Respect SyntaxShape when parsing spread operator (#11674)

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This fixes an issue brought up by nihilander in
[Discord](https://discord.com/channels/601130461678272522/614593951969574961/1201594105986285649).

# Description
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Nushell panics when the spread operator is used like this (the
`...$rest` shouldn't actually be parsed as a spread operator at all):

```nu
$ def foo [...rest: string] {...$rest}                      
$ foo bar baz                                               
thread 'main' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/nu-protocol-0.89.0/src/signature.rs:650:9:
Internal error: can't run a predeclaration without a body
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: <nu_protocol::signature::Predeclaration as nu_protocol::engine::command::Command>::run
   3: nu_engine::eval::eval_call
   4: nu_engine::eval::eval_expression_with_input
   5: nu_engine::eval::eval_element_with_input
   6: nu_engine::eval::eval_block
   7: nu_cli::util::eval_source
   8: nu_cli::repl::evaluate_repl
   9: nu::run::run_repl
  10: nu::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```

The problem was that whenever the parser saw something like `{...$`,
`{...(`, or `{...[`, it would treat that as a record with a spread
expression, ignoring the syntax shape of the block it was parsing. This
should now be fixed, and the snippet above instead gives the following
error:

```nu
Error: nu:🐚:external_command

  × External command failed
   ╭─[entry #1:1:1]
 1 │  def foo [...rest] {...$rest}
   ·                     ────┬───
   ·                         ╰── executable was not found
   ╰────
  help: No such file or directory (os error 2)
```

# User-Facing Changes
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Stuff like `do { ...$rest }` will now try to run a command `...$rest`
rather than complaining that variable `$rest` doesn't exist.

# Tests + Formatting
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Sorry about the issue, I am not touching the parser again for a long
time :)

crates/nu-parser/src/parser.rs

@@ -1700,16 +1700,18 @@ pub fn parse_brace_expr(
         parse_closure_expression(working_set, shape, span)
     } else if matches!(third_token, Some(b":")) {
         parse_full_cell_path(working_set, None, span)
-    } else if second_token.is_some_and(|c| {
-        c.len() > 3 && c.starts_with(b"...") && (c[3] == b'$' || c[3] == b'{' || c[3] == b'(')
-    }) {
-        parse_record(working_set, span)
-    } else if matches!(shape, SyntaxShape::Closure(_)) || matches!(shape, SyntaxShape::Any) {
+    } else if matches!(shape, SyntaxShape::Closure(_)) {
         parse_closure_expression(working_set, shape, span)
     } else if matches!(shape, SyntaxShape::Block) {
         parse_block_expression(working_set, span)
     } else if matches!(shape, SyntaxShape::MatchBlock) {
         parse_match_block_expression(working_set, span)
+    } else if second_token.is_some_and(|c| {
+        c.len() > 3 && c.starts_with(b"...") && (c[3] == b'$' || c[3] == b'{' || c[3] == b'(')
+    }) {
+        parse_record(working_set, span)
+    } else if matches!(shape, SyntaxShape::Any) {
+        parse_closure_expression(working_set, shape, span)
     } else {
         working_set.error(ParseError::ExpectedWithStringMsg(
             format!("non-block value: {shape}"),

src/tests/test_spread.rs

@@ -190,3 +190,15 @@ fn deprecate_implicit_spread_for_externals() {
         .contains("Automatically spreading lists is deprecated"));
     assert_eq!(result.out, "1 2");
 }
+
+#[test]
+fn respect_shape() -> TestResult {
+    fail_test(
+        "def foo [...rest] { ...$rest }; foo bar baz",
+        "executable was not found",
+    )
+    .unwrap();
+    fail_test("module foo { ...$bar }", "expected_keyword").unwrap();
+    run_test(r#"def "...$foo" [] {2}; do { ...$foo }"#, "2").unwrap();
+    run_test(r#"match "...$foo" { ...$foo => 5 }"#, "5")
+}