Identify unreachable subpatterns more reliably

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -1,6 +1,6 @@
-use super::usefulness::Usefulness::*;
 use super::usefulness::{
-    compute_match_usefulness, expand_pattern, MatchArm, MatchCheckCtxt, UsefulnessReport,
+    compute_match_usefulness, expand_pattern, MatchArm, MatchCheckCtxt, Reachability,
+    UsefulnessReport,
 };
 use super::{PatCtxt, PatKind, PatternError};
 
@@ -398,10 +398,11 @@ fn report_arm_reachability<'p, 'tcx>(
     report: &UsefulnessReport<'p, 'tcx>,
     source: hir::MatchSource,
 ) {
+    use Reachability::*;
     let mut catchall = None;
     for (arm_index, (arm, is_useful)) in report.arm_usefulness.iter().enumerate() {
         match is_useful {
-            NotUseful => {
+            Unreachable => {
                 match source {
                     hir::MatchSource::WhileDesugar => bug!(),
 
@@ -430,17 +431,16 @@ fn report_arm_reachability<'p, 'tcx>(
                     hir::MatchSource::AwaitDesugar | hir::MatchSource::TryDesugar => {}
                 }
             }
-            Useful(unreachables) if unreachables.is_empty() => {}
+            Reachable(unreachables) if unreachables.is_empty() => {}
             // The arm is reachable, but contains unreachable subpatterns (from or-patterns).
-            Useful(unreachables) => {
-                let mut unreachables: Vec<_> = unreachables.iter().collect();
+            Reachable(unreachables) => {
+                let mut unreachables = unreachables.clone();
                 // Emit lints in the order in which they occur in the file.
                 unreachables.sort_unstable();
                 for span in unreachables {
                     unreachable_pattern(cx.tcx, span, arm.hir_id, None);
                 }
             }
-            UsefulWithWitness(_) => bug!(),
         }
         if !arm.has_guard && catchall.is_none() && pat_is_catchall(arm.pat) {
             catchall = Some(arm.pat.span);

compiler/rustc_mir_build/src/thir/pattern/deconstruct_pat.rs

@@ -724,8 +724,6 @@ impl<'tcx> Constructor<'tcx> {
     where
         'tcx: 'a,
     {
-        debug!("Constructor::split({:#?})", self);
-
         match self {
             Wildcard => {
                 let mut split_wildcard = SplitWildcard::new(pcx);

src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.rs

@@ -48,6 +48,25 @@ fn main() {
         (1 | 1,) => {} //~ ERROR unreachable
         _ => {}
     }
+    match 0 {
+        (0 | 1) | 1 => {} //~ ERROR unreachable
+        _ => {}
+    }
+    match 0 {
+        // We get two errors because recursive or-pattern expansion means we don't notice the two
+        // errors span a whole pattern. This could be better but doesn't matter much
+        0 | (0 | 0) => {}
+        //~^ ERROR unreachable
+        //~| ERROR unreachable
+        _ => {}
+    }
+    match None {
+        // There is only one error that correctly points to the whole subpattern
+        Some(0) |
+            Some( //~ ERROR unreachable
+                0 | 0) => {}
+        _ => {}
+    }
     match [0; 2] {
         [0
             | 0 //~ ERROR unreachable
@@ -84,8 +103,8 @@ fn main() {
     }
     macro_rules! t_or_f {
         () => {
-            (true // FIXME: should be unreachable
-                        | false)
+            (true //~ ERROR unreachable
+            | false)
         };
     }
     match (true, None) {

src/test/ui/or-patterns/exhaustiveness-unreachable-pattern.stderr

@@ -77,58 +77,94 @@ LL |         (1 | 1,) => {}
    |              ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:53:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:52:19
+   |
+LL |         (0 | 1) | 1 => {}
+   |                   ^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:58:14
+   |
+LL |         0 | (0 | 0) => {}
+   |              ^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:58:18
+   |
+LL |         0 | (0 | 0) => {}
+   |                  ^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:66:13
+   |
+LL | /             Some(
+LL | |                 0 | 0) => {}
+   | |______________________^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:72:15
    |
 LL |             | 0
    |               ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:55:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:74:15
    |
 LL |             | 0] => {}
    |               ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:63:10
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:82:10
    |
 LL |         [1
    |          ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:75:10
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:94:10
    |
 LL |         [true
    |          ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:82:36
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:101:36
    |
 LL |         (true | false, None | Some(true
    |                                    ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:98:14
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:106:14
+   |
+LL |             (true
+   |              ^^^^
+...
+LL |         (true | false, None | Some(t_or_f!())) => {}
+   |                                    --------- in this macro invocation
+   |
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:117:14
    |
 LL |         Some(0
    |              ^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:117:19
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:136:19
    |
 LL |                 | false) => {}
    |                   ^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:125:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:144:15
    |
 LL |             | true) => {}
    |               ^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:131:15
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:150:15
    |
 LL |             | true,
    |               ^^^^
 
-error: aborting due to 21 previous errors
+error: aborting due to 26 previous errors
 

src/test/ui/pattern/usefulness/issue-80501-or-pat-and-macro.rs

@@ -0,0 +1,27 @@
+// check-pass
+#![deny(unreachable_patterns)]
+pub enum TypeCtor {
+    Slice,
+    Array,
+}
+
+pub struct ApplicationTy(TypeCtor);
+
+macro_rules! ty_app {
+    ($ctor:pat) => {
+        ApplicationTy($ctor)
+    };
+}
+
+fn _foo(ty: ApplicationTy) {
+    match ty {
+        ty_app!(TypeCtor::Array) | ty_app!(TypeCtor::Slice) => {}
+    }
+
+    // same as above, with the macro expanded
+    match ty {
+        ApplicationTy(TypeCtor::Array) | ApplicationTy(TypeCtor::Slice) => {}
+    }
+}
+
+fn main() {}