Bug 707579, xpt.py shouldn't try to generate destination file if inputs are all older, r=khuey

xpcom/typelib/xpt/tools/xpt.py

@@ -1321,12 +1321,25 @@ def xpt_dump(file):
 def xpt_link(dest, inputs):
     """
     Link all of the xpt files in |inputs| together and write the
-    result ot |dest|.
+    result to |dest|.
 
     """
+
     if not inputs:
         print >>sys.stderr, "Usage: xpt_link <destination file> <input files>"
         return
+
+    # Don't re-create dest if newer than the input files.
+    if os.path.exists(dest):
+      maxInputChange = 0;
+      for f in inputs:
+        s = os.stat(f).st_mtime
+        if s > maxInputChange:
+          maxInputChange = s
+      if maxInputChange < os.stat(dest).st_mtime:
+        print dest, " is already up-to-date."
+        return
+
     t1 = Typelib.read(inputs[0])
     for f in inputs[1:]:
         t2 = Typelib.read(f)