Check types live across yields in generators too

compiler/rustc_hir_analysis/src/check/check.rs

@@ -18,7 +18,7 @@ use rustc_infer::traits::{Obligation, TraitEngineExt as _};
 use rustc_lint_defs::builtin::REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::middle::stability::EvalResult;
-use rustc_middle::traits::DefiningAnchor;
+use rustc_middle::traits::{DefiningAnchor, ObligationCauseCode};
 use rustc_middle::ty::fold::BottomUpFolder;
 use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
 use rustc_middle::ty::util::{Discr, IntTypeExt};
@@ -1626,6 +1626,25 @@ pub(super) fn check_generator_obligations(tcx: TyCtxt<'_>, def_id: LocalDefId) {
         let obligation = Obligation::new(tcx, cause.clone(), param_env, *predicate);
         fulfillment_cx.register_predicate_obligation(&infcx, obligation);
     }
+
+    if (tcx.features().unsized_locals || tcx.features().unsized_fn_params)
+        && let Some(generator) = tcx.mir_generator_witnesses(def_id)
+    {
+        for field_ty in generator.field_tys.iter() {
+            fulfillment_cx.register_bound(
+                &infcx,
+                param_env,
+                field_ty.ty,
+                tcx.require_lang_item(hir::LangItem::Sized, Some(field_ty.source_info.span)),
+                ObligationCause::new(
+                    field_ty.source_info.span,
+                    def_id,
+                    ObligationCauseCode::SizedGeneratorInterior(def_id),
+                ),
+            );
+        }
+    }
+
     let errors = fulfillment_cx.select_all_or_error(&infcx);
     debug!(?errors);
     if !errors.is_empty() {

compiler/rustc_hir_typeck/src/generator_interior/mod.rs

@@ -15,6 +15,7 @@ use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{Arm, Expr, ExprKind, Guard, HirId, Pat, PatKind};
 use rustc_infer::infer::{DefineOpaqueTypes, RegionVariableOrigin};
 use rustc_middle::middle::region::{self, Scope, ScopeData, YieldData};
+use rustc_middle::traits::ObligationCauseCode;
 use rustc_middle::ty::fold::FnMutDelegate;
 use rustc_middle::ty::{self, BoundVariableKind, RvalueScopes, Ty, TyCtxt, TypeVisitableExt};
 use rustc_span::symbol::sym;
@@ -214,6 +215,16 @@ pub fn resolve_interior<'a, 'tcx>(
     // The types are already kept in insertion order.
     let types = visitor.types;
 
+    if fcx.tcx.features().unsized_locals || fcx.tcx.features().unsized_fn_params {
+        for interior_ty in &types {
+            fcx.require_type_is_sized(
+                interior_ty.ty,
+                interior_ty.span,
+                ObligationCauseCode::SizedGeneratorInterior(def_id.expect_local()),
+            );
+        }
+    }
+
     // The types in the generator interior contain lifetimes local to the generator itself,
     // which should not be exposed outside of the generator. Therefore, we replace these
     // lifetimes with existentially-bound lifetimes, which reflect the exact value of the

compiler/rustc_middle/src/traits/mod.rs

@@ -299,8 +299,10 @@ pub enum ObligationCauseCode<'tcx> {
     SizedYieldType,
     /// Inline asm operand type must be `Sized`.
     InlineAsmSized,
-    /// Captured closure type type must be `Sized`.
+    /// Captured closure type must be `Sized`.
     SizedClosureCapture(LocalDefId),
+    /// Types live across generator yields must be `Sized`.
+    SizedGeneratorInterior(LocalDefId),
     /// `[expr; N]` requires `type_of(expr): Copy`.
     RepeatElementCopy {
         /// If element is a `const fn` we display a help message suggesting to move the

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -3018,6 +3018,13 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                     err.span_label(span, "this closure captures all values by move");
                 }
             }
+            ObligationCauseCode::SizedGeneratorInterior(generator_def_id) => {
+                let what = match self.tcx.generator_kind(generator_def_id) {
+                    None | Some(hir::GeneratorKind::Gen) => "yield",
+                    Some(hir::GeneratorKind::Async(..)) => "await",
+                };
+                err.note(format!("all values live across `{what}` must have a statically known size"));
+            }
             ObligationCauseCode::ConstPatternStructural => {
                 err.note("constants used for pattern-matching must derive `PartialEq` and `Eq`");
             }

tests/ui/async-await/awaiting-unsized-param.drop_tracking_mir.stderr

@@ -0,0 +1,21 @@
+warning: the feature `unsized_locals` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/awaiting-unsized-param.rs:5:31
+   |
+LL | #![feature(unsized_fn_params, unsized_locals)]
+   |                               ^^^^^^^^^^^^^^
+   |
+   = note: see issue #48055 <https://github.com/rust-lang/rust/issues/48055> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0277]: the size for values of type `(dyn Future<Output = T> + Unpin + 'static)` cannot be known at compilation time
+  --> $DIR/awaiting-unsized-param.rs:10:17
+   |
+LL | async fn bug<T>(mut f: dyn Future<Output = T> + Unpin) -> T {
+   |                 ^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `(dyn Future<Output = T> + Unpin + 'static)`
+   = note: all values captured by value by a closure must have a statically known size
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/async-await/awaiting-unsized-param.no_drop_tracking.stderr

