Auto merge of #97860 - Dylan-DPC:rollup-t3vxos8, r=Dylan-DPC

Rollup of 5 pull requests

Successful merges:

 - #97595 (Remove unwrap from get_vtable)
 - #97597 (Preserve unused pointer to address casts)
 - #97819 (Recover `import` instead of `use` in item)
 - #97823 (Recover missing comma after match arm)
 - #97851 (Use repr(C) when depending on struct layout in ptr tests)

Failed merges:

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

8 files changed, 141 insertions, 55 deletions

diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 07ba3ce0408..4fe81a91d1a 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -2605,9 +2605,34 @@ pub enum Rvalue<'tcx> {
 static_assert_size!(Rvalue<'_>, 40);
 
 impl<'tcx> Rvalue<'tcx> {
+    /// Returns true if rvalue can be safely removed when the result is unused.
     #[inline]
-    pub fn is_pointer_int_cast(&self) -> bool {
-        matches!(self, Rvalue::Cast(CastKind::PointerExposeAddress, _, _))
+    pub fn is_safe_to_remove(&self) -> bool {
+        match self {
+            // Pointer to int casts may be side-effects due to exposing the provenance.
+            // While the model is undecided, we should be conservative. See
+            // <https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html>
+            Rvalue::Cast(CastKind::PointerExposeAddress, _, _) => false,
+
+            Rvalue::Use(_)
+            | Rvalue::Repeat(_, _)
+            | Rvalue::Ref(_, _, _)
+            | Rvalue::ThreadLocalRef(_)
+            | Rvalue::AddressOf(_, _)
+            | Rvalue::Len(_)
+            | Rvalue::Cast(
+                CastKind::Misc | CastKind::Pointer(_) | CastKind::PointerFromExposedAddress,
+                _,
+                _,
+            )
+            | Rvalue::BinaryOp(_, _)
+            | Rvalue::CheckedBinaryOp(_, _)
+            | Rvalue::NullaryOp(_, _)
+            | Rvalue::UnaryOp(_, _)
+            | Rvalue::Discriminant(_)
+            | Rvalue::Aggregate(_, _)
+            | Rvalue::ShallowInitBox(_, _) => true,
+        }
     }
 }
 
diff --git a/compiler/rustc_mir_dataflow/src/impls/liveness.rs b/compiler/rustc_mir_dataflow/src/impls/liveness.rs
index 7076fbe1bdb..9b62ee5473c 100644
--- a/compiler/rustc_mir_dataflow/src/impls/liveness.rs
+++ b/compiler/rustc_mir_dataflow/src/impls/liveness.rs
@@ -244,13 +244,10 @@ impl<'a, 'tcx> Analysis<'tcx> for MaybeTransitiveLiveLocals<'a> {
         // Compute the place that we are storing to, if any
         let destination = match &statement.kind {
             StatementKind::Assign(assign) => {
-                if assign.1.is_pointer_int_cast() {
-                    // Pointer to int casts may be side-effects due to exposing the provenance.
-                    // While the model is undecided, we should be conservative. See
-                    // <https://www.ralfj.de/blog/2022/04/11/provenance-exposed.html>
-                    None
-                } else {
+                if assign.1.is_safe_to_remove() {
                     Some(assign.0)
+                } else {
+                    None
                 }
             }
             StatementKind::SetDiscriminant { place, .. } | StatementKind::Deinit(place) => {
diff --git a/compiler/rustc_mir_transform/src/dead_store_elimination.rs b/compiler/rustc_mir_transform/src/dead_store_elimination.rs
index 8becac34ed7..779f3c77815 100644
--- a/compiler/rustc_mir_transform/src/dead_store_elimination.rs
+++ b/compiler/rustc_mir_transform/src/dead_store_elimination.rs
@@ -34,7 +34,7 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>, borrowed: &BitS
         for (statement_index, statement) in bb_data.statements.iter().enumerate().rev() {
             let loc = Location { block: bb, statement_index };
             if let StatementKind::Assign(assign) = &statement.kind {
-                if assign.1.is_pointer_int_cast() {
+                if !assign.1.is_safe_to_remove() {
                     continue;
                 }
             }
diff --git a/compiler/rustc_mir_transform/src/simplify.rs b/compiler/rustc_mir_transform/src/simplify.rs
index 72e08343925..8a78ea5c82b 100644
--- a/compiler/rustc_mir_transform/src/simplify.rs
+++ b/compiler/rustc_mir_transform/src/simplify.rs
@@ -494,8 +494,12 @@ impl<'tcx> Visitor<'tcx> for UsedLocals {
             StatementKind::StorageLive(_local) | StatementKind::StorageDead(_local) => {}
 
