Auto merge of rust-lang#130631 - GuillaumeGomez:rollup-jpgy1iv, r=GuillaumeGomez

Rollup of 7 pull requests

Successful merges:

 - rust-lang#128209 (Remove macOS 10.10 dynamic linker bug workaround)
 - rust-lang#130526 (Begin experimental support for pin reborrowing)
 - rust-lang#130611 (Address diagnostics regression for `const_char_encode_utf8`.)
 - rust-lang#130614 (Add arm64e-apple-tvos target)
 - rust-lang#130617 (bail if there are too many non-region infer vars in the query response)
 - rust-lang#130619 (Fix scraped examples height)
 - rust-lang#130624 (Add `Vec::as_non_null`)

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

Author: bors

compiler/rustc_borrowck/messages.ftl

@@ -207,7 +207,7 @@ borrowck_simd_intrinsic_arg_const =
         *[other] {$arg}th
     } argument of `{$intrinsic}` is required to be a `const` item
 
-borrowck_suggest_create_freash_reborrow =
+borrowck_suggest_create_fresh_reborrow =
     consider reborrowing the `Pin` instead of moving it
 
 borrowck_suggest_iterate_over_slice =

compiler/rustc_borrowck/src/session_diagnostics.rs

@@ -415,7 +415,7 @@ pub(crate) enum CaptureReasonSuggest<'tcx> {
         span: Span,
     },
     #[suggestion(
-        borrowck_suggest_create_freash_reborrow,
+        borrowck_suggest_create_fresh_reborrow,
         applicability = "maybe-incorrect",
         code = ".as_mut()",
         style = "verbose"

compiler/rustc_codegen_llvm/src/consts.rs

@@ -443,58 +443,6 @@ impl<'ll> CodegenCx<'ll, '_> {
 
             if attrs.flags.contains(CodegenFnAttrFlags::THREAD_LOCAL) {
                 llvm::set_thread_local_mode(g, self.tls_model);
-
-                // Do not allow LLVM to change the alignment of a TLS on macOS.
-                //
-                // By default a global's alignment can be freely increased.
-                // This allows LLVM to generate more performant instructions
-                // e.g., using load-aligned into a SIMD register.
-                //
-                // However, on macOS 10.10 or below, the dynamic linker does not
-                // respect any alignment given on the TLS (radar 24221680).
-                // This will violate the alignment assumption, and causing segfault at runtime.
-                //
-                // This bug is very easy to trigger. In `println!` and `panic!`,
-                // the `LOCAL_STDOUT`/`LOCAL_STDERR` handles are stored in a TLS,
-                // which the values would be `mem::replace`d on initialization.
-                // The implementation of `mem::replace` will use SIMD
-                // whenever the size is 32 bytes or higher. LLVM notices SIMD is used
-                // and tries to align `LOCAL_STDOUT`/`LOCAL_STDERR` to a 32-byte boundary,
-                // which macOS's dyld disregarded and causing crashes
-                // (see issues #51794, #51758, #50867, #48866 and #44056).
-                //
-                // To workaround the bug, we trick LLVM into not increasing
-                // the global's alignment by explicitly assigning a section to it
-                // (equivalent to automatically generating a `#[link_section]` attribute).
-                // See the comment in the `GlobalValue::canIncreaseAlignment()` function
-                // of `lib/IR/Globals.cpp` for why this works.
-                //
-                // When the alignment is not increased, the optimized `mem::replace`
-                // will use load-unaligned instructions instead, and thus avoiding the crash.
-                //
-                // We could remove this hack whenever we decide to drop macOS 10.10 support.
-                if self.tcx.sess.target.is_like_osx {
-                    // The `inspect` method is okay here because we checked for provenance, and
-                    // because we are doing this access to inspect the final interpreter state
-                    // (not as part of the interpreter execution).
-                    //
-                    // FIXME: This check requires that the (arbitrary) value of undefined bytes
-                    // happens to be zero. Instead, we should only check the value of defined bytes
-                    // and set all undefined bytes to zero if this allocation is headed for the
-                    // BSS.
-                    let all_bytes_are_zero = alloc.provenance().ptrs().is_empty()
-                        && alloc
-                            .inspect_with_uninit_and_ptr_outside_interpreter(0..alloc.len())
-                            .iter()
-                            .all(|&byte| byte == 0);
-
-                    let sect_name = if all_bytes_are_zero {
-                        c"__DATA,__thread_bss"
-                    } else {
-                        c"__DATA,__thread_data"
-                    };
-                    llvm::LLVMSetSection(g, sect_name.as_ptr());
-                }
             }
 
             // Wasm statics with custom link sections get special treatment as they

compiler/rustc_feature/src/unstable.rs

@@ -558,6 +558,8 @@ declare_features! (
     (unstable, optimize_attribute, "1.34.0", Some(54882)),
     /// Allows specifying nop padding on functions for dynamic patching.
     (unstable, patchable_function_entry, "1.81.0", Some(123115)),
+    /// Experimental features that make `Pin` more ergonomic.
+    (incomplete, pin_ergonomics, "CURRENT_RUSTC_VERSION", Some(130494)),
     /// Allows postfix match `expr.match { ... }`
     (unstable, postfix_match, "1.79.0", Some(121618)),
     /// Allows macro attributes on expressions, statements and non-inline modules.

