required keyword arguments

[timziebart]

Following up on the comment by @Keno in this PR JuliaLang/METADATA.jl#15489 I added the functionality to understand required keyword arguments to @compat. Basically that means

@compat f(;x) = [...]

is equivalent to

f(;x=error("RequiredKeywordArgumentError: `x` is a required keyword argument, please provide `x = ...`.")) = [...]

As this is my first submission to a JuliaLang rep, could you check that the style etc. matches what you would expect?

[KristofferC]

Restarting CI.

[fredrikekre]

I suggest that you add a

struct UndefKeywordError <: Exception
    kw
end
Base.showerror(io::IO, e::UndefKeywordError) = print(io, "keyword argument $(e.kw) not assigned")

to make it look the same as on Julia 0.7.

[fredrikekre]

Instead of try-catch you can use @test_throws, for example

julia> f(;y) = y
f (generic function with 1 method)

julia> @test_throws UndefKeywordError f()
Test Passed
      Thrown: UndefKeywordError

[timziebart]

thanks @fredrikekre , I will add that

[timziebart]

The errors seem to be due to the export UndefKeywordError line. Should I simply not export it (which would make it a different usage than in 0.7) or should I add a condition (see below)?

if !isdefined(:UndefKeywordError)
    struct UndefKeywordError <: Exception
        kw
    end
    Base.showerror(io::IO, e::UndefKeywordError) = print(io, "keyword argument $(e.kw) not assigned")
    export UndefKeywordError
end

?

[fredrikekre]

Yes, you can use !isdefined(Base, :UndefKeywordError), and also in the macro implementation, since this should just pass through @compat unchanged on julia 0.7

[timziebart]

Thanks, seems to work now!

[fredrikekre]

Sorry, this should also print the exception type, so

print(io, "UndefKeywordError: keyword argument $(e.kw) not assigned")

as it does on Julia v0.7:

julia> f(;y) = y
f (generic function with 1 method)

julia> f()
ERROR: UndefKeywordError: keyword argument y not assigned

otherwise LGTM

[timziebart]

True, corrected that.

[stevengj]

Needs a README item.

[timziebart]

@stevengj: absolutely. I added a description in the README, is it okai like this?

[stevengj]

Some fixes:

* Required keyword arguments ([#25830]). For example, `@compat foo(; x, y)` makes `x` and `y` required keyword arguments: when calling `foo`, an error is thrown if `x` or `y` is not explicitly provided.

[stevengj]

(The link to JuliaLang/julia#25830 is added if you run julia /path/to/julia/doc/NEWS-update.jl README.jl to run https://github.com/JuliaLang/julia/blob/master/doc/NEWS-update.jl)

[timziebart]

I just pushed the update README.md.

[timziebart]

@stevengj I responded to your comment and updated the README.md a few days ago. Do you agree with the result?

[stevengj]

Thanks!

[stevengj]

This doesn't handle the case where the argument has a type. It should probably be:

arg2kw(arg, sym) = Expr(:kw, arg, Expr(:call, throw, UndefKeywordError(sym)))
symbol2kw(arg::Symbol) = arg2kw(arg, arg)
symbol2kw(arg::Expr) = isexpr(arg, :(::)) ? arg2kw(arg, arg.args[1]) : arg
symbol2kw(arg) = arg

[stevengj]

(See https://discourse.julialang.org/t/make-function-arguments-positional-or-keyword/2984/35)

[timziebart]

Yes, that seems reasonable, should I update the PR? Can I even or should this be a new PR?