1 files changed, 118 insertions, 0 deletions
diff --git a/vendor/chalk-ir-0.87.0/src/fold/subst.rs b/vendor/chalk-ir-0.87.0/src/fold/subst.rs
new file mode 100644
index 000000000..7cff8d89c
--- /dev/null
+++ b/vendor/chalk-ir-0.87.0/src/fold/subst.rs
@@ -0,0 +1,118 @@
+use super::*;
+use crate::fold::shift::Shift;
+
+/// Substitution used during folding
+#[derive(FallibleTypeFolder)]
+pub struct Subst<'s, I: Interner> {
+    /// Values to substitute. A reference to a free variable with
+    /// index `i` will be mapped to `parameters[i]` -- if `i >
+    /// parameters.len()`, then we will leave the variable untouched.
+    parameters: &'s [GenericArg<I>],
+    interner: I,
+}
+
+impl<I: Interner> Subst<'_, I> {
+    /// Applies the substitution by folding
+    pub fn apply<T: TypeFoldable<I>>(interner: I, parameters: &[GenericArg<I>], value: T) -> T {
+        value
+            .try_fold_with(
+                &mut Subst {
+                    parameters,
+                    interner,
+                },
+                DebruijnIndex::INNERMOST,
+            )
+            .unwrap()
+    }
+}
+
+impl<I: Interner> TypeFolder<I> for Subst<'_, I> {
+    fn as_dyn(&mut self) -> &mut dyn TypeFolder<I> {
+        self
+    }
+
+    /// We are eliminating one binder, but binders outside of that get preserved.
+    ///
+    /// So e.g. consider this:
+    ///
+    /// ```notrust
+    /// for<A, B> { for<C> { [A, C] } }
+    /// //          ^ the binder we are substituing with `[u32]`
+    /// ```
+    ///
+    /// Here, `A` would be `^1.0` and `C` would be `^0.0`. We will replace `^0.0` with the
+    /// 0th index from the list (`u32`). We will convert `^1.0` (A) to `^0.0` -- i.e., shift
+    /// it **out** of one level of binder (the `for<C>` binder we are eliminating).
+    ///
+    /// This gives us as a result:
+    ///
+    /// ```notrust
+    /// for<A, B> { [A, u32] }
+    ///              ^ represented as `^0.0`
+    /// ```
+    fn fold_free_var_ty(&mut self, bound_var: BoundVar, outer_binder: DebruijnIndex) -> Ty<I> {
+        if let Some(index) = bound_var.index_if_innermost() {
+            match self.parameters[index].data(TypeFolder::interner(self)) {
+                GenericArgData::Ty(t) => t
+                    .clone()
+                    .shifted_in_from(TypeFolder::interner(self), outer_binder),
+                _ => panic!("mismatched kinds in substitution"),
+            }
+        } else {
+            bound_var
+                .shifted_out()
+                .expect("cannot fail because this is not the innermost")
+                .shifted_in_from(outer_binder)
+                .to_ty(TypeFolder::interner(self))
+        }
+    }
+
+    /// see `fold_free_var_ty`
+    fn fold_free_var_lifetime(
+        &mut self,
+        bound_var: BoundVar,
+        outer_binder: DebruijnIndex,
+    ) -> Lifetime<I> {
+        if let Some(index) = bound_var.index_if_innermost() {
+            match self.parameters[index].data(TypeFolder::interner(self)) {
+                GenericArgData::Lifetime(l) => l
+                    .clone()
+                    .shifted_in_from(TypeFolder::interner(self), outer_binder),
+                _ => panic!("mismatched kinds in substitution"),
+            }
+        } else {
+            bound_var
+                .shifted_out()
+                .unwrap()
+                .shifted_in_from(outer_binder)
+                .to_lifetime(TypeFolder::interner(self))
+        }
+    }
+
+    /// see `fold_free_var_ty`
+    fn fold_free_var_const(
+        &mut self,
+        ty: Ty<I>,
+        bound_var: BoundVar,
+        outer_binder: DebruijnIndex,
+    ) -> Const<I> {
+        if let Some(index) = bound_var.index_if_innermost() {
+            match self.parameters[index].data(TypeFolder::interner(self)) {
+                GenericArgData::Const(c) => c
+                    .clone()
+                    .shifted_in_from(TypeFolder::interner(self), outer_binder),
+                _ => panic!("mismatched kinds in substitution"),
+            }
+        } else {
+            bound_var
+                .shifted_out()
+                .unwrap()
+                .shifted_in_from(outer_binder)
+                .to_const(TypeFolder::interner(self), ty)
+        }
+    }
+
+    fn interner(&self) -> I {
+        self.interner
+    }
+}