Auto merge of #53745 - nikomatsakis:nll-issue-53570, r=pnkfelix

do not propagate closure requirements if we can prove them locally

Fixes #53570

cc @mikhail-m1 -- you're the one who last touched this code

r? @pnkfelix

15 files changed, 70 insertions, 0 deletions

diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
index 89291068643..fa14d496a14 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
@@ -12,6 +12,9 @@ LL | |         },
                i16,
                for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#3r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>))
            ]
+   = note: late-bound region is '_#4r
+   = note: late-bound region is '_#5r
+   = note: late-bound region is '_#6r
 
 error: unsatisfied lifetime constraints
   --> $DIR/propagate-approximated-fail-no-postdom.rs:56:13
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-ref.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-ref.stderr
index 1ff9374c212..1af96b97e73 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-ref.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-ref.stderr
@@ -14,6 +14,8 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
            ]
+   = note: late-bound region is '_#3r
+   = note: late-bound region is '_#4r
    = note: number of external vids: 5
    = note: where '_#1r: '_#2r
 
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr
index f50864d946b..9de9e21ba43 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-no-bound.stderr
@@ -15,6 +15,8 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) u32>))
            ]
+   = note: late-bound region is '_#2r
+   = note: late-bound region is '_#3r
    = note: number of external vids: 4
    = note: where '_#1r: '_#0r
 
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr
index 8a89320d10c..6acb6750055 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-wrong-bound.stderr
@@ -14,6 +14,8 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
            ]
+   = note: late-bound region is '_#3r
+   = note: late-bound region is '_#4r
    = note: number of external vids: 5
    = note: where '_#1r: '_#0r
 
diff --git a/src/test/ui/nll/closure-requirements/propagate-approximated-val.stderr b/src/test/ui/nll/closure-requirements/propagate-approximated-val.stderr
index 71dbc412fef..e0902ca1ddb 100644
--- a/src/test/ui/nll/closure-requirements/propagate-approximated-val.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-approximated-val.stderr
@@ -14,6 +14,8 @@ LL | |     });
                i16,
                for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>))
            ]
+   = note: late-bound region is '_#3r
+   = note: late-bound region is '_#4r
    = note: number of external vids: 5
    = note: where '_#1r: '_#2r
 
diff --git a/src/test/ui/nll/closure-requirements/propagate-despite-same-free-region.stderr b/src/test/ui/nll/closure-requirements/propagate-despite-same-free-region.stderr
index d189385213f..a3f78507d8d 100644
--- a/src/test/ui/nll/closure-requirements/propagate-despite-same-free-region.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-despite-same-free-region.stderr
@@ -12,6 +12,7 @@ LL | |         },
                i16,
                for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#2r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>))
            ]
+   = note: late-bound region is '_#3r
    = note: number of external vids: 4
    = note: where '_#1r: '_#2r
 
diff --git a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
index a63c6b16708..31cad6ba1b5 100644
--- a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
@@ -13,6 +13,8 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>))
            ]
+   = note: late-bound region is '_#2r
+   = note: late-bound region is '_#3r
 
 error: unsatisfied lifetime constraints
   --> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:47:9
diff --git a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
index 67510a5a81f..4e21816e8c0 100644
--- a/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
+++ b/src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
@@ -13,6 +13,8 @@ LL | |     });
                i16,
                for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) &'_#2r u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
            ]
+   = note: late-bound region is '_#3r
+   = note: late-bound region is '_#4r
 
