Variable update not reflected outside nested try blocks

[tkf]

Minimal example:

assertstring(::AbstractString) = nothing

function test_trytry()
    x = nothing
    try
        try
            x = "/"
            assertstring(x)
            error("err")
        catch
            rethrow()
        end
    catch
    end
    assertstring(x)
end

test_trytry()

throws

ERROR: LoadError: MethodError: no method matching assertstring(::Nothing)

As a sanity check, using Ref instead of a slot works:

function test_trytry_ref()
    x = Ref{Any}(nothing)
    try
        try
            x[] = "/"
            assertstring(x[])
            error("err")
        catch
            rethrow()
        end
    catch
    end
    assertstring(x[])
end

test_trytry_ref()  # no error

Looking at @code_typed optimize=false test_trytry():

CodeInfo(
1 ─      (x = Main.nothing)::Core.Const(nothing)
2 ─ %2 = $(Expr(:enter, #7))
3 ─      $(Expr(:enter, #5))
4 ─      (x = "/")::Core.Const("/")
│        Main.assertstring(x::Core.Const("/"))::Any
│        Main.error("err")::Union{}
│        Core.Const(:($(Expr(:leave, 1))))::Union{}
└──      Core.Const(:(goto %12))::Union{}
5 ┄      $(Expr(:leave, 1))
6 ─      Main.rethrow()::Union{}
│        Core.Const(:($(Expr(:pop_exception, :(%3)))))::Union{}
│        Core.Const(:($(Expr(:leave, 1))))::Union{}
└──      Core.Const(:(goto %16))::Union{}
7 ┄      $(Expr(:leave, 1))
8 ─      $(Expr(:pop_exception, :(%2)))::Any
│        Main.assertstring(x::Core.Const(nothing))::Union{}
└──      Core.Const(:(return %16))::Union{}
) => Union{}

Note Main.assertstring(x::Core.Const(nothing))::Union{} in BB 8. Does this indicate that there are some problems in the inference?

[vtjnash]

ah, that is a remarkable find. I see what is wrong: we only propagate changes to the nearest exception handler, but we must propagate to all of them