Validator: `catch_ref` and `catch_all_ref` wrongly assume nullable exception type

[simolus3]

When a catch block is reached with an exception reference, it can be declared with a non-nullable (ref exn), e.g. this is a valid WebAssembly module:

(module
  (tag $my_error)
  (func $try_and_catch
    (block $handler (result (ref exn))
      (try_table (catch_ref $my_error $handler)
      )
      (return)
    )
    (drop)
  )
  (export "main" (func $try_and_catch))
)

wasm-tools validate agrees with this being valid, I used wasm-tools parse to turn it into a binary module. Attempting to load this module with endive fails:

Exception in thread "main" run.endive.wasm.InvalidException: type mismatch: instruction requires [ref[-23]] but stack has [refnull[-23]]
	at run.endive.wasm.Validator.validateFunction(Validator.java:2799)
	at run.endive.wasm.Validator.validateFunctions(Validator.java:906)
	at run.endive.wasm.WasmModule$Builder.build(WasmModule.java:289)
	at run.endive.wasm.Parser.parse(Parser.java:301)
	at run.endive.wasm.Parser.parse(Parser.java:262)
	at run.endive.wasm.Parser.parse(Parser.java:254)

The reason is that in validateFunction, validating a try_block pushes a ValType.ExnRef for CATCH_REF and CATCH_ALL_REF. exnref (aka (ref null exn) is not the same as (ref exn) though, which is what is required by the spec.

[andreaTP]

Hi @simolus3 and thanks for your interest in Endive!

Sorry for the delay, I'm having a look, will report progress and findings