 error: unsatisfied lifetime constraints
   --> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:51:9
diff --git a/src/test/ui/nll/issue-53570.rs b/src/test/ui/nll/issue-53570.rs
new file mode 100644
index 00000000000..9617e40ec39
--- /dev/null
+++ b/src/test/ui/nll/issue-53570.rs
@@ -0,0 +1,46 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Regression test for #53570. Here, we need to propagate that `T: 'a`
+// but in some versions of NLL we were propagating a stronger
+// requirement that `T: 'static`. This arose because we actually had
+// to propagate both that `T: 'a` but also `T: 'b` where `'b` is the
+// higher-ranked lifetime that appears in the type of the closure
+// parameter `x` -- since `'b` cannot be expressed in the caller's
+// space, that got promoted th `'static`.
+//
+// compile-pass
+
+#![feature(nll)]
+#![feature(rustc_attrs)]
+#![allow(dead_code)]
+
+use std::cell::{RefCell, Ref};
+
+trait AnyVec<'a> {
+}
+
+trait GenericVec<T> {
+    fn unwrap<'a, 'b>(vec: &'b AnyVec<'a>) -> &'b [T] where T: 'a;
+}
+
+struct Scratchpad<'a> {
+    buffers: RefCell<Box<AnyVec<'a>>>,
+}
+
+impl<'a> Scratchpad<'a> {
+    fn get<T: GenericVec<T>>(&self) -> Ref<[T]>
+    where T: 'a
+    {
+        Ref::map(self.buffers.borrow(), |x| T::unwrap(x.as_ref()))
+    }
+}
+
+fn main() { }
diff --git a/src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr b/src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr
index 24f4bea1ba2..a91761f3ece 100644
--- a/src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr
+++ b/src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr
@@ -10,6 +10,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#2r ()>, T))
            ]
+   = note: late-bound region is '_#3r
    = note: number of external vids: 4
    = note: where T: '_#2r
    = note: where '_#1r: '_#2r
diff --git a/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-closure.stderr b/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-closure.stderr
index df4f619b776..0064393f271 100644
--- a/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-closure.stderr
+++ b/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-closure.stderr
@@ -10,6 +10,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#2r ()>, T))
            ]
+   = note: late-bound region is '_#3r
    = note: number of external vids: 4
    = note: where '_#1r: '_#2r
 
diff --git a/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-static-closure.stderr b/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-static-closure.stderr
index 136e143e80e..3f8ed324f56 100644
--- a/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-static-closure.stderr
+++ b/src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-static-closure.stderr
@@ -10,6 +10,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#2r ()>, T))
            ]
+   = note: late-bound region is '_#3r
 
 note: No external requirements
   --> $DIR/projection-one-region-trait-bound-static-closure.rs:42:1
diff --git a/src/test/ui/nll/ty-outlives/projection-two-region-trait-bound-closure.stderr b/src/test/ui/nll/ty-outlives/projection-two-region-trait-bound-closure.stderr
index 176e45ae098..19dcb5f93da 100644
--- a/src/test/ui/nll/ty-outlives/projection-two-region-trait-bound-closure.stderr
+++ b/src/test/ui/nll/ty-outlives/projection-two-region-trait-bound-closure.stderr
@@ -11,6 +11,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#3r ()>, T))
            ]
+   = note: late-bound region is '_#4r
    = note: number of external vids: 5
    = note: where <T as Anything<ReClosureBound('_#1r), ReClosureBound('_#2r)>>::AssocType: '_#3r
 
@@ -212,6 +213,7 @@ LL |     with_signature(cell, t, |cell, t| require(cell, t));
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#2r ()>, T))
            ]
+   = note: late-bound region is '_#3r
    = note: number of external vids: 4
    = note: where <T as Anything<ReClosureBound('_#1r), ReClosureBound('_#1r)>>::AssocType: '_#2r
 
diff --git a/src/test/ui/nll/ty-outlives/ty-param-closure-approximate-lower-bound.stderr b/src/test/ui/nll/ty-outlives/ty-param-closure-approximate-lower-bound.stderr
index 1f5edf08957..106eaa6a3ab 100644
--- a/src/test/ui/nll/ty-outlives/ty-param-closure-approximate-lower-bound.stderr
+++ b/src/test/ui/nll/ty-outlives/ty-param-closure-approximate-lower-bound.stderr
@@ -36,6 +36,7 @@ LL |     twice(cell, value, |a, b| invoke(a, b));
                i16,
                for<'r, 's> extern "rust-call" fn((std::option::Option<std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 'r)) ()>>, &ReLateBound(DebruijnIndex(0), BrNamed(crate0:DefIndex(0:0), 's)) T))
            ]
+   = note: late-bound region is '_#2r
    = note: number of external vids: 3
    = note: where T: '_#1r
 
diff --git a/src/test/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.stderr b/src/test/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.stderr
index 1b9baf61305..f0e86a580b2 100644
--- a/src/test/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.stderr
+++ b/src/test/ui/nll/ty-outlives/ty-param-closure-outlives-from-where-clause.stderr
@@ -16,6 +16,7 @@ LL | |     })
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#1r ()>, T))
            ]
+   = note: late-bound region is '_#2r
    = note: number of external vids: 3
    = note: where T: '_#1r
 
@@ -106,6 +107,7 @@ LL | |     })
                i32,
                extern "rust-call" fn((std::cell::Cell<&'_#2r ()>, T))
            ]
+   = note: late-bound region is '_#3r
    = note: number of external vids: 4
    = note: where T: '_#2r