Prevent spurious unreachable pattern lints

oli-obk · oli-obk · commit b8ed2f811bfa · 2023-09-28T15:55:04.000Z
Means you'll get more `non-exhaustive` patterns
diff --git a/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs b/compiler/rustc_mir_build/src/thir/pattern/const_to_pat.rs
@@ -180,23 +180,26 @@ impl<'tcx> ConstToPat<'tcx> {
 
             if let Some(non_sm_ty) = structural {
                 if !self.type_has_partial_eq_impl(cv.ty()) {
-                    if let ty::Adt(def, ..) = non_sm_ty.kind() {
+                    let e = if let ty::Adt(def, ..) = non_sm_ty.kind() {
                         if def.is_union() {
                             let err = UnionPattern { span: self.span };
-                            self.tcx().sess.emit_err(err);
+                            self.tcx().sess.emit_err(err)
                         } else {
                             // fatal avoids ICE from resolution of nonexistent method (rare case).
                             self.tcx()
                                 .sess
-                                .emit_fatal(TypeNotStructural { span: self.span, non_sm_ty });
+                                .emit_fatal(TypeNotStructural { span: self.span, non_sm_ty })
                         }
                     } else {
                         let err = InvalidPattern { span: self.span, non_sm_ty };
-                        self.tcx().sess.emit_err(err);
-                    }
+                        self.tcx().sess.emit_err(err)
+                    };
                     // All branches above emitted an error. Don't print any more lints.
                     // The pattern we return is irrelevant since we errored.
-                    return Box::new(Pat { span: self.span, ty: cv.ty(), kind: PatKind::Wild });
+                    let kind = PatKind::Constant {
+                        value: mir::Const::Ty(ty::Const::new_error(self.tcx(), e, cv.ty())),
+                    };
+                    return Box::new(Pat { span: self.span, ty: cv.ty(), kind });
                 } else if !self.saw_const_match_lint.get() {
                     if let Some(mir_structural_match_violation) = mir_structural_match_violation {
                         match non_sm_ty.kind() {
@@ -346,17 +349,17 @@ impl<'tcx> ConstToPat<'tcx> {
             }
             ty::FnDef(..) => {
                 self.saw_const_match_error.set(true);
-                tcx.sess.emit_err(InvalidPattern { span, non_sm_ty: ty });
-                // We errored, so the pattern we generate is irrelevant.
-                PatKind::Wild
+                let e = tcx.sess.emit_err(InvalidPattern { span, non_sm_ty: ty });
+                // We errored. Signal that in the pattern, so that follow up errors can be silenced.
+                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)) }
             }
             ty::Adt(adt_def, _) if !self.type_marked_structural(ty) => {
                 debug!("adt_def {:?} has !type_marked_structural for cv.ty: {:?}", adt_def, ty,);
                 self.saw_const_match_error.set(true);
                 let err = TypeNotStructural { span, non_sm_ty: ty };
-                tcx.sess.emit_err(err);
-                // We errored, so the pattern we generate is irrelevant.
-                PatKind::Wild
+                let e = tcx.sess.emit_err(err);
+                // We errored. Signal that in the pattern, so that follow up errors can be silenced.
+                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)) }
             }
             ty::Adt(adt_def, args) if adt_def.is_enum() => {
                 let (&variant_index, fields) = cv.unwrap_branch().split_first().unwrap();
@@ -427,14 +430,20 @@ impl<'tcx> ConstToPat<'tcx> {
                         }
                         return Err(FallbackToOpaqueConst);
                     } else {
-                        if !self.saw_const_match_error.get() {
+                        if self.saw_const_match_error.get() {
+                            // We already errored. Signal that in the pattern, so that follow up errors can be silenced.
+                            PatKind::Constant {
+                                value: mir::Const::Ty(ty::Const::new_misc_error(tcx, ty)),
+                            }
+                        } else {
                             self.saw_const_match_error.set(true);
                             let err = TypeNotStructural { span, non_sm_ty: *pointee_ty };
-                            tcx.sess.emit_err(err);
+                            let e = tcx.sess.emit_err(err);
+                            // We errored. Signal that in the pattern, so that follow up errors can be silenced.
+                            PatKind::Constant {
+                                value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)),
+                            }
                         }
-                        tcx.sess.delay_span_bug(span, "`saw_const_match_error` set but no error?");
-                        // We errored, so the pattern we generate is irrelevant.
-                        PatKind::Wild
                     }
                 }
                 // All other references are converted into deref patterns and then recursively
@@ -443,11 +452,11 @@ impl<'tcx> ConstToPat<'tcx> {
                 _ => {
                     if !pointee_ty.is_sized(tcx, param_env) && !pointee_ty.is_slice() {
                         let err = UnsizedPattern { span, non_sm_ty: *pointee_ty };
-                        tcx.sess.emit_err(err);
-
-                        // FIXME: introduce PatKind::Error to silence follow up diagnostics due to unreachable patterns.
-                        // We errored, so the pattern we generate is irrelevant.
-                        PatKind::Wild
+                        let e = tcx.sess.emit_err(err);
+                        // We errored. Signal that in the pattern, so that follow up errors can be silenced.
+                        PatKind::Constant {
+                            value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)),
+                        }
                     } else {
                         let old = self.behind_reference.replace(true);
                         // `b"foo"` produces a `&[u8; 3]`, but you can't use constants of array type when
@@ -476,9 +485,9 @@ impl<'tcx> ConstToPat<'tcx> {
             _ => {
                 self.saw_const_match_error.set(true);
                 let err = InvalidPattern { span, non_sm_ty: ty };
-                tcx.sess.emit_err(err);
-                // We errored, so the pattern we generate is irrelevant.
-                PatKind::Wild
+                let e = tcx.sess.emit_err(err);
+                // We errored. Signal that in the pattern, so that follow up errors can be silenced.
+                PatKind::Constant { value: mir::Const::Ty(ty::Const::new_error(tcx, e, ty)) }
             }
         };
 
