Rollup of 10 pull requests

compiler/rustc_borrowck/src/region_infer/opaque_types/mod.rs

@@ -155,13 +155,6 @@ fn add_hidden_type<'tcx>(
     }
 }
 
-fn get_hidden_type<'tcx>(
-    hidden_types: &DefinitionSiteHiddenTypes<'tcx>,
-    def_id: LocalDefId,
-) -> Option<EarlyBinder<'tcx, OpaqueHiddenType<'tcx>>> {
-    hidden_types.0.get(&def_id).map(|ty| EarlyBinder::bind(*ty))
-}
-
 #[derive(Debug)]
 struct DefiningUse<'tcx> {
     /// The opaque type using non NLL vars. This uses the actual
@@ -508,7 +501,8 @@ pub(crate) fn apply_definition_site_hidden_types<'tcx>(
     let tcx = infcx.tcx;
     let mut errors = Vec::new();
     for &(key, hidden_type) in opaque_types {
-        let Some(expected) = get_hidden_type(hidden_types, key.def_id) else {
+        let Some(expected) = hidden_types.0.get(&key.def_id).map(|ty| EarlyBinder::bind(*ty))
+        else {
             if !tcx.use_typing_mode_borrowck() {
                 if let ty::Alias(ty::Opaque, alias_ty) = hidden_type.ty.kind()
                     && alias_ty.def_id == key.def_id.to_def_id()

compiler/rustc_hir_typeck/src/expr.rs

@@ -1817,12 +1817,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expr: &'tcx hir::Expr<'tcx>,
     ) -> Ty<'tcx> {
         let element_ty = if !args.is_empty() {
+            // This shouldn't happen unless there's another error
+            // (e.g., never patterns in inappropriate contexts).
+            if self.diverges.get() != Diverges::Maybe {
+                self.dcx()
+                    .struct_span_err(expr.span, "unexpected divergence state in checking array")
+                    .delay_as_bug();
+            }
+
             let coerce_to = expected
                 .to_option(self)
                 .and_then(|uty| self.try_structurally_resolve_type(expr.span, uty).builtin_index())
                 .unwrap_or_else(|| self.next_ty_var(expr.span));
             let mut coerce = CoerceMany::with_coercion_sites(coerce_to, args);
-            assert_eq!(self.diverges.get(), Diverges::Maybe);
+
             for e in args {
                 let e_ty = self.check_expr_with_hint(e, coerce_to);
                 let cause = self.misc(e.span);

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -104,8 +104,8 @@ pub(crate) struct FnCtxt<'a, 'tcx> {
     /// the diverges flag is set to something other than `Maybe`.
     pub(super) diverges: Cell<Diverges>,
 
-    /// If one of the function arguments is a never pattern, this counts as diverging code. This
-    /// affect typechecking of the function body.
+    /// If one of the function arguments is a never pattern, this counts as diverging code.
+    /// This affect typechecking of the function body.
     pub(super) function_diverges_because_of_empty_arguments: Cell<Diverges>,
 
     /// Whether the currently checked node is the whole body of the function.

compiler/rustc_hir_typeck/src/lib.rs

@@ -219,6 +219,12 @@ fn typeck_with_inspect<'tcx>(
     // the future.
     fcx.check_repeat_exprs();
 
+    // We need to handle opaque types before emitting ambiguity errors as applying
+    // defining uses may guide type inference.
+    if fcx.next_trait_solver() {
+        fcx.try_handle_opaque_type_uses_next();
+    }
+
     fcx.type_inference_fallback();
 
     // Even though coercion casts provide type hints, we check casts after fallback for

