From 4030b7394845602eebb42f40c0e847be803af58f Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Thu, 2 Jul 2020 21:03:59 +0100
Subject: [PATCH 1/2] Use `Span`s to identify unreachable subpatterns in
or-patterns
---
src/librustc_mir_build/hair/pattern/_match.rs | 14 +++++++-------
src/librustc_mir_build/hair/pattern/check_match.rs | 4 ++--
2 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/src/librustc_mir_build/hair/pattern/_match.rs b/src/librustc_mir_build/hair/pattern/_match.rs
index 18b92bf29bf..b5a655e4218 100644
--- a/src/librustc_mir_build/hair/pattern/_match.rs
+++ b/src/librustc_mir_build/hair/pattern/_match.rs
@@ -1246,15 +1246,15 @@ impl<'p, 'tcx> Fields<'p, 'tcx> {
}
#[derive(Clone, Debug)]
-crate enum Usefulness<'tcx, 'p> {
+crate enum Usefulness<'tcx> {
/// Carries a list of unreachable subpatterns. Used only in the presence of or-patterns.
- Useful(Vec<&'p Pat<'tcx>>),
+ Useful(Vec<Span>),
/// Carries a list of witnesses of non-exhaustiveness.
UsefulWithWitness(Vec<Witness<'tcx>>),
NotUseful,
}
-impl<'tcx, 'p> Usefulness<'tcx, 'p> {
+impl<'tcx> Usefulness<'tcx> {
fn new_useful(preference: WitnessPreference) -> Self {
match preference {
ConstructWitness => UsefulWithWitness(vec![Witness(vec![])]),
@@ -1269,7 +1269,7 @@ impl<'tcx, 'p> Usefulness<'tcx, 'p> {
}
}
- fn apply_constructor(
+ fn apply_constructor<'p>(
self,
cx: &MatchCheckCtxt<'p, 'tcx>,
ctor: &Constructor<'tcx>,
@@ -1828,7 +1828,7 @@ crate fn is_useful<'p, 'tcx>(
hir_id: HirId,
is_under_guard: bool,
is_top_level: bool,
-) -> Usefulness<'tcx, 'p> {
+) -> Usefulness<'tcx> {
let &Matrix(ref rows) = matrix;
debug!("is_useful({:#?}, {:#?})", matrix, v);
@@ -1861,7 +1861,7 @@ crate fn is_useful<'p, 'tcx>(
any_is_useful = true;
unreachable_pats.extend(pats);
}
- NotUseful => unreachable_pats.push(v.head()),
+ NotUseful => unreachable_pats.push(v.head().span),
UsefulWithWitness(_) => {
bug!("Encountered or-pat in `v` during exhaustiveness checking")
}
@@ -2014,7 +2014,7 @@ fn is_useful_specialized<'p, 'tcx>(
witness_preference: WitnessPreference,
hir_id: HirId,
is_under_guard: bool,
-) -> Usefulness<'tcx, 'p> {
+) -> Usefulness<'tcx> {
debug!("is_useful_specialized({:#?}, {:#?}, {:?})", v, ctor, ty);
// We cache the result of `Fields::wildcards` because it is used a lot.
diff --git a/src/librustc_mir_build/hair/pattern/check_match.rs b/src/librustc_mir_build/hair/pattern/check_match.rs
index 6fc447a87f5..6b8110fde69 100644
--- a/src/librustc_mir_build/hair/pattern/check_match.rs
+++ b/src/librustc_mir_build/hair/pattern/check_match.rs
@@ -392,8 +392,8 @@ fn check_arms<'p, 'tcx>(
}
}
Useful(unreachable_subpatterns) => {
- for pat in unreachable_subpatterns {
- unreachable_pattern(cx.tcx, pat.span, id, None);
+ for span in unreachable_subpatterns {
+ unreachable_pattern(cx.tcx, span, id, None);
}
}
UsefulWithWitness(_) => bug!(),
From 3cb31b6699558737b1a4650537f0facdc8cb7852 Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Thu, 2 Jul 2020 21:49:58 +0100
Subject: [PATCH 2/2] Fix #71977
---
src/librustc_mir_build/hair/pattern/_match.rs | 36 ++++++++++++++---
.../exhaustiveness-unreachable-pattern.rs | 28 +++++++++++++
.../exhaustiveness-unreachable-pattern.stderr | 40 ++++++++++++-------
.../ui/or-patterns/search-via-bindings.rs | 1 -
4 files changed, 85 insertions(+), 20 deletions(-)
diff --git a/src/librustc_mir_build/hair/pattern/_match.rs b/src/librustc_mir_build/hair/pattern/_match.rs
index b5a655e4218..372cb783f50 100644
--- a/src/librustc_mir_build/hair/pattern/_match.rs
+++ b/src/librustc_mir_build/hair/pattern/_match.rs
@@ -276,6 +276,7 @@ use self::Usefulness::*;
use self::WitnessPreference::*;
use rustc_data_structures::captures::Captures;
+use rustc_data_structures::fx::FxHashSet;
use rustc_index::vec::Idx;
use super::{compare_const_vals, PatternFoldable, PatternFolder};
@@ -1852,16 +1853,35 @@ crate fn is_useful<'p, 'tcx>(
// We need to push the already-seen patterns into the matrix in order to detect redundant
// branches like `Some(_) | Some(0)`. We also keep track of the unreachable subpatterns.
let mut matrix = matrix.clone();
- let mut unreachable_pats = Vec::new();
+ // `Vec` of all the unreachable branches of the current or-pattern.
