Restrict closure expression to be something like {|| ...} (#8290)

# Description

As title, closes: #7921 closes: #8273

# User-Facing Changes

when define a closure without pipe, nushell will raise error for now:
```
❯ let x = {ss ss}
Error: nu::parser::closure_missing_pipe

  × Missing || inside closure
   ╭─[entry #2:1:1]
 1 │ let x = {ss ss}
   ·         ───┬───
   ·            ╰── Parsing as a closure, but || is missing
   ╰────
  help: Try add || to the beginning of closure
```

`any`, `each`, `all`, `where` command accepts closure, it forces user
input closure like `{||`, or parse error will returned.
```
❯ {major:2, minor:1, patch:4} | values | each { into string }
Error: nu::parser::closure_missing_pipe

  × Missing || inside closure
   ╭─[entry #4:1:1]
 1 │ {major:2, minor:1, patch:4} | values | each { into string }
   ·                                             ───────┬───────
   ·                                                    ╰── Parsing as a closure, but || is missing
   ╰────
  help: Try add || to the beginning of closure
```

`with-env`, `do`, `def`, `try` are special, they still remain the same,
although it says that it accepts a closure, but they don't need to be
written like `{||`, it's more likely a block but can capture variable
outside of scope:
```
❯ def test [input] { echo [0 1 2] | do { do { echo $input } } }; test aaa
aaa
```

Just realize that It's a big breaking change, we need to update config
and scripts...

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-parser/src/errors.rs

@@ -38,6 +38,13 @@ pub enum ParseError {
     #[diagnostic(code(nu::parser::parse_mismatch))]
     Expected(String, #[label("expected {0}")] Span),
 
+    #[error("Missing || inside closure")]
+    #[diagnostic(
+        code(nu::parser::closure_missing_pipe),
+        help("Try add || to the beginning of closure")
+    )]
+    ClosureMissingPipe(#[label("Parsing as a closure, but || is missing")] Span),
+
     #[error("Type mismatch during operation.")]
     #[diagnostic(code(nu::parser::type_mismatch))]
     Mismatch(String, String, #[label("expected {0}, found {1}")] Span), // expected, found, span
@@ -487,6 +494,7 @@ impl ParseError {
             ParseError::UnknownOperator(_, _, s) => *s,
             ParseError::InvalidLiteral(_, _, s) => *s,
             ParseError::NotAConstant(s) => *s,
+            ParseError::ClosureMissingPipe(s) => *s,
         }
     }
 }

crates/nu-parser/src/parser.rs

@@ -1779,8 +1779,10 @@ pub fn parse_brace_expr(
 
     if matches!(second_token, None) {
         // If we're empty, that means an empty record or closure
-        if matches!(shape, SyntaxShape::Closure(_)) {
-            parse_closure_expression(working_set, shape, span, expand_aliases_denylist)
+        if matches!(shape, SyntaxShape::Closure(None)) {
+            parse_closure_expression(working_set, shape, span, expand_aliases_denylist, false)
+        } else if matches!(shape, SyntaxShape::Closure(Some(_))) {
+            parse_closure_expression(working_set, shape, span, expand_aliases_denylist, true)
         } else if matches!(shape, SyntaxShape::Block) {
             parse_block_expression(working_set, span, expand_aliases_denylist)
         } else {
@@ -1789,11 +1791,13 @@ pub fn parse_brace_expr(
     } else if matches!(second_token_contents, Some(TokenContents::Pipe))
         || matches!(second_token_contents, Some(TokenContents::PipePipe))
     {
-        parse_closure_expression(working_set, shape, span, expand_aliases_denylist)
+        parse_closure_expression(working_set, shape, span, expand_aliases_denylist, true)
     } else if matches!(third_token, Some(b":")) {
         parse_full_cell_path(working_set, None, span, expand_aliases_denylist)
-    } else if matches!(shape, SyntaxShape::Closure(_)) || matches!(shape, SyntaxShape::Any) {
-        parse_closure_expression(working_set, shape, span, expand_aliases_denylist)
+    } else if matches!(shape, SyntaxShape::Closure(None)) {
+        parse_closure_expression(working_set, shape, span, expand_aliases_denylist, false)
+    } else if matches!(shape, SyntaxShape::Closure(Some(_))) || matches!(shape, SyntaxShape::Any) {
+        parse_closure_expression(working_set, shape, span, expand_aliases_denylist, true)
     } else if matches!(shape, SyntaxShape::Block) {
         parse_block_expression(working_set, span, expand_aliases_denylist)
     } else {
@@ -4414,6 +4418,7 @@ pub fn parse_closure_expression(
     shape: &SyntaxShape,
     span: Span,
     expand_aliases_denylist: &[usize],
+    require_pipe: bool,
 ) -> (Expression, Option<ParseError>) {
     trace!("parsing: closure expression");
 
@@ -4490,7 +4495,15 @@ pub fn parse_closure_expression(
             Some((Box::new(Signature::new("closure".to_string())), *span)),
             1,
         ),
-        _ => (None, 0),
+        _ => {
+            if require_pipe {
+                error = error.or(Some(ParseError::ClosureMissingPipe(span)));
+                working_set.exit_scope();
+                return (garbage(span), error);
+            } else {
+                (None, 0)
+            }
+        }
     };
 
     // TODO: Finish this

crates/nu-parser/tests/test_parser.rs

@@ -1563,7 +1563,13 @@ mod input_types {
                 )
                 .optional(
                     "else_expression",
-                    SyntaxShape::Keyword(b"else".to_vec(), Box::new(SyntaxShape::Expression)),
+                    SyntaxShape::Keyword(
+                        b"else".to_vec(),
+                        Box::new(SyntaxShape::OneOf(vec![
+                            SyntaxShape::Block,
+                            SyntaxShape::Expression,
+                        ])),
+                    ),
                     "expression or block to run if check fails",
                 )
                 .category(Category::Core)