Auto merge of rust-lang#99346 - matthiaskrgr:rollup-p4dl1qt, r=matthiaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#98582 (Allow destructuring opaque types in their defining scopes)
 - rust-lang#99213 (migrate some of `rustc_passes::check_attr`'s diagnostics and derive improvements)
 - rust-lang#99258 (Provide structured suggestion for dropped temp value)
 - rust-lang#99259 (interpret/visitor: support visiting with a PlaceTy)
 - rust-lang#99287 ([rustdoc-json] JSON no longer inlines)
 - rust-lang#99290 (Revert "Highlight conflicting param-env candidates")
 - rust-lang#99316 (docs: add missing word)
 - rust-lang#99317 (Borrow Vec<T, A> as [T])
 - rust-lang#99323 (Fix flakyness of GUI tests)
 - rust-lang#99342 (Avoid some `Symbol` to `String` conversions)

Failed merges:

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

Author: bors

Cargo.lock

@@ -4239,6 +4239,7 @@ dependencies = [
  "rustc_hir",
  "rustc_index",
  "rustc_lexer",
+ "rustc_macros",
  "rustc_middle",
  "rustc_serialize",
  "rustc_session",

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -7,7 +7,7 @@ use rustc_errors::{
 };
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
-use rustc_hir::intravisit::{walk_expr, Visitor};
+use rustc_hir::intravisit::{walk_block, walk_expr, Visitor};
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::ObligationCause;
@@ -23,7 +23,7 @@ use rustc_middle::ty::{
 use rustc_mir_dataflow::move_paths::{InitKind, MoveOutIndex, MovePathIndex};
 use rustc_span::hygiene::DesugaringKind;
 use rustc_span::symbol::sym;
-use rustc_span::{BytePos, Span};
+use rustc_span::{BytePos, Span, Symbol};
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::TraitEngineExt as _;
 
@@ -1227,8 +1227,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     from_closure: false,
                     region_name:
                         RegionName {
-                            source:
-                                RegionNameSource::AnonRegionFromUpvar(upvar_span, ref upvar_name),
+                            source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name),
                             ..
                         },
                     span,
@@ -1500,7 +1499,70 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             | BorrowExplanation::UsedLaterInLoop(..)
             | BorrowExplanation::UsedLaterWhenDropped { .. } => {
                 // Only give this note and suggestion if it could be relevant.
-                err.note("consider using a `let` binding to create a longer lived value");
+                let sm = self.infcx.tcx.sess.source_map();
+                let mut suggested = false;
+                let msg = "consider using a `let` binding to create a longer lived value";
+
+                /// We check that there's a single level of block nesting to ensure always correct
+                /// suggestions. If we don't, then we only provide a free-form message to avoid
+                /// misleading users in cases like `src/test/ui/nll/borrowed-temporary-error.rs`.
+                /// We could expand the analysis to suggest hoising all of the relevant parts of
+                /// the users' code to make the code compile, but that could be too much.
+                struct NestedStatementVisitor {
+                    span: Span,
+                    current: usize,
+                    found: usize,
+                }
+
+                impl<'tcx> Visitor<'tcx> for NestedStatementVisitor {
+                    fn visit_block(&mut self, block: &hir::Block<'tcx>) {
+                        self.current += 1;
+                        walk_block(self, block);
+                        self.current -= 1;
+                    }
+                    fn visit_expr(&mut self, expr: &hir::Expr<'tcx>) {
+                        if self.span == expr.span {
+                            self.found = self.current;
+                        }
+                        walk_expr(self, expr);
+                    }
+                }
+                let source_info = self.body.source_info(location);
+                if let Some(scope) = self.body.source_scopes.get(source_info.scope)
+                    && let ClearCrossCrate::Set(scope_data) = &scope.local_data
+                    && let Some(node) = self.infcx.tcx.hir().find(scope_data.lint_root)
+                    && let Some(id) = node.body_id()
+                    && let hir::ExprKind::Block(block, _) = self.infcx.tcx.hir().body(id).value.kind
+                {
+                    for stmt in block.stmts {
+                        let mut visitor = NestedStatementVisitor {
+                            span: proper_span,
+                            current: 0,
+                            found: 0,
+                        };
+                        visitor.visit_stmt(stmt);
+                        if visitor.found == 0
+                            && stmt.span.contains(proper_span)
+                            && let Some(p) = sm.span_to_margin(stmt.span)
+                            && let Ok(s) = sm.span_to_snippet(proper_span)
+                        {
+                            let addition = format!("let binding = {};\n{}", s, " ".repeat(p));
+                            err.multipart_suggestion_verbose(
+                                msg,
+                                vec![
+                                    (stmt.span.shrink_to_lo(), addition),
+                                    (proper_span, "binding".to_string()),
+                                ],
+                                Applicability::MaybeIncorrect,
+                            );
+                            suggested = true;
+                            break;
+                        }
+                    }
+                }
+                if !suggested {
+                    err.note(msg);
+                }
             }
             _ => {}
         }
@@ -1699,7 +1761,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         borrow_span: Span,
         name: &Option<String>,
         upvar_span: Span,
-        upvar_name: &str,
+        upvar_name: Symbol,
         escape_span: Span,
     ) -> DiagnosticBuilder<'cx, ErrorGuaranteed> {
         let tcx = self.infcx.tcx;
@@ -2093,7 +2155,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                             }
                             StorageDeadOrDrop::Destructor(_) => kind,
                         },
-                        ProjectionElem::Field(..) | ProjectionElem::Downcast(..) => {
+                        ProjectionElem::OpaqueCast { .. }
+                        | ProjectionElem::Field(..)
+                        | ProjectionElem::Downcast(..) => {
                             match place_ty.ty.kind() {
                                 ty::Adt(def, _) if def.has_dtor(tcx) => {
                                     // Report the outermost adt with a destructor

