Vararg{T,T} where T leads to internal error in code_typed

[simeonschaub]

Originally reported by @vtjnash in JuliaDebug/Cthulhu.jl#505, but as a different bug:

julia> f(x) = 1
f (generic function with 1 method)

julia> f(::Vararg{T,T}) where {T} = "2"
f (generic function with 2 methods)

julia> g(x) = f(x)
g (generic function with 1 method)

julia> code_typed(g, (Any,); optimize=false)
ERROR: MethodError: no method matching ⊑(::Core.Compiler.JLTypeLattice, ::Int64, ::Type{Any})
The function `⊑` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  ⊑(::Core.Compiler.JLTypeLattice, ::Type, ::Type)
   @ Core compiler/abstractlattice.jl:153
  ⊑(::Core.Compiler.ConstsLattice, ::Any, ::Any)
   @ Core compiler/typelattice.jl:553
  ⊑(::Core.Compiler.PartialsLattice, ::Any, ::Any)
   @ Core compiler/typelattice.jl:479
  ...

Stacktrace:
  [1] ⊑
    @ ./compiler/typelattice.jl:572 [inlined]
  [2] ⊑(lattice::Core.Compiler.PartialsLattice{Core.Compiler.ConstsLattice}, a::Any, b::Any)
    @ Core.Compiler ./compiler/typelattice.jl:550
  [3] tmerge_fast_path(lattice::Core.Compiler.PartialsLattice{Core.Compiler.ConstsLattice}, typea::Any, typeb::Any)
    @ Core.Compiler ./compiler/typelimits.jl:403
  [4] tmerge(lattice::Core.Compiler.PartialsLattice{Core.Compiler.ConstsLattice}, typea::Any, typeb::Any)
    @ Core.Compiler ./compiler/typelimits.jl:650
  [5] tmerge
    @ ./compiler/typelimits.jl:530
  [6] tmerge
    @ ./compiler/typelimits.jl:490 [inlined]
  [7] #tmerge##0
    @ ./compiler/abstractlattice.jl:291 [inlined]
  [8] collect_slot_refinements
    @ ./compiler/abstractinterpretation.jl:563
  [9] 
    @ Core.Compiler ./compiler/abstractinterpretation.jl:218
 [10] abstract_call_known
    @ ./compiler/abstractinterpretation.jl:2358
 [11] abstract_call(interp::Core.Compiler.NativeInterpreter, arginfo::Core.Compiler.ArgInfo, si::Core.Compiler.StmtInfo, sv::Core.Compiler.InferenceState, max_methods::Int64)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:2448
 [12] abstract_call(interp::Core.Compiler.NativeInterpreter, arginfo::Core.Compiler.ArgInfo, si::Core.Compiler.StmtInfo, sv::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:2441
 [13] abstract_call(interp::Core.Compiler.NativeInterpreter, arginfo::Core.Compiler.ArgInfo, sv::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:2595
 [14] abstract_eval_call(interp::Core.Compiler.NativeInterpreter, e::Expr, vtypes::Vector{Core.Compiler.VarState}, sv::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:2608
 [15] abstract_eval_statement_expr(interp::Core.Compiler.NativeInterpreter, e::Expr, vtypes::Vector{Core.Compiler.VarState}, sv::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:2843
 [16] abstract_eval_statement(interp::Core.Compiler.NativeInterpreter, e::Any, vtypes::Vector{Core.Compiler.VarState}, sv::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:2953
 [17] abstract_eval_basic_statement(interp::Core.Compiler.NativeInterpreter, stmt::Any, pc_vartable::Vector{Core.Compiler.VarState}, frame::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:3278
 [18] typeinf_local(interp::Core.Compiler.NativeInterpreter, frame::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:3540
 [19] typeinf_nocycle(interp::Core.Compiler.NativeInterpreter, frame::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/abstractinterpretation.jl:3656
 [20] _typeinf(interp::Core.Compiler.NativeInterpreter, frame::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/typeinfer.jl:262
 [21] typeinf(interp::Core.Compiler.NativeInterpreter, frame::Core.Compiler.InferenceState)
    @ Core.Compiler ./compiler/typeinfer.jl:207
 [22] typeinf_frame(interp::Core.Compiler.NativeInterpreter, mi::Core.MethodInstance, run_optimizer::Bool)
    @ Core.Compiler ./compiler/typeinfer.jl:1052
 [23] typeinf_code
    @ ./compiler/typeinfer.jl:1007 [inlined]
 [24] typeinf_code
    @ ./compiler/typeinfer.jl:1001 [inlined]
 [25] code_typed_by_type(tt::Type; optimize::Bool, debuginfo::Symbol, world::UInt64, interp::Core.Compiler.NativeInterpreter)
    @ Base ./reflection.jl:1710
 [26] code_typed_by_type
    @ ./reflection.jl:1689 [inlined]
 [27] code_typed(f::Any, types::Any; kwargs::@Kwargs{optimize::Bool})
    @ Base ./reflection.jl:1662
 [28] top-level scope
    @ REPL[10]:1
Some type information was truncated. Use `show(err)` to see complete types.

Regular execution still works though:

julia> g(1)
1