allow lists to have type annotations (#8529)

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

crates/nu-parser/src/lex.rs

@@ -31,6 +31,7 @@ pub enum BlockKind {
     Paren,
     CurlyBracket,
     SquareBracket,
+    AngleBracket,
 }
 
 impl BlockKind {
@@ -39,6 +40,7 @@ impl BlockKind {
             BlockKind::Paren => b')',
             BlockKind::SquareBracket => b']',
             BlockKind::CurlyBracket => b'}',
+            BlockKind::AngleBracket => b'>',
         }
     }
 }
@@ -77,6 +79,7 @@ pub fn lex_item(
     span_offset: usize,
     additional_whitespace: &[u8],
     special_tokens: &[u8],
+    in_signature: bool,
 ) -> (Token, Option<ParseError>) {
     // This variable tracks the starting character of a string literal, so that
     // we remain inside the string literal lexer mode until we encounter the
@@ -156,6 +159,12 @@ pub fn lex_item(
         } else if c == b'[' {
             // We encountered an opening `[` delimiter.
             block_level.push(BlockKind::SquareBracket);
+        } else if c == b'<' && in_signature {
+            block_level.push(BlockKind::AngleBracket);
+        } else if c == b'>' && in_signature {
+            if let Some(BlockKind::AngleBracket) = block_level.last() {
+                let _ = block_level.pop();
+            }
         } else if c == b']' {
             // We encountered a closing `]` delimiter. Pop off the opening `[`
             // delimiter.
@@ -299,12 +308,48 @@ pub fn lex_item(
     }
 }
 
+pub fn lex_signature(
+    input: &[u8],
+    span_offset: usize,
+    additional_whitespace: &[u8],
+    special_tokens: &[u8],
+    skip_comment: bool,
+) -> (Vec<Token>, Option<ParseError>) {
+    lex_internal(
+        input,
+        span_offset,
+        additional_whitespace,
+        special_tokens,
+        skip_comment,
+        true,
+    )
+}
+
 pub fn lex(
     input: &[u8],
     span_offset: usize,
     additional_whitespace: &[u8],
     special_tokens: &[u8],
     skip_comment: bool,
+) -> (Vec<Token>, Option<ParseError>) {
+    lex_internal(
+        input,
+        span_offset,
+        additional_whitespace,
+        special_tokens,
+        skip_comment,
+        false,
+    )
+}
+
+fn lex_internal(
+    input: &[u8],
+    span_offset: usize,
+    additional_whitespace: &[u8],
+    special_tokens: &[u8],
+    skip_comment: bool,
+    // within signatures we want to treat `<` and `>` specially
+    in_signature: bool,
 ) -> (Vec<Token>, Option<ParseError>) {
     let mut error = None;
 
@@ -427,6 +472,7 @@ pub fn lex(
                 span_offset,
                 additional_whitespace,
                 special_tokens,
+                in_signature,
             );
             if error.is_none() {
                 error = err;

crates/nu-parser/src/lib.rs

@@ -16,7 +16,7 @@ pub use flatten::{
     flatten_block, flatten_expression, flatten_pipeline, flatten_pipeline_element, FlatShape,
 };
 pub use known_external::KnownExternal;
-pub use lex::{lex, Token, TokenContents};
+pub use lex::{lex, lex_signature, Token, TokenContents};
 pub use lite_parser::{lite_parse, LiteBlock, LiteElement};
 pub use parse_keywords::*;
 

crates/nu-parser/src/parser.rs

@@ -1,6 +1,6 @@
 use crate::{
     eval::{eval_constant, value_as_string},
-    lex,
+    lex::{lex, lex_signature},
     lite_parser::{lite_parse, LiteCommand, LiteElement},
     parse_mut,
     parse_patterns::{parse_match_pattern, parse_pattern},
@@ -3039,6 +3039,8 @@ pub fn parse_shape_name(
     bytes: &[u8],
     span: Span,
 ) -> (SyntaxShape, Option<ParseError>) {
+    let mut error = None;
+
     let result = match bytes {
         b"any" => SyntaxShape::Any,
         b"binary" => SyntaxShape::Binary,
@@ -3060,7 +3062,11 @@ pub fn parse_shape_name(
         b"int" => SyntaxShape::Int,
         b"import-pattern" => SyntaxShape::ImportPattern,
         b"keyword" => SyntaxShape::Keyword(vec![], Box::new(SyntaxShape::Any)),
-        b"list" => SyntaxShape::List(Box::new(SyntaxShape::Any)),
+        _ if bytes.starts_with(b"list") => {
+            let (sig, err) = parse_list_shape(working_set, bytes, span);
+            error = error.or(err);
+            sig
+        }
         b"math" => SyntaxShape::MathExpression,
         b"nothing" => SyntaxShape::Nothing,
         b"number" => SyntaxShape::Number,
@@ -3104,7 +3110,51 @@ pub fn parse_shape_name(
         }
     };
 
-    (result, None)
+    (result, error)
+}
+
+fn parse_list_shape(
+    working_set: &StateWorkingSet,
+    bytes: &[u8],
+    span: Span,
+) -> (SyntaxShape, Option<ParseError>) {
+    assert!(bytes.starts_with(b"list"));
+
+    if bytes == b"list" {
+        (SyntaxShape::List(Box::new(SyntaxShape::Any)), None)
+    } else if bytes.starts_with(b"list<") {
+        let start = span.start + 5;
+
+        // if the annotation is unterminated, we want to return early to avoid
+        // overflows with spans
+        let end = if bytes.ends_with(b">") {
+            span.end - 1
+        } else {
+            let err = ParseError::Unclosed(">".into(), span);
+            return (SyntaxShape::List(Box::new(SyntaxShape::Any)), Some(err));
+        };
+
+        let inner_span = Span::new(start, end);
+
+        let inner_text = String::from_utf8_lossy(working_set.get_span_contents(inner_span));
+
+        // remove any extra whitespace, for example `list< string >` becomes `list<string>`
+        let inner_bytes = inner_text.trim().as_bytes();
+
+        // list<>
+        if inner_bytes.is_empty() {
+            (SyntaxShape::List(Box::new(SyntaxShape::Any)), None)
+        } else {
+            let (inner_sig, err) = parse_shape_name(working_set, inner_bytes, inner_span);
+
+            (SyntaxShape::List(Box::new(inner_sig)), err)
+        }
+    } else {
+        (
+            SyntaxShape::List(Box::new(SyntaxShape::Any)),
+            Some(ParseError::UnknownType(span)),
+        )
+    }
 }
 
 pub fn parse_type(_working_set: &StateWorkingSet, bytes: &[u8]) -> Type {
@@ -3518,13 +3568,14 @@ pub fn parse_signature_helper(
     let mut error = None;
     let source = working_set.get_span_contents(span);
 
-    let (output, err) = lex(
+    let (output, err) = lex_signature(
         source,
         span.start,
         &[b'\n', b'\r'],
         &[b':', b'=', b','],
         false,
     );
+
     error = error.or(err);
 
     let mut args: Vec<Arg> = vec![];