Consistently warn unreachable subpatterns

Author: Nadrieril

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

@@ -391,10 +391,26 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
         arms: &[MatchArm<'p, 'tcx>],
         scrut_ty: Ty<'tcx>,
     ) -> Result<UsefulnessReport<'p, 'tcx>, ErrorGuaranteed> {
-        rustc_pattern_analysis::analyze_match(&cx, &arms, scrut_ty).map_err(|err| {
-            self.error = Err(err);
-            err
-        })
+        let report =
+            rustc_pattern_analysis::analyze_match(&cx, &arms, scrut_ty).map_err(|err| {
+                self.error = Err(err);
+                err
+            })?;
+
+        // Warn unreachable subpatterns.
+        for (arm, is_useful) in report.arm_usefulness.iter() {
+            if let Usefulness::Useful(redundant_subpats) = is_useful
+                && !redundant_subpats.is_empty()
+            {
+                let mut redundant_subpats = redundant_subpats.clone();
+                // Emit lints in the order in which they occur in the file.
+                redundant_subpats.sort_unstable_by_key(|pat| pat.data().unwrap().span);
+                for pat in redundant_subpats {
+                    report_unreachable_pattern(cx, arm.arm_data, pat.data().unwrap().span, None)
+                }
+            }
+        }
+        Ok(report)
     }
 
     #[instrument(level = "trace", skip(self))]
@@ -567,7 +583,6 @@ impl<'p, 'tcx> MatchVisitor<'p, 'tcx> {
     ) -> Result<RefutableFlag, ErrorGuaranteed> {
         let (cx, report) = self.analyze_binding(pat, Refutable, scrut)?;
         // Report if the pattern is unreachable, which can only occur when the type is uninhabited.
-        // This also reports unreachable sub-patterns.
         report_arm_reachability(&cx, &report);
         // If the list of witnesses is empty, the match is exhaustive, i.e. the `if let` pattern is
         // irrefutable.
@@ -837,39 +852,30 @@ fn report_irrefutable_let_patterns(
     }
 }
 
+/// Report unreachable arms, if any.
+fn report_unreachable_pattern<'p, 'tcx>(
+    cx: &MatchCheckCtxt<'p, 'tcx>,
+    hir_id: HirId,
+    span: Span,
+    catchall: Option<Span>,
+) {
+    cx.tcx.emit_spanned_lint(
+        UNREACHABLE_PATTERNS,
+        hir_id,
+        span,
+        UnreachablePattern { span: if catchall.is_some() { Some(span) } else { None }, catchall },
+    );
+}
+
 /// Report unreachable arms, if any.
 fn report_arm_reachability<'p, 'tcx>(
     cx: &MatchCheckCtxt<'p, 'tcx>,
     report: &UsefulnessReport<'p, 'tcx>,
 ) {
-    let report_unreachable_pattern = |span, hir_id, catchall: Option<Span>| {
-        cx.tcx.emit_spanned_lint(
-            UNREACHABLE_PATTERNS,
-            hir_id,
-            span,
-            UnreachablePattern {
-                span: if catchall.is_some() { Some(span) } else { None },
-                catchall,
-            },
-        );
-    };
-
     let mut catchall = None;
     for (arm, is_useful) in report.arm_usefulness.iter() {
-        match is_useful {
-            Usefulness::Redundant => {
-                report_unreachable_pattern(arm.pat.data().unwrap().span, arm.arm_data, catchall)
-            }
-            Usefulness::Useful(redundant_subpats) if redundant_subpats.is_empty() => {}
-            // The arm is reachable, but contains redundant subpatterns (from or-patterns).
-            Usefulness::Useful(redundant_subpats) => {
-                let mut redundant_subpats = redundant_subpats.clone();
-                // Emit lints in the order in which they occur in the file.
-                redundant_subpats.sort_unstable_by_key(|pat| pat.data().unwrap().span);
-                for pat in redundant_subpats {
-                    report_unreachable_pattern(pat.data().unwrap().span, arm.arm_data, None);
-                }
-            }
+        if matches!(is_useful, Usefulness::Redundant) {
+            report_unreachable_pattern(cx, arm.arm_data, arm.pat.data().unwrap().span, catchall)
         }
         if !arm.has_guard && catchall.is_none() && pat_is_catchall(arm.pat) {
             catchall = Some(arm.pat.data().unwrap().span);

