diff --git a/compiler/rustc_infer/src/infer/glb.rs b/compiler/rustc_infer/src/infer/glb.rs index 0d38b94965afe..1570a08f3ca8b 100644 --- a/compiler/rustc_infer/src/infer/glb.rs +++ b/compiler/rustc_infer/src/infer/glb.rs @@ -95,12 +95,20 @@ impl<'tcx> TypeRelation<'tcx> for Glb<'_, '_, 'tcx> { T: Relate<'tcx>, { debug!("binders(a={:?}, b={:?})", a, b); - - // When higher-ranked types are involved, computing the LUB is - // very challenging, switch to invariance. This is obviously - // overly conservative but works ok in practice. - self.relate_with_variance(ty::Variance::Invariant, ty::VarianceDiagInfo::default(), a, b)?; - Ok(a) + if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() { + // When higher-ranked types are involved, computing the GLB is + // very challenging, switch to invariance. This is obviously + // overly conservative but works ok in practice. + self.relate_with_variance( + ty::Variance::Invariant, + ty::VarianceDiagInfo::default(), + a, + b, + )?; + Ok(a) + } else { + Ok(ty::Binder::dummy(self.relate(a.skip_binder(), b.skip_binder())?)) + } } } diff --git a/compiler/rustc_infer/src/infer/lub.rs b/compiler/rustc_infer/src/infer/lub.rs index 498c1e907c4e1..9f96d52c85034 100644 --- a/compiler/rustc_infer/src/infer/lub.rs +++ b/compiler/rustc_infer/src/infer/lub.rs @@ -95,12 +95,20 @@ impl<'tcx> TypeRelation<'tcx> for Lub<'_, '_, 'tcx> { T: Relate<'tcx>, { debug!("binders(a={:?}, b={:?})", a, b); - - // When higher-ranked types are involved, computing the LUB is - // very challenging, switch to invariance. This is obviously - // overly conservative but works ok in practice. - self.relate_with_variance(ty::Variance::Invariant, ty::VarianceDiagInfo::default(), a, b)?; - Ok(a) + if a.skip_binder().has_escaping_bound_vars() || b.skip_binder().has_escaping_bound_vars() { + // When higher-ranked types are involved, computing the LUB is + // very challenging, switch to invariance. This is obviously + // overly conservative but works ok in practice. + self.relate_with_variance( + ty::Variance::Invariant, + ty::VarianceDiagInfo::default(), + a, + b, + )?; + Ok(a) + } else { + Ok(ty::Binder::dummy(self.relate(a.skip_binder(), b.skip_binder())?)) + } } } diff --git a/src/test/ui/lub-glb/empty-binder-future-compat.rs b/src/test/ui/lub-glb/empty-binder-future-compat.rs new file mode 100644 index 0000000000000..8700a88a36ea0 --- /dev/null +++ b/src/test/ui/lub-glb/empty-binder-future-compat.rs @@ -0,0 +1,22 @@ +// check-pass +fn lt_in_fn_fn<'a: 'a>() -> fn(fn(&'a ())) { + |_| () +} + + +fn foo<'a, 'b, 'lower>(v: bool) +where + 'a: 'lower, + 'b: 'lower, +{ + // if we infer `x` to be higher ranked in the future, + // this would cause a type error. + let x = match v { + true => lt_in_fn_fn::<'a>(), + false => lt_in_fn_fn::<'b>(), + }; + + let _: fn(fn(&'lower())) = x; +} + +fn main() {} diff --git a/src/test/ui/lub-glb/empty-binders-err.rs b/src/test/ui/lub-glb/empty-binders-err.rs new file mode 100644 index 0000000000000..557480173ee62 --- /dev/null +++ b/src/test/ui/lub-glb/empty-binders-err.rs @@ -0,0 +1,55 @@ +fn lt<'a: 'a>() -> &'a () { + &() +} + +fn lt_in_fn<'a: 'a>() -> fn(&'a ()) { + |_| () +} + +struct Contra<'a>(fn(&'a ())); +fn lt_in_contra<'a: 'a>() -> Contra<'a> { + Contra(|_| ()) +} + +fn covariance<'a, 'b, 'upper>(v: bool) +where + 'upper: 'a, + 'upper: 'b, + +{ + let _: &'upper () = match v { + //~^ ERROR lifetime may not live long enough + //~| ERROR lifetime may not live long enough + true => lt::<'a>(), + false => lt::<'b>(), + }; +} + +fn contra_fn<'a, 'b, 'lower>(v: