propagate user-type annotation for constants in expressions

Author: nikomatsakis

src/librustc_mir/hair/cx/expr.rs

@@ -771,13 +771,11 @@ fn user_substs_applied_to_def(
         Def::Fn(_) |
         Def::Method(_) |
         Def::StructCtor(_, CtorKind::Fn) |
-        Def::VariantCtor(_, CtorKind::Fn) =>
+        Def::VariantCtor(_, CtorKind::Fn) |
+        Def::Const(_) |
+        Def::AssociatedConst(_) =>
             Some(UserTypeAnnotation::TypeOf(def.def_id(), cx.tables().user_substs(hir_id)?)),
 
-        Def::Const(_def_id) |
-        Def::AssociatedConst(_def_id) =>
-            bug!("unimplemented"),
-
         // A unit struct/variant which is used as a value (e.g.,
         // `None`). This has the type of the enum/struct that defines
         // this variant -- but with the substitutions given by the
@@ -889,14 +887,17 @@ fn convert_path_expr<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         },
 
         Def::Const(def_id) |
-        Def::AssociatedConst(def_id) => ExprKind::Literal {
-            literal: ty::Const::unevaluated(
-                cx.tcx,
-                def_id,
-                substs,
-                cx.tables().node_id_to_type(expr.hir_id),
-            ),
-            user_ty: None, // FIXME(#47184) -- user given type annot on constants
+        Def::AssociatedConst(def_id) => {
+            let user_ty = user_substs_applied_to_def(cx, expr.hir_id, &def);
+            ExprKind::Literal {
+                literal: ty::Const::unevaluated(
+                    cx.tcx,
+                    def_id,
+                    substs,
+                    cx.tables().node_id_to_type(expr.hir_id),
+                ),
+                user_ty,
+            }
         },
 
         Def::StructCtor(def_id, CtorKind::Const) |

src/test/ui/nll/user-annotations/constant-in-expr-inherent-1.rs

@@ -0,0 +1,15 @@
+#![feature(nll)]
+
+struct Foo<'a> { x: &'a u32 }
+
+impl<'a> Foo<'a> {
+    const C: &'a u32 = &22;
+}
+
+fn foo<'a>(_: &'a u32) -> &'static u32 {
+    <Foo<'a>>::C //~ ERROR
+}
+
+fn main() {
+}
+

src/test/ui/nll/user-annotations/constant-in-expr-inherent-1.stderr

@@ -0,0 +1,10 @@
+error: unsatisfied lifetime constraints
+  --> $DIR/constant-in-expr-inherent-1.rs:10:5
+   |
+LL | fn foo<'a>(_: &'a u32) -> &'static u32 {
+   |        -- lifetime `'a` defined here
+LL |     <Foo<'a>>::C //~ ERROR
+   |     ^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to previous error
+

src/test/ui/nll/user-annotations/constant-in-expr-trait-item-1.rs

@@ -0,0 +1,16 @@
+#![feature(nll)]
+
+trait Foo<'a> {
+    const C: &'a u32;
+}
+
+impl<'a, T> Foo<'a> for T {
+    const C: &'a u32 = &22;
+}
+
+fn foo<'a>(_: &'a u32) -> &'static u32 {
+    <() as Foo<'a>>::C //~ ERROR
+}
+
+fn main() {
+}

src/test/ui/nll/user-annotations/constant-in-expr-trait-item-1.stderr

@@ -0,0 +1,10 @@
+error: unsatisfied lifetime constraints
+  --> $DIR/constant-in-expr-trait-item-1.rs:12:5
+   |
+LL | fn foo<'a>(_: &'a u32) -> &'static u32 {
+   |        -- lifetime `'a` defined here
+LL |     <() as Foo<'a>>::C //~ ERROR
+   |     ^^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to previous error
+

src/test/ui/nll/user-annotations/constant-in-expr-trait-item-2.rs

@@ -0,0 +1,16 @@
+#![feature(nll)]
+
+trait Foo<'a> {
+    const C: &'a u32;
+}
+
+impl<'a, T> Foo<'a> for T {
+    const C: &'a u32 = &22;
+}
+
+fn foo<'a, T: Foo<'a>>() -> &'static u32 {
+    <T as Foo<'a>>::C //~ ERROR
+}
+
+fn main() {
+}

src/test/ui/nll/user-annotations/constant-in-expr-trait-item-2.stderr

@@ -0,0 +1,10 @@
+error: unsatisfied lifetime constraints
+  --> $DIR/constant-in-expr-trait-item-2.rs:12:5
+   |
+LL | fn foo<'a, T: Foo<'a>>() -> &'static u32 {
+   |        -- lifetime `'a` defined here
+LL |     <T as Foo<'a>>::C //~ ERROR
+   |     ^^^^^^^^^^^^^^^^^ returning this value requires that `'a` must outlive `'static`
+
+error: aborting due to previous error
+