compiler/rustc_hir_typeck/src/coercion.rs

@@ -214,6 +214,12 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             ty::Dynamic(predicates, region, ty::DynStar) if self.tcx.features().dyn_star => {
                 return self.coerce_dyn_star(a, b, predicates, region);
             }
+            ty::Adt(pin, _)
+                if self.tcx.features().pin_ergonomics
+                    && self.tcx.is_lang_item(pin.did(), hir::LangItem::Pin) =>
+            {
+                return self.coerce_pin(a, b);
+            }
             _ => {}
         }
 
@@ -774,6 +780,62 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
         })
     }
 
+    /// Applies reborrowing for `Pin`
+    ///
+    /// We currently only support reborrowing `Pin<&mut T>` as `Pin<&mut T>`. This is accomplished
+    /// by inserting a call to `Pin::as_mut` during MIR building.
+    ///
+    /// In the future we might want to support other reborrowing coercions, such as:
+    /// - `Pin<&mut T>` as `Pin<&T>`
+    /// - `Pin<&T>` as `Pin<&T>`
+    /// - `Pin<Box<T>>` as `Pin<&T>`
+    /// - `Pin<Box<T>>` as `Pin<&mut T>`
+    #[instrument(skip(self), level = "trace")]
+    fn coerce_pin(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> CoerceResult<'tcx> {
+        // We need to make sure the two types are compatible for coercion.
+        // Then we will build a ReborrowPin adjustment and return that as an InferOk.
+
+        // Right now we can only reborrow if this is a `Pin<&mut T>`.
+        let extract_pin_mut = |ty: Ty<'tcx>| {
+            // Get the T out of Pin<T>
+            let (pin, ty) = match ty.kind() {
+                ty::Adt(pin, args) if self.tcx.is_lang_item(pin.did(), hir::LangItem::Pin) => {
+                    (*pin, args[0].expect_ty())
+                }
+                _ => {
+                    debug!("can't reborrow {:?} as pinned", ty);
+                    return Err(TypeError::Mismatch);
+                }
+            };
+            // Make sure the T is something we understand (just `&mut U` for now)
+            match ty.kind() {
+                ty::Ref(region, ty, mutbl) => Ok((pin, *region, *ty, *mutbl)),
+                _ => {
+                    debug!("can't reborrow pin of inner type {:?}", ty);
+                    Err(TypeError::Mismatch)
+                }
+            }
+        };
+
+        let (pin, a_region, a_ty, mut_a) = extract_pin_mut(a)?;
+        let (_, b_region, _b_ty, mut_b) = extract_pin_mut(b)?;
+
+        coerce_mutbls(mut_a, mut_b)?;
+
+        // update a with b's mutability since we'll be coercing mutability
+        let a = Ty::new_adt(
+            self.tcx,
+            pin,
+            self.tcx.mk_args(&[Ty::new_ref(self.tcx, a_region, a_ty, mut_b).into()]),
+        );
+
+        // To complete the reborrow, we need to make sure we can unify the inner types, and if so we
+        // add the adjustments.
+        self.unify_and(a, b, |_inner_ty| {
+            vec![Adjustment { kind: Adjust::ReborrowPin(b_region, mut_b), target: b }]
+        })
+    }
+
     fn coerce_from_safe_fn<F, G>(
         &self,
         a: Ty<'tcx>,

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -780,6 +780,16 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
                 adjustment::Adjust::Borrow(ref autoref) => {
                     self.walk_autoref(expr, &place_with_id, autoref);
                 }
+
+                adjustment::Adjust::ReborrowPin(_, mutbl) => {
+                    // Reborrowing a Pin is like a combinations of a deref and a borrow, so we do
+                    // both.
+                    let bk = match mutbl {
+                        ty::Mutability::Not => ty::BorrowKind::ImmBorrow,
+                        ty::Mutability::Mut => ty::BorrowKind::MutBorrow,
+                    };
+                    self.delegate.borrow_mut().borrow(&place_with_id, place_with_id.hir_id, bk);
+                }
             }
             place_with_id = self.cat_expr_adjusted(expr, place_with_id, adjustment)?;
         }
@@ -1284,6 +1294,7 @@ impl<'tcx, Cx: TypeInformationCtxt<'tcx>, D: Delegate<'tcx>> ExprUseVisitor<'tcx
             adjustment::Adjust::NeverToAny
             | adjustment::Adjust::Pointer(_)
             | adjustment::Adjust::Borrow(_)
+            | adjustment::Adjust::ReborrowPin(..)
             | adjustment::Adjust::DynStar => {
                 // Result is an rvalue.
                 Ok(self.cat_rvalue(expr.hir_id, target))

compiler/rustc_middle/src/ty/adjustment.rs

@@ -104,6 +104,9 @@ pub enum Adjust<'tcx> {
 
     /// Cast into a dyn* object.
     DynStar,
+
+    /// Take a pinned reference and reborrow as a `Pin<&mut T>` or `Pin<&T>`.
+    ReborrowPin(ty::Region<'tcx>, hir::Mutability),
 }
 
