Check Copy lifetimes bounds when copying from a projection

Author: matthewjasper

src/librustc_mir/borrow_check/type_check/mod.rs

@@ -497,46 +497,6 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
             }
         };
 
-        if place.projection.is_empty() {
-            if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
-                let is_promoted = match place.as_ref() {
-                    PlaceRef {
-                        base: &PlaceBase::Static(box Static {
-                            kind: StaticKind::Promoted(..),
-                            ..
-                        }),
-                        projection: &[],
-                    } => true,
-                    _ => false,
-                };
-
-                if !is_promoted {
-                    let tcx = self.tcx();
-                    let trait_ref = ty::TraitRef {
-                        def_id: tcx.lang_items().copy_trait().unwrap(),
-                        substs: tcx.mk_substs_trait(place_ty.ty, &[]),
-                    };
-
-                    // To have a `Copy` operand, the type `T` of the
-                    // value must be `Copy`. Note that we prove that `T: Copy`,
-                    // rather than using the `is_copy_modulo_regions`
-                    // test. This is important because
-                    // `is_copy_modulo_regions` ignores the resulting region
-                    // obligations and assumes they pass. This can result in
-                    // bounds from `Copy` impls being unsoundly ignored (e.g.,
-                    // #29149). Note that we decide to use `Copy` before knowing
-                    // whether the bounds fully apply: in effect, the rule is
-                    // that if a value of some type could implement `Copy`, then
-                    // it must.
-                    self.cx.prove_trait_ref(
-                        trait_ref,
-                        location.to_locations(),
-                        ConstraintCategory::CopyBound,
-                    );
-                }
-            }
-        }
-
         for elem in place.projection.iter() {
             if place_ty.variant_index.is_none() {
                 if place_ty.ty.references_error() {
@@ -547,6 +507,44 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
             place_ty = self.sanitize_projection(place_ty, elem, place, location)
         }
 
+        if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
+            let is_promoted = match place.as_ref() {
+                PlaceRef {
+                    base: &PlaceBase::Static(box Static {
+                        kind: StaticKind::Promoted(..),
+                        ..
+                    }),
+                    projection: &[],
+                } => true,
+                _ => false,
+            };
+
+            if !is_promoted {
+                let tcx = self.tcx();
+                let trait_ref = ty::TraitRef {
+                    def_id: tcx.lang_items().copy_trait().unwrap(),
+                    substs: tcx.mk_substs_trait(place_ty.ty, &[]),
+                };
+
+                // To have a `Copy` operand, the type `T` of the
+                // value must be `Copy`. Note that we prove that `T: Copy`,
+                // rather than using the `is_copy_modulo_regions`
+                // test. This is important because
+                // `is_copy_modulo_regions` ignores the resulting region
+                // obligations and assumes they pass. This can result in
+                // bounds from `Copy` impls being unsoundly ignored (e.g.,
+                // #29149). Note that we decide to use `Copy` before knowing
+                // whether the bounds fully apply: in effect, the rule is
+                // that if a value of some type could implement `Copy`, then
+                // it must.
+                self.cx.prove_trait_ref(
+                    trait_ref,
+                    location.to_locations(),
+                    ConstraintCategory::CopyBound,
+                );
+            }
+        }
+
         place_ty
     }
 

src/test/ui/nll/do-not-ignore-lifetime-bounds-in-copy-proj.rs

@@ -0,0 +1,12 @@
+// Test that the 'static bound from the Copy impl is respected. Regression test for #29149.
+
+#[derive(Clone)]
+struct Foo<'a>(&'a u32);
+impl Copy for Foo<'static> {}
+
+fn main() {
+    let s = 2;
+    let a = (Foo(&s),); //~ ERROR `s` does not live long enough [E0597]
+    drop(a.0);
+    drop(a.0);
+}

src/test/ui/nll/do-not-ignore-lifetime-bounds-in-copy-proj.stderr

@@ -0,0 +1,14 @@
+error[E0597]: `s` does not live long enough
+  --> $DIR/do-not-ignore-lifetime-bounds-in-copy-proj.rs:9:18
+   |
+LL |     let a = (Foo(&s),);
+   |                  ^^ borrowed value does not live long enough
+LL |     drop(a.0);
+   |          --- copying this value requires that `s` is borrowed for `'static`
+LL |     drop(a.0);
+LL | }
+   | - `s` dropped here while still borrowed
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0597`.