As noted in #14734, the WrapperGenerator behaves oddly when it encounters circular includes. (A.idl imports B.idl, and B.idl imports A.idl, possibly with several imports in between.) Sometimes it reports an error about something being undefined. Sometimes it runs fine but silently skips parts that were imported.

Ideally, we would recognise that a file has already been imported and not import it again. Then, wait until all referenced files are parsed before generating any code, to make sure nothing is missed.

An exception might be made for Foo includes Bar; statements - specs often put them in Bar.idl, which would mean that when Baz.idl imports Bar.idl, we should not consider Foo being undefined as an error. Though moving the statement to the file that uses it works too.