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -12,7 +12,7 @@ use rustc_middle::mir::{
 };
 use rustc_middle::ty::adjustment::PointerCast;
 use rustc_middle::ty::{self, RegionVid, TyCtxt};
-use rustc_span::symbol::Symbol;
+use rustc_span::symbol::{kw, Symbol};
 use rustc_span::{sym, DesugaringKind, Span};
 
 use crate::region_infer::BlameConstraint;
@@ -282,7 +282,7 @@ impl<'tcx> BorrowExplanation<'tcx> {
     ) {
         if let ConstraintCategory::OpaqueType = category {
             let suggestable_name =
-                if region_name.was_named() { region_name.to_string() } else { "'_".to_string() };
+                if region_name.was_named() { region_name.name } else { kw::UnderscoreLifetime };
 
             let msg = format!(
                 "you can add a bound to the {}to make it last less than `'static` and match `{}`",

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -226,6 +226,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
                 ProjectionElem::Downcast(..) if including_downcast.0 => return None,
                 ProjectionElem::Downcast(..) => (),
+                ProjectionElem::OpaqueCast(..) => (),
                 ProjectionElem::Field(field, _ty) => {
                     // FIXME(project-rfc_2229#36): print capture precisely here.
                     if let Some(field) = self.is_upvar_field_projection(PlaceRef {
@@ -286,6 +287,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     PlaceRef { local, projection: proj_base }.ty(self.body, self.infcx.tcx)
                 }
                 ProjectionElem::Downcast(..) => place.ty(self.body, self.infcx.tcx),
+                ProjectionElem::OpaqueCast(ty) => PlaceTy::from_ty(*ty),
                 ProjectionElem::Field(_, field_type) => PlaceTy::from_ty(*field_type),
             },
         };

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -169,6 +169,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         ..,
                         ProjectionElem::Index(_)
                         | ProjectionElem::ConstantIndex { .. }
+                        | ProjectionElem::OpaqueCast { .. }
                         | ProjectionElem::Subslice { .. }
                         | ProjectionElem::Downcast(..),
                     ],

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -19,8 +19,7 @@ use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::Region;
 use rustc_middle::ty::TypeVisitor;
 use rustc_middle::ty::{self, RegionVid, Ty};
-use rustc_span::symbol::sym;
-use rustc_span::symbol::Ident;
+use rustc_span::symbol::{kw, sym, Ident};
 use rustc_span::Span;
 
 use crate::borrowck_errors;
@@ -758,7 +757,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                 return;
             };
 
