Highlight line-level (aka word) differences in files

We now highlight any changed words within a line replace edit,
making the actual changes stand out against the surrounding context
that makes up the line.

The highlight is computed by constructing a string that covers the
entire replaced region and then running the Myers diff algorithm
over the individual characters of those two regions.

To avoid tiny edits interleaved at every other character in a
sentance we combine two neighboring character edits together if
there are only 1 or 2 characters between them.  There are probably
many ways to improve on this algorithm to avoid some nasty corner
display cases, but this rule is good enough for now.

The highlight data is computed and stored as part of the diff cache,
which requires a schema change in this commit.  So existing diff
cache records will be flushed on the next server start, and they
will be recomputed on demand.

Bug: issue 169
Change-Id: I69142ebef600e8c3c65821272dad3ee04a497654
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-prettify/src/main/java/com/google/gerrit/prettify/common/PrettyFormatter.java

@@ -17,14 +17,74 @@ package com.google.gerrit.prettify.common;
 import com.google.gwtexpui.safehtml.client.SafeHtml;
 import com.google.gwtexpui.safehtml.client.SafeHtmlBuilder;
 
+import org.eclipse.jgit.diff.Edit;
+import org.eclipse.jgit.diff.ReplaceEdit;
+
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
 public abstract class PrettyFormatter {
+  public static abstract class EditFilter {
+    protected abstract int getBegin(Edit e);
+
+    protected abstract int getEnd(Edit e);
+
+    protected abstract String getStyleName();
+
+    protected final boolean in(int line, Edit e) {
+      return getBegin(e) <= line && line < getEnd(e);
+    }
+
+    protected final boolean after(int line, Edit e) {
+      return getEnd(e) < line;
+    }
+  }
+
+  public static final EditFilter A = new EditFilter() {
+    @Override
+    protected String getStyleName() {
+      return "wdd";
+    }
+
+    @Override
+    protected int getBegin(Edit e) {
+      return e.getBeginA();
+    }
+
+    @Override
+    protected int getEnd(Edit e) {
+      return e.getEndA();
+    }
+  };
+
+  public static final EditFilter B = new EditFilter() {
+    @Override
+    protected String getStyleName() {
+      return "wdi";
+    }
+
+    @Override
+    protected int getBegin(Edit e) {
+      return e.getBeginB();
+    }
+
+    @Override
+    protected int getEnd(Edit e) {
+      return e.getEndB();
+    }
+  };
+
   protected List<String> lines = Collections.emptyList();
+  protected EditFilter side = A;
+  protected List<Edit> lineEdits = Collections.emptyList();
   protected PrettySettings settings;
 
+  private int col;
+  private int line;
+  private Tag lastTag;
+  private StringBuilder buf;
+
   /** @return the line of formatted HTML. */
   public SafeHtml getLine(int lineNo) {
     return SafeHtml.asis(lines.get(lineNo));
@@ -35,6 +95,14 @@ public abstract class PrettyFormatter {
     return lines.size();
   }
 
+  public void setEditFilter(EditFilter f) {
+    side = f;
+  }
+
+  public void setEditList(List<Edit> all) {
+    lineEdits = all;
+  }
+
   /**
    * Parse and format a complete source code file.
    *
@@ -49,10 +117,12 @@ public abstract class PrettyFormatter {
     String html = prettify(toHTML(srcText));
     int pos = 0;
     int textChunkStart = 0;
-    int col = 0;
-    Tag lastTag = Tag.NULL;
 
-    StringBuilder buf = new StringBuilder();
+    lastTag = Tag.NULL;
+    col = 0;
+    line = 0;
+
+    buf = new StringBuilder();
     while (pos <= html.length()) {
       int tagStart = html.indexOf('<', pos);
 
@@ -62,7 +132,7 @@ public abstract class PrettyFormatter {
         assert lastTag == Tag.NULL;
         pos = html.length();
         if (textChunkStart < pos) {
-          col = htmlText(col, buf, html.substring(textChunkStart, pos));
+          htmlText(html.substring(textChunkStart, pos));
         }
         if (0 < buf.length()) {
           lines.add(buf.toString());
@@ -82,7 +152,7 @@ public abstract class PrettyFormatter {
       //
       if (textChunkStart < tagStart) {
         lastTag.open(buf, html);
-        col = htmlText(col, buf, html.substring(textChunkStart, tagStart));
+        htmlText(html.substring(textChunkStart, tagStart));
       }
       textChunkStart = pos;
 
@@ -91,6 +161,7 @@ public abstract class PrettyFormatter {
         lines.add(buf.toString());
         buf = new StringBuilder();
         col = 0;
+        line++;
 
       } else if (html.charAt(tagStart + 1) == '/') {
         lastTag = lastTag.pop(buf, html);
@@ -99,18 +170,18 @@ public abstract class PrettyFormatter {
         lastTag = new Tag(lastTag, tagStart, tagEnd);
       }
     }
+    buf = null;
   }
 
