user0/rust
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

only propagate ClosureRegionRequirements if non-trivial

Browse source 
Before, we would always have a `Some` ClosureRegionRequirements if we
were inferring values for a closure. Now we only do is it has a
non-empty set of outlives requirements.
This commit is contained in:
Niko Matsakis 2017-12-03 06:16:52 -05:00
parent a0f0392a6d
commit cd564d20ff
9 changed files with 148 additions and 99 deletions
Download patch file Download diff file Expand all files Collapse all files

173
src/librustc_mir/borrow_check/nll/region_infer/mod.rs
View file

@ -251,24 +251,88 @@ impl<'tcx> RegionInferenceContext<'tcx> {
mir_def_id: DefId,
) -> Option<ClosureRegionRequirements> {
assert!(self.inferred_values.is_none(), "values already inferred");
let tcx = infcx.tcx;
// Find the minimal regions that can solve the constraints. This is infallible.
self.propagate_constraints(mir);
// Now, see whether any of the constraints were too strong. In
// particular, we want to check for a case where a universally
// quantified region exceeded its bounds. Consider:
//
// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
//
// In this case, returning `x` requires `&'a u32 <: &'b u32`
// and hence we establish (transitively) a constraint that
// `'a: 'b`. The `propagate_constraints` code above will
// therefore add `end('a)` into the region for `'b` -- but we
// have no evidence that `'a` outlives `'b`, so we want to report
// an error.
let outlives_requirements = self.check_universal_regions(infcx, mir_def_id);
if outlives_requirements.is_empty() {
None
} else {
let num_external_vids = self.universal_regions.num_global_and_external_regions();
Some(ClosureRegionRequirements {
num_external_vids,
outlives_requirements,
})
}
}
/// Propagate the region constraints: this will grow the values
/// for each region variable until all the constraints are
/// satisfied. Note that some values may grow **too** large to be
/// feasible, but we check this later.
fn propagate_constraints(&mut self, mir: &Mir<'tcx>) {
let mut changed = true;
debug!("propagate_constraints()");
debug!("propagate_constraints: constraints={:#?}", {
let mut constraints: Vec<_> = self.constraints.iter().collect();
constraints.sort();
constraints
});
// The initial values for each region are derived from the liveness
// constraints we have accumulated.
let mut inferred_values = self.liveness_constraints.clone();
while changed {
changed = false;
debug!("propagate_constraints: --------------------");
for constraint in &self.constraints {
debug!("propagate_constraints: constraint={:?}", constraint);
// Grow the value as needed to accommodate the
// outlives constraint.
let Ok(made_changes) = self.dfs(
mir,
CopyFromSourceToTarget {
source_region: constraint.sub,
target_region: constraint.sup,
inferred_values: &mut inferred_values,
constraint_point: constraint.point,
},
);
if made_changes {
debug!("propagate_constraints: sub={:?}", constraint.sub);
debug!("propagate_constraints: sup={:?}", constraint.sup);
changed = true;
}
}
debug!("\n");
}
self.inferred_values = Some(inferred_values);
}
/// Once regions have been propagated, this method is used to see
/// whether any of the constraints were too strong. In particular,
/// we want to check for a case where a universally quantified
/// region exceeded its bounds. Consider:
///
/// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x }
///
/// In this case, returning `x` requires `&'a u32 <: &'b u32`
/// and hence we establish (transitively) a constraint that
/// `'a: 'b`. The `propagate_constraints` code above will
/// therefore add `end('a)` into the region for `'b` -- but we
/// have no evidence that `'b` outlives `'a`, so we want to report
/// an error.
fn check_universal_regions(
&self,
infcx: &InferCtxt<'_, '_, 'tcx>,
mir_def_id: DefId,
) -> Vec<ClosureOutlivesRequirement> {
// The universal regions are always found in a prefix of the
// full list.
let universal_definitions = self.definitions
@ -283,27 +347,23 @@ impl<'tcx> RegionInferenceContext<'tcx> {
self.check_universal_region(infcx, fr, &mut outlives_requirements);
}
// If this is not a closure, then there is no caller to which we can
// "pass the buck". So if there are any outlives-requirements that were
// not satisfied, we just have to report a hard error here.
if !tcx.is_closure(mir_def_id) {
for outlives_requirement in outlives_requirements {
self.report_error(
infcx,
outlives_requirement.free_region,
outlives_requirement.outlived_free_region,
outlives_requirement.blame_span,
);
}
return None;
// If this is a closure, we can propagate unsatisfied
// `outlives_requirements` to our creator. Otherwise, we have
// to report a hard error here.
if infcx.tcx.is_closure(mir_def_id) {
return outlives_requirements;
}
let num_external_vids = self.universal_regions.num_global_and_external_regions();
for outlives_requirement in outlives_requirements {
self.report_error(
infcx,
outlives_requirement.free_region,
outlives_requirement.outlived_free_region,
outlives_requirement.blame_span,
);
}
Some(ClosureRegionRequirements {
num_external_vids,
outlives_requirements,
})
vec![]
}
/// Check the final value for the free region `fr` to see if it
@ -396,54 +456,6 @@ impl<'tcx> RegionInferenceContext<'tcx> {
);
}
/// Propagate the region constraints: this will grow the values
/// for each region variable until all the constraints are
/// satisfied. Note that some values may grow **too** large to be
/// feasible, but we check this later.
fn propagate_constraints(&mut self, mir: &Mir<'tcx>) {
let mut changed = true;
debug!("propagate_constraints()");
debug!("propagate_constraints: constraints={:#?}", {
let mut constraints: Vec<_> = self.constraints.iter().collect();
constraints.sort();
constraints
});
// The initial values for each region are derived from the liveness
// constraints we have accumulated.
let mut inferred_values = self.liveness_constraints.clone();
while changed {
changed = false;
debug!("propagate_constraints: --------------------");
for constraint in &self.constraints {
debug!("propagate_constraints: constraint={:?}", constraint);
// Grow the value as needed to accommodate the
// outlives constraint.
let Ok(made_changes) = self.dfs(
mir,
CopyFromSourceToTarget {
source_region: constraint.sub,
target_region: constraint.sup,
inferred_values: &mut inferred_values,
constraint_point: constraint.point,
},
);
if made_changes {
debug!("propagate_constraints: sub={:?}", constraint.sub);
debug!("propagate_constraints: sup={:?}", constraint.sup);
changed = true;
}
}
debug!("\n");
}
self.inferred_values = Some(inferred_values);
}
/// Tries to finds a good span to blame for the fact that `fr1`
/// contains `fr2`.
fn blame_span(&self, fr1: RegionVid, fr2: RegionVid) -> Span {
@ -589,4 +601,3 @@ impl ClosureRegionRequirementsExt for ClosureRegionRequirements {
}
}
}