-            let lifetime = if f.has_name() { fr_name.to_string() } else { "'_".to_string() };
+            let lifetime = if f.has_name() { fr_name.name } else { kw::UnderscoreLifetime };
 
             let arg = match param.param.pat.simple_ident() {
                 Some(simple_ident) => format!("argument `{}`", simple_ident),
@@ -770,7 +769,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                 self.infcx.tcx,
                 diag,
                 fn_returns,
-                lifetime,
+                lifetime.to_string(),
                 Some(arg),
                 captures,
                 Some((param.param_ty_span, param.param_ty.to_string())),

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -34,13 +34,13 @@ pub(crate) enum RegionNameSource {
     /// The `'static` region.
     Static,
     /// The free region corresponding to the environment of a closure.
-    SynthesizedFreeEnvRegion(Span, String),
+    SynthesizedFreeEnvRegion(Span, &'static str),
     /// The region corresponding to an argument.
     AnonRegionFromArgument(RegionNameHighlight),
     /// The region corresponding to a closure upvar.
-    AnonRegionFromUpvar(Span, String),
+    AnonRegionFromUpvar(Span, Symbol),
     /// The region corresponding to the return type of a closure.
-    AnonRegionFromOutput(RegionNameHighlight, String),
+    AnonRegionFromOutput(RegionNameHighlight, &'static str),
     /// The region from a type yielded by a generator.
     AnonRegionFromYieldTy(Span, String),
     /// An anonymous region from an async fn.
@@ -110,7 +110,7 @@ impl RegionName {
             }
             RegionNameSource::SynthesizedFreeEnvRegion(span, note) => {
                 diag.span_label(*span, format!("lifetime `{self}` represents this closure's body"));
-                diag.note(note);
+                diag.note(*note);
             }
             RegionNameSource::AnonRegionFromArgument(RegionNameHighlight::CannotMatchHirTy(
                 span,
@@ -350,10 +350,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
                     Some(RegionName {
                         name: region_name,
-                        source: RegionNameSource::SynthesizedFreeEnvRegion(
-                            fn_decl_span,
-                            note.to_string(),
-                        ),
+                        source: RegionNameSource::SynthesizedFreeEnvRegion(fn_decl_span, note),
                     })
                 }
 
@@ -678,7 +675,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
         Some(RegionName {
             name: region_name,
-            source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name.to_string()),
+            source: RegionNameSource::AnonRegionFromUpvar(upvar_span, upvar_name),
         })
     }
 
@@ -756,7 +753,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
         Some(RegionName {
             name: self.synthesize_region_name(),
-            source: RegionNameSource::AnonRegionFromOutput(highlight, mir_description.to_string()),
+            source: RegionNameSource::AnonRegionFromOutput(highlight, mir_description),
         })
     }
 

compiler/rustc_borrowck/src/lib.rs

@@ -1788,6 +1788,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         for (place_base, elem) in place.iter_projections().rev() {
             match elem {
                 ProjectionElem::Index(_/*operand*/) |
+                ProjectionElem::OpaqueCast(_) |
                 ProjectionElem::ConstantIndex { .. } |
                 // assigning to P[i] requires P to be valid.
                 ProjectionElem::Downcast(_/*adt_def*/, _/*variant_idx*/) =>
@@ -2179,6 +2180,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     | ProjectionElem::Index(..)
                     | ProjectionElem::ConstantIndex { .. }
                     | ProjectionElem::Subslice { .. }
+                    | ProjectionElem::OpaqueCast { .. }
                     | ProjectionElem::Downcast(..) => {
                         let upvar_field_projection = self.is_upvar_field_projection(place);
                         if let Some(field) = upvar_field_projection {

