Auto merge of rust-lang#116042 - Nadrieril:linear-pass-take-2, r=<try>

[Experiment] Rewrite exhaustiveness in one pass

Arm reachability checking does a quadratic amount of work: for each arm we check if it is reachable given the arms above it. This feels wasteful since we often end up re-exploring the same cases when we check for exhaustiveness.

This PR is an attempt to check reachability at the same time as exhaustiveness. This opens the door to a bunch of code simplifications I'm very excited about. The main question is whether I can get actual performance gains out of this.

I had started the experiment in rust-lang#111720 but I can't reopen it.

r? `@ghost`

tests/ui/closures/2229_closure_analysis/match/non-exhaustive-match.stderr

@@ -5,10 +5,10 @@ LL |     let _b = || { match l1 { L1::A => () } };
    |                         ^^ pattern `L1::B` not covered
    |
 note: `L1` defined here
-  --> $DIR/non-exhaustive-match.rs:12:14
+  --> $DIR/non-exhaustive-match.rs:12:6
    |
 LL | enum L1 { A, B }
-   |      --      ^ not covered
+   |      ^^      - not covered
    = note: the matched value is of type `L1`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |

tests/ui/error-codes/E0004.stderr

@@ -5,12 +5,12 @@ LL |     match x {
    |           ^ pattern `Terminator::HastaLaVistaBaby` not covered
    |
 note: `Terminator` defined here
-  --> $DIR/E0004.rs:2:5
+  --> $DIR/E0004.rs:1:6
    |
 LL | enum Terminator {
-   |      ----------
+   |      ^^^^^^^^^^
 LL |     HastaLaVistaBaby,
-   |     ^^^^^^^^^^^^^^^^ not covered
+   |     ---------------- not covered
    = note: the matched value is of type `Terminator`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |

tests/ui/feature-gates/feature-gate-non_exhaustive_omitted_patterns_lint.stderr

@@ -134,13 +134,13 @@ LL |     match Foo::A {
    |           ^^^^^^ pattern `Foo::C` not covered
    |
 note: `Foo` defined here
-  --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:16:9
+  --> $DIR/feature-gate-non_exhaustive_omitted_patterns_lint.rs:13:10
    |
 LL |     enum Foo {
-   |          ---
+   |          ^^^
 ...
 LL |         C,
-   |         ^ not covered
+   |         - not covered
    = note: the matched value is of type `Foo`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |

tests/ui/match/match_non_exhaustive.stderr

@@ -5,10 +5,10 @@ LL |     match l { L::A => () };
    |           ^ pattern `L::B` not covered
    |
 note: `L` defined here
-  --> $DIR/match_non_exhaustive.rs:10:13
+  --> $DIR/match_non_exhaustive.rs:10:6
    |
 LL | enum L { A, B }
-   |      -      ^ not covered
+   |      ^      - not covered
    = note: the matched value is of type `L`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |

tests/ui/or-patterns/exhaustiveness-pass.rs

@@ -35,6 +35,14 @@ fn main() {
         ((0, 0) | (1, 0),) => {}
         _ => {}
     }
+    match ((0, 0),) {
+        ((x, y) | (y, x),) if x == 0 => {}
+        _ => {}
+    }
+    match 0 {
+        0 | 0 if 0 == 0 => {}
+        _ => {}
+    }
 
     // This one caused ICE https://github.com/rust-lang/rust/issues/117378
     match (0u8, 0) {

tests/ui/or-patterns/exhaustiveness-unreachable-pattern.rs

@@ -1,6 +1,7 @@
 #![deny(unreachable_patterns)]
 
 // We wrap patterns in a tuple because top-level or-patterns were special-cased.
+#[rustfmt::skip]
 fn main() {
     match (0u8,) {
         (1 | 2,) => {}
@@ -73,6 +74,11 @@ fn main() {
             | 0] => {} //~ ERROR unreachable
         _ => {}
     }
+    match (true, 0) {
+        (true, 0 | 0) => {} //~ ERROR unreachable
+        (_, 0 | 0) => {} //~ ERROR unreachable
+        _ => {}
+    }
     match &[][..] {
         [0] => {}
         [0, _] => {}
@@ -149,4 +155,8 @@ fn main() {
             | true, //~ ERROR unreachable
             false | true) => {}
     }
+    match (true, true) {
+        (x, y)
+            | (y, x) => {} //~ ERROR unreachable
+    }
 }

