From c7b6e1de661419a67a59ad59fba70a451c27cbb6 Mon Sep 17 00:00:00 2001
From: lcnr <rust@lcnr.de>
Date: Wed, 8 Jun 2022 12:39:14 +0200
Subject: [PATCH 1/2] lub: don't bail out due to empty binders
---
compiler/rustc_infer/src/infer/glb.rs | 20 +++++--
compiler/rustc_infer/src/infer/lub.rs | 20 +++++--
src/test/ui/lub-glb/empty-binders-err.rs | 61 ++++++++++++++++++++
src/test/ui/lub-glb/empty-binders-err.stderr | 59 +++++++++++++++++++
src/test/ui/lub-glb/empty-binders.rs | 45 +++++++++++++++
5 files changed, 193 insertions(+), 12 deletions(-)
create mode 100644 src/test/ui/lub-glb/empty-binders-err.rs
create mode 100644 src/test/ui/lub-glb/empty-binders-err.stderr
create mode 100644 src/test/ui/lub-glb/empty-binders.rs
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-binders-err.rs b/src/test/ui/lub-glb/empty-binders-err.rs
new file mode 100644
index 0000000000000..ee28dd7c97d61
--- /dev/null
+++ b/src/test/ui/lub-glb/empty-binders-err.rs
@@ -0,0 +1,61 @@
+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, 'lower>(v: bool)
+where
+ 'upper: 'a,
+ 'upper: 'b,
+ 'a: 'lower,
+ 'b: 'lower,
+
+{
+ 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, 'upper, 'lower>(v: bool)
+where
+ 'upper: 'a,
+ 'upper: 'b,
+ '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, 'upper, 'lower>(v: bool)
+where
+ 'upper: 'a,
+ 'upper: 'b,
+ '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..0d5de978e4301
--- /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:22:12
+ |
+LL | fn covariance<'a, 'b, 'upper, 'lower>(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:22:12
+ |
+LL | fn covariance<'a, 'b, 'upper, 'lower>(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:39:12
+ |
+LL | fn contra_fn<'a, 'b, 'upper, '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:54:12
+ |
+LL | fn contra_struct<'a, 'b, 'upper, '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() {}
From 0667b00acf939634ff1fd310ed5de2d49c65c6bb Mon Sep 17 00:00:00 2001
From: lcnr <rust@lcnr.de>
Date: Wed, 8 Jun 2022 21:03:52 +0200
Subject: [PATCH 2/2] update tests + add future compat test
---
.../ui/lub-glb/empty-binder-future-compat.rs | 22 +++++++++++++++++++
src/test/ui/lub-glb/empty-binders-err.rs | 12 +++-------
src/test/ui/lub-glb/empty-binders-err.stderr | 20 ++++++++---------
3 files changed, 35 insertions(+), 19 deletions(-)
create mode 100644 src/test/ui/lub-glb/empty-binder-future-compat.rs
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
index ee28dd7c97d61..557480173ee62 100644
--- a/src/test/ui/lub-glb/empty-binders-err.rs
+++ b/src/test/ui/lub-glb/empty-binders-err.rs
@@ -11,12 +11,10 @@ fn lt_in_contra<'a: 'a>() -> Contra<'a> {
Contra(|_| ())
}
-fn covariance<'a, 'b, 'upper, 'lower>(v: bool)
+fn covariance<'a, 'b, 'upper>(v: bool)
where
'upper: 'a,
'upper: 'b,
- 'a: 'lower,
- 'b: 'lower,
{
let _: &'upper () = match v {
@@ -27,10 +25,8 @@ where
};
}
-fn contra_fn<'a, 'b, 'upper, 'lower>(v: bool)
+fn contra_fn<'a, 'b, 'lower>(v: bool)
where
- 'upper: 'a,
- 'upper: 'b,
'a: 'lower,
'b: 'lower,
@@ -43,10 +39,8 @@ where
};
}
-fn contra_struct<'a, 'b, 'upper, 'lower>(v: bool)
+fn contra_struct<'a, 'b, 'lower>(v: bool)
where
- 'upper: 'a,
- 'upper: 'b,
'a: 'lower,
'b: 'lower,
diff --git a/src/test/ui/lub-glb/empty-binders-err.stderr b/src/test/ui/lub-glb/empty-binders-err.stderr
index 0d5de978e4301..f86f22d5e40bf 100644
--- a/src/test/ui/lub-glb/empty-binders-err.stderr
+++ b/src/test/ui/lub-glb/empty-binders-err.stderr
@@ -1,7 +1,7 @@
error: lifetime may not live long enough
- --> $DIR/empty-binders-err.rs:22:12
+ --> $DIR/empty-binders-err.rs:20:12
|
-LL | fn covariance<'a, 'b, 'upper, 'lower>(v: bool)
+LL | fn covariance<'a, 'b, 'upper>(v: bool)
| -- ------ lifetime `'upper` defined here
| |
| lifetime `'a` defined here
@@ -12,9 +12,9 @@ LL | let _: &'upper () = match v {
= help: consider adding the following bound: `'a: 'upper`
error: lifetime may not live long enough
- --> $DIR/empty-binders-err.rs:22:12
+ --> $DIR/empty-binders-err.rs:20:12
|
-LL | fn covariance<'a, 'b, 'upper, 'lower>(v: bool)
+LL | fn covariance<'a, 'b, 'upper>(v: bool)
| -- ------ lifetime `'upper` defined here
| |
| lifetime `'b` defined here
@@ -30,10 +30,10 @@ help: the following changes may resolve your lifetime errors
= help: add bound `'b: 'upper`
error: lifetime may not live long enough
- --> $DIR/empty-binders-err.rs:39:12
+ --> $DIR/empty-binders-err.rs:35:12
|
-LL | fn contra_fn<'a, 'b, 'upper, 'lower>(v: bool)
- | -- ------ lifetime `'lower` defined here
+LL | fn contra_fn<'a, 'b, 'lower>(v: bool)
+ | -- ------ lifetime `'lower` defined here
| |
| lifetime `'a` defined here
...
@@ -43,10 +43,10 @@ LL | let _: fn(&'lower ()) = match v {
= help: consider adding the following bound: `'lower: 'a`
error: lifetime may not live long enough
- --> $DIR/empty-binders-err.rs:54:12
+ --> $DIR/empty-binders-err.rs:48:12
|
-LL | fn contra_struct<'a, 'b, 'upper, 'lower>(v: bool)
- | -- ------ lifetime `'lower` defined here
+LL | fn contra_struct<'a, 'b, 'lower>(v: bool)
+ | -- ------ lifetime `'lower` defined here
| |
| lifetime `'a` defined here
...