Auto merge of #120365 - matthiaskrgr:rollup-ly2w0d5, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #107464 (Add `str::Lines::remainder`)
 - #118803 (Add the `min_exhaustive_patterns` feature gate)
 - #119466 (Initial implementation of `str::from_raw_parts[_mut]`)
 - #120053 (Specialize `Bytes` on `StdinLock<'_>`)
 - #120124 (Split assembly tests for ELF and MachO)
 - #120204 (Builtin macros effectively have implicit #[collapse_debuginfo(yes)])
 - #120322 (Don't manually resolve async closures in `rustc_resolve`)
 - #120356 (Fix broken markdown in csky-unknown-linux-gnuabiv2.md)

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

7 files changed, 35 insertions, 40 deletions

diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index 29b70f33a6c..657e19277a7 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -796,9 +796,15 @@ impl SyntaxExtension {
     /// | external      | no  | if-ext        | if-ext   | yes |
     /// | yes           | yes | yes           | yes      | yes |
     fn get_collapse_debuginfo(sess: &Session, attrs: &[ast::Attribute], is_local: bool) -> bool {
-        let collapse_debuginfo_attr = attr::find_by_name(attrs, sym::collapse_debuginfo)
+        let mut collapse_debuginfo_attr = attr::find_by_name(attrs, sym::collapse_debuginfo)
             .map(|v| Self::collapse_debuginfo_by_name(sess, v))
             .unwrap_or(CollapseMacroDebuginfo::Unspecified);
+        if collapse_debuginfo_attr == CollapseMacroDebuginfo::Unspecified
+            && attr::contains_name(attrs, sym::rustc_builtin_macro)
+        {
+            collapse_debuginfo_attr = CollapseMacroDebuginfo::Yes;
+        }
+
         let flag = sess.opts.unstable_opts.collapse_macro_debuginfo;
         let attr = collapse_debuginfo_attr;
         let ext = !is_local;
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 6eed2178ead..e66a66e23dc 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -516,6 +516,9 @@ declare_features! (
     (unstable, macro_metavar_expr, "1.61.0", Some(83527)),
     /// Allows `#[marker]` on certain traits allowing overlapping implementations.
     (unstable, marker_trait_attr, "1.30.0", Some(29864)),
+    /// Allows exhaustive pattern matching on types that contain uninhabited types in cases that are
+    /// unambiguously sound.
+    (incomplete, min_exhaustive_patterns, "CURRENT_RUSTC_VERSION", Some(119612)),
     /// A minimal, sound subset of specialization intended to be used by the
     /// standard library until the soundness issues with specialization
     /// are fixed.
diff --git a/compiler/rustc_pattern_analysis/src/lib.rs b/compiler/rustc_pattern_analysis/src/lib.rs
index a55d53dfdac..6374874165f 100644
--- a/compiler/rustc_pattern_analysis/src/lib.rs
+++ b/compiler/rustc_pattern_analysis/src/lib.rs
@@ -95,6 +95,7 @@ pub trait TypeCx: Sized + fmt::Debug {
     type PatData: Clone;
 
     fn is_exhaustive_patterns_feature_on(&self) -> bool;
+    fn is_min_exhaustive_patterns_feature_on(&self) -> bool;
 
     /// The number of fields for this constructor.
     fn ctor_arity(&self, ctor: &Constructor<Self>, ty: &Self::Ty) -> usize;
diff --git a/compiler/rustc_pattern_analysis/src/rustc.rs b/compiler/rustc_pattern_analysis/src/rustc.rs
index 23cab5f43ab..ef90d24b0bf 100644
--- a/compiler/rustc_pattern_analysis/src/rustc.rs
+++ b/compiler/rustc_pattern_analysis/src/rustc.rs
@@ -181,7 +181,9 @@ impl<'p, 'tcx> RustcMatchCheckCtxt<'p, 'tcx> {
             // `field.ty()` doesn't normalize after substituting.
             let ty = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
             let is_visible = adt.is_enum() || field.vis.is_accessible_from(cx.module, cx.tcx);
-            let is_uninhabited = cx.tcx.features().exhaustive_patterns && cx.is_uninhabited(ty);
+            let is_uninhabited = (cx.tcx.features().exhaustive_patterns
+                || cx.tcx.features().min_exhaustive_patterns)
+                && cx.is_uninhabited(ty);
 
             if is_uninhabited && (!is_visible || is_non_exhaustive) {
                 None
@@ -863,6 +865,9 @@ impl<'p, 'tcx> TypeCx for RustcMatchCheckCtxt<'p, 'tcx> {
     fn is_exhaustive_patterns_feature_on(&self) -> bool {
         self.tcx.features().exhaustive_patterns
     }
+    fn is_min_exhaustive_patterns_feature_on(&self) -> bool {
+        self.tcx.features().min_exhaustive_patterns
+    }
 