             StatementKind::Assign(box (ref place, ref rvalue)) => {
-                self.visit_lhs(place, location);
-                self.visit_rvalue(rvalue, location);
+                if rvalue.is_safe_to_remove() {
+                    self.visit_lhs(place, location);
+                    self.visit_rvalue(rvalue, location);
+                } else {
+                    self.super_statement(statement, location);
+                }
             }
 
             StatementKind::SetDiscriminant { ref place, variant_index: _ }
diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index b786c52e688..324e04b1981 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2718,13 +2718,12 @@ impl<'a> Parser<'a> {
                     ));
                 }
                 this.expect_one_of(&[token::Comma], &[token::CloseDelim(Delimiter::Brace)])
-                    .map_err(|mut err| {
-                        match (sm.span_to_lines(expr.span), sm.span_to_lines(arm_start_span)) {
-                            (Ok(ref expr_lines), Ok(ref arm_start_lines))
-                                if arm_start_lines.lines[0].end_col
-                                    == expr_lines.lines[0].end_col
-                                    && expr_lines.lines.len() == 2
-                                    && this.token == token::FatArrow =>
+                    .or_else(|mut err| {
+                        if this.token == token::FatArrow {
+                            if let Ok(expr_lines) = sm.span_to_lines(expr.span)
+                            && let Ok(arm_start_lines) = sm.span_to_lines(arm_start_span)
+                            && arm_start_lines.lines[0].end_col == expr_lines.lines[0].end_col
+                            && expr_lines.lines.len() == 2
                             {
                                 // We check whether there's any trailing code in the parse span,
                                 // if there isn't, we very likely have the following:
@@ -2743,15 +2742,41 @@ impl<'a> Parser<'a> {
                                     ",".to_owned(),
                                     Applicability::MachineApplicable,
                                 );
+                                return Err(err);
                             }
-                            _ => {
-                                err.span_label(
-                                    arrow_span,
-                                    "while parsing the `match` arm starting here",
-                                );
+                        } else {
+                            // FIXME(compiler-errors): We could also recover `; PAT =>` here
+
+                            // Try to parse a following `PAT =>`, if successful
+                            // then we should recover.
+                            let mut snapshot = this.create_snapshot_for_diagnostic();
+                            let pattern_follows = snapshot
+                                .parse_pat_allow_top_alt(
+                                    None,
+                                    RecoverComma::Yes,
+                                    RecoverColon::Yes,
+                                    CommaRecoveryMode::EitherTupleOrPipe,
+                                )
+                                .map_err(|err| err.cancel())
+                                .is_ok();
+                            if pattern_follows && snapshot.check(&TokenKind::FatArrow) {
+                                err.cancel();
+                                this.struct_span_err(
+                                    hi.shrink_to_hi(),
+                                    "expected `,` following `match` arm",
+                                )
+                                .span_suggestion(
+                                    hi.shrink_to_hi(),
+                                    "missing a comma here to end this `match` arm",
+                                    ",".to_owned(),
+                                    Applicability::MachineApplicable,
+                                )
+                                .emit();
+                                return Ok(true);
                             }
                         }
-                        err
+                        err.span_label(arrow_span, "while parsing the `match` arm starting here");
+                        Err(err)
                     })?;
             } else {
                 this.eat(&token::Comma);
diff --git a/compiler/rustc_parse/src/parser/item.rs b/compiler/rustc_parse/src/parser/item.rs
index 6720399aacb..48c3c467bec 100644
--- a/compiler/rustc_parse/src/parser/item.rs
+++ b/compiler/rustc_parse/src/parser/item.rs
@@ -204,25 +204,7 @@ impl<'a> Parser<'a> {
         let mut def = || mem::replace(def, Defaultness::Final);
 
         let info = if self.eat_keyword(kw::Use) {
-            // USE ITEM
-            let tree = self.parse_use_tree()?;
-
-            // If wildcard or glob-like brace syntax doesn't have `;`,
-            // the user may not know `*` or `{}` should be the last.
-            if let Err(mut e) = self.expect_semi() {
-                match tree.kind {
-                    UseTreeKind::Glob => {
-                        e.note("the wildcard token must be last on the path");
-                    }
-                    UseTreeKind::Nested(..) => {
-                        e.note("glob-like brace syntax must be last on the path");
-                    }
-                    _ => (),
-                }
-                return Err(e);
-            }
-
-            (Ident::empty(), ItemKind::Use(tree))
+            self.parse_use_item()?
         } else if self.check_fn_front_matter(def_final) {
             // FUNCTION ITEM
             let (ident, sig, generics, body) = self.parse_fn(attrs, fn_parse_mode, lo, vis)?;
@@ -288,7 +270,12 @@ impl<'a> Parser<'a> {
         } else if let IsMacroRulesItem::Yes { has_bang } = self.is_macro_rules_item() {
             // MACRO_RULES ITEM
             self.parse_item_macro_rules(vis, has_bang)?
-        } else if vis.kind.is_pub() && self.isnt_macro_invocation() {
+        } else if self.isnt_macro_invocation()
+            && (self.token.is_ident_named(Symbol::intern("import"))
+                || self.token.is_ident_named(Symbol::intern("using")))
+        {
+            return self.recover_import_as_use();
+        } else if self.isnt_macro_invocation() && vis.kind.is_pub() {
             self.recover_missing_kw_before_item()?;
             return Ok(None);
         } else if macros_allowed && self.check_path() {
@@ -300,6 +287,48 @@ impl<'a> Parser<'a> {
         Ok(Some(info))
     }
 
