inference: fix JuliaLang#46207, make sure we never form nested `Condi…

…tional` (JuliaLang#46208)

base/compiler/abstractinterpretation.jl

@@ -1498,20 +1498,26 @@ function abstract_call_builtin(interp::AbstractInterpreter, f::Builtin, (; fargs
  if isa(aty, Const) && isa(b, SlotNumber)
  if rt === Const(false)
  aty = Union{}
+ bty = widenconditional(bty)
  elseif rt === Const(true)
  bty = Union{}
  elseif bty isa Type && isdefined(typeof(aty.val), :instance) # can only widen a if it is a singleton
  bty = typesubtract(bty, typeof(aty.val), InferenceParams(interp).MAX_UNION_SPLITTING)
+ else
+ bty = widenconditional(bty)
  end
  return Conditional(b, aty, bty)
  end
  if isa(bty, Const) && isa(a, SlotNumber)
  if rt === Const(false)
  bty = Union{}
+ aty = widenconditional(aty)
  elseif rt === Const(true)
  aty = Union{}
  elseif aty isa Type && isdefined(typeof(bty.val), :instance) # same for b
  aty = typesubtract(aty, typeof(bty.val), InferenceParams(interp).MAX_UNION_SPLITTING)
+ else
+ aty = widenconditional(aty)
  end
  return Conditional(a, bty, aty)
  end

test/compiler/inference.jl

@@ -2102,6 +2102,16 @@ let M = Module()
  @test rt == Tuple{Union{Nothing,Int},Any}
 end
 
+# make sure we never form nested `Conditional` (https://github.com/JuliaLang/julia/issues/46207)
+@test Base.return_types((Any,)) do a
+ c = isa(a, Integer)
+ 42 === c ? :a : "b"
+end |> only === String
+@test Base.return_types((Any,)) do a
+ c = isa(a, Integer)
+ c === 42 ? :a : "b"
+end |> only === String
+
 @testset "conditional constraint propagation from non-`Conditional` object" begin
  @test Base.return_types((Bool,)) do b
  if b