     fn ctor_arity(&self, ctor: &crate::constructor::Constructor<Self>, ty: &Self::Ty) -> usize {
         self.ctor_arity(ctor, *ty)
diff --git a/compiler/rustc_pattern_analysis/src/usefulness.rs b/compiler/rustc_pattern_analysis/src/usefulness.rs
index 0de48c9f3c0..a627bdeef81 100644
--- a/compiler/rustc_pattern_analysis/src/usefulness.rs
+++ b/compiler/rustc_pattern_analysis/src/usefulness.rs
@@ -548,11 +548,12 @@
 //! [`ValidityConstraint::specialize`].
 //!
 //! Having said all that, in practice we don't fully follow what's been presented in this section.
-//! Under `exhaustive_patterns`, we allow omitting empty arms even in `!known_valid` places, for
-//! backwards-compatibility until we have a better alternative. Without `exhaustive_patterns`, we
-//! mostly treat empty types as inhabited, except specifically a non-nested `!` or empty enum. In
-//! this specific case we also allow the empty match regardless of place validity, for
-//! backwards-compatibility. Hopefully we can eventually deprecate this.
+//! Let's call "toplevel exception" the case where the match scrutinee itself has type `!` or
+//! `EmptyEnum`. First, on stable rust, we require `_` patterns for empty types in all cases apart
+//! from the toplevel exception. The `exhaustive_patterns` and `min_exaustive_patterns` allow
+//! omitting patterns in the cases described above. There's a final detail: in the toplevel
+//! exception or with the `exhaustive_patterns` feature, we ignore place validity when checking
+//! whether a pattern is required for exhaustiveness. I (Nadrieril) hope to deprecate this behavior.
 //!
 //!
 //!
@@ -1442,10 +1443,17 @@ fn compute_exhaustiveness_and_usefulness<'a, 'p, Cx: TypeCx>(
     // We treat match scrutinees of type `!` or `EmptyEnum` differently.
     let is_toplevel_exception =
         is_top_level && matches!(ctors_for_ty, ConstructorSet::NoConstructors);
-    // Whether empty patterns can be omitted for exhaustiveness.
-    let can_omit_empty_arms = is_toplevel_exception || mcx.tycx.is_exhaustive_patterns_feature_on();
-    // Whether empty patterns are counted as useful or not.
-    let empty_arms_are_unreachable = place_validity.is_known_valid() && can_omit_empty_arms;
+    // Whether empty patterns are counted as useful or not. We only warn an empty arm unreachable if
+    // it is guaranteed unreachable by the opsem (i.e. if the place is `known_valid`).
+    let empty_arms_are_unreachable = place_validity.is_known_valid()
+        && (is_toplevel_exception
+            || mcx.tycx.is_exhaustive_patterns_feature_on()
+            || mcx.tycx.is_min_exhaustive_patterns_feature_on());
+    // Whether empty patterns can be omitted for exhaustiveness. We ignore place validity in the
+    // toplevel exception and `exhaustive_patterns` cases for backwards compatibility.
+    let can_omit_empty_arms = empty_arms_are_unreachable
+        || is_toplevel_exception
+        || mcx.tycx.is_exhaustive_patterns_feature_on();
 
     // Analyze the constructors present in this column.
     let ctors = matrix.heads().map(|p| p.ctor());
diff --git a/compiler/rustc_resolve/src/late.rs b/compiler/rustc_resolve/src/late.rs
index abd724a6cc2..18926463d6b 100644
--- a/compiler/rustc_resolve/src/late.rs
+++ b/compiler/rustc_resolve/src/late.rs
@@ -4424,35 +4424,6 @@ impl<'a: 'ast, 'b, 'ast, 'tcx> LateResolutionVisitor<'a, 'b, 'ast, 'tcx> {
             ExprKind::Type(ref _type_expr, ref _ty) => {
                 visit::walk_expr(self, expr);
             }
-            // `async |x| ...` gets desugared to `|x| async {...}`, so we need to
-            // resolve the arguments within the proper scopes so that usages of them inside the
-            // closure are detected as upvars rather than normal closure arg usages.
-            //
-            // Similarly, `gen |x| ...` gets desugared to `|x| gen {...}`, so we handle that too.
-            ExprKind::Closure(box ast::Closure {
-                coroutine_kind: Some(_),
-                ref fn_decl,
-                ref body,
-                ..
-            }) => {
-                self.with_rib(ValueNS, RibKind::Normal, |this| {
-                    this.with_label_rib(RibKind::FnOrCoroutine, |this| {
-                        // Resolve arguments:
-                        this.resolve_params(&fn_decl.inputs);
-                        // No need to resolve return type --
-                        // the outer closure return type is `FnRetTy::Default`.
-
-                        // Now resolve the inner closure
-                        {
-                            // No need to resolve arguments: the inner closure has none.
-                            // Resolve the return type:
-                            visit::walk_fn_ret_ty(this, &fn_decl.output);
-                            // Resolve the body
-                            this.visit_expr(body);
-                        }
-                    })
-                });
-            }
             // For closures, RibKind::FnOrCoroutine is added in visit_fn
             ExprKind::Closure(box ast::Closure {
                 binder: ClosureBinder::For { ref generic_params, span },
diff --git a/compiler/rustc_span/src/symbol.rs b/compiler/rustc_span/src/symbol.rs
index 4a1c222a528..514d65abbe3 100644
--- a/compiler/rustc_span/src/symbol.rs
+++ b/compiler/rustc_span/src/symbol.rs
@@ -1029,6 +1029,7 @@ symbols! {
         min_const_fn,
         min_const_generics,
         min_const_unsafe_fn,
+        min_exhaustive_patterns,
         min_specialization,
         min_type_alias_impl_trait,
         minnumf32,