wat2wasm: function variable resolution broken

[Horcrux7]

The first sample works with 1.0.23 but produce with the version main from today an error.

error: test.wat:2:10: error: undefined function variable "$.<start>"
command line: wat2wasm.exe test.wat --enable-all
OS: Windows 10

(module
  (start $.<start>)
  (event (param externref))
  (func $.<start>
  )
)

This sample works with version 1.0.23 and the current version form main.

(module
  (start $.<start>)
  (func $.<start>
  )
)

The same problem occurs with export of a function. A possible workaround may be to change the order. First the declaration of the function and then the usage. But why change the behavior when an event has been declared?

[7ombie]

When did event get added? I can't find the proposal it is part of.

[Horcrux7]

It is part of the exception handling: https://github.com/WebAssembly/exception-handling/blob/master/proposals/exception-handling/Exceptions.md

Now it is named tag instead event: WebAssembly/exception-handling#161

[7ombie]

Thank you, @Horcrux7.

[ngzhian]

I think the error message is misleading, since event is now tag, your example works if we rename it to tag. I'm not sure why the error message becomes a undefined function though.

[ngzhian]

Here's a trace with #define WABT_TRACING 1:

-> ParseModule()
  -> ParseModuleCommand()
    -> ParseScriptModule()
      -> ParseBindVarOpt()
      <- ParseBindVarOpt
      -> ParseModuleFieldList()
        -> ParseModuleField()
          -> ParseStartModuleField()
            -> ParseVar()
            <- ParseVar
          <- ParseStartModuleField
        <- ParseModuleField
      <- ParseModuleFieldList
    <- ParseScriptModule
  <- ParseModuleCommand
<- ParseModule

Seems like we stop parsing module fields once we encounter event, which is unkown, so we fail to parse the func, then later when we check for bound variables we don't have an undefined variable.

[Horcrux7]

Thanks for the analyze. I had not expect such behavior.