3
src/test/ui/nll/closure-requirements/escape-argument-callee.stderr
View file

@ -10,7 +10,7 @@ error: free region `'_#4r` does not outlive free region `'_#3r`
36 | let mut closure = expect_sig(|p, y| *p = y);
| ^^^^^^
note: External requirements
note: No external requirements
--> $DIR/escape-argument-callee.rs:36:38
|
36 | let mut closure = expect_sig(|p, y| *p = y);
@ -20,7 +20,6 @@ note: External requirements
i16,
for<'r, 's, 't0> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) mut &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) i32, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) i32))
]
= note: number of external vids: 1
note: No external requirements
--> $DIR/escape-argument-callee.rs:30:1

3
src/test/ui/nll/closure-requirements/escape-argument.stderr
View file

@ -1,4 +1,4 @@
note: External requirements
note: No external requirements
--> $DIR/escape-argument.rs:36:38
|
36 | let mut closure = expect_sig(|p, y| *p = y);
@ -8,7 +8,6 @@ note: External requirements
i16,
for<'r, 's> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) mut &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) i32, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) i32))
]
= note: number of external vids: 1
note: No external requirements
--> $DIR/escape-argument.rs:30:1

3
src/test/ui/nll/closure-requirements/propagate-approximated-fail-no-postdom.stderr
View file

@ -10,7 +10,7 @@ error: free region `'_#5r` does not outlive free region `'_#6r`
57 | demand_y(x, y, p)
| ^
note: External requirements
note: No external requirements
--> $DIR/propagate-approximated-fail-no-postdom.rs:53:9
|
53 | / |_outlives1, _outlives2, _outlives3, x, y| {
@ -26,7 +26,6 @@ note: External requirements
i16,
for<'r, 's> extern "rust-call" fn((std::cell::Cell<&'_#1r &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&'_#2r &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) &'_#3r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) u32>, std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>))
]
= note: number of external vids: 4
note: No external requirements
--> $DIR/propagate-approximated-fail-no-postdom.rs:48:1

3
src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr
View file

@ -10,7 +10,7 @@ error: free region `'_#2r` does not outlive free region `'_#1r`
33 | cell_a.set(cell_x.get()); // forces 'x: 'a, error in closure
| ^^^^^^
note: External requirements
note: No external requirements
--> $DIR/propagate-approximated-shorter-to-static-comparing-against-free.rs:31:15
|
31 | foo(cell, |cell_a, cell_x| {
@ -25,7 +25,6 @@ note: External requirements
i32,
for<'r> extern "rust-call" fn((std::cell::Cell<&'_#1r u32>, std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) u32>))
]
= note: number of external vids: 2
note: No external requirements
--> $DIR/propagate-approximated-shorter-to-static-comparing-against-free.rs:28:1