@@ -0,0 +1,21 @@
+warning: the feature `unsized_locals` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/awaiting-unsized-param.rs:5:31
+   |
+LL | #![feature(unsized_fn_params, unsized_locals)]
+   |                               ^^^^^^^^^^^^^^
+   |
+   = note: see issue #48055 <https://github.com/rust-lang/rust/issues/48055> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0277]: the size for values of type `(dyn Future<Output = T> + Unpin + 'static)` cannot be known at compilation time
+  --> $DIR/awaiting-unsized-param.rs:10:17
+   |
+LL | async fn bug<T>(mut f: dyn Future<Output = T> + Unpin) -> T {
+   |                 ^^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `(dyn Future<Output = T> + Unpin + 'static)`
+   = note: all values captured by value by a closure must have a statically known size
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/async-await/awaiting-unsized-param.rs

@@ -0,0 +1,15 @@
+// edition: 2021
+// revisions: no_drop_tracking drop_tracking_mir
+// [drop_tracking_mir] compile-flags: -Zdrop-tracking-mir
+
+#![feature(unsized_fn_params, unsized_locals)]
+//~^ WARN the feature `unsized_locals` is incomplete
+
+use std::future::Future;
+
+async fn bug<T>(mut f: dyn Future<Output = T> + Unpin) -> T {
+    //~^ ERROR the size for values of type `(dyn Future<Output = T> + Unpin + 'static)` cannot be known at compilation time
+    (&mut f).await
+}
+
+fn main() {}

tests/ui/async-await/unsized-across-await.drop_tracking_mir.stderr

@@ -0,0 +1,21 @@
+warning: the feature `unsized_locals` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/unsized-across-await.rs:5:12
+   |
+LL | #![feature(unsized_locals)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: see issue #48055 <https://github.com/rust-lang/rust/issues/48055> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0277]: the size for values of type `dyn std::fmt::Display` cannot be known at compilation time
+  --> $DIR/unsized-across-await.rs:11:9
+   |
+LL |     let _x = *x;
+   |         ^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `dyn std::fmt::Display`
+   = note: all values live across `await` must have a statically known size
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/async-await/unsized-across-await.no_drop_tracking.stderr

@@ -0,0 +1,21 @@
+warning: the feature `unsized_locals` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/unsized-across-await.rs:5:12
+   |
+LL | #![feature(unsized_locals)]
+   |            ^^^^^^^^^^^^^^
+   |
+   = note: see issue #48055 <https://github.com/rust-lang/rust/issues/48055> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+error[E0277]: the size for values of type `dyn std::fmt::Display` cannot be known at compilation time
+  --> $DIR/unsized-across-await.rs:11:9
+   |
+LL |     let _x = *x;
+   |         ^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `dyn std::fmt::Display`
+   = note: all values live across `yield` must have a statically known size
+
+error: aborting due to previous error; 1 warning emitted
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/async-await/unsized-across-await.rs

@@ -0,0 +1,18 @@
+// edition: 2021
+// revisions: no_drop_tracking drop_tracking_mir
+// [drop_tracking_mir] compile-flags: -Zdrop-tracking-mir
+
+#![feature(unsized_locals)]
+//~^ WARN the feature `unsized_locals` is incomplete
+
+async fn f() {}
+
+async fn g(x: Box<dyn std::fmt::Display>) {
+    let _x = *x;
+    //~^ ERROR the size for values of type `dyn std::fmt::Display` cannot be known at compilation time
+    f().await;
+}
+
+fn main() {
+    let _a = g(Box::new(5));
+}

tests/ui/generator/unsized-across-yield.rs

@@ -0,0 +1,19 @@
+#![feature(generator_trait)]
+#![feature(generators)]
+#![feature(unsized_locals)]
+
+use std::ops::Generator;
+
+fn blah() -> impl Generator {
+    move || {
+        let b: [u8] = *(Box::new([]) as Box<[u8]>);
+
+        yield;
+
+        for elem in b.iter() {}
+    }
+}
+
+fn main() {
+    blah();
+}