Don't aggressively coalesce across lines

Don't bother trying to coalesce over line boundaries when the
common region that contains the LF is less than 5 characters.
Its likely that the common region is actually a trailing "*/" or
"}" to close out the current statement.  We are usually better off
reporting this as common to the user.

Bug: issue 473
Change-Id: I93762d07d34eb71269ea6758ac3466a5351f8dbf
Signed-off-by: Shawn O. Pearce <sop@google.com>

gerrit-server/src/main/java/com/google/gerrit/server/patch/PatchListCacheImpl.java

@@ -246,9 +246,12 @@ public class PatchListCacheImpl implements PatchListCache {
             int bb = c.getBeginB();
             int be = n.getEndB();
 
-            wordEdits.set(j, new Edit(ab, ae, bb, be));
-            wordEdits.remove(j + 1);
-            continue;
+            if (canCoalesce(a, c.getEndA(), n.getBeginA())
+                && canCoalesce(b, c.getEndB(), n.getBeginB())) {
+              wordEdits.set(j, new Edit(ab, ae, bb, be));
+              wordEdits.remove(j + 1);
+              continue;
+            }
           }
 
           j++;
@@ -367,6 +370,15 @@ public class PatchListCacheImpl implements PatchListCache {
     return new PatchListEntry(fileHeader, edits);
   }
 
+  private static boolean canCoalesce(CharText a, int b, int e) {
+    while (b < e) {
+      if (a.charAt(b++) == '\n') {
+        return false;
+      }
+    }
+    return true;
+  }
+
   private static int findLF(List<Edit> edits, int j, CharText t, int b) {
     int lf = b;
     int limit = 0 < j ? edits.get(j - 1).getEndB() : 0;