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-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/collect.rs

@@ -1,105 +0,0 @@
-use nu_engine::{eval_block, redirect_env, CallExt};
-use nu_protocol::ast::Call;
-use nu_protocol::engine::{Closure, Command, EngineState, Stack};
-use nu_protocol::{
-    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Type,
-    Value,
-};
-
-#[derive(Clone)]
-pub struct Collect;
-
-impl Command for Collect {
-    fn name(&self) -> &str {
-        "collect"
-    }
-
-    fn signature(&self) -> Signature {
-        Signature::build("collect")
-            .input_output_types(vec![(Type::List(Box::new(Type::Any)), Type::Any)])
-            .required(
-                "closure",
-                SyntaxShape::Closure(Some(vec![SyntaxShape::Any])),
-                "the closure to run once the stream is collected",
-            )
-            .switch(
-                "keep-env",
-                "let the block affect environment variables",
-                None,
-            )
-            .category(Category::Filters)
-    }
-
-    fn usage(&self) -> &str {
-        "Collect the stream and pass it to a block."
-    }
-
-    fn run(
-        &self,
-        engine_state: &EngineState,
-        stack: &mut Stack,
-        call: &Call,
-        input: PipelineData,
-    ) -> Result<PipelineData, ShellError> {
-        let capture_block: Closure = call.req(engine_state, stack, 0)?;
-
-        let block = engine_state.get_block(capture_block.block_id).clone();
-        let mut stack_captures = stack.captures_to_stack(&capture_block.captures);
-
-        let metadata = input.metadata();
-        let input: Value = input.into_value(call.head);
-
-        let mut saved_positional = None;
-        if let Some(var) = block.signature.get_positional(0) {
-            if let Some(var_id) = &var.var_id {
-                stack_captures.add_var(*var_id, input.clone());
-                saved_positional = Some(*var_id);
-            }
-        }
-
-        let result = eval_block(
-            engine_state,
-            &mut stack_captures,
-            &block,
-            input.into_pipeline_data(),
-            call.redirect_stdout,
-            call.redirect_stderr,
-        )
-        .map(|x| x.set_metadata(metadata));
-
-        if call.has_flag("keep-env") {
-            redirect_env(engine_state, stack, &stack_captures);
-            // for when we support `data | let x = $in;`
-            // remove the variables added earlier
-            for var_id in capture_block.captures.keys() {
-                stack_captures.vars.remove(var_id);
-            }
-            if let Some(u) = saved_positional {
-                stack_captures.vars.remove(&u);
-            }
-            // add any new variables to the stack
-            stack.vars.extend(stack_captures.vars);
-        }
-        result
-    }
-
-    fn examples(&self) -> Vec<Example> {
-        vec![Example {
-            description: "Use the second value in the stream",
-            example: "[1 2 3] | collect { |x| $x.1 }",
-            result: Some(Value::test_int(2)),
-        }]
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn test_examples() {
-        use crate::test_examples;
-
-        test_examples(Collect {})
-    }
-}

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;