[Bug] Wrong error message with normal args behind varargs

[BWindey]

When creating a macro or function (same behaviour) with varargs and then a normal argument, the compiler gives an error from where the function is called, instead of on the declaration of the function.

Example:

import std::io;

macro void print(int... nums, String test) { }

fn void main() {
	print(1, 2, 3, "numbers");
}

Error message:

 3: fn void print(int... nums, String test) { }
 4: 
 5: fn void main() {
 6:     print(1, 2, 3, "numbers");
                       ^^^^^^^^^
Error: You cannot cast 'String' to 'int'.

This seems not the expected behaviour.

It even gets stranger when the types do match:

import std::io;

fn void print(int... nums, int num) { }

fn void main() {
	print(1, 2, 3);
}

Error message:

 3: fn void print(int... nums, int num) { }
 4: 
 5: fn void main() {
 6:     print(1, 2, 3);
                     ^
Error: Expected 'num: ...' after this argument.

1: import std::io;
2: 
3: fn void print(int... nums, int num) { }
           ^^^^^
Note: The definition was here.

[lerno]

This is actually correct!

[BWindey]

So you imply that a function with those arguments is correct? Why? And how would you call it?

[lerno]

You always need to call those trailing arguments with a named parameter. This is because otherwise default parameters would not make sense:

fn void print(int... nums, int num = 1) { }

In the above, given print(1, 2, 3) how would you know what would be assigned to num? So the rule is that any parameters after a vaarg must be named.

We can consider a better example. Let's say we want this:

fn void do_something(int x, Context context = default_context) { ... }

As long as we have non-vaargs, this is straightforward: do_something(1) or do_something(1, the_context). However, if we want vaargs it becomes a problem:

fn void do_something2(int... y, Context context = default_context) { ... }

So in order to make all uses consistent, we require that named parameter. We then have:

do_something(1);
do_something2(1, 2, 3);
do_something(4, context: my_context);
do_something2(1, 2, 3, 4, 5, context: my_context);
// There is do_something(4, my_context); available
// but the programmer could avoid that for consistency

[BWindey]

Ok, that makes sense. I'm not convinced that the shown error message is the best one possible though. Can it hint at using named arguments?

[lerno]

What heuristic should be used?

[EroMrinin134]

What heuristic should be used?

Maybe if after varargs exist any args then add to error message: "Perhabs, patameter name after ... was not mentioned?" (or something like that).