Bug 1223142 - make XPIDL set default nullptrs for optional out parameters, r=bz

--HG--
extra : commitid : 8pSPKD5AdOY
extra : transplant_source : %F2%8D%0D%20D4%98%7C%2A%16L%04%C0%88%24%AB%19%19%B2s

xpcom/idl-parser/xpidl/header.py

@@ -111,6 +111,19 @@ def paramlistAsNative(m, empty='void'):
                                            location=None,
                                            realtype=m.realtype)))
 
+    # Set any optional out params to default to nullptr. Skip if we just added
+    # extra non-optional args to l.
+    if len(l) == len(m.params):
+        paramIter = len(m.params) - 1
+        while (paramIter >= 0 and m.params[paramIter].optional and
+                m.params[paramIter].paramtype == "out"):
+            t = m.params[paramIter].type
+            # Strings can't be optional, so this shouldn't happen, but let's make sure:
+            if t == "AString" or t == "ACString" or t == "DOMString" or t == "AUTF8String":
+                break
+            l[paramIter] += " = nullptr"
+            paramIter -= 1
+
     if len(l) == 0:
         return empty