compiler/rustc_hir_typeck/src/opaque_types.rs

@@ -22,35 +22,50 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
     /// inference variables.
     ///
     /// It then uses these defining uses to guide inference for all other uses.
+    ///
+    /// Unlike `handle_opaque_type_uses_next`, this does not report errors.
+    #[instrument(level = "debug", skip(self))]
+    pub(super) fn try_handle_opaque_type_uses_next(&mut self) {
+        // We clone the opaques instead of stealing them here as we still need
+        // to use them after fallback.
+        let opaque_types: Vec<_> = self.infcx.clone_opaque_types();
+
+        self.compute_definition_site_hidden_types(opaque_types, false);
+    }
+
+    /// This takes all the opaque type uses during HIR typeck. It first computes
+    /// the concrete hidden type by iterating over all defining uses.
+    ///
+    /// A use during HIR typeck is defining if all non-lifetime arguments are
+    /// unique generic parameters and the hidden type does not reference any
+    /// inference variables.
+    ///
+    /// It then uses these defining uses to guide inference for all other uses.
     #[instrument(level = "debug", skip(self))]
     pub(super) fn handle_opaque_type_uses_next(&mut self) {
         // We clone the opaques instead of stealing them here as they are still used for
         // normalization in the next generation trait solver.
-        let mut opaque_types: Vec<_> = self.infcx.clone_opaque_types();
+        let opaque_types: Vec<_> = self.infcx.clone_opaque_types();
         let num_entries = self.inner.borrow_mut().opaque_types().num_entries();
         let prev = self.checked_opaque_types_storage_entries.replace(Some(num_entries));
         debug_assert_eq!(prev, None);
-        for entry in &mut opaque_types {
-            *entry = self.resolve_vars_if_possible(*entry);
-        }
-        debug!(?opaque_types);
 
-        self.compute_definition_site_hidden_types(&opaque_types);
-        self.apply_definition_site_hidden_types(&opaque_types);
+        self.compute_definition_site_hidden_types(opaque_types, true);
     }
 }
 
+#[derive(Copy, Clone, Debug)]
 enum UsageKind<'tcx> {
     None,
     NonDefiningUse(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>),
     UnconstrainedHiddenType(OpaqueHiddenType<'tcx>),
-    HasDefiningUse,
+    HasDefiningUse(OpaqueHiddenType<'tcx>),
 }
 
 impl<'tcx> UsageKind<'tcx> {
     fn merge(&mut self, other: UsageKind<'tcx>) {
         match (&*self, &other) {
-            (UsageKind::HasDefiningUse, _) | (_, UsageKind::None) => unreachable!(),
+            (UsageKind::HasDefiningUse(_), _) | (_, UsageKind::None) => unreachable!(),
             (UsageKind::None, _) => *self = other,
             // When mergining non-defining uses, prefer earlier ones. This means
             // the error happens as early as possible.
@@ -64,7 +79,7 @@ impl<'tcx> UsageKind<'tcx> {
             // intended to be defining.
             (
                 UsageKind::NonDefiningUse(..) | UsageKind::UnconstrainedHiddenType(..),
-                UsageKind::UnconstrainedHiddenType(..) | UsageKind::HasDefiningUse,
+                UsageKind::UnconstrainedHiddenType(..) | UsageKind::HasDefiningUse(_),
             ) => *self = other,
         }
     }
@@ -73,8 +88,14 @@ impl<'tcx> UsageKind<'tcx> {
 impl<'tcx> FnCtxt<'_, 'tcx> {
     fn compute_definition_site_hidden_types(
         &mut self,
-        opaque_types: &[(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>)],
+        mut opaque_types: Vec<(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>)>,
+        error_on_missing_defining_use: bool,
     ) {
+        for entry in opaque_types.iter_mut() {
+            *entry = self.resolve_vars_if_possible(*entry);
+        }
+        debug!(?opaque_types);
+
         let tcx = self.tcx;
         let TypingMode::Analysis { defining_opaque_types_and_generators } = self.typing_mode()
         else {
@@ -88,19 +109,47 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
                 _ => unreachable!("not opaque or generator: {def_id:?}"),
             }
 
+            // We do actually need to check this the second pass (we can't just
+            // store this), because we can go from `UnconstrainedHiddenType` to
+            // `HasDefiningUse` (because of fallback)
             let mut usage_kind = UsageKind::None;
-            for &(opaque_type_key, hidden_type) in opaque_types {
+            for &(opaque_type_key, hidden_type) in &opaque_types {
                 if opaque_type_key.def_id != def_id {
                     continue;
                 }
 
                 usage_kind.merge(self.consider_opaque_type_use(opaque_type_key, hidden_type));
-                if let UsageKind::HasDefiningUse = usage_kind {
+
+                if let UsageKind::HasDefiningUse(..) = usage_kind {
                     break;
                 }
             }
 
