wat-related fuzz bug with "distinct rec groups would be identical after binary writing"

[kripken]

The wasm file does not have GC, but does have exceptions - I am guessing that is relevant somehow. First, the wasm is valid with the right features:

$ bin/wasm-opt a.wasm --all-features --disable-fp16 --disable-simd --disable-bulk-memory --disable-gc --disable-strings --disable-stack-switching --disable-custom-descriptors --disable-memory64 --disable-strings --disable-multimemory --disable-shared-everything --disable-bulk-memory-opt --disable-relaxed-atomics --print > a.wat

That also prints out the wat text. But that wat is not valid with the same features:

$ bin/wasm-opt a.wat --all-features --disable-fp16 --disable-simd --disable-bulk-memory --disable-gc --disable-strings --disable-stack-switching --disable-custom-descriptors --disable-memory64 --disable-strings --disable-multimemory --disable-shared-everything --disable-bulk-memory-opt --disable-relaxed-atomics
Fatal: a.wat:73:1: error: invalid type: distinct rec groups would be identical after binary writing

But there are no rec groups (as there is no GC). Line 73 has

 (type $71 (func (result f64 exnref i64 nullexternref)))

cc @tlively

a.wasm.gz

[tlively]

Minimized reproducing command (enabling more features narrows down the disabled features that could cause the issue): bin/wasm-opt a.wasm -all --disable-gc -S -o - | bin/wasm-opt -all --disable-gc -S -o -.

[tlively]

Minimized reproducer (manually reduced after running wasm-tools print on the original reproducer, since it depends on stacky code):

;; test.wat
(module
  (type $tuple (func (result i32 externref)))

  (func $f (result i32 externref)
    block $l (type $tuple) (result i32 externref)
      i32.const 0
      ref.null extern
      i32.const 0
      br_if $l ;; package the i32 and nullexternref into a tuple
      nop      ;; force creation of a scratch local
      br $l    ;; consume a scratch local block with (result i32 nullexternref)
    end
  )
)

This parses into:

(module
 (type $tuple (func (result i32 externref)))
 (type $1 (func (result i32 nullexternref))) ;; conflicts with $tuple
 (func $f (result i32 externref)
  (local $scratch (tuple i32 nullexternref))
  (block $l (type $tuple) (result i32 externref)
   (br $l
    (block (type $1) (result i32 nullexternref)
     (local.set $scratch
      (br_if $l
       (tuple.make 2
        (i32.const 0)
        (ref.null noextern)
       )
       (i32.const 0)
      )
     )
     (nop)
     (local.get $scratch)
    )
   )
  )
 )
)

bin/wasm-opt test.wat -all --disable-gc -S -o - | bin/wasm-opt -all --disable-gc -S -o -

Looks like the fix will be to use asWrittenGivenFeatures when creating the signatures for scratch local blocks.