diff --git a/tests/ui/const-generics/generic_const_exprs/typeid-equality-by-subtyping.stderr b/tests/ui/const-generics/generic_const_exprs/typeid-equality-by-subtyping.stderr
@@ -7,5 +7,17 @@ LL |         WHAT_A_TYPE => 0,
    = note: the traits must be derived, manual `impl`s are not sufficient
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
-error: aborting due to previous error
+error[E0015]: cannot match on `TypeId` in constant functions
+  --> $DIR/typeid-equality-by-subtyping.rs:18:9
+   |
+LL |         WHAT_A_TYPE => 0,
+   |         ^^^^^^^^^^^
+   |
+   = note: `TypeId` cannot be compared in compile-time, and therefore cannot be used in `match`es
+note: impl defined here, but it is not `const`
+  --> $SRC_DIR/core/src/any.rs:LL:COL
+   = note: calls in constant functions are limited to constant functions, tuple structs and tuple variants
+
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0015`.
diff --git a/tests/ui/consts/const_in_pattern/issue-78057.rs b/tests/ui/consts/const_in_pattern/issue-78057.rs
@@ -12,6 +12,5 @@ fn main() {
         FOO => {},
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
         _ => {}
-        //~^ ERROR unreachable pattern
     }
 }
diff --git a/tests/ui/consts/const_in_pattern/issue-78057.stderr b/tests/ui/consts/const_in_pattern/issue-78057.stderr
@@ -7,20 +7,5 @@ LL |         FOO => {},
    = note: the traits must be derived, manual `impl`s are not sufficient
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
-error: unreachable pattern
-  --> $DIR/issue-78057.rs:14:9
-   |
-LL |         FOO => {},
-   |         --- matches any value
-LL |
-LL |         _ => {}
-   |         ^ unreachable pattern
-   |
-note: the lint level is defined here
-  --> $DIR/issue-78057.rs:1:9
-   |
-LL | #![deny(unreachable_patterns)]
-   |         ^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
diff --git a/tests/ui/consts/match_ice.rs b/tests/ui/consts/match_ice.rs
@@ -7,7 +7,7 @@ struct T;
 
 fn main() {
     const C: &S = &S;
-    match C {
+    match C { //~ ERROR: non-exhaustive patterns: `&_` not covered
         C => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
     }
diff --git a/tests/ui/consts/match_ice.stderr b/tests/ui/consts/match_ice.stderr
@@ -7,5 +7,24 @@ LL |         C => {}
    = note: the traits must be derived, manual `impl`s are not sufficient
    = note: see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
 
-error: aborting due to previous error
+error[E0004]: non-exhaustive patterns: `&_` not covered
+  --> $DIR/match_ice.rs:10:11
+   |
+LL |     match C {
+   |           ^ pattern `&_` not covered
+   |
+note: `S` defined here
+  --> $DIR/match_ice.rs:3:8
+   |
+LL | struct S;
+   |        ^
+   = note: the matched value is of type `&S`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL ~         C => {},
+LL +         &_ => todo!()
+   |
+
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0004`.
diff --git a/tests/ui/pattern/issue-72565.rs b/tests/ui/pattern/issue-72565.rs
@@ -2,7 +2,7 @@ const F: &'static dyn PartialEq<u32> = &7u32;
 
 fn main() {
     let a: &dyn PartialEq<u32> = &7u32;
-    match a {
+    match a { //~ ERROR: non-exhaustive patterns: `&_` not covered
         F => panic!(), //~ ERROR: `dyn PartialEq<u32>` cannot be used in patterns
     }
 }
diff --git a/tests/ui/pattern/issue-72565.stderr b/tests/ui/pattern/issue-72565.stderr
@@ -4,5 +4,18 @@ error: `dyn PartialEq<u32>` cannot be used in patterns
 LL |         F => panic!(),
    |         ^
 
