Dispatch failure or failure to throw error regression

[KristofferC]

Code to repro the issue:

julia> using Dash

julia> app = dash(assets_folder = "assets_compressed", compress = true);

julia> make_handler(app)

In 1.7:

julia> make_handler(app)
ERROR: The layout must be a component, tree of components, or a function which returns a component.
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:33
 [2] validate_layout(layout::Nothing)
   @ Dash ~/PkgEval/Dash.jl/src/handler/make_handler.jl:44
 [3] make_handler(app::Dash.DashApp, registry::DashBase.ResourcesRegistry; check_layout::Bool)
   @ Dash ~/PkgEval/Dash.jl/src/handler/make_handler.jl:123
 [4] make_handler(app::Dash.DashApp)
   @ Dash ~/PkgEval/Dash.jl/src/handler/make_handler.jl:158

In 1.8:

julia> make_handler(app); # No error

Now, this should cleary error because what ends up getting called is

https://github.com/plotly/Dash.jl/blob/f0606e07d2479fd8b5be1da4a6a59656e24acfa3/src/handler/make_handler.jl#L123

which has these three definitions:

https://github.com/plotly/Dash.jl/blob/f0606e07d2479fd8b5be1da4a6a59656e24acfa3/src/handler/make_handler.jl#L40-L44

and app.layout is nothing:

julia> app.layout === nothing
true

In fact, it errors if we execute it manually:

julia> Dash.validate_layout(Dash.get_layout(app))
ERROR: The layout must be a component, tree of components, or a function which returns a component.
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] validate_layout(layout::Nothing)
   @ Dash ~/PkgEval/Dash.jl/src/handler/make_handler.jl:44

and also when running it through the debugger:

julia> using Debugger

julia> @run make_handler(app)
ERROR: The layout must be a component, tree of components, or a function which returns a component.

So something here makes the dispatch go to the wrong function or the error to be swallowed.

[vtjnash]

Fascinating. It declares it called consteval on nothing and confidently concluded (during inlining) that the method has no side-effects and returns nothing.

    ┌ @ /home/vtjnash/.julia/packages/Dash/yscRy/src/app/dashapp.jl:69 within `get_layout`
    │┌ @ Base.jl:37 within `getproperty`
6 ──││ %17  = Base.getfield(app, :layout)::Union{Nothing, Function, Component}
│   └└
│    %18  = (isa)(%17, Nothing)::Bool
└───        goto #8 if not %18
7 ──        goto #11
8 ── %21  = (isa)(%17, Component)::Bool
└───        goto #10 if not %21
9 ── %23  = π (%17, Component)
│   ┌ @ /home/vtjnash/.julia/packages/Dash/yscRy/src/handler/make_handler.jl:40 within `validate_layout`
│   │┌ @ /home/vtjnash/.julia/packages/Dash/yscRy/src/Components.jl:23 within `validate`
│   ││┌ @ set.jl:9 within `Set`
│   │││ %24  = invoke Dict{Symbol, Nothing}()::Dict{Symbol, Nothing}
│   │││┌ @ set.jl:6 within `_Set`
│   ││││ %25  = %new(Set{Symbol}, %24)::Set{Symbol}
│   ││└└
│   ││        invoke Dash._validate(%23::Component, %25::Set{Symbol})::Union{Nothing, Bool}
│   └└
└───        goto #11
10 ─        Dash.validate_layout(%17)::Any
└───        goto #11
11 ┄        nothing::Nothing

 • %12  = < consteval > validate_layout(::Union{Nothing, Function, Component})::Any
   %12  = validate_layout(::Function)::Any
   %12  = validate_layout(::Component)::Any

[aviatesk]

We seem to propagate effects of a thrown concrete-call wrongly. #44762 should fix this.