From 41f84c258ad5fc12775e25aafe4d67e3304a5bda Mon Sep 17 00:00:00 2001
From: Jacob Pratt <jacob@jhpratt.dev>
Date: Wed, 17 Nov 2021 21:06:17 -0500
Subject: [PATCH] Require const stability on all stable const items

This was supposed to be the case previously, but a missed method call
meant that trait impls were not checked.
---
 compiler/rustc_passes/src/stability.rs        | 36 +++++++++----------
 .../missing-const-stability.rs                | 24 +++++++++----
 .../missing-const-stability.stderr            | 12 +++++--
 3 files changed, 45 insertions(+), 27 deletions(-)

diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index 3521b6fc169..136059677c5 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -577,17 +577,21 @@ impl<'tcx> MissingStabilityAnnotations<'tcx> {
     }
 
     fn check_missing_const_stability(&self, def_id: LocalDefId, span: Span) {
-        let stab_map = self.tcx.stability();
-        let stab = stab_map.local_stability(def_id);
-        if stab.map_or(false, |stab| stab.level.is_stable()) {
-            let const_stab = stab_map.local_const_stability(def_id);
-            if const_stab.is_none() {
-                self.tcx.sess.span_err(
-                    span,
-                    "`#[stable]` const functions must also be either \
-                    `#[rustc_const_stable]` or `#[rustc_const_unstable]`",
-                );
-            }
+        if !self.tcx.features().staged_api {
+            return;
+        }
+
+        let is_const = self.tcx.is_const_fn(def_id.to_def_id());
+        let is_stable = self
+            .tcx
+            .lookup_stability(def_id)
+            .map_or(false, |stability| stability.level.is_stable());
+        let missing_const_stability_attribute = self.tcx.lookup_const_stability(def_id).is_none();
+        let is_reachable = self.access_levels.is_reachable(def_id);
+
+        if is_const && is_stable && missing_const_stability_attribute && is_reachable {
+            let descr = self.tcx.def_kind(def_id).descr(def_id.to_def_id());
+            self.tcx.sess.span_err(span, &format!("{descr} has missing const stability attribute"));
         }
     }
 }
@@ -612,13 +616,8 @@ impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
             self.check_missing_stability(i.def_id, i.span);
         }
 
-        // Ensure `const fn` that are `stable` have one of `rustc_const_unstable` or
-        // `rustc_const_stable`.
-        if self.tcx.features().staged_api
-            && matches!(&i.kind, hir::ItemKind::Fn(sig, ..) if sig.header.is_const())
-        {
-            self.check_missing_const_stability(i.def_id, i.span);
-        }
+        // Ensure stable `const fn` have a const stability attribute.
+        self.check_missing_const_stability(i.def_id, i.span);
 
         intravisit::walk_item(self, i)
     }
@@ -632,6 +631,7 @@ impl<'tcx> Visitor<'tcx> for MissingStabilityAnnotations<'tcx> {
         let impl_def_id = self.tcx.hir().get_parent_item(ii.hir_id());
         if self.tcx.impl_trait_ref(impl_def_id).is_none() {
             self.check_missing_stability(ii.def_id, ii.span);
+            self.check_missing_const_stability(ii.def_id, ii.span);
         }
         intravisit::walk_impl_item(self, ii);
     }
diff --git a/src/test/ui/stability-attribute/missing-const-stability.rs b/src/test/ui/stability-attribute/missing-const-stability.rs
index 7d499c611a4..39af6e9e3b9 100644
--- a/src/test/ui/stability-attribute/missing-const-stability.rs
+++ b/src/test/ui/stability-attribute/missing-const-stability.rs
@@ -1,12 +1,24 @@
 #![feature(staged_api)]
+#![stable(feature = "stable", since = "1.0.0")]
 
-#![stable(feature = "rust1", since = "1.0.0")]
+#[stable(feature = "stable", since = "1.0.0")]
+pub const fn foo() {} //~ ERROR function has missing const stability attribute
 
-#[stable(feature = "foo", since = "1.0.0")]
-pub const fn foo() {}
-//~^ ERROR rustc_const_stable
+#[unstable(feature = "unstable", issue = "none")]
+pub const fn bar() {} // ok for now
 
-#[unstable(feature = "bar", issue = "none")]
-pub const fn bar() {} // ok
+#[stable(feature = "stable", since = "1.0.0")]
+pub struct Foo;
+impl Foo {
+    #[stable(feature = "stable", since = "1.0.0")]
+    pub const fn foo() {} //~ ERROR associated function has missing const stability attribute
+
+    #[unstable(feature = "unstable", issue = "none")]
+    pub const fn bar() {} // ok for now
+}
+
+// FIXME When #![feature(const_trait_impl)] is stabilized, add tests for const
+// trait impls. Right now, a "trait methods cannot be stable const fn" error is
+// emitted, but that's not in the scope of this test.
 
 fn main() {}
diff --git a/src/test/ui/stability-attribute/missing-const-stability.stderr b/src/test/ui/stability-attribute/missing-const-stability.stderr
index 450a5303fd8..ee98e7b0e3f 100644
--- a/src/test/ui/stability-attribute/missing-const-stability.stderr
+++ b/src/test/ui/stability-attribute/missing-const-stability.stderr
@@ -1,8 +1,14 @@
-error: `#[stable]` const functions must also be either `#[rustc_const_stable]` or `#[rustc_const_unstable]`
-  --> $DIR/missing-const-stability.rs:6:1
+error: function has missing const stability attribute
+  --> $DIR/missing-const-stability.rs:5:1
    |
 LL | pub const fn foo() {}
    | ^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to previous error
+error: associated function has missing const stability attribute
+  --> $DIR/missing-const-stability.rs:14:5
+   |
+LL |     pub const fn foo() {}
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors