Add into cell-path for dynamic cell-path creation (#11322)

# Description

The `cell-path` is a type that can be created statically with
`$.nested.structure.5`, but can't be created from user input. This makes
it difficult to take advantage of commands that accept a cell-path to
operate on data structures.

This PR adds `into cell-path` for dynamic cell-path creation.

`into cell-path` accepts the following input shapes:
* Bare integer (equivalent to `$.1`)
* List of strings and integers
* List of records with entries `value` and `optional`
* String (parsed into a cell-path)

## Example usage

An example of where `into cell-path` can be used is in working with `git
config --list`. The git configuration has a tree structure that maps
well to nushell records. With dynamic cell paths it is easy to convert
`git config list` to a record:

```nushell
git config --list
| lines
| parse -r '^(?<key>[^=]+)=(?<value>.*)'
| reduce --fold {} {|entry, result|
  let path = $entry.key | into cell-path

  $result
  | upsert $path {||
    $entry.value
  }
}
| select remote
```

Output:

```
╭────────┬──────────────────────────────────────────────────────────────────╮
│        │ ╭──────────┬───────────────────────────────────────────────────╮ │
│ remote │ │          │ ╭───────┬───────────────────────────────────────╮ │ │
│        │ │ upstream │ │ url   │ git@github.com:nushell/nushell.git    │ │ │
│        │ │          │ │ fetch │ +refs/heads/*:refs/remotes/upstream/* │ │ │
│        │ │          │ ╰───────┴───────────────────────────────────────╯ │ │
│        │ │          │ ╭───────┬─────────────────────────────────────╮   │ │
│        │ │ origin   │ │ url   │ git@github.com:drbrain/nushell      │   │ │
│        │ │          │ │ fetch │ +refs/heads/*:refs/remotes/origin/* │   │ │
│        │ │          │ ╰───────┴─────────────────────────────────────╯   │ │
│        │ ╰──────────┴───────────────────────────────────────────────────╯ │
╰────────┴──────────────────────────────────────────────────────────────────╯
```

## Errors

`lex()` + `parse_cell_path()` are forgiving about what is allowed in a
cell-path so it will allow what appears to be nonsense to become a
cell-path:

```nushell
let table = [["!@$%^&*" value]; [key value]]

$table | get ("!@$%^&*.0" | into cell-path)
# => key
```

But it will reject bad cell-paths:

```
❯ "a b" | into cell-path
Error: nu:🐚:cant_convert

  × Can't convert to cell-path.
   ╭─[entry #14:1:1]
 1 │ "a b" | into cell-path
   ·         ───────┬──────
   ·                ╰── can't convert string to cell-path
   ╰────
  help: "a b" is not a valid cell-path (Parse mismatch during operation.)
```

# User-Facing Changes

New conversion command `into cell-path`

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Automatic documentation updates