compiler/rustc_borrowck/src/places_conflict.rs

@@ -255,6 +255,7 @@ fn place_components_conflict<'tcx>(
                 | (ProjectionElem::Index { .. }, _, _)
                 | (ProjectionElem::ConstantIndex { .. }, _, _)
                 | (ProjectionElem::Subslice { .. }, _, _)
+                | (ProjectionElem::OpaqueCast { .. }, _, _)
                 | (ProjectionElem::Downcast { .. }, _, _) => {
                     // Recursive case. This can still be disjoint on a
                     // further iteration if this a shallow access and
@@ -322,6 +323,17 @@ fn place_projection_conflict<'tcx>(
             debug!("place_element_conflict: DISJOINT-OR-EQ-DEREF");
             Overlap::EqualOrDisjoint
         }
+        (ProjectionElem::OpaqueCast(v1), ProjectionElem::OpaqueCast(v2)) => {
+            if v1 == v2 {
+                // same type - recur.
+                debug!("place_element_conflict: DISJOINT-OR-EQ-OPAQUE");
+                Overlap::EqualOrDisjoint
+            } else {
+                // Different types. Disjoint!
+                debug!("place_element_conflict: DISJOINT-OPAQUE");
+                Overlap::Disjoint
+            }
+        }
         (ProjectionElem::Field(f1, _), ProjectionElem::Field(f2, _)) => {
             if f1 == f2 {
                 // same field (e.g., `a.y` vs. `a.y`) - recur.
@@ -525,6 +537,7 @@ fn place_projection_conflict<'tcx>(
             | ProjectionElem::Field(..)
             | ProjectionElem::Index(..)
             | ProjectionElem::ConstantIndex { .. }
+            | ProjectionElem::OpaqueCast { .. }
             | ProjectionElem::Subslice { .. }
             | ProjectionElem::Downcast(..),
             _,

compiler/rustc_borrowck/src/prefixes.rs

@@ -81,6 +81,7 @@ impl<'cx, 'tcx> Iterator for Prefixes<'cx, 'tcx> {
                         }
                         ProjectionElem::Downcast(..)
                         | ProjectionElem::Subslice { .. }
+                        | ProjectionElem::OpaqueCast { .. }
                         | ProjectionElem::ConstantIndex { .. }
                         | ProjectionElem::Index(_) => {
                             cursor = cursor_base;

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -790,6 +790,19 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
                 }
                 PlaceTy::from_ty(fty)
             }
+            ProjectionElem::OpaqueCast(ty) => {
+                let ty = self.sanitize_type(place, ty);
+                let ty = self.cx.normalize(ty, location);
+                self.cx
+                    .eq_types(
+                        base.ty,
+                        ty,
+                        location.to_locations(),
+                        ConstraintCategory::TypeAnnotation,
+                    )
+                    .unwrap();
+                PlaceTy::from_ty(ty)
+            }
         }
     }
 
@@ -1195,10 +1208,11 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 tcx,
                 self.param_env,
                 proj,
-                |this, field, ()| {
+                |this, field, _| {
                     let ty = this.field_ty(tcx, field);
                     self.normalize(ty, locations)
                 },
+                |_, _| unreachable!(),
             );
             curr_projected_ty = projected_ty;
         }
@@ -2493,6 +2507,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 }
                 ProjectionElem::Field(..)
                 | ProjectionElem::Downcast(..)
+                | ProjectionElem::OpaqueCast(..)
                 | ProjectionElem::Index(..)
                 | ProjectionElem::ConstantIndex { .. }
                 | ProjectionElem::Subslice { .. } => {

compiler/rustc_codegen_cranelift/src/base.rs

@@ -825,6 +825,7 @@ pub(crate) fn codegen_place<'tcx>(
                     cplace = cplace.place_deref(fx);
                 }
             }
+            PlaceElem::OpaqueCast(ty) => cplace = cplace.place_opaque_cast(fx, ty),
             PlaceElem::Field(field, _ty) => {
                 cplace = cplace.place_field(fx, field);
             }

compiler/rustc_codegen_cranelift/src/value_and_place.rs

@@ -615,6 +615,14 @@ impl<'tcx> CPlace<'tcx> {
         }
     }
 
+    pub(crate) fn place_opaque_cast(
+        self,
+        fx: &mut FunctionCx<'_, '_, 'tcx>,
+        ty: Ty<'tcx>,
+    ) -> CPlace<'tcx> {
+        CPlace { inner: self.inner, layout: fx.layout_of(ty) }
+    }
+
     pub(crate) fn place_field(
         self,
         fx: &mut FunctionCx<'_, '_, 'tcx>,