-  private int htmlText(int col, StringBuilder buf, String txt) {
+  private void htmlText(String txt) {
     int pos = 0;
-
     while (pos < txt.length()) {
       int start = txt.indexOf('&', pos);
       if (start < 0) {
         break;
       }
 
-      col = cleanText(col, buf, txt, pos, start);
+      cleanText(txt, pos, start);
       pos = txt.indexOf(';', start + 1) + 1;
 
       if (settings.getLineLength() <= col) {
@@ -122,10 +193,10 @@ public abstract class PrettyFormatter {
       col++;
     }
 
-    return cleanText(col, buf, txt, pos, txt.length());
+    cleanText(txt, pos, txt.length());
   }
 
-  private int cleanText(int col, StringBuilder buf, String txt, int pos, int end) {
+  private void cleanText(String txt, int pos, int end) {
     while (pos < end) {
       int free = settings.getLineLength() - col;
       if (free <= 0) {
@@ -142,7 +213,6 @@ public abstract class PrettyFormatter {
       col += n;
       pos += n;
     }
-    return col;
   }
 
   /** Run the prettify engine over the text and return the result. */
@@ -212,7 +282,7 @@ public abstract class PrettyFormatter {
   }
 
   private String toHTML(String src) {
-    SafeHtml html = new SafeHtmlBuilder().append(src);
+    SafeHtml html = colorLineEdits(src);
 
     // The prettify parsers don't like &#39; as an entity for the
     // single quote character. Replace them all out so we don't
@@ -236,6 +306,74 @@ public abstract class PrettyFormatter {
     return html.asString();
   }
 
+  private SafeHtml colorLineEdits(String src) {
+    SafeHtmlBuilder buf = new SafeHtmlBuilder();
+
+    int lIdx = 0;
+    Edit lCur = lIdx < lineEdits.size() ? lineEdits.get(lIdx) : null;
+
+    int pos = 0;
+    int line = 0;
+    while (pos < src.length()) {
+      if (lCur instanceof ReplaceEdit && side.in(line, lCur)) {
+        List<Edit> wordEdits = ((ReplaceEdit) lCur).getInternalEdits();
+        if (!wordEdits.isEmpty()) {
+          // Copy the result using the word edits to guide us.
+          //
+
+          int last = 0;
+          for (Edit w : wordEdits) {
+            int b = side.getBegin(w);
+            int e = side.getEnd(w);
+
+            // If there is text between edits, copy it as-is.
+            //
+            int cnt = b - last;
+            if (0 < cnt) {
+              buf.append(src.substring(pos, pos + cnt));
+              pos += cnt;
+              last = b;
+            }
+
+            // If this is an edit, wrap it in a span.
+            //
+            cnt = e - b;
+            if (0 < cnt) {
+              buf.openSpan();
+              buf.setStyleName(side.getStyleName());
+              buf.append(src.substring(pos, pos + cnt));
+              buf.closeSpan();
+              pos += cnt;
+              last = e;
+            }
+          }
+
+          // We've consumed the entire region, so we are on the end.
+          // Fall through, what's left of this edit is only the tail
+          // of the final line.
+          //
+          line = side.getEnd(lCur) - 1;
+        }
+      }
+
+      int lf = src.indexOf('\n', pos);
+      if (lf < 0)
+        lf = src.length();
+      else
+        lf++;
+
+      buf.append(src.substring(pos, lf));
+      pos = lf;
+      line++;
+
+      if (lCur != null && side.after(line, lCur)) {
+        lIdx++;
+        lCur = lIdx < lineEdits.size() ? lineEdits.get(lIdx) : null;
+      }
+    }
+    return buf;
+  }
+
   private SafeHtml showTabAfterSpace(SafeHtml src) {
     src = src.replaceFirst("^(  *\t)", "<span class=\"wse\">$1</span>");
     src = src.replaceAll("\n(  *\t)", "\n<span class=\"wse\">$1</span>");

gerrit-prettify/src/main/java/com/google/gerrit/prettify/common/PrettySettings.java

@@ -23,7 +23,7 @@ public class PrettySettings {
   protected boolean showTabs;
 
   public PrettySettings() {
-    showWhiteSpaceErrors = false;
+    showWhiteSpaceErrors = true;
     lineLength = 100;
     tabSize = 2;
     showTabs = true;

gerrit-prettify/src/main/resources/com/google/gerrit/prettify/client/gerrit.css

@@ -15,6 +15,8 @@
 
 @external .wse;
 @external .vt;
+@external .wdd;
+@external .wdi;
 
 .wse {
   background: red;
@@ -27,3 +29,10 @@
 .wse .vt {
   border-left: 2px dotted black;
 }
+
+.wdd {
+  background: #FAA;
+}
+.wdi {
+  background: #9F9;
+}