Auto merge of #90203 - matthiaskrgr:rollup-v215wew, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #85833 (Scrape code examples from examples/ directory for Rustdoc)
 - #88041 (Make all proc-macro back-compat lints deny-by-default)
 - #89829 (Consider types appearing in const expressions to be invariant)
 - #90168 (Reset qualifs when a storage of a local ends)
 - #90198 (Add caveat about changing parallelism and function call overhead)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

compiler/rustc_const_eval/src/transform/check_consts/resolver.rs

@@ -4,7 +4,7 @@
 
 use rustc_index::bit_set::BitSet;
 use rustc_middle::mir::visit::Visitor;
-use rustc_middle::mir::{self, BasicBlock, Local, Location};
+use rustc_middle::mir::{self, BasicBlock, Local, Location, Statement, StatementKind};
 
 use std::marker::PhantomData;
 
@@ -120,6 +120,15 @@ where
         self.super_assign(place, rvalue, location);
     }
 
+    fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
+        match statement.kind {
+            StatementKind::StorageDead(local) => {
+                self.qualifs_per_local.remove(local);
+            }
+            _ => self.super_statement(statement, location),
+        }
+    }
+
     fn visit_terminator(&mut self, terminator: &mir::Terminator<'tcx>, location: Location) {
         // The effect of assignment to the return place in `TerminatorKind::Call` is not applied
         // here; that occurs in `apply_call_return_effect`.

compiler/rustc_lint_defs/src/builtin.rs

@@ -1957,7 +1957,7 @@ declare_lint! {
     /// [issue #50504]: https://github.com/rust-lang/rust/issues/50504
     /// [future-incompatible]: ../index.md#future-incompatible-lints
     pub PROC_MACRO_DERIVE_RESOLUTION_FALLBACK,
-    Warn,
+    Deny,
     "detects proc macro derives using inaccessible names from parent modules",
     @future_incompatible = FutureIncompatibleInfo {
         reference: "issue #83583 <https://github.com/rust-lang/rust/issues/83583>",
@@ -3253,7 +3253,7 @@ declare_lint! {
     /// [issue #83125]: https://github.com/rust-lang/rust/issues/83125
     /// [future-incompatible]: ../index.md#future-incompatible-lints
     pub PROC_MACRO_BACK_COMPAT,
-    Warn,
+    Deny,
     "detects usage of old versions of certain proc-macro crates",
     @future_incompatible = FutureIncompatibleInfo {
         reference: "issue #83125 <https://github.com/rust-lang/rust/issues/83125>",

compiler/rustc_typeck/src/variance/constraints.rs

@@ -223,8 +223,8 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                     self.add_constraints_from_region(current, lt, variance_i)
                 }
                 GenericArgKind::Type(ty) => self.add_constraints_from_ty(current, ty, variance_i),
-                GenericArgKind::Const(_) => {
-                    // Consts impose no constraints.
+                GenericArgKind::Const(val) => {
+                    self.add_constraints_from_const(current, val, variance_i)
                 }
             }
         }
@@ -263,7 +263,8 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                 self.add_constraints_from_mt(current, &ty::TypeAndMut { ty, mutbl }, variance);
             }
 
-            ty::Array(typ, _) => {
+            ty::Array(typ, len) => {
+                self.add_constraints_from_const(current, len, variance);
                 self.add_constraints_from_ty(current, typ, variance);
             }
 
@@ -385,13 +386,32 @@ impl<'a, 'tcx> ConstraintContext<'a, 'tcx> {
                     self.add_constraints_from_region(current, lt, variance_i)
                 }
                 GenericArgKind::Type(ty) => self.add_constraints_from_ty(current, ty, variance_i),
-                GenericArgKind::Const(_) => {
-                    // Consts impose no constraints.
+                GenericArgKind::Const(val) => {
+                    self.add_constraints_from_const(current, val, variance)
                 }
             }
         }
     }
 
+    /// Adds constraints appropriate for a const expression `val`
+    /// in a context with ambient variance `variance`
+    fn add_constraints_from_const(
+        &mut self,
+        current: &CurrentItem,
+        val: &ty::Const<'tcx>,
+        variance: VarianceTermPtr<'a>,
+    ) {
+        debug!("add_constraints_from_const(val={:?}, variance={:?})", val, variance);
+
+        match &val.val {
+            ty::ConstKind::Unevaluated(uv) => {
+                let substs = uv.substs(self.tcx());
+                self.add_constraints_from_invariant_substs(current, substs, variance);
+            }
+            _ => {}
+        }
+    }
+
     /// Adds constraints appropriate for a function with signature
     /// `sig` appearing in a context with ambient variance `variance`
     fn add_constraints_from_sig(