject;
+import com.google.gwt.core.client.JsArray;
+import com.google.gwt.core.client.JsArrayString;
 import com.google.gwt.dom.client.Element;
+import com.google.gwt.i18n.client.DateTimeFormat;
 import com.google.gwt.user.client.DOM;
 
 import net.codemirror.lib.CodeMirror.LineHandle;
 
+import java.util.Date;
 import java.util.Objects;
 
 /** Additional features added to CodeMirror by Gerrit Code Review. */
 public class Extras {
+  public static final String ANNOTATION_GUTTER_ID = "CodeMirror-lint-markers";
+
+  static final BlameConfig C = GWT.create(BlameConfig.class);
+
   static final native Extras get(CodeMirror c) /*-{ return c.gerritExtras }-*/;
   private static native void set(CodeMirror c, Extras e)
   /*-{ c.gerritExtras = e }-*/;
@@ -43,6 +57,7 @@ public class Extras {
   private double charWidthPx;
   private double lineHeightPx;
   private LineHandle activeLine;
+  private boolean annotated;
 
   private Extras(CodeMirror cm) {
     this.cm = cm;
@@ -140,4 +155,68 @@ public class Extras {
       activeLine = null;
     }
   }
+
+  public boolean isAnnotated() {
+    return annotated;
+  }
+
+  public final void clearAnnotations() {
+    JsArrayString gutters = ((JsArrayString) JsArrayString.createArray());
+    cm.setOption("gutters", gutters);
+    annotated = false;
+  }
+
+  public final void setAnnotations(JsArray<BlameInfo> blameInfos) {
+    if (blameInfos.length() > 0) {
+      setBlameInfo(blameInfos);
+      JsArrayString gutters = ((JsArrayString) JsArrayString.createArray());
+      gutters.push(ANNOTATION_GUTTER_ID);
+      cm.setOption("gutters", gutters);
+      annotated = true;
+      DateTimeFormat format = DateTimeFormat.getFormat(
+          DateTimeFormat.PredefinedFormat.DATE_SHORT);
+      JsArray<LintLine> annotations = JsArray.createArray().cast();
+      for (BlameInfo blameInfo : Natives.asList(blameInfos)) {
+        for (RangeInfo range : Natives.asList(blameInfo.ranges())) {
+          Date commitTime = new Date(blameInfo.time() * 1000L);
+          String shortId = blameInfo.id().substring(0, 8);
+          String shortBlame = C.shortBlameMsg(
+              shortId, format.format(commitTime), blameInfo.author());
+          String detailedBlame = C.detailedBlameMsg(blameInfo.id(),
+              blameInfo.author(), FormatUtil.mediumFormat(commitTime),
+              blameInfo.commitMsg());
+
+          annotations.push(LintLine.create(shortBlame, detailedBlame, shortId,
+              Pos.create(range.start() - 1)));
+        }
+      }
+      cm.setOption("lint", getAnnotation(annotations));
+    }
+  }
+
+  private native JavaScriptObject getAnnotation(JsArray<LintLine> annotations) /*-{
+     return {
+        getAnnotations: function(text, options, cm) { return annotations; }
+     };
+  }-*/;
+
+  public final native JsArray<BlameInfo> getBlameInfo() /*-{
+    return this.blameInfos;
+  }-*/;
+
+  public final native void setBlameInfo(JsArray<BlameInfo> blameInfos) /*-{
+    this['blameInfos'] = blameInfos;
+  }-*/;
+
+  public final void toggleAnnotation() {
+    toggleAnnotation(getBlameInfo());
+  }
+
+  public final void toggleAnnotation(JsArray<BlameInfo> blameInfos) {
+    if (isAnnotated()) {
+      clearAnnotations();
+    } else {
+      setAnnotations(blameInfos);
+    }
+  }
 }

