Highlight common whitespace errors such as whitespace on end of line

Show trailing whitespace (space and/or tab after the end of line,
but before the LF) by displaying it with a red background, so it
stands out visually against the rest of the patch.

Also show tab-after-space within the leading indentation for the
line, as this is an abnormal way to indent a line of code that
usually results in badly formatted code.

Bug: GERRIT-23
Signed-off-by: Shawn O. Pearce <sop@google.com>

4 files changed, 34 insertions, 3 deletions

diff --git a/src/main/java/com/google/gerrit/client/patches/PatchUtil.java b/src/main/java/com/google/gerrit/client/patches/PatchUtil.java
index 0f7f175a21..1e95950b3f 100644
--- a/src/main/java/com/google/gerrit/client/patches/PatchUtil.java
+++ b/src/main/java/com/google/gerrit/client/patches/PatchUtil.java
@@ -29,10 +29,15 @@ public class PatchUtil {
     JsonUtil.bind(DETAIL_SVC, "rpc/PatchDetailService");
   }
 
-  public static String lineToHTML(final String src, final int lineLength) {
+  public static String lineToHTML(final String src, final int lineLength,
+      final boolean showWhiteSpaceErrors) {
     final boolean hasTab = src.indexOf('\t') >= 0;
     String brokenSrc = wrapLines(src, hasTab, lineLength);
     String html = DomUtil.escape(brokenSrc);
+    if (showWhiteSpaceErrors) {
+      html = showTabAfterSpace(html);
+      html = showTrailingWhitespace(html);
+    }
     if (brokenSrc != src) {
       // If we had line breaks inserted into the source text we need
       // to expand the line breaks into <br> tags in HTML, so the
@@ -81,4 +86,10 @@ public class PatchUtil {
 
   private native static String expandLFs(String src)
   /*-{ return src.replace(/\n/g, '<br>'); }-*/;
+
+  private native static String showTabAfterSpace(String src)
+  /*-{ return src.replace(/^(  *\t)/, '<span class="gerrit-whitespaceerror">$1</span>'); }-*/;
+
+  private native static String showTrailingWhitespace(String src)
+  /*-{ return src.replace(/([ \t][ \t]*)(\r?\n?)$/, '<span class="gerrit-whitespaceerror">$1</span>$2'); }-*/;
 }
diff --git a/src/main/java/com/google/gerrit/client/patches/SideBySideTable.java b/src/main/java/com/google/gerrit/client/patches/SideBySideTable.java
index 4a09d24897..d051b1bb67 100644
--- a/src/main/java/com/google/gerrit/client/patches/SideBySideTable.java
+++ b/src/main/java/com/google/gerrit/client/patches/SideBySideTable.java
@@ -311,8 +311,16 @@ public class SideBySideTable extends AbstractPatchContentTable {
         nc.append(s.getType().name());
         nc.append("\">");
         if (!"".equals(s.getText())) {
+          boolean showWhitespaceErrors = false;
+          if (fileId == fileCnt - 1
+              && s.getType() == SideBySideLine.Type.INSERT) {
+            // Only show whitespace errors in the last column, and
+            // only if the line is introduced here.
+            //
+            showWhitespaceErrors = true;
+          }
           nc.append(PatchUtil.lineToHTML(s.getText(),
-              PatchUtil.DEFAULT_LINE_LENGTH));
+              PatchUtil.DEFAULT_LINE_LENGTH, showWhitespaceErrors));
         } else {
           nc.append("&nbsp;");
         }
diff --git a/src/main/java/com/google/gerrit/client/patches/UnifiedDiffTable.java b/src/main/java/com/google/gerrit/client/patches/UnifiedDiffTable.java
index b2d6682c3d..642aa7aa25 100644
--- a/src/main/java/com/google/gerrit/client/patches/UnifiedDiffTable.java
+++ b/src/main/java/com/google/gerrit/client/patches/UnifiedDiffTable.java
@@ -110,7 +110,15 @@ public class UnifiedDiffTable extends AbstractPatchContentTable {
     nc.append(line.getType().name());
     nc.append("\">");
     if (!"".equals(line.getText())) {
-      nc.append(PatchUtil.lineToHTML(line.getText(), 0));
+      boolean showWhitespaceErrors = false;
+      switch (line.getType()) {
+        case POST_IMAGE:
+          // Only show whitespace errors if the error was introduced.
+          //
+          showWhitespaceErrors = true;
+          break;
+      }
+      nc.append(PatchUtil.lineToHTML(line.getText(), 0, showWhitespaceErrors));
     } else {
       nc.append("&nbsp;");
     }
diff --git a/src/main/java/com/google/gerrit/public/Gerrit.css b/src/main/java/com/google/gerrit/public/Gerrit.css
index de3a0a11ba..72c2f45adb 100644
--- a/src/main/java/com/google/gerrit/public/Gerrit.css
+++ b/src/main/java/com/google/gerrit/public/Gerrit.css
@@ -53,6 +53,10 @@
   font-size: 8pt;
 }
 
+.gerrit-whitespaceerror {
+  background: red;
+}
+
 .gerrit-preformat {
 	white-space: pre;
   font-family: monospace;