+            if let UsageKind::HasDefiningUse(ty) = usage_kind {
+                for &(opaque_type_key, hidden_type) in &opaque_types {
+                    if opaque_type_key.def_id != def_id {
+                        continue;
+                    }
+
+                    let expected = EarlyBinder::bind(ty.ty).instantiate(tcx, opaque_type_key.args);
+                    self.demand_eqtype(hidden_type.span, expected, hidden_type.ty);
+                }
+
+                // Being explicit here: it may be possible that we in a
+                // previous call to this function we did an insert, but this
+                // should be just fine, since they all get equated anyways and
+                // we shouldn't ever go from `HasDefiningUse` to anyway else.
+                let _ = self.typeck_results.borrow_mut().hidden_types.insert(def_id, ty);
+            }
+
+            // If we're in `fn try_handle_opaque_type_uses_next` then do not
+            // report any errors.
+            if !error_on_missing_defining_use {
+                continue;
+            }
+
             let guar = match usage_kind {
+                UsageKind::HasDefiningUse(_) => continue,
                 UsageKind::None => {
                     if let Some(guar) = self.tainted_by_errors() {
                         guar
@@ -137,7 +186,6 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
                             .emit()
                     }
                 }
-                UsageKind::HasDefiningUse => continue,
             };
 
             self.typeck_results
@@ -148,8 +196,9 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         }
     }
 
+    #[tracing::instrument(skip(self), ret)]
     fn consider_opaque_type_use(
-        &mut self,
+        &self,
         opaque_type_key: OpaqueTypeKey<'tcx>,
         hidden_type: OpaqueHiddenType<'tcx>,
     ) -> UsageKind<'tcx> {
@@ -161,11 +210,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
         ) {
             match err {
                 NonDefiningUseReason::Tainted(guar) => {
-                    self.typeck_results.borrow_mut().hidden_types.insert(
-                        opaque_type_key.def_id,
-                        OpaqueHiddenType::new_error(self.tcx, guar),
-                    );
-                    return UsageKind::HasDefiningUse;
+                    return UsageKind::HasDefiningUse(OpaqueHiddenType::new_error(self.tcx, guar));
                 }
                 _ => return UsageKind::NonDefiningUse(opaque_type_key, hidden_type),
             };
@@ -193,27 +238,7 @@ impl<'tcx> FnCtxt<'_, 'tcx> {
             self.tcx,
             DefiningScopeKind::HirTypeck,
         );
-
-        let prev = self
-            .typeck_results
-            .borrow_mut()
-            .hidden_types
-            .insert(opaque_type_key.def_id, hidden_type);
-        assert!(prev.is_none());
-        UsageKind::HasDefiningUse
-    }
-
-    fn apply_definition_site_hidden_types(
-        &mut self,
-        opaque_types: &[(OpaqueTypeKey<'tcx>, OpaqueHiddenType<'tcx>)],
-    ) {
-        let tcx = self.tcx;
-        for &(key, hidden_type) in opaque_types {
-            let expected = *self.typeck_results.borrow_mut().hidden_types.get(&key.def_id).unwrap();
-
-            let expected = EarlyBinder::bind(expected.ty).instantiate(tcx, key.args);
-            self.demand_eqtype(hidden_type.span, expected, hidden_type.ty);
-        }
+        UsageKind::HasDefiningUse(hidden_type)
     }
 
     /// We may in theory add further uses of an opaque after cloning the opaque

compiler/rustc_middle/src/mir/loops.rs

@@ -0,0 +1,29 @@
+use rustc_index::bit_set::DenseBitSet;
+
+use super::*;
+
+/// Compute the set of loop headers in the given body. A loop header is usually defined as a block
+/// which dominates one of its predecessors. This definition is only correct for reducible CFGs.
+/// However, computing dominators is expensive, so we approximate according to the post-order
+/// traversal order. A loop header for us is a block which is visited after its predecessor in
+/// post-order. This is ok as we mostly need a heuristic.
+pub fn maybe_loop_headers(body: &Body<'_>) -> DenseBitSet<BasicBlock> {
+    let mut maybe_loop_headers = DenseBitSet::new_empty(body.basic_blocks.len());
+    let mut visited = DenseBitSet::new_empty(body.basic_blocks.len());
+    for (bb, bbdata) in traversal::postorder(body) {
+        // Post-order means we visit successors before the block for acyclic CFGs.
+        // If the successor is not visited yet, consider it a loop header.
+        for succ in bbdata.terminator().successors() {
+            if !visited.contains(succ) {
+                maybe_loop_headers.insert(succ);
+            }
+        }
+
+        // Only mark `bb` as visited after we checked the successors, in case we have a self-loop.
+        //     bb1: goto -> bb1;
+        let _new = visited.insert(bb);
+        debug_assert!(_new);
+    }
+
+    maybe_loop_headers
+}

compiler/rustc_middle/src/mir/mod.rs

@@ -51,6 +51,7 @@ mod statement;
 mod syntax;
 mod terminator;
 
