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If julia functions which was brought to R throws an error, no real error is thrown, but an error object is returned #216 #508

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schlichtanders opened this issue Nov 18, 2023 · 3 comments · May be fixed by #525
Open

If julia functions which was brought to R throws an error, no real error is thrown, but an error object is returned #216 #508

schlichtanders opened this issue Nov 18, 2023 · 3 comments · May be fixed by #525

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@schlichtanders
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schlichtanders commented Nov 18, 2023 •
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I created an issue at JuliaCall however after a first inspection, I think it is actually an RCall issue.

Concretely something in the following is not raising julia errors when run on R. Also the stacktrace is not reported.

RCall.jl/src/callback.jl

Lines 122 to 147 in 69c22dd

"""
Wrap a callable Julia object `f` an a R `ClosSxpPtr`.
Constructs the following R code
function(...) .External(juliaCallback, fExPtr, ...)
"""
function sexp(::Type{RClass{:function}}, f)
fptr = protect(sexp(RClass{:externalptr}, f))
body = protect(rlang_p(Symbol(".External"),
juliaCallback,
fptr,
Const.DotsSymbol))
nprotect = 2
local clos
try
args = protect(sexp_arglist_dots())
nprotect += 1
lang = rlang_p(:function, args, body)
clos = reval_p(lang)
finally
unprotect(nprotect)
end
clos
end

Helpful steps to provide error support

Looking into JuliaCall's error handling, there are two places:

  1. on JuliaCall julia side the following try catch converts a julia error to an R object https://github.com/Non-Contradiction/JuliaCall/blob/c05473bea78a0197c639f7e82ab1c6f2e943e1cc/inst/julia/setup.jl#L165-L194
function docall(call1)
    try
        # ...
    catch e
        Rerror(e, stacktrace(catch_backtrace())).p;
    end;
end
  1. on JuliaCall R side the following intercepts these R objects and raises them as R errors https://github.com/Non-Contradiction/JuliaCall/blob/c05473bea78a0197c639f7e82ab1c6f2e943e1cc/R/interface.R#L76-L78
    r <- .julia$do.call_(jcall)

    if (inherits(r, "error")) stop(r)

Both these steps would need to be replicated inside the conversion of a Julia Function to an R function.
@schlichtanders
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I found where the julia error object is transformed into a simpleError, skipping stacktrace entirely

RCall.jl/src/callback.jl

Line 61 in 69c22dd

err = rcall(reval("base::simpleError"), string(e))

this should be changed to the RCall equivalent of JuliaCall's

err = Rerror(e, stacktrace(catch_backtrace())).p;

@schlichtanders
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The second step needed is to surround the following with the if (inherits(r, "error")) stop(r) logic

RCall.jl/src/callback.jl

Lines 132 to 135 in 69c22dd

body = protect(rlang_p(Symbol(".External"),
juliaCallback,
fptr,
Const.DotsSymbol))

Unfortunately, I couldn't find a way yet how to add such if else logic from Julia.

@schlichtanders
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schlichtanders commented Nov 18, 2023 •
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I fixed the one part for me now, but it seems juliaCallback cannot be fixed outside of RCall itself.

As soon as I call setup_callbacks() again and run a typical failing example

julia_eval('() = error("fail")')()

I get the following error (or sometimes also a Segmentation fault)

ERROR: UndefVarError: `error_msg` not defined

I bet this has something todo with creating C functions and would be solved if this is officially fixed in RCall.jl

@schlichtanders schlichtanders linked a pull request May 2, 2024 that will close this issue
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raise julia errors jolin-io/RCall.jl
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@schlichtanders