Imply outlives-bounds on lazy type aliases

Author: fmease

compiler/rustc_hir_analysis/src/outlives/implicit_infer.rs

@@ -59,6 +59,17 @@ pub(super) fn infer_predicates(
                     }
                 }
 
+                DefKind::TyAlias if tcx.type_alias_is_lazy(item_did) => {
+                    insert_required_predicates_to_be_wf(
+                        tcx,
+                        tcx.type_of(item_did).instantiate_identity(),
+                        tcx.def_span(item_did),
+                        &global_inferred_outlives,
+                        &mut item_required_predicates,
+                        &mut explicit_map,
+                    );
+                }
+
                 _ => {}
             };
 
@@ -212,6 +223,21 @@ fn insert_required_predicates_to_be_wf<'tcx>(
                 );
             }
 
+            ty::Alias(ty::Weak, alias) => {
+                // This corresponds to a type like `Type<'a, T>`.
+                // Contrary to a GAT like `<() as Trait>::Type<'a, T>`,
+                // we do use the own explicit predicates.
+                debug!("Weak");
+                check_explicit_predicates(
+                    tcx,
+                    alias.def_id,
+                    alias.args,
+                    required_predicates,
+                    explicit_map,
+                    None,
+                );
+            }
+
             // FIXME(inherent_associated_types): Handle this case properly.
             ty::Alias(ty::Inherent, _) => {}
 

compiler/rustc_hir_analysis/src/outlives/mod.rs

@@ -21,6 +21,10 @@ fn inferred_outlives_of(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[(ty::Clau
             let crate_map = tcx.inferred_outlives_crate(());
             crate_map.predicates.get(&item_def_id.to_def_id()).copied().unwrap_or(&[])
         }
+        DefKind::TyAlias if tcx.type_alias_is_lazy(item_def_id) => {
+            let crate_map = tcx.inferred_outlives_crate(());
+            crate_map.predicates.get(&item_def_id.to_def_id()).copied().unwrap_or(&[])
+        }
         DefKind::AnonConst if tcx.features().generic_const_exprs => {
             let id = tcx.local_def_id_to_hir_id(item_def_id);
             if tcx.hir().opt_const_param_default_param_def_id(id).is_some() {

tests/ui/lazy-type-alias/dont-imply-implied-outlives-bounds.rs

@@ -0,0 +1,12 @@
+// Ensure that we don't imply the *implied* outlives-bounds of weak aliases.
+// For context, we only imply the explicit bounds.
+#![feature(lazy_type_alias)]
+#![allow(incomplete_features)]
+
+type Alias<'a, T> = &'a T; // implied bound `T: 'a`
+
+struct Outer0<'a, T>(Alias<'a, T>); //~ ERROR the parameter type `T` may not live long enough
+
+type Outer1<'a, T> = Alias<'a, T>; //~ ERROR the parameter type `T` may not live long enough
+
+fn main() {}

tests/ui/lazy-type-alias/dont-imply-implied-outlives-bounds.stderr

@@ -0,0 +1,29 @@
+error[E0309]: the parameter type `T` may not live long enough
+  --> $DIR/dont-imply-implied-outlives-bounds.rs:8:22
+   |
+LL | struct Outer0<'a, T>(Alias<'a, T>);
+   |               --     ^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
+   |               |
+   |               the parameter type `T` must be valid for the lifetime `'a` as defined here...
+   |
+help: consider adding an explicit lifetime bound
+   |
+LL | struct Outer0<'a, T: 'a>(Alias<'a, T>);
+   |                    ++++
+
+error[E0309]: the parameter type `T` may not live long enough
+  --> $DIR/dont-imply-implied-outlives-bounds.rs:10:22
+   |
+LL | type Outer1<'a, T> = Alias<'a, T>;
+   |             --       ^^^^^^^^^^^^ ...so that the type `T` will meet its required lifetime bounds
+   |             |
+   |             the parameter type `T` must be valid for the lifetime `'a` as defined here...
+   |
+help: consider adding an explicit lifetime bound
+   |
+LL | type Outer1<'a, T: 'a> = Alias<'a, T>;
+   |                  ++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0309`.

tests/ui/lazy-type-alias/implied-outlives-bounds.neg.stderr

@@ -0,0 +1,26 @@
+error: lifetime may not live long enough
+  --> $DIR/implied-outlives-bounds.rs:18:12
+   |
+LL | fn env0<'any>() {
+   |         ---- lifetime `'any` defined here
+LL |     let _: TypeOutlives<'static, &'any ()>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'any` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/implied-outlives-bounds.rs:23:12
+   |
+LL | fn env1<'any>() {
+   |         ---- lifetime `'any` defined here
+LL |     let _: RegionOutlives<'static, 'any>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'any` must outlive `'static`
+
+error: lifetime may not live long enough
+  --> $DIR/implied-outlives-bounds.rs:28:12
+   |
+LL | fn env2<'any>() {
+   |         ---- lifetime `'any` defined here
+LL |     let _: Outer0<'static, &'any ()>;
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'any` must outlive `'static`
+
+error: aborting due to 3 previous errors
+

tests/ui/lazy-type-alias/implied-outlives-bounds.rs

@@ -0,0 +1,31 @@
+// Check that we imply outlives-bounds on lazy type aliases.
+
+// revisions: pos neg
+//[pos] check-pass
+
+#![feature(lazy_type_alias)]
+#![allow(incomplete_features)]
+
+type TypeOutlives<'a, T> = &'a T;
+type RegionOutlives<'a, 'b> = &'a &'b ();
+
+// Ensure that we imply `T: 'a` from the explicit predicates of the weak alias `Alias`.
+struct Outer0<'a, T>(Alias<'a, T>);
+type Alias<'a, T: 'a> = &'a T;
+
+#[cfg(neg)]
+fn env0<'any>() {
+    let _: TypeOutlives<'static, &'any ()>; //[neg]~ ERROR lifetime may not live long enough
+}
+
+#[cfg(neg)]
+fn env1<'any>() {
+    let _: RegionOutlives<'static, 'any>; //[neg]~ ERROR lifetime may not live long enough
+}
+
+#[cfg(neg)]
+fn env2<'any>() {
+    let _: Outer0<'static, &'any ()>; //[neg]~ ERROR lifetime may not live long enough
+}
+
+fn main() {}