Lower and resolve precise captures in HIR

compiler/rustc_hir/src/hir.rs

@@ -2557,6 +2557,15 @@ pub struct OpaqueTy<'hir> {
     /// originating from a trait method. This makes it so that the opaque is
     /// lowered as an associated type.
     pub in_trait: bool,
+    /// List of arguments captured via `impl use<'a, P, ...> Trait` syntax.
+    pub precise_capturing_args: Option<&'hir [PreciseCapturingArg<'hir>]>,
+}
+
+#[derive(Debug, Clone, Copy, HashStable_Generic)]
+pub enum PreciseCapturingArg<'hir> {
+    Lifetime(&'hir Lifetime),
+    /// Non-lifetime argument (type or const)
+    Param(Res, HirId),
 }
 
 /// From whence the opaque type came.

compiler/rustc_hir/src/intravisit.rs

@@ -413,6 +413,9 @@ pub trait Visitor<'v>: Sized {
     fn visit_param_bound(&mut self, bounds: &'v GenericBound<'v>) -> Self::Result {
         walk_param_bound(self, bounds)
     }
+    fn visit_precise_capturing_arg(&mut self, arg: &'v PreciseCapturingArg<'v>) -> Self::Result {
+        walk_precise_capturing_arg(self, arg)
+    }
     fn visit_poly_trait_ref(&mut self, t: &'v PolyTraitRef<'v>) -> Self::Result {
         walk_poly_trait_ref(self, t)
     }
@@ -526,10 +529,15 @@ pub fn walk_item<'v, V: Visitor<'v>>(visitor: &mut V, item: &'v Item<'v>) -> V::
             try_visit!(visitor.visit_ty(ty));
             try_visit!(visitor.visit_generics(generics));
         }
-        ItemKind::OpaqueTy(&OpaqueTy { generics, bounds, .. }) => {
+        ItemKind::OpaqueTy(&OpaqueTy { generics, bounds, precise_capturing_args, .. }) => {
             try_visit!(visitor.visit_id(item.hir_id()));
             try_visit!(walk_generics(visitor, generics));
             walk_list!(visitor, visit_param_bound, bounds);
+            if let Some(precise_capturing_args) = precise_capturing_args {
+                for arg in precise_capturing_args {
+                    try_visit!(visitor.visit_precise_capturing_arg(arg));
+                }
+            }
         }
         ItemKind::Enum(ref enum_definition, ref generics) => {
             try_visit!(visitor.visit_generics(generics));
@@ -1137,6 +1145,16 @@ pub fn walk_param_bound<'v, V: Visitor<'v>>(
     }
 }
 
+pub fn walk_precise_capturing_arg<'v, V: Visitor<'v>>(
+    visitor: &mut V,
+    arg: &'v PreciseCapturingArg<'v>,
+) -> V::Result {
+    match *arg {
+        PreciseCapturingArg::Lifetime(lt) => visitor.visit_lifetime(lt),
+        PreciseCapturingArg::Param(_, hir_id) => visitor.visit_id(hir_id),
+    }
+}
+
 pub fn walk_poly_trait_ref<'v, V: Visitor<'v>>(
     visitor: &mut V,
     trait_ref: &'v PolyTraitRef<'v>,