gerrit-gwtui/src/main/java/net/codemirror/lib/LintLine.java

@@ -0,0 +1,54 @@
+// 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 net.codemirror.lib;
+
+import com.google.gwt.core.client.JavaScriptObject;
+import com.google.gwt.dom.client.StyleInjector;
+
+public class LintLine extends JavaScriptObject {
+  public static LintLine create(String shortMsg, String msg, String sev,
+      Pos line) {
+    StyleInjector.inject(".CodeMirror-lint-marker-" + sev + " {\n"
+        + "  visibility: hidden;\n"
+        + "  text-overflow: ellipsis;\n"
+        + "  white-space: nowrap;\n"
+        + "  overflow: hidden;\n"
+        + "  position: relative;\n"
+        + "}\n"
+        + ".CodeMirror-lint-marker-" + sev + ":after {\n"
+        + "  content:'" + shortMsg + "';\n"
+        + "  visibility: visible;\n"
+        + "}");
+    return create(msg, sev, line, null);
+  }
+
+  public static native LintLine create(String msg, String sev, Pos f, Pos t) /*-{
+    return {
+      message : msg,
+      severity : sev,
+      from : f,
+      to : t
+    };
+  }-*/;
+
+  public final native String message() /*-{ return this.message; }-*/;
+  public final native String detailedMessage() /*-{ return this.message; }-*/;
+  public final native String severity() /*-{ return this.severity; }-*/;
+  public final native Pos from() /*-{ return this.from; }-*/;
+  public final native Pos to() /*-{ return this.to; }-*/;
+
+  protected LintLine() {
+  }
+}

gerrit-gwtui/src/main/java/net/codemirror/lib/style.css

@@ -16,6 +16,8 @@
 @external .CodeMirror;
 @external .CodeMirror-lines;
 @external .CodeMirror-linenumber;
+@external .CodeMirror-lint-markers;
+@external .CodeMirror-lint-tooltip;
 @external .CodeMirror-overlayscroll-horizontal;
 @external .CodeMirror-overlayscroll-vertical;
 @external .CodeMirror-scrollbar-filler;
@@ -94,3 +96,29 @@
   z-index: 2;
   cursor: text;
 }
+
+.CodeMirror-lint-markers {
+  width: 250px;
+}
+
+.CodeMirror-lint-tooltip {
+  background-color: infobackground;
+  border: 1px solid black;
+  border-radius: 4px 4px 4px 4px;
+  color: infotext;
+  font-family: monospace;
+  font-size: 10pt;
+  overflow: hidden;
+  padding: 2px 5px;
+  position: fixed;
+  white-space: pre;
+  white-space: pre-wrap;
+  z-index: 100;
+  max-width: 600px;
+  opacity: 0;
+  transition: opacity .4s;
+  -moz-transition: opacity .4s;
+  -webkit-transition: opacity .4s;
+  -o-transition: opacity .4s;
+  -ms-transition: opacity .4s;
+}

gerrit-server/BUCK

@@ -34,6 +34,7 @@ java_library(
     '//gerrit-util-ssl:ssl',
     '//lib:args4j',
     '//lib:automaton',
+    '//lib:blame-cache',
     '//lib:grappa',
     '//lib:gson',
     '//lib:guava',

