From 3b573c9b986a98064b6c155c7029f8ce253ed69c Mon Sep 17 00:00:00 2001 From: Michael Goulet Date: Wed, 3 Aug 2022 03:30:17 +0000 Subject: [PATCH] fn pointers don't implement Fn/FnMut/FnOnce traits if its return type is unsized --- .../src/traits/select/confirmation.rs | 31 +++++++++++++++- .../function-pointer/sized-ret-with-binder.rs | 15 ++++++++ src/test/ui/function-pointer/unsized-ret.rs | 14 ++++++++ .../ui/function-pointer/unsized-ret.stderr | 35 +++++++++++++++++++ .../issue-53398-cyclic-types.stderr | 3 +- 5 files changed, 96 insertions(+), 2 deletions(-) create mode 100644 src/test/ui/function-pointer/sized-ret-with-binder.rs create mode 100644 src/test/ui/function-pointer/unsized-ret.rs create mode 100644 src/test/ui/function-pointer/unsized-ret.stderr diff --git a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs index e44f6665795..59529832615 100644 --- a/compiler/rustc_trait_selection/src/traits/select/confirmation.rs +++ b/compiler/rustc_trait_selection/src/traits/select/confirmation.rs @@ -617,7 +617,36 @@ fn confirm_fn_pointer_candidate( ) .map_bound(|(trait_ref, _)| trait_ref); - let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?; + let mut nested = self.confirm_poly_trait_refs(obligation, trait_ref)?; + + // Confirm the `type Output: Sized;` bound that is present on `FnOnce` + let cause = obligation.derived_cause(BuiltinDerivedObligation); + // The binder on the Fn obligation is "less" important than the one on + // the signature, as evidenced by how we treat it during projection. + // The safe thing to do here is to liberate it, though, which should + // have no worse effect than skipping the binder here. + let liberated_fn_ty = self.infcx.replace_bound_vars_with_placeholders(obligation.self_ty()); + let output_ty = self + .infcx + .replace_bound_vars_with_placeholders(liberated_fn_ty.fn_sig(self.tcx()).output()); + let output_ty = normalize_with_depth_to( + self, + obligation.param_env, + cause.clone(), + obligation.recursion_depth, + output_ty, + &mut nested, + ); + let tr = ty::Binder::dummy(ty::TraitRef::new( + self.tcx().require_lang_item(LangItem::Sized, None), + self.tcx().mk_substs_trait(output_ty, &[]), + )); + nested.push(Obligation::new( + cause, + obligation.param_env, + tr.to_poly_trait_predicate().to_predicate(self.tcx()), + )); + Ok(ImplSourceFnPointerData { fn_ty: self_ty, nested }) } diff --git a/src/test/ui/function-pointer/sized-ret-with-binder.rs b/src/test/ui/function-pointer/sized-ret-with-binder.rs new file mode 100644 index 00000000000..104ac4d222e --- /dev/null +++ b/src/test/ui/function-pointer/sized-ret-with-binder.rs @@ -0,0 +1,15 @@ +// check-pass + +#![feature(unboxed_closures)] + +fn is_fn Fn<(&'a (),)>>() {} +fn is_fn2 Fn<(&'a &'b (),)>>() {} + +struct Outlives<'a, 'b>(std::marker::PhantomData<&'a &'b ()>); + +fn main() { + is_fn:: fn(&'a ()) -> &'a ()>(); + is_fn:: fn(&'a ()) -> &'a dyn std::fmt::Debug>(); + is_fn2:: fn(&'a &'b ()) -> Outlives<'a, 'b>>(); + is_fn2:: fn(&'a &'b ()) -> (&'a (), &'a ())>(); +} diff --git a/src/test/ui/function-pointer/unsized-ret.rs b/src/test/ui/function-pointer/unsized-ret.rs new file mode 100644 index 00000000000..60af5769d6d --- /dev/null +++ b/src/test/ui/function-pointer/unsized-ret.rs @@ -0,0 +1,14 @@ +#![feature(fn_traits)] +#![feature(unboxed_closures)] + +fn foo, T>(f: Option, t: T) { + let y = (f.unwrap()).call(t); +} + +fn main() { + foo:: str, _>(None, ()); + //~^ ERROR the size for values of type `str` cannot be known at compilation time + + foo:: fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),)); + //~^ ERROR the size for values of type `(dyn std::fmt::Display + 'a)` cannot be known at compilation time +} diff --git a/src/test/ui/function-pointer/unsized-ret.stderr b/src/test/ui/function-pointer/unsized-ret.stderr new file mode 100644 index 00000000000..bec3e2aa3fe --- /dev/null +++ b/src/test/ui/function-pointer/unsized-ret.stderr @@ -0,0 +1,35 @@ +error[E0277]: the size for values of type `str` cannot be known at compilation time + --> $DIR/unsized-ret.rs:9:27 + | +LL | foo:: str, _>(None, ()); + | --------------------- ^^^^ doesn't have a size known at compile-time + | | + | required by a bound introduced by this call + | + = help: within `fn() -> str`, the trait `Sized` is not implemented for `str` + = note: required because it appears within the type `fn() -> str` +note: required by a bound in `foo` + --> $DIR/unsized-ret.rs:4:11 + | +LL | fn foo, T>(f: Option, t: T) { + | ^^^^^ required by this bound in `foo` + +error[E0277]: the size for values of type `(dyn std::fmt::Display + 'a)` cannot be known at compilation time + --> $DIR/unsized-ret.rs:12:66 + | +LL | foo:: fn(&'a ()) -> (dyn std::fmt::Display + 'a), _>(None, (&(),)); + | ------------------------------------------------------------ ^^^^ doesn't have a size known at compile-time + | | + | required by a bound introduced by this call + | + = help: within `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)`, the trait `for<'a> Sized` is not implemented for `(dyn std::fmt::Display + 'a)` + = note: required because it appears within the type `for<'a> fn(&'a ()) -> (dyn std::fmt::Display + 'a)` +note: required by a bound in `foo` + --> $DIR/unsized-ret.rs:4:11 + | +LL | fn foo, T>(f: Option, t: T) { + | ^^^^^ required by this bound in `foo` + +error: aborting due to 2 previous errors + +For more information about this error, try `rustc --explain E0277`. diff --git a/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr b/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr index d20b1cc6d85..0a34e8486a5 100644 --- a/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr +++ b/src/test/ui/type-alias-impl-trait/issue-53398-cyclic-types.stderr @@ -1,10 +1,11 @@ -error[E0275]: overflow evaluating the requirement `fn() -> Foo {foo}: Sized` +error[E0275]: overflow evaluating the requirement `Foo: Sized` --> $DIR/issue-53398-cyclic-types.rs:5:13 | LL | fn foo() -> Foo { | ^^^ | = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`issue_53398_cyclic_types`) + = note: required because it appears within the type `fn() -> Foo {foo}` error: aborting due to previous error