crates/nu-command/src/conversions/into/cell_path.rs

@@ -0,0 +1,225 @@
+use nu_protocol::{
+    ast::{Call, CellPath, PathMember},
+    engine::{Command, EngineState, Stack},
+    Category, Example, IntoPipelineData, PipelineData, Record, ShellError, Signature, Span, Type,
+    Value,
+};
+
+#[derive(Clone)]
+pub struct IntoCellPath;
+
+impl Command for IntoCellPath {
+    fn name(&self) -> &str {
+        "into cell-path"
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("into cell-path")
+            .input_output_types(vec![
+                (Type::Int, Type::CellPath),
+                (Type::List(Box::new(Type::Any)), Type::CellPath),
+                (
+                    Type::List(Box::new(Type::Record(vec![
+                        ("value".into(), Type::Any),
+                        ("optional".into(), Type::Bool),
+                    ]))),
+                    Type::CellPath,
+                ),
+            ])
+            .category(Category::Conversions)
+            .allow_variants_without_examples(true)
+    }
+
+    fn usage(&self) -> &str {
+        "Convert value to a cell-path."
+    }
+
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["convert"]
+    }
+
+    fn extra_usage(&self) -> &str {
+        "Converting a string directly into a cell path is intentionally not supported."
+    }
+
+    fn run(
+        &self,
+        _engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        into_cell_path(call, input)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                description: "Convert integer into cell path",
+                example: "5 | into cell-path",
+                result: Some(Value::test_cell_path(CellPath {
+                    members: vec![PathMember::test_int(5, false)],
+                })),
+            },
+            Example {
+                description: "Convert string into cell path",
+                example: "'some.path' | split row '.' | into cell-path",
+                result: Some(Value::test_cell_path(CellPath {
+                    members: vec![
+                        PathMember::test_string("some".into(), false),
+                        PathMember::test_string("path".into(), false),
+                    ],
+                })),
+            },
+            Example {
+                description: "Convert list into cell path",
+                example: "[5 c 7 h] | into cell-path",
+                result: Some(Value::test_cell_path(CellPath {
+                    members: vec![
+                        PathMember::test_int(5, false),
+                        PathMember::test_string("c".into(), false),
+                        PathMember::test_int(7, false),
+                        PathMember::test_string("h".into(), false),
+                    ],
+                })),
+            },
+            Example {
+                description: "Convert table into cell path",
+                example: "[[value, optional]; [5 true] [c false]] | into cell-path",
+                result: Some(Value::test_cell_path(CellPath {
+                    members: vec![
+                        PathMember::test_int(5, true),
+                        PathMember::test_string("c".into(), false),
+                    ],
+                })),
+            },
+        ]
+    }
+}
+
+fn into_cell_path(call: &Call, input: PipelineData) -> Result<PipelineData, ShellError> {
+    let head = call.head;
+
+    match input {
+        PipelineData::Value(value, _) => Ok(value_to_cell_path(&value, head)?.into_pipeline_data()),
+        PipelineData::ListStream(stream, ..) => {
+            let list: Vec<_> = stream.collect();
+            Ok(list_to_cell_path(&list, head)?.into_pipeline_data())
+        }
+        PipelineData::ExternalStream { span, .. } => Err(ShellError::OnlySupportsThisInputType {
+            exp_input_type: "list, int".into(),
+            wrong_type: "raw data".into(),
+            dst_span: head,
+            src_span: span,
+        }),
+        PipelineData::Empty => Err(ShellError::PipelineEmpty { dst_span: head }),
+    }
+}
+
+fn int_to_cell_path(val: i64, span: Span) -> Value {
+    let member = match int_to_path_member(val, span) {
+        Ok(m) => m,
+        Err(e) => {
+            return Value::error(e, span);
+        }
+    };
+
+    let path = CellPath {
+        members: vec![member],
+    };
+
+    Value::cell_path(path, span)
+}
+
+fn int_to_path_member(val: i64, span: Span) -> Result<PathMember, ShellError> {
+    let Ok(val) = val.try_into() else {
+        return Err(ShellError::NeedsPositiveValue { span });
+    };
+
+    Ok(PathMember::int(val, false, span))
+}
+
+fn list_to_cell_path(vals: &[Value], span: Span) -> Result<Value, ShellError> {
+    let mut members = vec![];
+
+    for val in vals {
+        members.push(value_to_path_member(val, span)?);
+    }
+
+    let path = CellPath { members };
+
+    Ok(Value::cell_path(path, span))
+}
+
+fn record_to_path_member(
+    record: &Record,
+    val_span: Span,
+    span: Span,
+) -> Result<PathMember, ShellError> {
+    let Some(value) = record.get("value") else {
+        return Err(ShellError::CantFindColumn {
+            col_name: "value".into(),
+            span: val_span,
+            src_span: span,
+        });
+    };
+
+    let mut member = value_to_path_member(value, span)?;
+
+    if let Some(optional) = record.get("optional") {
+        if optional.as_bool()? {
+            member.make_optional();
+        }
+    };
+
+    Ok(member)
+}
+
+fn value_to_cell_path(value: &Value, span: Span) -> Result<Value, ShellError> {
+    match value {
+        Value::Int { val, .. } => Ok(int_to_cell_path(*val, span)),
+        Value::List { vals, .. } => list_to_cell_path(vals, span),
+        other => Err(ShellError::OnlySupportsThisInputType {
+            exp_input_type: "int, list".into(),
+            wrong_type: other.get_type().to_string(),
+            dst_span: span,
+            src_span: other.span(),
+        }),
+    }
+}
+
+fn value_to_path_member(val: &Value, span: Span) -> Result<PathMember, ShellError> {
+    let member = match val {
+        Value::Int {
+            val,
+            internal_span: span,
+        } => int_to_path_member(*val, *span)?,
+        Value::String {
+            val,
+            internal_span: span,
+        } => PathMember::string(val.into(), false, *span),
+        Value::Record { val, internal_span } => record_to_path_member(val, *internal_span, span)?,
+        other => {
+            return Err(ShellError::CantConvert {
+                to_type: "int or string".to_string(),
+                from_type: other.get_type().to_string(),
+                span: val.span(),
+                help: None,
+            })
+        }
+    };
+
+    Ok(member)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(IntoCellPath {})
+    }
+}

crates/nu-command/src/conversions/into/mod.rs

@@ -1,5 +1,6 @@
 mod binary;
 mod bool;
+mod cell_path;
 mod command;
 mod datetime;
 mod duration;
@@ -13,6 +14,7 @@ mod value;
 pub use self::bool::SubCommand as IntoBool;
 pub use self::filesize::SubCommand as IntoFilesize;
 pub use binary::SubCommand as IntoBinary;
+pub use cell_path::IntoCellPath;
 pub use command::Into;
 pub use datetime::SubCommand as IntoDatetime;
 pub use duration::SubCommand as IntoDuration;

crates/nu-command/src/default_context.rs

@@ -293,6 +293,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Into,
             IntoBool,
             IntoBinary,
+            IntoCellPath,
             IntoDatetime,
             IntoDuration,
             IntoFloat,