AU: When checking if we've visited a file before, don't follow symlinks.

delta_diff_generator.cc

Index: delta_diff_generator.cc
diff --git a/delta_diff_generator.cc b/delta_diff_generator.cc
index ccdf27ad5ce56341ccbfde8ac0bc5299a5f0da7a..82bce8a5ca024ab728414e5dfc625370e6aed3a3 100644
--- a/delta_diff_generator.cc
+++ b/delta_diff_generator.cc
@@ -169,11 +169,11 @@ bool DeltaReadFiles(Graph* graph,
     // from using a graph/cycle detection/etc to generate diffs, and at that
     // time, it will be easy (non-complex) to have many operations read
     // from the same source blocks. At that time, this code can die. -adlr
-    bool should_diff_from_source = true;
+    bool should_diff_from_source = false;
     string src_path = old_root + fs_iter.GetPartialPath();
-    if (utils::FileExists(src_path.c_str())) {
-      struct stat src_stbuf;
-      TEST_AND_RETURN_FALSE_ERRNO(0 == stat(src_path.c_str(), &src_stbuf));
+    struct stat src_stbuf;
+    if (0 == lstat(src_path.c_str(), &src_stbuf) &&
+        S_ISREG(src_stbuf.st_mode)) {
       should_diff_from_source = !utils::SetContainsKey(visited_src_inodes,
                                                        src_stbuf.st_ino);
       visited_src_inodes.insert(src_stbuf.st_ino);