45
src/test/ui/nll/closure-requirements/propagate-approximated-to-empty.stderr Normal file
View file

@ -0,0 +1,45 @@
warning: not reporting region error due to -Znll
--> $DIR/propagate-approximated-to-empty.rs:41:9
|
41 | demand_y(x, y, x.get())
| ^^^^^^^^^^^^^^^^^^^^^^^
error: free region `'_#6r` does not outlive free region `'_#4r`
--> $DIR/propagate-approximated-to-empty.rs:41:21
|
41 | demand_y(x, y, x.get())
| ^
note: No external requirements
--> $DIR/propagate-approximated-to-empty.rs:39:47
|
39 | establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
| _______________________________________________^
40 | | // Only works if 'x: 'y:
41 | | demand_y(x, y, x.get())
42 | | //~^ WARN not reporting region error due to -Znll
43 | | //~| ERROR free region `'_#6r` does not outlive free region `'_#4r`
44 | | });
| |_____^
|
= note: defining type: DefId(0/1:18 ~ propagate_approximated_to_empty[317d]::supply[0]::{{closure}}[0]) with closure substs [
i16,
for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>))
]
note: No external requirements
--> $DIR/propagate-approximated-to-empty.rs:38:1
|
38 | / fn supply<'a, 'b>(cell_a: Cell<&'a u32>, cell_b: Cell<&'b u32>) {
39 | | establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
40 | | // Only works if 'x: 'y:
41 | | demand_y(x, y, x.get())
... |
44 | | });
45 | | }
| |_^
|
= note: defining type: DefId(0/0:6 ~ propagate_approximated_to_empty[317d]::supply[0]) with substs []
error: aborting due to previous error

7
src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-no-bounds.stderr
View file

@ -5,12 +5,12 @@ warning: not reporting region error due to -Znll
| ^^^^^^^^^^^^^^^^^^^^^^^
error: free region `'_#6r` does not outlive free region `'_#4r`
--> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:47:21
--> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:47:18
|
47 | demand_y(x, y, x.get())
| ^
| ^
note: External requirements
note: No external requirements
--> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:45:47
|
45 | establish_relationships(&cell_a, &cell_b, |_outlives, x, y| {
@ -26,7 +26,6 @@ note: External requirements
i16,
for<'r, 's, 't0, 't1, 't2> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>))
]
= note: number of external vids: 2
note: No external requirements
--> $DIR/propagate-fail-to-approximate-longer-no-bounds.rs:44:1

7
src/test/ui/nll/closure-requirements/propagate-fail-to-approximate-longer-wrong-bounds.stderr
View file

@ -5,12 +5,12 @@ warning: not reporting region error due to -Znll
| ^^^^^^^^^^^^^^^^^^^^^^^
error: free region `'_#5r` does not outlive free region `'_#7r`
--> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:51:21
--> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:51:18
|
51 | demand_y(x, y, x.get())
| ^
| ^
note: External requirements
note: No external requirements
--> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:49:47
|
49 | establish_relationships(&cell_a, &cell_b, |_outlives1, _outlives2, x, y| {
@ -26,7 +26,6 @@ note: External requirements
i16,
for<'r, 's, 't0, 't1, 't2, 't3> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) &'_#1r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't0)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) &'_#2r u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't2)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) u32>, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't3)) std::cell::Cell<&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 't1)) u32>))
]
= note: number of external vids: 3
note: No external requirements
--> $DIR/propagate-fail-to-approximate-longer-wrong-bounds.rs:48:1

3
src/test/ui/nll/closure-requirements/return-wrong-bound-region.stderr
View file

@ -10,7 +10,7 @@ error: free region `'_#3r` does not outlive free region `'_#2r`
21 | expect_sig(|a, b| b); // ought to return `a`
| ^
note: External requirements
note: No external requirements
--> $DIR/return-wrong-bound-region.rs:21:16
|
21 | expect_sig(|a, b| b); // ought to return `a`
@ -20,7 +20,6 @@ note: External requirements
i16,
for<'r, 's> extern "rust-call" fn((&ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) i32, &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 's)) i32)) -> &ReLateBound(DebruijnIndex { depth: 1 }, BrNamed(crate0:DefIndex(0:0), 'r)) i32
]
= note: number of external vids: 1
note: No external requirements
--> $DIR/return-wrong-bound-region.rs:20:1