Better error reporting for map keys.

[nevertrimnuts]

Given this code:

Key :: struct {
    a: []u32
}

main :: proc() {
    my_map := make(map[Key]u32)
}

The error message is

/home/redacted/doing/programming/projects/odin_test/main.odin(90:20) Error: Invalid type of a key for a map, got 'Key'
	my_map := make(map[Key]u32)
	               ^~~~~~~~~~^

In this example, it is trivial to figure out why you can't use Key as a map key, but in a more complex codebase with nested struct definitions, it becomes more difficult.

It would be nice if it said something like

struct `Key` contains field `a: []u32`, which makes it incompatible to serve as a map key.