releasetools: Fix the bug in symlink deletion.

For file-based OTAs, symlinks in the source build but not in the target
build will be deleted. However, if a symlink is replaced by a regular
file in the target build, the file will be accidentally deleted when
applying (resuming) the same package again.

Verify the checksum of a symlink that will be unpacked or renamed to.
Delete the file only if it doesn't have the target checksum.

Bug: 23646151
Change-Id: Ie322abb6022b6fa812c6b36a3127872d9614fc3b

tools/releasetools/edify_generator.py

@@ -243,6 +243,15 @@ class EdifyGenerator(object):
     cmd = "delete(" + ",\0".join(['"%s"' % (i,) for i in file_list]) + ");"
     self.script.append(self.WordWrap(cmd))
 
+  def DeleteFilesIfNotMatching(self, file_list):
+    """Delete the file in file_list if not matching the checksum."""
+    if not file_list:
+      return
+    for name, sha1 in file_list:
+      cmd = ('sha1_check(read_file("{name}"), "{sha1}") || '
+             'delete("{name}");'.format(name=name, sha1=sha1))
+      self.script.append(self.WordWrap(cmd))
+
   def RenameFile(self, srcfile, tgtfile):
     """Moves a file from one location to another."""
     if self.info.get("update_rename_support", False):
@@ -254,7 +263,7 @@ class EdifyGenerator(object):
     """Prepend an action with an apply_patch_check in order to
        skip the action if the file exists.  Used when a patch
        is later renamed."""
-    cmd = ('sha1_check(read_file("%s"), %s) || ' % (tgtfile, tgtsha1))
+    cmd = ('sha1_check(read_file("%s"), %s) ||' % (tgtfile, tgtsha1))
     self.script.append(self.WordWrap(cmd))
 
   def ApplyPatch(self, srcfile, tgtfile, tgtsize, tgtsha1, *patchpairs):