Implement into path conversion (#3811)

This allows converting strings to filepaths without having to use
`path expand` roundtrip.

Filepaths are taken as-is without any validation/conversion.

crates/nu-command/src/commands/conversions/into/filepath.rs

@@ -0,0 +1,126 @@
+use std::path::PathBuf;
+
+use crate::prelude::*;
+use nu_engine::WholeStreamCommand;
+use nu_errors::ShellError;
+use nu_protocol::{ColumnPath, Primitive, Signature, SyntaxShape, UntaggedValue, Value};
+
+pub struct SubCommand;
+
+impl WholeStreamCommand for SubCommand {
+    fn name(&self) -> &str {
+        "into path"
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("into path").rest(
+            SyntaxShape::ColumnPath,
+            "column paths to convert to filepath (for table input)",
+        )
+    }
+
+    fn usage(&self) -> &str {
+        "Convert value to filepath"
+    }
+
+    fn run(&self, args: CommandArgs) -> Result<OutputStream, ShellError> {
+        into_filepath(args)
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                description: "Convert string to filepath in table",
+                example: "echo [[name]; ['/dev/null'] ['C:\\Program Files'] ['../../Cargo.toml']] | into path name",
+                result: Some(vec![
+                    UntaggedValue::row(indexmap! {
+                        "name".to_string() => UntaggedValue::filepath("/dev/null").into(),
+                    })
+                    .into(),
+                    UntaggedValue::row(indexmap! {
+                        "name".to_string() => UntaggedValue::filepath("C:\\Program Files").into(),
+                    })
+                    .into(),
+                    UntaggedValue::row(indexmap! {
+                        "name".to_string() => UntaggedValue::filepath("../../Cargo.toml").into(),
+                    })
+                    .into(),
+                ]),
+            },
+            Example {
+                description: "Convert string to filepath",
+                example: "echo 'Cargo.toml' | into path",
+                result: Some(vec![UntaggedValue::filepath("Cargo.toml").into()]),
+            },
+        ]
+    }
+}
+
+fn into_filepath(args: CommandArgs) -> Result<OutputStream, ShellError> {
+    let column_paths: Vec<ColumnPath> = args.rest(0)?;
+
+    Ok(args
+        .input
+        .map(move |v| {
+            if column_paths.is_empty() {
+                action(&v, v.tag())
+            } else {
+                let mut ret = v;
+                for path in &column_paths {
+                    ret = ret.swap_data_by_column_path(
+                        path,
+                        Box::new(move |old| action(old, old.tag())),
+                    )?;
+                }
+
+                Ok(ret)
+            }
+        })
+        .into_input_stream())
+}
+
+pub fn action(input: &Value, tag: impl Into<Tag>) -> Result<Value, ShellError> {
+    let tag = tag.into();
+    match &input.value {
+        UntaggedValue::Primitive(prim) => Ok(UntaggedValue::filepath(match prim {
+            Primitive::String(a_string) => match filepath_from_string(a_string, &tag) {
+                Ok(n) => n,
+                Err(e) => {
+                    return Err(e);
+                }
+            },
+            Primitive::FilePath(a_filepath) => a_filepath.clone(),
+            _ => {
+                return Err(ShellError::unimplemented(
+                    "'into path' for non-string primitives",
+                ))
+            }
+        })
+        .into_value(&tag)),
+        UntaggedValue::Row(_) => Err(ShellError::labeled_error(
+            "specify column name to use, with 'into path COLUMN'",
+            "found table",
+            tag,
+        )),
+        _ => Err(ShellError::unimplemented(
+            "'into path' for unsupported type",
+        )),
+    }
+}
+
+fn filepath_from_string(a_string: &str, _tag: &Tag) -> Result<PathBuf, ShellError> {
+    Ok(PathBuf::from(a_string))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::ShellError;
+    use super::SubCommand;
+
+    #[test]
+    fn examples_work_as_expected() -> Result<(), ShellError> {
+        use crate::examples::test as test_examples;
+
+        test_examples(SubCommand {})
+    }
+}

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

@@ -1,9 +1,11 @@
 mod binary;
 mod command;
+mod filepath;
 mod int;
 pub mod string;
 
 pub use binary::SubCommand as IntoBinary;
 pub use command::Command as Into;
+pub use filepath::SubCommand as IntoFilepath;
 pub use int::SubCommand as IntoInt;
 pub use string::SubCommand as IntoString;

crates/nu-command/src/default_context.rs

@@ -131,6 +131,7 @@ pub fn create_default_context(interactive: bool) -> Result<EvaluationContext, Bo
             whole_stream_command(Into),
             whole_stream_command(IntoBinary),
             whole_stream_command(IntoInt),
+            whole_stream_command(IntoFilepath),
             whole_stream_command(IntoString),
             whole_stream_command(SplitBy),
             // Row manipulation