3 files changed, 31 insertions, 19 deletions

diff --git a/dhall/src/ctxt.rs b/dhall/src/ctxt.rs
index a171ebe..8bdf99d 100644
--- a/dhall/src/ctxt.rs
+++ b/dhall/src/ctxt.rs
@@ -1,14 +1,16 @@
 use elsa::vec::FrozenVec;
 use once_cell::sync::OnceCell;
+use std::marker::PhantomData;
+use std::ops::{Deref, Index};
 
 use crate::semantics::{Import, ImportLocation};
 use crate::syntax::Span;
 use crate::Typed;
 
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub struct ImportId(usize);
+pub struct ImportId<'cx>(usize, PhantomData<&'cx ()>);
 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
-pub struct ImportResultId(usize);
+pub struct ImportResultId<'cx>(usize, PhantomData<&'cx ()>);
 
 /// What's stored for each `ImportId`. Allows getting and setting a result for this import.
 pub struct StoredImport<'cx> {
@@ -16,7 +18,7 @@ pub struct StoredImport<'cx> {
     pub base_location: ImportLocation,
     pub import: Import,
     pub span: Span,
-    result: OnceCell<ImportResultId>,
+    result: OnceCell<ImportResultId<'cx>>,
 }
 
 /// Implementation detail. Made public for the `Index` instances.
@@ -45,7 +47,7 @@ impl<'cx> Ctxt<'cx> {
         base_location: ImportLocation,
         import: Import,
         span: Span,
-    ) -> ImportId {
+    ) -> ImportId<'cx> {
         let stored = StoredImport {
             cx: self,
             base_location,
@@ -55,24 +57,24 @@ impl<'cx> Ctxt<'cx> {
         };
         let id = self.0.imports.len();
         self.0.imports.push(Box::new(stored));
-        ImportId(id)
+        ImportId(id, PhantomData)
     }
     /// Store the result of fetching an import.
-    pub fn push_import_result(self, res: Typed<'cx>) -> ImportResultId {
+    pub fn push_import_result(self, res: Typed<'cx>) -> ImportResultId<'cx> {
         let id = self.0.import_results.len();
         self.0.import_results.push(Box::new(res));
-        ImportResultId(id)
+        ImportResultId(id, PhantomData)
     }
 }
 
 impl<'cx> StoredImport<'cx> {
     /// Get the id of the result of fetching this import. Returns `None` if the result has not yet
     /// been fetched.
-    pub fn get_resultid(&self) -> Option<ImportResultId> {
+    pub fn get_resultid(&self) -> Option<ImportResultId<'cx>> {
         self.result.get().copied()
     }
     /// Store the result of fetching this import.
-    pub fn set_resultid(&self, res: ImportResultId) {
+    pub fn set_resultid(&self, res: ImportResultId<'cx>) {
         let _ = self.result.set(res);
     }
     /// Get the result of fetching this import. Returns `None` if the result has not yet been
@@ -82,32 +84,42 @@ impl<'cx> StoredImport<'cx> {
         Some(&self.cx[res])
     }
     /// Store the result of fetching this import.
-    pub fn set_result(&self, res: Typed<'cx>) -> ImportResultId {
+    pub fn set_result(&self, res: Typed<'cx>) -> ImportResultId<'cx> {
         let res = self.cx.push_import_result(res);
         self.set_resultid(res);
         res
     }
 }
 
-impl<'cx> std::ops::Deref for Ctxt<'cx> {
+impl<'cx> Deref for Ctxt<'cx> {
     type Target = &'cx CtxtS<'cx>;
     fn deref(&self) -> &&'cx CtxtS<'cx> {
         &self.0
     }
 }
 
-impl<'cx> std::ops::Index<ImportId> for CtxtS<'cx> {
+impl<'cx> Index<ImportId<'cx>> for CtxtS<'cx> {
     type Output = StoredImport<'cx>;
-    fn index(&self, id: ImportId) -> &StoredImport<'cx> {
+    fn index(&self, id: ImportId<'cx>) -> &StoredImport<'cx> {
         &self.imports[id.0]
     }
 }
-impl<'cx> std::ops::Index<ImportResultId> for CtxtS<'cx> {
+impl<'cx> Index<ImportResultId<'cx>> for CtxtS<'cx> {
     type Output = Typed<'cx>;
-    fn index(&self, id: ImportResultId) -> &Typed<'cx> {
+    fn index(&self, id: ImportResultId<'cx>) -> &Typed<'cx> {
         &self.import_results[id.0]
     }
 }
+impl<'a, 'cx, T> Index<&'a T> for CtxtS<'cx>
+where
+    Self: Index<T>,
+    T: Copy,
+{
+    type Output = <Self as Index<T>>::Output;
+    fn index(&self, id: &'a T) -> &Self::Output {
+        &self[*id]
+    }
+}
 
 /// Empty impl, because `FrozenVec` does not implement `Debug` and I can't be bothered to do it
 /// myself.
diff --git a/dhall/src/semantics/resolve/env.rs b/dhall/src/semantics/resolve/env.rs
index 2b998f8..ba6205f 100644
--- a/dhall/src/semantics/resolve/env.rs
+++ b/dhall/src/semantics/resolve/env.rs
@@ -17,7 +17,7 @@ pub type CyclesStack = Vec<ImportLocation>;
 pub struct ImportEnv<'cx> {
     cx: Ctxt<'cx>,
     disk_cache: Option<Cache>, // `None` if it failed to initialize
-    mem_cache: HashMap<ImportLocation, ImportResultId>,
+    mem_cache: HashMap<ImportLocation, ImportResultId<'cx>>,
     stack: CyclesStack,
 }
 
@@ -82,7 +82,7 @@ impl<'cx> ImportEnv<'cx> {
     pub fn get_from_mem_cache(
         &self,
         location: &ImportLocation,
-    ) -> Option<ImportResultId> {
+    ) -> Option<ImportResultId<'cx>> {
         Some(*self.mem_cache.get(location)?)
     }
 
@@ -98,7 +98,7 @@ impl<'cx> ImportEnv<'cx> {
     pub fn write_to_mem_cache(
         &mut self,
         location: ImportLocation,
-        result: ImportResultId,
+        result: ImportResultId<'cx>,
     ) {
         self.mem_cache.insert(location, result);
     }
diff --git a/dhall/src/semantics/resolve/resolve.rs b/dhall/src/semantics/resolve/resolve.rs
index 488c516..9021155 100644
--- a/dhall/src/semantics/resolve/resolve.rs
+++ b/dhall/src/semantics/resolve/resolve.rs
@@ -398,7 +398,7 @@ fn traverse_resolve_expr<'cx>(
 /// Fetch the import and store the result in the global context.
 fn fetch_import<'cx>(
     env: &mut ImportEnv<'cx>,
-    import_id: ImportId,
+    import_id: ImportId<'cx>,
 ) -> Result<(), Error> {
     let cx = env.cx();
     let import = &cx[import_id].import;