bool) +where + 'a: 'lower, + 'b: 'lower, + +{ + + let _: fn(&'lower ()) = match v { + //~^ ERROR lifetime may not live long enough + true => lt_in_fn::<'a>(), + false => lt_in_fn::<'b>(), + }; +} + +fn contra_struct<'a, 'b, 'lower>(v: bool) +where + 'a: 'lower, + 'b: 'lower, + +{ + let _: Contra<'lower> = match v { + //~^ ERROR lifetime may not live long enough + true => lt_in_contra::<'a>(), + false => lt_in_contra::<'b>(), + }; +} + +fn main() {} diff --git a/src/test/ui/lub-glb/empty-binders-err.stderr b/src/test/ui/lub-glb/empty-binders-err.stderr new file mode 100644 index 0000000000000..f86f22d5e40bf --- /dev/null +++ b/src/test/ui/lub-glb/empty-binders-err.stderr @@ -0,0 +1,59 @@ +error: lifetime may not live long enough + --> $DIR/empty-binders-err.rs:20:12 + | +LL | fn covariance<'a, 'b, 'upper>(v: bool) + | -- ------ lifetime `'upper` defined here + | | + | lifetime `'a` defined here +... +LL | let _: &'upper () = match v { + | ^^^^^^^^^^ type annotation requires that `'a` must outlive `'upper` + | + = help: consider adding the following bound: `'a: 'upper` + +error: lifetime may not live long enough + --> $DIR/empty-binders-err.rs:20:12 + | +LL | fn covariance<'a, 'b, 'upper>(v: bool) + | -- ------ lifetime `'upper` defined here + | | + | lifetime `'b` defined here +... +LL | let _: &'upper () = match v { + | ^^^^^^^^^^ type annotation requires that `'b` must outlive `'upper` + | + = help: consider adding the following bound: `'b: 'upper` + +help: the following changes may resolve your lifetime errors + | + = help: add bound `'a: 'upper` + = help: add bound `'b: 'upper` + +error: lifetime may not live long enough + --> $DIR/empty-binders-err.rs:35:12 + | +LL | fn contra_fn<'a, 'b, 'lower>(v: bool) + | -- ------ lifetime `'lower` defined here + | | + | lifetime `'a` defined here +... +LL | let _: fn(&'lower ()) = match v { + | ^^^^^^^^^^^^^^ type annotation requires that `'lower` must outlive `'a` + | + = help: consider adding the following bound: `'lower: 'a` + +error: lifetime may not live long enough + --> $DIR/empty-binders-err.rs:48:12 + | +LL | fn contra_struct<'a, 'b, 'lower>(v: bool) + | -- ------ lifetime `'lower` defined here + | | + | lifetime `'a` defined here +... +LL | let _: Contra<'lower> = match v { + | ^^^^^^^^^^^^^^ type annotation requires that `'lower` must outlive `'a` + | + = help: consider adding the following bound: `'lower: 'a` + +error: aborting due to 4 previous errors + diff --git a/src/test/ui/lub-glb/empty-binders.rs b/src/test/ui/lub-glb/empty-binders.rs new file mode 100644 index 0000000000000..f9d07e79fdabf --- /dev/null +++ b/src/test/ui/lub-glb/empty-binders.rs @@ -0,0 +1,45 @@ +// check-pass +// +// Check that computing the lub works even for empty binders. +fn lt<'a: 'a>() -> &'a () { + &() +} + +fn lt_in_fn<'a: 'a>() -> fn(&'a ()) { + |_| () +} + +struct Contra<'a>(fn(&'a ())); +fn lt_in_contra<'a: 'a>() -> Contra<'a> { + Contra(|_| ()) +} + +fn ok<'a, 'b, 'upper, 'lower>(v: bool) +where + 'upper: 'a, + 'upper: 'b, + 'a: 'lower, + 'b: 'lower, + +{ + let _: &'lower () = match v { + true => lt::<'a>(), + false => lt::<'b>(), + }; + + // This errored in the past because LUB and GLB always + // bailed out when encountering binders, even if they were + // empty. + let _: fn(&'upper ()) = match v { + true => lt_in_fn::<'a>(), + false => lt_in_fn::<'b>(), + }; + + // This was already accepted, as relate didn't encounter any binders. + let _: Contra<'upper> = match v { + true => lt_in_contra::<'a>(), + false => lt_in_contra::<'b>(), + }; +} + +fn main() {}