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

@@ -162,12 +162,14 @@ fn main() {
 }
 
 fn unreachable_in_param((_ | (_, _)): (bool, bool)) {}
+//~^ ERROR unreachable
 
 fn unreachable_in_binding() {
     let bool_pair = (true, true);
     let bool_option = Some(true);
 
     let (_ | (_, _)) = bool_pair;
+    //~^ ERROR unreachable
     for (_ | (_, _)) in [bool_pair] {}
     //~^ ERROR unreachable
 

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

@@ -184,29 +184,41 @@ error: unreachable pattern
 LL |             | (y, x) => {}
    |               ^^^^^^
 
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:164:30
+   |
+LL | fn unreachable_in_param((_ | (_, _)): (bool, bool)) {}
+   |                              ^^^^^^
+
 error: unreachable pattern
   --> $DIR/exhaustiveness-unreachable-pattern.rs:171:14
    |
+LL |     let (_ | (_, _)) = bool_pair;
+   |              ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:173:14
+   |
 LL |     for (_ | (_, _)) in [bool_pair] {}
    |              ^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:174:20
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:176:20
    |
 LL |     let (Some(_) | Some(true)) = bool_option else { return };
    |                    ^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:176:22
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:178:22
    |
 LL |     if let Some(_) | Some(true) = bool_option {}
    |                      ^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/exhaustiveness-unreachable-pattern.rs:178:25
+  --> $DIR/exhaustiveness-unreachable-pattern.rs:180:25
    |
 LL |     while let Some(_) | Some(true) = bool_option {}
    |                         ^^^^^^^^^^
 
-error: aborting due to 33 previous errors
+error: aborting due to 35 previous errors
 

tests/ui/rfcs/rfc-0000-never_patterns/unreachable.exh_pats.stderr

@@ -11,22 +11,34 @@ LL | #![deny(unreachable_patterns)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/unreachable.rs:21:12
+  --> $DIR/unreachable.rs:20:19
+   |
+LL |     let (Ok(_x) | Err(!)) = res_void;
+   |                   ^^^^^^
+
+error: unreachable pattern
+  --> $DIR/unreachable.rs:22:12
    |
 LL |     if let Err(!) = res_void {}
    |            ^^^^^^
 
 error: unreachable pattern
-  --> $DIR/unreachable.rs:23:24
+  --> $DIR/unreachable.rs:24:24
    |
 LL |     if let (Ok(true) | Err(!)) = res_void {}
    |                        ^^^^^^
 
 error: unreachable pattern
-  --> $DIR/unreachable.rs:25:23
+  --> $DIR/unreachable.rs:26:23
    |
 LL |     for (Ok(mut _x) | Err(!)) in [res_void] {}
    |                       ^^^^^^
 
-error: aborting due to 4 previous errors
+error: unreachable pattern
+  --> $DIR/unreachable.rs:30:18
+   |
+LL | fn foo((Ok(_x) | Err(!)): Result<bool, Void>) {}
+   |                  ^^^^^^
+
+error: aborting due to 6 previous errors
 

tests/ui/rfcs/rfc-0000-never_patterns/unreachable.rs

@@ -18,6 +18,7 @@ fn main() {
         //[exh_pats]~^ ERROR unreachable
     }
     let (Ok(_x) | Err(!)) = res_void;
+    //[exh_pats]~^ ERROR unreachable
     if let Err(!) = res_void {}
     //[exh_pats]~^ ERROR unreachable
     if let (Ok(true) | Err(!)) = res_void {}
@@ -27,3 +28,4 @@ fn main() {
 }
 
 fn foo((Ok(_x) | Err(!)): Result<bool, Void>) {}
+//[exh_pats]~^ ERROR unreachable

tests/ui/unsafe/union_destructure.rs

@@ -1,4 +1,5 @@
 // run-pass
+#![allow(unreachable_patterns)]
 
 #[derive(Copy, Clone)]
 #[allow(dead_code)]