Distinguish different types of Nix paths at the type level

- Added distinct token and node types for different path varieties:
  - PathAbs: Absolute paths starting with `/` (e.g., `/nix/store/...`)
  - PathRel: Relative paths (e.g., `./foo`, `foo/bar`)
  - PathHome: Home-relative paths starting with `~/` (e.g., `~/foo/bar`)
  - PathSearch: NIX_PATH expressions (e.g., `<nixpkgs>`)

- Created `InterpolatablePath` trait for paths that support interpolation
  (all except search paths)

- Added helper methods to path content for easier path type checking and
  access through `match_path`, `is_search`, `is_interpolatable`, etc.

This allows code to determine what kind of path it's dealing with without
having to re-parse the path string, improving type safety, correctness,
and making path-specific operations more explicit.

Author: domenkozar

flake.lock

@@ -5,6 +5,8 @@ mod interpol;
 mod nodes;
 mod operators;
 mod path_util;
+
+pub use path_util::{InterpolatablePath, Path, PathNode, PathPart, SearchPath};
 mod str_util;
 mod tokens;
 

src/ast.rs

@@ -176,7 +176,10 @@ node! {
         IfElse,
         Select,
         Str,
-        Path,
+        PathAbs,
+        PathRel,
+        PathHome,
+        PathSearch,
         Literal,
         Lambda,
         LegacyLet,
@@ -279,7 +282,20 @@ impl InheritFrom {
     tg! { r_paren_token, ')' }
 }
 
-node! { #[from(NODE_PATH)] struct Path; }
+node! { #[from(NODE_PATH_ABS)]    struct PathAbs; }
+node! { #[from(NODE_PATH_REL)]    struct PathRel; }
+node! { #[from(NODE_PATH_HOME)]   struct PathHome; }
+node! { #[from(NODE_PATH_SEARCH)] struct PathSearch; }
+
+node! {
+    #[from(
+        PathAbs,
+        PathRel,
+        PathHome,
+        PathSearch,
+    )]
+    enum Path;
+}
 
 node! { #[from(NODE_STRING)] struct Str; }