julia nightly build throws TypeError in the implementation of Base.methods()

[gafter]

Testing my code passes my tests on 1.6.2, 1.8, 1.8.2, and 1.9. However, it fails on nightly with an exception.

  TypeError: in typeassert, expected Vector, got a value of type Nothing
  Stacktrace:
    [1] methods(f::Any, t::Any, mod::Nothing)
      @ Base ./reflection.jl:1060
    [2] methods (repeats 2 times)
      @ Base ./reflection.jl:1082 [inlined]
    [3] enumerate_children_names(node_type::Type{Sub})
      @ TreeTransform ~/Repos/TreeTransform.jl/src/TreeTransform.jl:221

versioninfo() reports

Julia Version 1.10.0-DEV.1392
Commit 248ceda3c49 (2023-05-27 13:39 UTC)
Platform Info:
  OS: macOS (arm64-apple-darwin22.4.0)
  CPU: 12 × Apple M2 Max
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-15.0.7 (ORCJIT, apple-m1)
  Threads: 1 on 8 virtual cores
Environment:
  JULIA_SSL_CA_ROOTS_PATH = 
  JULIA_EDITOR = code

I installed the nightly by downloading the Apple silicon nightly build, mounting it, and dragging the app into my Applications folder.

You can reproduce the failure as follows (my repo is only a couple of hundred lines of code):

git clone https://github.com/RelationalAI/TreeTransform.jl
cd TreeTransform.jl
git checkout julia-nightly-issue
/Applications/Julia-1.10.app/Contents/Resources/julia/bin/julia
] # enter package mode
activate .
instantiate
# exit package mode
include("test/runtests.jl")

This will result, in short order, in

Check some simple cases: Error During Test at /Users/nealgafter/Repos/TreeTransform.jl/test/treetransform.jl:80
  Test threw exception
  Expression: simplify(Sub(x, Neg(y))) == Add(x, y)
  TypeError: in typeassert, expected Vector, got a value of type Nothing
  Stacktrace:
    [1] methods(f::Any, t::Any, mod::Nothing)
      @ Base ./reflection.jl:1060
    [2] methods (repeats 2 times)
      @ Base ./reflection.jl:1082 [inlined]
    [3] enumerate_children_names(node_type::Type{Sub})
      @ TreeTransform ~/Repos/TreeTransform.jl/src/TreeTransform.jl:220
    [4] #s7#16
      @ TreeTransform ~/Repos/TreeTransform.jl/src/TreeTransform.jl:266 [inlined]
    [5] var"#s7#16"(T::Any, ::Any, ctx::Any, node::Any)
      @ TreeTransform ./none:0
    [6] (::Core.GeneratedFunctionStub)(::UInt64, ::LineNumberNode, ::Any, ::Vararg{Any})
      @ Core ./boot.jl:598
    [7] fixed_point(ctx::TreeTransform.RewriteContext, node::Sub, rebuild::Bool)
      @ TreeTransform ~/Repos/TreeTransform.jl/src/TreeTransform.jl:336
    [8] bottom_up_rewrite(xform::Function, data::Sub; detect_cycles::Bool, max_transformations_per_node::Int64, recursive::Bool)
      @ TreeTransform ~/Repos/TreeTransform.jl/src/TreeTransform.jl:152
    [9] bottom_up_rewrite(xform::typeof(xform), data::Sub)
      @ TreeTransform ~/Repos/TreeTransform.jl/src/TreeTransform.jl:137 [inlined]
   [10] simplify(node::Sub)
      @ Main ~/Repos/TreeTransform.jl/test/treetransform.jl:73
   [11] macro expansion
      @ /Applications/Julia-1.10.app/Contents/Resources/julia/share/julia/stdlib/v1.10/Test/src/Test.jl:669 [inlined]
   [12] macro expansion
      @ ~/Repos/TreeTransform.jl/test/treetransform.jl:80 [inlined]
   [13] macro expansion
      @ /Applications/Julia-1.10.app/Contents/Resources/julia/share/julia/stdlib/v1.10/Test/src/Test.jl:1547 [inlined]
   [14] top-level scope
      @ ~/Repos/TreeTransform.jl/test/treetransform.jl:77

[vtjnash]

It looks like you are trying to call methods from a generated function, and that is not supposed to work since the answer is not something legal for a generated function to inspect typically. The runtime now does a better job validating code for some errors.

[gafter]

I'm not sure why it would not be a good idea for a generated method to inspect the methods (in my case, constructors of a type).

Should I build a data structure that caches the information needed by the generated method before invoking it, and have the method pull the data from that data structure?

[gafter]

@vtnash Are you saying it is expected/intentional that Base.methods sometimes throws TypeError?

[vtjnash]

We should probably make that error message clearer, though it is not unexpected