gerrit-server/src/main/java/com/google/gerrit/server/change/GetBlame.java

@@ -0,0 +1,164 @@
+// Copyright (C) 2015 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.change;
+
+import com.google.common.collect.ArrayListMultimap;
+import com.google.common.collect.ListMultimap;
+import com.google.gerrit.extensions.common.BlameInfo;
+import com.google.gerrit.extensions.common.RangeInfo;
+import com.google.gerrit.extensions.restapi.BadRequestException;
+import com.google.gerrit.extensions.restapi.CacheControl;
+import com.google.gerrit.extensions.restapi.ResourceNotFoundException;
+import com.google.gerrit.extensions.restapi.Response;
+import com.google.gerrit.extensions.restapi.RestApiException;
+import com.google.gerrit.extensions.restapi.RestReadView;
+import com.google.gerrit.reviewdb.client.Project;
+import com.google.gerrit.server.config.GerritServerConfig;
+import com.google.gerrit.server.git.GitRepositoryManager;
+import com.google.gerrit.server.git.MergeUtil;
+import com.google.gerrit.server.patch.AutoMerger;
+import com.google.gerrit.server.project.InvalidChangeOperationException;
+import com.google.gitiles.blame.BlameCache;
+import com.google.gitiles.blame.Region;
+import com.google.gwtorm.server.OrmException;
+import com.google.inject.Inject;
+
+import org.eclipse.jgit.lib.Config;
+import org.eclipse.jgit.lib.ObjectId;
+import org.eclipse.jgit.lib.PersonIdent;
+import org.eclipse.jgit.lib.Ref;
+import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.merge.ThreeWayMergeStrategy;
+import org.eclipse.jgit.revwalk.RevCommit;
+import org.eclipse.jgit.revwalk.RevWalk;
+import org.kohsuke.args4j.Option;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+public class GetBlame implements RestReadView<FileResource> {
+
+  private final GitRepositoryManager repoManager;
+  private final BlameCache blameCache;
+  private final boolean allowBlame;
+  private final ThreeWayMergeStrategy mergeStrategy;
+  private final AutoMerger autoMerger;
+
+  @Option(name = "--base", aliases = {"-b"},
+    usage = "whether to load the blame of the base revision (the direct"
+      + " parent of the change) instead of the change")
+  private boolean base;
+
+  @Inject
+  GetBlame(GitRepositoryManager repoManager,
+      BlameCache blameCache,
+      @GerritServerConfig Config cfg,
+      AutoMerger autoMerger) {
+    this.repoManager = repoManager;
+    this.blameCache = blameCache;
+    this.mergeStrategy = MergeUtil.getMergeStrategy(cfg);
+    this.autoMerger = autoMerger;
+    allowBlame = cfg.getBoolean("change", "allowBlame", true);
+  }
+
+  @Override
+  public Response<List<BlameInfo>> apply(FileResource resource)
+      throws RestApiException, OrmException, IOException,
+      InvalidChangeOperationException {
+    if (!allowBlame) {
+      throw new BadRequestException("blame is disabled");
+    }
+
+    Project.NameKey project = resource.getRevision().getChange().getProject();
+    try (Repository repository = repoManager.openRepository(project);
+        RevWalk revWalk = new RevWalk(repository)) {
+      String refName = resource.getRevision().getEdit().isPresent()
+          ? resource.getRevision().getEdit().get().getRefName()
+          : resource.getRevision().getPatchSet().getRefName();
+
+      Ref ref = repository.findRef(refName);
+      if (ref == null) {
+        throw new ResourceNotFoundException("unknown ref " + refName);
+      }
+      ObjectId objectId = ref.getObjectId();
+      RevCommit revCommit = revWalk.parseCommit(objectId);
+      RevCommit[] parents = revCommit.getParents();
+
+      String path = resource.getPatchKey().getFileName();
+
+      List<BlameInfo> result;
+      if (!base) {
+        result = blame(revCommit, path, repository, revWalk);
+
+      } else if (parents.length == 0) {
+        throw new ResourceNotFoundException("Initial commit doesn't have base");
+
+      } else if (parents.length == 1) {
+        result = blame(parents[0], path, repository, revWalk);
+
+      } else if (parents.length == 2) {
+        ObjectId automerge = autoMerger.merge(repository, revWalk, revCommit,
+            mergeStrategy);
+        result = blame(automerge, path, repository, revWalk);
+
+      } else {
+        throw new ResourceNotFoundException(
+            "Cannot generate blame for merge commit with more than 2 parents");
+      }
+
+      Response<List<BlameInfo>> r = Response.ok(result);
+      if (resource.isCacheable()) {
+        r.caching(CacheControl.PRIVATE(7, TimeUnit.DAYS));
+      }
+      return r;
+    }
+  }
+
+  private List<BlameInfo> blame(ObjectId id, String path,
+      Repository repository, RevWalk revWalk) throws IOException {
+    ListMultimap<BlameInfo, RangeInfo> ranges = ArrayListMultimap.create();
+    List<BlameInfo> result = new ArrayList<>();
+    if (blameCache.findLastCommit(repository, id, path) == null) {
+      return result;
+    }
+
+    List<Region> blameRegions = blameCache.get(repository, id, path);
+    int from = 1;
+    for (Region region : blameRegions) {
+      RevCommit commit = revWalk.parseCommit(region.getSourceCommit());
+      BlameInfo blameInfo = toBlameInfo(commit, region.getSourceAuthor());
+      ranges.put(blameInfo, new RangeInfo(from, from + region.getCount() - 1));
+      from += region.getCount();
+    }
+
+    for (BlameInfo key : ranges.keySet()) {
+      key.ranges = ranges.get(key);
+      result.add(key);
+    }
+    return result;
+  }
+
+  private static BlameInfo toBlameInfo(RevCommit commit,
+      PersonIdent sourceAuthor) {
+    BlameInfo blameInfo = new BlameInfo();
+    blameInfo.author = sourceAuthor.getName();
+    blameInfo.id = commit.getName();
+    blameInfo.commitMsg = commit.getFullMessage();
+    blameInfo.time = commit.getCommitTime();
+    return blameInfo;
+  }
+}