 /// An overloaded autoderef step, representing a `Deref(Mut)::deref(_mut)`

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -74,6 +74,7 @@ impl<'tcx> Cx<'tcx> {
         self.thir.exprs.push(expr)
     }
 
+    #[instrument(level = "trace", skip(self, expr, span))]
     fn apply_adjustment(
         &mut self,
         hir_expr: &'tcx hir::Expr<'tcx>,
@@ -146,6 +147,67 @@ impl<'tcx> Cx<'tcx> {
                 ExprKind::RawBorrow { mutability, arg: self.thir.exprs.push(expr) }
             }
             Adjust::DynStar => ExprKind::Cast { source: self.thir.exprs.push(expr) },
+            Adjust::ReborrowPin(region, mutbl) => {
+                debug!("apply ReborrowPin adjustment");
+                // Rewrite `$expr` as `Pin { __pointer: &(mut)? *($expr).__pointer }`
+
+                // We'll need these types later on
+                let pin_ty_args = match expr.ty.kind() {
+                    ty::Adt(_, args) => args,
+                    _ => bug!("ReborrowPin with non-Pin type"),
+                };
+                let pin_ty = pin_ty_args.iter().next().unwrap().expect_ty();
+                let ptr_target_ty = match pin_ty.kind() {
+                    ty::Ref(_, ty, _) => *ty,
+                    _ => bug!("ReborrowPin with non-Ref type"),
+                };
+
+                // pointer = ($expr).__pointer
+                let pointer_target = ExprKind::Field {
+                    lhs: self.thir.exprs.push(expr),
+                    variant_index: FIRST_VARIANT,
+                    name: FieldIdx::from(0u32),
+                };
+                let arg = Expr { temp_lifetime, ty: pin_ty, span, kind: pointer_target };
+                let arg = self.thir.exprs.push(arg);
+
+                // arg = *pointer
+                let expr = ExprKind::Deref { arg };
+                let arg = self.thir.exprs.push(Expr {
+                    temp_lifetime,
+                    ty: ptr_target_ty,
+                    span,
+                    kind: expr,
+                });
+
+                // expr = &mut target
+                let borrow_kind = match mutbl {
+                    hir::Mutability::Mut => BorrowKind::Mut { kind: mir::MutBorrowKind::Default },
+                    hir::Mutability::Not => BorrowKind::Shared,
+                };
+                let new_pin_target = Ty::new_ref(self.tcx, region, ptr_target_ty, mutbl);
+                let expr = self.thir.exprs.push(Expr {
+                    temp_lifetime,
+                    ty: new_pin_target,
+                    span,
+                    kind: ExprKind::Borrow { borrow_kind, arg },
+                });
+
+                // kind = Pin { __pointer: pointer }
+                let pin_did = self.tcx.require_lang_item(rustc_hir::LangItem::Pin, Some(span));
+                let args = self.tcx.mk_args(&[new_pin_target.into()]);
+                let kind = ExprKind::Adt(Box::new(AdtExpr {
+                    adt_def: self.tcx.adt_def(pin_did),
+                    variant_index: FIRST_VARIANT,
+                    args,
+                    fields: Box::new([FieldExpr { name: FieldIdx::from(0u32), expr }]),
+                    user_ty: None,
+                    base: None,
+                }));
+
+                debug!(?kind);
+                kind
+            }
         };
 
         Expr { temp_lifetime, ty: adjustment.target, span, kind }
@@ -1014,7 +1076,7 @@ impl<'tcx> Cx<'tcx> {
 
         // Reconstruct the output assuming it's a reference with the
         // same region and mutability as the receiver. This holds for
-        // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
+        // `Deref(Mut)::deref(_mut)` and `Index(Mut)::index(_mut)`.
         let ty::Ref(region, _, mutbl) = *self.thir[args[0]].ty.kind() else {
             span_bug!(span, "overloaded_place: receiver is not a reference");
         };

compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs

@@ -157,6 +157,17 @@ where
             },
         );
 
+        // HACK: We bail with overflow if the response would have too many non-region
+        // inference variables. This tends to only happen if we encounter a lot of
+        // ambiguous alias types which get replaced with fresh inference variables
+        // during generalization. This prevents a hang in nalgebra.
+        let num_non_region_vars = canonical.variables.iter().filter(|c| !c.is_region()).count();
+        if num_non_region_vars > self.cx().recursion_limit() {
+            return Ok(self.make_ambiguous_response_no_constraints(MaybeCause::Overflow {
+                suggest_increasing_limit: true,
+            }));
+        }
+
         Ok(canonical)
     }
 

compiler/rustc_span/src/symbol.rs

@@ -1453,6 +1453,7 @@ symbols! {
         pic,
         pie,
         pin,
+        pin_ergonomics,
         platform_intrinsics,
         plugin,
         plugin_registrar,