Print a tip in MethodError

[Bumblebee00]

If a function with only one method accepting a certain number of arguments, gets called with a different number of arguments, a Tip is printed in the MethodError like this:

f(x,y)=x+y
f(1)

ERROR: MethodError: no method matching f(::Int64)
The function `f` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  f(::Any, ::Any)
   @ Main REPL[1]:1


Tip: the function `f` was called with 1 arguments, but has only one method accepting 2 argument.

See the original pull request and issue #56325

[ararslan]

I'm not sure this is quite right; f doesn't need to be a function in order for there to be a mismatch in the number of arguments (i.e. it could be a type or callable object), but also, I believe this tip will be printed when the correct number of arguments is provided but the sole method does not apply to them. For example, consider:

julia> f(x::Int) = x + 1
f (generic function with 1 method)

julia> f("hi")
ERROR: MethodError: no method matching f(::String)
The function `f` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  f(::Int64)
   @ Main REPL[1]:1

Stacktrace:
 [1] top-level scope
   @ REPL[2]:1

As currently implemented, the error message would include

Tip: the function `f` was called with 1 arguments, but has only one method accepting 1 argument.

which I don't think would help a user determine the source of the issue or how to fix it.

[Bumblebee00]

That is correct I didnt think about this. But could be easly resolved by also checking if the number of arguments with wich the function was called is different from the accepted arguments, like so:

    if f isa Function && length(methods(f)) == 1 && length(arg_types_param) !== length(methods(f)[1].sig.parameters)-1
        print(...)
    end

can you think of other cases in wich this tip could be misleading?

[ararslan]

That's a good start but I don't think it will handle vararg signatures correctly. For example, consider:

julia> f(x::Int, y::Float64...) = x + sum(y; init=0.0)
f (generic function with 1 method)

julia> m = only(methods(f));

julia> nargs = length(m.sig.parameters) - 1  # number of defined arguments in the signature
2

julia> f(1)  # provided arguments < nargs, no error
1.0

julia> f(1.0)  # provided arguments < nargs but error is irrelevant to that
ERROR: MethodError: no method matching f(::Float64)
[...]

julia> f(1, 2)  # provided arguments == nargs
ERROR: MethodError: no method matching f(::Int64, ::Int64)
[...]

julia> f(1, 2, 3)  # provided arguments > nargs
ERROR: MethodError: no method matching f(::Int64, ::Int64, ::Int64)
[...]

You could use isvatuple(m.sig) to identify this case.