tests/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr

@@ -1,5 +1,5 @@
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:7:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:8:9
    |
 LL |         (1,) => {}
    |         ^^^^
@@ -11,128 +11,140 @@ LL | #![deny(unreachable_patterns)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:12:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:13:9
    |
 LL |         (2,) => {}
    |         ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:18:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:19:9
    |
 LL |         (1 | 2,) => {}
    |         ^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:23:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:24:9
    |
 LL |         (1, 3) => {}
    |         ^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:24:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:25:9
    |
 LL |         (1, 4) => {}
    |         ^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:25:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:26:9
    |
 LL |         (2, 4) => {}
    |         ^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:26:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:27:9
    |
 LL |         (2 | 1, 4) => {}
    |         ^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:28:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:29:9
    |
 LL |         (1, 4 | 5) => {}
    |         ^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:36:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:37:9
    |
 LL |         (Some(1),) => {}
    |         ^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:37:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:38:9
    |
 LL |         (None,) => {}
    |         ^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:42:9
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:43:9
    |
 LL |         ((1..=4,),) => {}
    |         ^^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:47:14
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:48:14
    |
 LL |         (1 | 1,) => {}
    |              ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:51:19
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:52:19
    |
 LL |         (0 | 1) | 1 => {}
    |                   ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:57:14
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:58:14
    |
 LL |         0 | (0 | 0) => {}
    |              ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:57:18
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:58:18
    |
 LL |         0 | (0 | 0) => {}
    |                  ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:65:13
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:66:13
    |
 LL | /             Some(
 LL | |                 0 | 0) => {}
    | |______________________^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:71:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:72:15
    |
 LL |             | 0
    |               ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:73:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:74:15
    |
 LL |             | 0] => {}
    |               ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:81:10
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:78:20
+   |
+LL |         (true, 0 | 0) => {}
+   |                    ^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:79:17
+   |
+LL |         (_, 0 | 0) => {}
+   |                 ^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:87:10
    |
 LL |         [1
    |          ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:93:10
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:99:10
    |
 LL |         [true
    |          ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:100:36
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:106:36
    |
 LL |         (true | false, None | Some(true
    |                                    ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:105:14
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:111:14
    |
 LL |             (true
    |              ^^^^
@@ -143,28 +155,34 @@ LL |         (true | false, None | Some(t_or_f!())) => {}
    = note: this error originates in the macro `t_or_f` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:116:14
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:122:14
    |
 LL |         Some(0
    |              ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:135:19
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:141:19
    |
 LL |                 | false) => {}
    |                   ^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:143:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:149:15
    |
 LL |             | true) => {}
    |               ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:149:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:155:15
    |
 LL |             | true,
    |               ^^^^
 
-error: aborting due to 26 previous errors
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:160:15
+   |
+LL |             | (y, x) => {}
+   |               ^^^^^^
+
+error: aborting due to 29 previous errors
 

tests/ui/pattern/issue-94866.stderr

@@ -5,10 +5,10 @@ LL |     match Enum::A {
    |           ^^^^^^^ pattern `Enum::B` not covered
    |
 note: `Enum` defined here
-  --> $DIR/issue-94866.rs:7:16
+  --> $DIR/issue-94866.rs:7:6
    |
 LL | enum Enum { A, B }
-   |      ----      ^ not covered
+   |      ^^^^      - not covered
    = note: the matched value is of type `Enum`
 help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |

tests/ui/pattern/usefulness/conflicting_bindings.rs

@@ -0,0 +1,24 @@
+#![feature(if_let_guard, let_chains)]
+
+fn main() {
+    let mut x = Some(String::new());
+    let ref mut y @ ref mut z = x;
+    //~^ ERROR: mutable more than once
+    let Some(ref mut y @ ref mut z) = x else { return };
+    //~^ ERROR: mutable more than once
+    if let Some(ref mut y @ ref mut z) = x {}
+    //~^ ERROR: mutable more than once
+    if let Some(ref mut y @ ref mut z) = x && true {}
+    //~^ ERROR: mutable more than once
+    while let Some(ref mut y @ ref mut z) = x {}
+    //~^ ERROR: mutable more than once
+    while let Some(ref mut y @ ref mut z) = x && true {}
+    //~^ ERROR: mutable more than once
+    match x {
+        ref mut y @ ref mut z => {} //~ ERROR: mutable more than once
+    }
+    match () {
+        () if let Some(ref mut y @ ref mut z) = x => {} //~ ERROR: mutable more than once
+        _ => {}
+    }
+}