inference: fix #42090, make sure not to wrap Conditional in PartialStruct

base/compiler/abstractinterpretation.jl

@@ -1533,7 +1533,7 @@ function abstract_eval_statement(interp::AbstractInterpreter, @nospecialize(e),
  anyconst = false
  allconst = true
  for i = 2:length(e.args)
- at = abstract_eval_value(interp, e.args[i], vtypes, sv)
+ at = widenconditional(abstract_eval_value(interp, e.args[i], vtypes, sv))
  if !anyconst
  anyconst = has_nontrivial_const_info(at)
  end

test/compiler/inference.jl

@@ -1827,16 +1827,39 @@ end
  return c, d # ::Tuple{Int,Int}
  end == Any[Tuple{Int,Int}]
 
- # shouldn't use the old constraint when the subject of condition has changed
+ # should invalidate old constraint when the subject of condition has changed
  @test Base.return_types((Union{Nothing,Int},)) do a
- b = a === nothing
- c = b ? 0 : a # c::Int
+ cond = a === nothing
+ r1 = cond ? 0 : a # r1::Int
  a = 0
- d = b ? a : 1 # d::Int, not d::Union{Nothing,Int}
- return c, d # ::Tuple{Int,Int}
+ r2 = cond ? a : 1 # r2::Int, not r2::Union{Nothing,Int}
+ return r1, r2 # ::Tuple{Int,Int}
  end == Any[Tuple{Int,Int}]
 end
 
+# https://github.com/JuliaLang/julia/issues/42090#issuecomment-911824851
+# `PartialStruct` shoudln't wrap `Conditional`
+let M = Module()
+ @eval M begin
+ struct BePartialStruct
+ val::Int
+ cond
+ end
+ end
+
+ rt = @eval M begin
+ Base.return_types((Union{Nothing,Int},)) do a
+ cond = a === nothing
+ obj = $(Expr(:new, M.BePartialStruct, 42, :cond))
+ r1 = getfield(obj, :cond) ? 0 : a # r1::Union{Nothing,Int}, not r1::Int (because PartialStruct doesn't wrap Conditional)
+ a = $(gensym(:anyvar))::Any
+ r2 = getfield(obj, :cond) ? a : nothing # r2::Any, not r2::Const(nothing) (we don't need to worry about constrait invalidation here)
+ return r1, r2 # ::Tuple{Union{Nothing,Int},Any}
+ end |> only
+ end
+ @test rt == Tuple{Union{Nothing,Int},Any}
+end
+
 @testset "conditional constraint propagation from non-`Conditional` object" begin
  @test Base.return_types((Bool,)) do b
  if b