From e179d5dad21001a04e82ae08fb186f101b361c25 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Thu, 10 Aug 2023 21:42:56 +0000
Subject: [PATCH] Don't allow consts with unconstrained lifetimes in their
 types

---
 .../rustc_hir_analysis/src/impl_wf_check.rs   |  6 +++---
 .../assoc-const-unconstrained-lifetime.rs     |  8 ++++++++
 .../assoc-const-unconstrained-lifetime.stderr |  9 +++++++++
 tests/ui/nll/trait-associated-constant.rs     |  2 +-
 tests/ui/nll/trait-associated-constant.stderr | 19 +++----------------
 5 files changed, 24 insertions(+), 20 deletions(-)
 create mode 100644 tests/ui/consts/assoc-const-unconstrained-lifetime.rs
 create mode 100644 tests/ui/consts/assoc-const-unconstrained-lifetime.stderr

diff --git a/compiler/rustc_hir_analysis/src/impl_wf_check.rs b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
index 4f705eaf10aac..b669cb8a07a82 100644
--- a/compiler/rustc_hir_analysis/src/impl_wf_check.rs
+++ b/compiler/rustc_hir_analysis/src/impl_wf_check.rs
@@ -94,21 +94,21 @@ fn enforce_impl_params_are_constrained(tcx: TyCtxt<'_>, impl_def_id: LocalDefId)
         &mut input_parameters,
     );
 
-    // Disallow unconstrained lifetimes, but only if they appear in assoc types.
+    // Disallow unconstrained lifetimes, but only if they appear in assoc types or consts.
     let lifetimes_in_associated_types: FxHashSet<_> = tcx
         .associated_item_def_ids(impl_def_id)
         .iter()
         .flat_map(|def_id| {
             let item = tcx.associated_item(def_id);
             match item.kind {
-                ty::AssocKind::Type => {
+                ty::AssocKind::Type | ty::AssocKind::Const => {
                     if item.defaultness(tcx).has_value() {
                         cgp::parameters_for(&tcx.type_of(def_id).instantiate_identity(), true)
                     } else {
                         vec![]
                     }
                 }
-                ty::AssocKind::Fn | ty::AssocKind::Const => vec![],
+                ty::AssocKind::Fn => vec![],
             }
         })
         .collect();
diff --git a/tests/ui/consts/assoc-const-unconstrained-lifetime.rs b/tests/ui/consts/assoc-const-unconstrained-lifetime.rs
new file mode 100644
index 0000000000000..f3897c67dd168
--- /dev/null
+++ b/tests/ui/consts/assoc-const-unconstrained-lifetime.rs
@@ -0,0 +1,8 @@
+struct Foo;
+
+impl<'a> Foo {
+    const CONST: &'a str = "";
+    //~^ ERROR the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
+}
+
+fn main() {}
diff --git a/tests/ui/consts/assoc-const-unconstrained-lifetime.stderr b/tests/ui/consts/assoc-const-unconstrained-lifetime.stderr
new file mode 100644
index 0000000000000..cbb9a39f258f3
--- /dev/null
+++ b/tests/ui/consts/assoc-const-unconstrained-lifetime.stderr
@@ -0,0 +1,9 @@
+error[E0207]: the lifetime parameter `'a` is not constrained by the impl trait, self type, or predicates
+  --> $DIR/assoc-const-unconstrained-lifetime.rs:3:6
+   |
+LL | impl<'a> Foo {
+   |      ^^ unconstrained lifetime parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0207`.
diff --git a/tests/ui/nll/trait-associated-constant.rs b/tests/ui/nll/trait-associated-constant.rs
index e13ae80f918b2..b9c6a29756aa3 100644
--- a/tests/ui/nll/trait-associated-constant.rs
+++ b/tests/ui/nll/trait-associated-constant.rs
@@ -19,7 +19,7 @@ struct FailStruct { }
 
 impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct {
     const AC: Option<&'c str> = None;
-    //~^ ERROR: const not compatible with trait
+    //~^ ERROR: the lifetime parameter `'c` is not constrained by the impl trait, self type, or predicates
 }
 
 struct OKStruct2 { }
diff --git a/tests/ui/nll/trait-associated-constant.stderr b/tests/ui/nll/trait-associated-constant.stderr
index cf1c52ba7cc43..1f2c4c6c50c96 100644
--- a/tests/ui/nll/trait-associated-constant.stderr
+++ b/tests/ui/nll/trait-associated-constant.stderr
@@ -1,22 +1,9 @@
-error[E0308]: const not compatible with trait
-  --> $DIR/trait-associated-constant.rs:21:5
-   |
-LL |     const AC: Option<&'c str> = None;
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
-   |
-   = note: expected enum `Option<&'b str>`
-              found enum `Option<&'c str>`
-note: the lifetime `'c` as defined here...
+error[E0207]: the lifetime parameter `'c` is not constrained by the impl trait, self type, or predicates
   --> $DIR/trait-associated-constant.rs:20:18
    |
 LL | impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct {
-   |                  ^^
-note: ...does not necessarily outlive the lifetime `'b` as defined here
-  --> $DIR/trait-associated-constant.rs:20:14
-   |
-LL | impl<'a: 'b, 'b, 'c> Anything<'a, 'b> for FailStruct {
-   |              ^^
+   |                  ^^ unconstrained lifetime parameter
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0207`.