+pub mod loops;
 pub mod traversal;
 pub mod visit;
 

compiler/rustc_mir_transform/src/gvn.rs

@@ -129,6 +129,7 @@ impl<'tcx> crate::MirPass<'tcx> for GVN {
         let ssa = SsaLocals::new(tcx, body, typing_env);
         // Clone dominators because we need them while mutating the body.
         let dominators = body.basic_blocks.dominators().clone();
+        let maybe_loop_headers = loops::maybe_loop_headers(body);
 
         let arena = DroplessArena::default();
         let mut state =
@@ -141,6 +142,11 @@ impl<'tcx> crate::MirPass<'tcx> for GVN {
 
         let reverse_postorder = body.basic_blocks.reverse_postorder().to_vec();
         for bb in reverse_postorder {
+            // N.B. With loops, reverse postorder cannot produce a valid topological order.
+            // A statement or terminator from inside the loop, that is not processed yet, may have performed an indirect write.
+            if maybe_loop_headers.contains(bb) {
+                state.invalidate_derefs();
+            }
             let data = &mut body.basic_blocks.as_mut_preserves_cfg()[bb];
             state.visit_basic_block_data(bb, data);
         }

compiler/rustc_mir_transform/src/jump_threading.rs

@@ -84,7 +84,7 @@ impl<'tcx> crate::MirPass<'tcx> for JumpThreading {
             body,
             arena,
             map: Map::new(tcx, body, Some(MAX_PLACES)),
-            maybe_loop_headers: maybe_loop_headers(body),
+            maybe_loop_headers: loops::maybe_loop_headers(body),
             opportunities: Vec::new(),
         };
 
@@ -830,29 +830,3 @@ enum Update {
     Incr,
     Decr,
 }
-
-/// Compute the set of loop headers in the given body. A loop header is usually defined as a block
-/// which dominates one of its predecessors. This definition is only correct for reducible CFGs.
-/// However, computing dominators is expensive, so we approximate according to the post-order
-/// traversal order. A loop header for us is a block which is visited after its predecessor in
-/// post-order. This is ok as we mostly need a heuristic.
-fn maybe_loop_headers(body: &Body<'_>) -> DenseBitSet<BasicBlock> {
-    let mut maybe_loop_headers = DenseBitSet::new_empty(body.basic_blocks.len());
-    let mut visited = DenseBitSet::new_empty(body.basic_blocks.len());
-    for (bb, bbdata) in traversal::postorder(body) {
-        // Post-order means we visit successors before the block for acyclic CFGs.
-        // If the successor is not visited yet, consider it a loop header.
-        for succ in bbdata.terminator().successors() {
-            if !visited.contains(succ) {
-                maybe_loop_headers.insert(succ);
-            }
-        }
-
-        // Only mark `bb` as visited after we checked the successors, in case we have a self-loop.
-        //     bb1: goto -> bb1;
-        let _new = visited.insert(bb);
-        debug_assert!(_new);
-    }
-
-    maybe_loop_headers
-}

compiler/rustc_next_trait_solver/src/solve/search_graph.rs

@@ -99,19 +99,23 @@ where
         response_no_constraints(cx, input, Certainty::overflow(false))
     }
 
-    fn is_ambiguous_result(result: QueryResult<I>) -> bool {
-        result.is_ok_and(|response| {
-            has_no_inference_or_external_constraints(response)
+    fn is_ambiguous_result(result: QueryResult<I>) -> Option<Certainty> {
+        result.ok().and_then(|response| {
+            if has_no_inference_or_external_constraints(response)
                 && matches!(response.value.certainty, Certainty::Maybe { .. })
+            {
+                Some(response.value.certainty)
+            } else {
+                None
+            }
         })
     }
 
     fn propagate_ambiguity(
         cx: I,
         for_input: CanonicalInput<I>,
-        from_result: QueryResult<I>,
+        certainty: Certainty,
     ) -> QueryResult<I> {
-        let certainty = from_result.unwrap().value.certainty;
         response_no_constraints(cx, for_input, certainty)
     }