this pr refines #8270 and closes#8109
# description
examples:
the original syntax is okay
```nu
def okay [nums: list] {} # the type of list will be list<any>
```
empty annotations are allowed in any variation
the last two may be caught by a future formatter,
but do not affect `nu` code currently
```nu
def okay [nums: list<>] {} # okay
def okay [nums: list< >] {} # weird but also okay
def okay [nums: list<
>] {} # also weird but okay
```
types are allowed (See [notes](#notes) below)
```nu
def okay [nums: list<int>] {} # `test [a b c]` will throw an error
def okay [nums: list< int > {} # any amount of space within the angle brackets is okay
def err [nums: list <int>] {} # this is not okay, `nums` and `<int>` will be parsed as
# two separate params,
```
nested annotations are allowed in many variations
```nu
def okay [items: list<list<int>>] {}
def okay [items: list<list>] {}
```
any unterminated annotation is caught
```nu
Error: nu::parser::unexpected_eof
× Unexpected end of code.
╭─[source:1:1]
1 │ def err [nums: list<int] {}
· ▲
· ╰── expected closing >
╰────
```
unknown types are flagged
```nu
Error: nu::parser::unknown_type
× Unknown type.
╭─[source:1:1]
1 │ def err [nums: list<str>] {}
· ─┬─
· ╰── unknown type
╰────
Error: nu::parser::unknown_type
× Unknown type.
╭─[source:1:1]
1 │ def err [nums: list<int, string>] {}
· ─────┬─────
· ╰── unknown type
╰────
```
# notes
the error message for mismatched types in not as intuitive
```nu
Error: nu::parser::parse_mismatch
× Parse mismatch during operation.
╭─[source:1:1]
1 │ def err [nums: list<int>] {}; err [a b c]
· ┬
· ╰── expected int
╰────
```
it should be something like this
```nu
Error: nu::parser::parse_mismatch
× Parse mismatch during operation.
╭─[source:1:1]
1 │ def err [nums: list<int>] {}; err [a b c]
· ──┬──
· ╰── expected list<int>
╰────
```
this is currently not implemented
8cf9bc9993