+    fn recover_import_as_use(&mut self) -> PResult<'a, Option<(Ident, ItemKind)>> {
+        let span = self.token.span;
+        let token_name = super::token_descr(&self.token);
+        let snapshot = self.create_snapshot_for_diagnostic();
+        self.bump();
+        match self.parse_use_item() {
+            Ok(u) => {
+                self.struct_span_err(span, format!("expected item, found {token_name}"))
+                    .span_suggestion_short(
+                        span,
+                        "items are imported using the `use` keyword",
+                        "use".to_owned(),
+                        Applicability::MachineApplicable,
+                    )
+                    .emit();
+                Ok(Some(u))
+            }
+            Err(e) => {
+                e.cancel();
+                self.restore_snapshot(snapshot);
+                Ok(None)
+            }
+        }
+    }
+
+    fn parse_use_item(&mut self) -> PResult<'a, (Ident, ItemKind)> {
+        let tree = self.parse_use_tree()?;
+        if let Err(mut e) = self.expect_semi() {
+            match tree.kind {
+                UseTreeKind::Glob => {
+                    e.note("the wildcard token must be last on the path");
+                }
+                UseTreeKind::Nested(..) => {
+                    e.note("glob-like brace syntax must be last on the path");
+                }
+                _ => (),
+            }
+            return Err(e);
+        }
+        Ok((Ident::empty(), ItemKind::Use(tree)))
+    }
+
     /// When parsing a statement, would the start of a path be an item?
     pub(super) fn is_path_start_item(&mut self) -> bool {
         self.is_kw_followed_by_ident(kw::Union) // no: `union::b`, yes: `union U { .. }`
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index f2e31c068a0..3a00c41d90a 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -304,22 +304,24 @@ pub fn get_vtable_index_of_object_method<'tcx, N>(
     tcx: TyCtxt<'tcx>,
     object: &super::ImplSourceObjectData<'tcx, N>,
     method_def_id: DefId,
-) -> usize {
+) -> Option<usize> {
     let existential_trait_ref = object
         .upcast_trait_ref
         .map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
     let existential_trait_ref = tcx.erase_regions(existential_trait_ref);
+
     // Count number of methods preceding the one we are selecting and
     // add them to the total offset.
-    let index = tcx
+    if let Some(index) = tcx
         .own_existential_vtable_entries(existential_trait_ref)
         .iter()
         .copied()
         .position(|def_id| def_id == method_def_id)
-        .unwrap_or_else(|| {
-            bug!("get_vtable_index_of_object_method: {:?} was not found", method_def_id);
-        });
-    object.vtable_base + index
+    {
+        Some(object.vtable_base + index)
+    } else {
+        None
+    }
 }
 
 pub fn closure_trait_ref_and_return_type<'tcx>(
diff --git a/compiler/rustc_ty_utils/src/instance.rs b/compiler/rustc_ty_utils/src/instance.rs
index 9c450fe1e32..7c89ce125e0 100644
--- a/compiler/rustc_ty_utils/src/instance.rs
+++ b/compiler/rustc_ty_utils/src/instance.rs
@@ -349,11 +349,15 @@ fn resolve_associated_item<'tcx>(
             _ => None,
         },
         traits::ImplSource::Object(ref data) => {
-            let index = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id);
-            Some(Instance {
-                def: ty::InstanceDef::Virtual(trait_item_id, index),
-                substs: rcvr_substs,
-            })
+            if let Some(index) = traits::get_vtable_index_of_object_method(tcx, data, trait_item_id)
+            {
+                Some(Instance {
+                    def: ty::InstanceDef::Virtual(trait_item_id, index),
+                    substs: rcvr_substs,
+                })
+            } else {
+                None
+            }
         }
         traits::ImplSource::Builtin(..) => {
             if Some(trait_ref.def_id) == tcx.lang_items().clone_trait() {