+ let mut unreachable_branches = Vec::new();
+ // Subpatterns that are unreachable from all branches. E.g. in the following case, the last
+ // `true` is unreachable only from one branch, so it is overall reachable.
+ // ```
+ // match (true, true) {
+ // (true, true) => {}
+ // (false | true, false | true) => {}
+ // }
+ // ```
+ let mut unreachable_subpats = FxHashSet::default();
+ // Whether any branch at all is useful.
let mut any_is_useful = false;
+
for v in vs {
let res = is_useful(cx, &matrix, &v, witness_preference, hir_id, is_under_guard, false);
match res {
Useful(pats) => {
- any_is_useful = true;
- unreachable_pats.extend(pats);
+ if !any_is_useful {
+ any_is_useful = true;
+ // Initialize with the first set of unreachable subpatterns encountered.
+ unreachable_subpats = pats.into_iter().collect();
+ } else {
+ // Keep the patterns unreachable from both this and previous branches.
+ unreachable_subpats =
+ pats.into_iter().filter(|p| unreachable_subpats.contains(p)).collect();
+ }
}
- NotUseful => unreachable_pats.push(v.head().span),
+ NotUseful => unreachable_branches.push(v.head().span),
UsefulWithWitness(_) => {
bug!("Encountered or-pat in `v` during exhaustiveness checking")
}
@@ -1871,7 +1891,13 @@ crate fn is_useful<'p, 'tcx>(
matrix.push(v);
}
}
- return if any_is_useful { Useful(unreachable_pats) } else { NotUseful };
+ if any_is_useful {
+ // Collect all the unreachable patterns.
+ unreachable_branches.extend(unreachable_subpats);
+ return Useful(unreachable_branches);
+ } else {
+ return NotUseful;
+ }
}
// FIXME(Nadrieril): Hack to work around type normalization issues (see #72476).
diff --git a/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.rs b/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.rs
index 44bae282d88..a1147cb5cfc 100644
--- a/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.rs
+++ b/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.rs
@@ -29,6 +29,9 @@ fn main() {
(1, 4 | 5) => {} //~ ERROR unreachable pattern
_ => {}
}
+ match (true, true) {
+ (false | true, false | true) => (),
+ }
match (Some(0u8),) {
(None | Some(1 | 2),) => {}
(Some(1),) => {} //~ ERROR unreachable pattern
@@ -67,4 +70,29 @@ fn main() {
| 1) => {}
_ => {}
}
+
+ // A subpattern that is only unreachable in one branch is overall reachable.
+ match (true, true) {
+ (true, true) => {}
+ (false | true, false | true) => {}
+ }
+ match (true, true) {
+ (true, false) => {}
+ (false, true) => {}
+ (false | true, false | true) => {}
+ }
+ // A subpattern that is unreachable in all branches is overall unreachable.
+ match (true, true) {
+ (false, true) => {}
+ (true, true) => {}
+ (false | true, false
+ | true) => {} //~ ERROR unreachable
+ }
+ match (true, true) {
+ (true, false) => {}
+ (true, true) => {}
+ (false
+ | true, //~ ERROR unreachable
+ false | true) => {}
+ }
}
diff --git a/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr b/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr
index bef6f8270bc..d92b545a869 100644
--- a/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr
+++ b/src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr
@@ -53,52 +53,64 @@ LL | (1, 4 | 5) => {}
| ^^^^^^^^^^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:34:9
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:37:9
|
LL | (Some(1),) => {}
| ^^^^^^^^^^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:35:9
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:38:9
|
LL | (None,) => {}
| ^^^^^^^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:40:9
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:43:9
|
LL | ((1..=4,),) => {}
| ^^^^^^^^^^^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:45:14
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:48:14
|
LL | (1 | 1,) => {}
| ^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:52:15
- |
-LL | | 0] => {}
- | ^
-
-error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:50:15
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:53:15
|
LL | | 0
| ^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:60:10
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:55:15
+ |
+LL | | 0] => {}
+ | ^
+
+error: unreachable pattern
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:63:10
|
LL | [1
| ^
error: unreachable pattern
- --> $DIR/exhaustiveness-unreachable-pattern.rs:66:14
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:69:14
|
LL | Some(0
| ^
-error: aborting due to 16 previous errors
+error: unreachable pattern
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:89:15
+ |
+LL | | true) => {}
+ | ^^^^
+
+error: unreachable pattern
+ --> $DIR/exhaustiveness-unreachable-pattern.rs:95:15
+ |
+LL | | true,
+ | ^^^^
+
+error: aborting due to 18 previous errors
diff --git a/src/test/ui/or-patterns/search-via-bindings.rs b/src/test/ui/or-patterns/search-via-bindings.rs
index eb127b881cd..067e617373a 100644
--- a/src/test/ui/or-patterns/search-via-bindings.rs
+++ b/src/test/ui/or-patterns/search-via-bindings.rs
@@ -3,7 +3,6 @@
// run-pass
#![feature(or_patterns)]
-#![allow(unreachable_patterns)] // FIXME(or-patterns) this shouldn't trigger
fn search(target: (bool, bool, bool)) -> u32 {
let x = ((false, true), (false, true), (false, true));