Fix closures that use matches. Move 'collect' to core. (#8596)

# Description

Fix patterns in pattern matching to properly declare their variables
when discovering which variables need to be closed over when creating a
closure.

Also, moves `collect` to core, so that the core language can use `$in`.

Fixes #8595 

# User-Facing Changes

See above

# 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

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```

# 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-cmd-lang/src/core_commands/match_.rs

@@ -111,6 +111,11 @@ impl Command for Match {
                 example: "match [1, 2, 3] { [$a, $b, $c] => { $a + $b + $c }, _ => 0 }",
                 result: Some(Value::test_int(6)),
             },
+            Example {
+                description: "Match against pipeline input",
+                example: "{a: {b: 3}} | match $in.a { { $b } => ($b + 10) }",
+                result: Some(Value::test_int(13)),
+            },
         ]
     }
 }

crates/nu-cmd-lang/src/core_commands/mod.rs

@@ -1,5 +1,6 @@
 mod alias;
 mod break_;
+mod collect;
 mod commandline;
 mod const_;
 mod continue_;
@@ -41,6 +42,7 @@ mod while_;
 
 pub use alias::Alias;
 pub use break_::Break;
+pub use collect::Collect;
 pub use commandline::Commandline;
 pub use const_::Const;
 pub use continue_::Continue;

crates/nu-cmd-lang/src/default_context.rs

@@ -18,6 +18,7 @@ pub fn create_default_context() -> EngineState {
         bind_command! {
             Alias,
             Break,
+            Collect,
             Commandline,
             Const,
             Continue,

crates/nu-cmd-lang/src/example_test.rs

@@ -13,7 +13,7 @@ mod test_examples {
         check_example_evaluates_to_expected_output,
         check_example_input_and_output_types_match_command_signature,
     };
-    use crate::{Break, Describe, Mut};
+    use crate::{Break, Collect, Describe, Mut};
     use crate::{Echo, If, Let};
     use nu_protocol::{
         engine::{Command, EngineState, StateWorkingSet},
@@ -66,6 +66,7 @@ mod test_examples {
             working_set.add_decl(Box::new(If));
             working_set.add_decl(Box::new(Let));
             working_set.add_decl(Box::new(Mut));
+            working_set.add_decl(Box::new(Collect));
 
             // Adding the command that is being tested to the working set
             working_set.add_decl(cmd);

crates/nu-command/src/default_context.rs

@@ -36,7 +36,6 @@ pub fn create_default_context() -> EngineState {
             All,
             Any,
             Append,
-            Collect,
             Columns,
             Compact,
             Default,

crates/nu-command/src/filters/mod.rs

@@ -1,7 +1,6 @@
 mod all;
 mod any;
 mod append;
-mod collect;
 mod columns;
 mod compact;
 mod default;
@@ -58,7 +57,6 @@ mod zip;
 pub use all::All;
 pub use any::Any;
 pub use append::Append;
-pub use collect::Collect;
 pub use columns::Columns;
 pub use compact::Compact;
 pub use default::Default;

crates/nu-parser/src/parser.rs

@@ -11,8 +11,8 @@ use crate::{
 use nu_protocol::{
     ast::{
         Argument, Assignment, Bits, Block, Boolean, Call, CellPath, Comparison, Expr, Expression,
-        FullCellPath, ImportPattern, ImportPatternHead, ImportPatternMember, Math, Operator,
-        PathMember, Pipeline, PipelineElement, RangeInclusion, RangeOperator,
+        FullCellPath, ImportPattern, ImportPatternHead, ImportPatternMember, MatchPattern, Math,
+        Operator, PathMember, Pattern, Pipeline, PipelineElement, RangeInclusion, RangeOperator,
     },
     engine::StateWorkingSet,
     span, BlockId, Flag, PositionalArg, Signature, Span, Spanned, SyntaxShape, Type, Unit, VarId,
@@ -6005,6 +6005,23 @@ pub fn discover_captures_in_pipeline_element(
     }
 }
 
+pub fn discover_captures_in_pattern(pattern: &MatchPattern, seen: &mut Vec<VarId>) {
+    match &pattern.pattern {
+        Pattern::Variable(var_id) => seen.push(*var_id),
+        Pattern::List(items) => {
+            for item in items {
+                discover_captures_in_pattern(item, seen)
+            }
+        }
+        Pattern::Record(items) => {
+            for item in items {
+                discover_captures_in_pattern(&item.1, seen)
+            }
+        }
+        Pattern::Value(_) | Pattern::IgnoreValue | Pattern::Garbage => {}
+    }
+}
+
 // Closes over captured variables
 pub fn discover_captures_in_expr(
     working_set: &StateWorkingSet,
@@ -6206,6 +6223,7 @@ pub fn discover_captures_in_expr(
         Expr::MatchPattern(_) => {}
         Expr::MatchBlock(match_block) => {
             for match_ in match_block {
+                discover_captures_in_pattern(&match_.0, seen);
                 let result = discover_captures_in_expr(working_set, &match_.1, seen, seen_blocks)?;
                 output.extend(&result);
             }