I cannot generate type library with the Mac XPIDL pluging 1.0d4 if the idl file contains a forward declaration like: interface nsMsgHdr; The compiler return an unknow error! I don't have this problem on Unix or Windows.

Looks like we need another spin of Mac xpidl. Shaver, do you have fixes ready for this spin, or do you want to wait until the next one?

I have checked in an idl project that I cannot compile yet (it's not part of the build script). Please feel free to use it for your testing: mozilla/mailnews/base/macbuild/msgCoreIDL.mcp

You're correct. That's what 1.0d5 will correct. I will distribute that today. I've verified that your msgCoreIDL.mcp project builds.