Add new Path type with phantom data form tag (Any, Relative, Absolute, or Canonical).

crates/nu-path/src/form.rs

@@ -0,0 +1,86 @@
+mod private {
+    pub trait Sealed {}
+}
+
+pub trait PathForm: private::Sealed {}
+
+pub trait MaybeRelative: PathForm {}
+
+pub trait MaybeAbsolute: PathForm {}
+
+pub trait IsAbsolute: PathForm {}
+
+pub trait PathCast<Form: PathForm>: PathForm {}
+
+impl<Form: PathForm> PathCast<Form> for Form {}
+
+pub trait PathJoin: PathForm {
+    type Output: PathForm;
+}
+
+pub trait PathPush: PathForm {}
+
+pub trait PathSet: PathForm {}
+
+/// A path whose form is unknown. It could be a relative, absolute, or canonical path.
+///
+///
+pub struct Any;
+
+impl private::Sealed for Any {}
+
+impl PathForm for Any {}
+impl MaybeRelative for Any {}
+impl MaybeAbsolute for Any {}
+impl PathJoin for Any {
+    type Output = Self;
+}
+impl PathPush for Any {}
+impl PathSet for Any {}
+
+/// A strictly relative path.
+///
+/// The path is not guaranteed to be normalized. It may contain unresolved symlinks,
+/// trailing slashes, dot components (`..` or `.`), and duplicate path separators.
+pub struct Relative;
+
+impl private::Sealed for Relative {}
+impl PathForm for Relative {}
+impl PathCast<Any> for Relative {}
+impl MaybeRelative for Relative {}
+impl PathJoin for Relative {
+    type Output = Any;
+}
+impl PathSet for Relative {}
+
+/// An absolute path.
+///
+/// The path is not guaranteed to be normalized. It may contain unresolved symlinks,
+/// trailing slashes, dot components (`..` or `.`), and duplicate path separators.
+pub struct Absolute;
+
+impl private::Sealed for Absolute {}
+impl PathForm for Absolute {}
+impl PathCast<Any> for Absolute {}
+impl MaybeAbsolute for Absolute {}
+impl IsAbsolute for Absolute {}
+impl PathJoin for Absolute {
+    type Output = Self;
+}
+impl PathPush for Absolute {}
+impl PathSet for Absolute {}
+
+// A canonical path.
+//
+// An absolute path with all intermediate components normalized and symbolic links resolved.
+pub struct Canonical;
+
+impl private::Sealed for Canonical {}
+impl PathForm for Canonical {}
+impl PathCast<Any> for Canonical {}
+impl PathCast<Absolute> for Canonical {}
+impl MaybeAbsolute for Canonical {}
+impl IsAbsolute for Canonical {}
+impl PathJoin for Canonical {
+    type Output = Absolute;
+}

crates/nu-path/src/lib.rs

@@ -2,12 +2,15 @@ mod assert_path_eq;
 mod components;
 pub mod dots;
 pub mod expansions;
+pub mod form;
 mod helpers;
+mod path;
 mod tilde;
 mod trailing_slash;
 
 pub use components::components;
 pub use expansions::{canonicalize_with, expand_path_with, expand_to_real_path, locate_in_dirs};
 pub use helpers::{config_dir, config_dir_old, home_dir};
+pub use path::*;
 pub use tilde::expand_tilde;
 pub use trailing_slash::{has_trailing_slash, strip_trailing_slash};