Improving MethodError message for anonymous functions

[Bumblebee00]

This pull request aims to resolve issue #56325

In this example, you get a MethodError for your anonymous method (::var"#3#4"):

vals = [5,6,10,20];
accumulate(vals; init=0) do (old, new)
           old + new
       end

ERROR: MethodError: no method matching (::var"#3#4")(::Int64, ::Int64)
The function `#3` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  (::var"#3#4")(::Any)
   @ Main REPL[2]:2

This can be confusing for beginner julia programmers, because in the case of a do block, it might even be non-obvious that you wrote a function. I changed the error message adding the words "anonymous function" and adding a tip for the number of arguments:

ERROR: MethodError: no method of the anonymous function var"#2#3" matching (::var"#2#3")(::Int64, ::Int64)
The function `#2` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  (::var"#2#3")(::Any)
   @ Main REPL[2]:2


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

Of cousre if the function is not anonymous the error will not say "anonymous function" and if has more than one method will not display the tip:

vals = [5,6,10,20];

function f(x,y,z)
	x+y+z
end

function f(x,y,z,w)
	x+y+z+w
end
# f is a non anonymous function with more than one method, but
# both methods of f dont take two arguments and wn error will be trown
accumulate(f, vals; init=0)

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

Closest candidates are:
  f(::Any, ::Any, ::Any, ::Any)
   @ Main REPL[3]:1
  f(::Any, ::Any, ::Any)
   @ Main REPL[2]:1

I have done this by modifying the files base/errorshow.jl and test/errorshow.jl

[nsajko]

Suggested change

	# if the function has only on method, print a Tip about the number of arguments to be used
	# if the function has only one method, print a tip about the number of arguments to be used

[nsajko]

I think these are good changes, but IMO it might be better as two separate pull requests, seeing as it's really two unrelated changes:

• hint about a function being anonymous
• hint about the number of arguments for a function with only a single method

[Bumblebee00]

that is a sensible opinion, i created two different pull requests for the two features