implement Path type

fix-vm/src/lib.rs

@@ -98,6 +98,7 @@ pub enum ExtraScope {
 
 trait VmRuntimeCtxExt: VmRuntimeCtx {
     fn get_string<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str>;
+    fn get_string_or_path<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str>;
     fn get_string_id<'a, 'gc: 'a>(
         &'a mut self,
         val: StrictValue<'gc>,
@@ -114,6 +115,18 @@ impl<T: VmRuntimeCtx> VmRuntimeCtxExt for T {
         }
     }
 
+    /// Like `get_string`, but also accepts `Path` values (returning their
+    /// underlying canonical-path string). Use this in places where Nix
+    /// would coerce a path to a string (string interpolation, file IO
+    /// builtins, etc.).
+    fn get_string_or_path<'a, 'gc: 'a>(&'a self, val: StrictValue<'gc>) -> Option<&'a str> {
+        if let Some(p) = val.as_inline::<Path>() {
+            Some(self.resolve_string(p.0))
+        } else {
+            self.get_string(val)
+        }
+    }
+
     fn get_string_id<'a, 'gc: 'a>(
         &'a mut self,
         val: StrictValue<'gc>,
@@ -154,6 +167,8 @@ impl<T: VmRuntimeCtx> ConvertValueWithSeen for T {
             Value::String(s)
         } else if let Some(ns) = val.as_gc::<NixString>() {
             Value::String(ns.as_str().to_owned())
+        } else if let Some(p) = val.as_inline::<Path>() {
+            Value::Path(self.resolve_string(p.0).to_owned())
         } else if let Some(attrs) = val.as_gc::<AttrSet>() {
             let bits = val.to_bits();
             if attrs.entries.is_empty() {