gerrit-server/src/main/java/com/google/gerrit/server/change/Module.java

@@ -114,6 +114,7 @@ public class Module extends RestApiModule {
     get(FILE_KIND, "content").to(GetContent.class);
     get(FILE_KIND, "download").to(DownloadContent.class);
     get(FILE_KIND, "diff").to(GetDiff.class);
+    get(FILE_KIND, "blame").to(GetBlame.class);
 
     child(CHANGE_KIND, "edit").to(ChangeEdits.class);
     delete(CHANGE_KIND, "edit").to(DeleteChangeEdit.class);

gerrit-server/src/main/java/com/google/gerrit/server/config/GerritGlobalModule.java

@@ -145,6 +145,8 @@ import com.google.gerrit.server.validators.GroupCreationValidationListener;
 import com.google.gerrit.server.validators.HashtagValidationListener;
 import com.google.gerrit.server.validators.OutgoingEmailValidationListener;
 import com.google.gerrit.server.validators.ProjectCreationValidationListener;
+import com.google.gitiles.blame.BlameCache;
+import com.google.gitiles.blame.BlameCacheImpl;
 import com.google.inject.Inject;
 import com.google.inject.TypeLiteral;
 import com.google.inject.internal.UniqueAnnotations;
@@ -172,6 +174,7 @@ public class GerritGlobalModule extends FactoryModule {
 
     bind(IdGenerator.class);
     bind(RulesCache.class);
+    bind(BlameCache.class).to(BlameCacheImpl.class);
     bind(Sequences.class);
     install(authModule);
     install(AccountByEmailCacheImpl.module());

gerrit-server/src/main/java/com/google/gerrit/server/config/GetServerInfo.java

@@ -167,6 +167,7 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
 
   private ChangeConfigInfo getChangeInfo(Config cfg) {
     ChangeConfigInfo info = new ChangeConfigInfo();
+    info.allowBlame = toBoolean(cfg.getBoolean("change", "allowBlame", true));
     info.allowDrafts = toBoolean(cfg.getBoolean("change", "allowDrafts", true));
     info.largeChange = cfg.getInt("change", "largeChange", 500);
     info.replyTooltip =
@@ -358,6 +359,7 @@ public class GetServerInfo implements RestReadView<ConfigResource> {
   }
 
   public static class ChangeConfigInfo {
+    public Boolean allowBlame;
     public Boolean allowDrafts;
     public int largeChange;
     public String replyLabel;

lib/BUCK

@@ -261,3 +261,11 @@ maven_jar(
   sha1 = 'd9a09f7732226af26bf99f19e2cffe0ae219db5b',
   license = 'DO_NOT_DISTRIBUTE',
 )
+
+maven_jar(
+  name = 'blame-cache',
+  id = 'com/google/gitiles:blame-cache:0.1-9',
+  sha1 = '51d35e6f8bbc2412265066cea9653dd758c95826',
+  license = 'Apache2.0',
+  repository = GERRIT,
+)

lib/codemirror/cm.defs

@@ -3,6 +3,7 @@ CM_CSS = [
   'addon/dialog/dialog.css',
   'addon/scroll/simplescrollbars.css',
   'addon/search/matchesonscrollbar.css',
+  'addon/lint/lint.css',
 ]
 
 CM_JS = [
@@ -28,6 +29,7 @@ CM_ADDONS = [
   'mode/multiplex.js',
   'mode/overlay.js',
   'mode/simple.js',
+  'lint/lint.js',
 ]
 
 # Available themes must be enumerated here,