-error: aborting due to previous error
+error[E0004]: non-exhaustive patterns: `&_` not covered
+  --> $DIR/issue-72565.rs:5:11
+   |
+LL |     match a {
+   |           ^ pattern `&_` not covered
+   |
+   = note: the matched value is of type `&dyn PartialEq<u32>`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL |         F => panic!(), &_ => todo!(),
+   |                      +++++++++++++++
+
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0004`.
diff --git a/tests/ui/pattern/non-structural-match-types.rs b/tests/ui/pattern/non-structural-match-types.rs
@@ -5,10 +5,10 @@
 #![feature(inline_const_pat)]
 
 fn main() {
-    match loop {} {
+    match loop {} { //~ ERROR: non-exhaustive patterns: `_` not covered
         const { || {} } => {}, //~ ERROR cannot be used in patterns
     }
-    match loop {} {
+    match loop {} { //~ ERROR: non-exhaustive patterns: `_` not covered
         const { async {} } => {}, //~ ERROR cannot be used in patterns
     }
 }
diff --git a/tests/ui/pattern/non-structural-match-types.stderr b/tests/ui/pattern/non-structural-match-types.stderr
@@ -10,5 +10,30 @@ error: `{async block@$DIR/non-structural-match-types.rs:12:17: 12:25}` cannot be
 LL |         const { async {} } => {},
    |         ^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error[E0004]: non-exhaustive patterns: `_` not covered
+  --> $DIR/non-structural-match-types.rs:8:11
+   |
+LL |     match loop {} {
+   |           ^^^^^^^ pattern `_` not covered
+   |
+   = note: the matched value is of type `{closure@$DIR/non-structural-match-types.rs:9:17: 9:19}`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL |         const { || {} } => {}, _ => todo!(),
+   |                              ++++++++++++++
+
+error[E0004]: non-exhaustive patterns: `_` not covered
+  --> $DIR/non-structural-match-types.rs:11:11
+   |
+LL |     match loop {} {
+   |           ^^^^^^^ pattern `_` not covered
+   |
+   = note: the matched value is of type `{async block@$DIR/non-structural-match-types.rs:12:17: 12:25}`
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
+   |
+LL |         const { async {} } => {}, _ => todo!(),
+   |                                 ++++++++++++++
+
+error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0004`.
diff --git a/tests/ui/pattern/usefulness/consts-opaque.rs b/tests/ui/pattern/usefulness/consts-opaque.rs
@@ -30,15 +30,13 @@ fn main() {
     match FOO {
         FOO => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        _ => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
+        _ => {}
     }
 
     match FOO_REF {
         FOO_REF => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        Foo(_) => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
+        Foo(_) => {}
     }
 
     // This used to cause an ICE (https://github.com/rust-lang/rust/issues/78071)
@@ -51,56 +49,47 @@ fn main() {
 
     match BAR {
         Bar => {}
-        BAR => {} // should not be emitting unreachable warning
+        BAR => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        //~| ERROR unreachable pattern
         _ => {}
         //~^ ERROR unreachable pattern
     }
 
     match BAR {
         BAR => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        Bar => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
+        Bar => {}
         _ => {}
         //~^ ERROR unreachable pattern
     }
 
     match BAR {
         BAR => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        BAR => {} // should not be emitting unreachable warning
+        BAR => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        //~| ERROR unreachable pattern
-        _ => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
+        _ => {}
     }
 
     match BAZ {
         BAZ => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        Baz::Baz1 => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
+        Baz::Baz1 => {}
         _ => {}
-        //~^ ERROR unreachable pattern
     }
 
     match BAZ {
         Baz::Baz1 => {}
         BAZ => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
         _ => {}
-        //~^ ERROR unreachable pattern
     }
 
     match BAZ {
         BAZ => {}
         //~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
-        Baz::Baz2 => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
-        _ => {} // should not be emitting unreachable warning
-        //~^ ERROR unreachable pattern
+        Baz::Baz2 => {}
+        _ => {}
     }
 
     type Quux = fn(usize, usize) -> usize;
diff --git a/tests/ui/pattern/usefulness/consts-opaque.stderr b/tests/ui/pattern/usefulness/consts-opaque.stderr
diff --git a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/match-nonempty-array-forbidden-without-eq.rs b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/match-nonempty-array-forbidden-without-eq.rs
diff --git a/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/match-nonempty-array-forbidden-without-eq.stderr b/tests/ui/rfcs/rfc-1445-restrict-constants-in-patterns/match-nonempty-array-forbidden-without-eq.stderr

Original file line number	Diff line number	Diff line change
`@@ -12,6 +12,5 @@ fn main() {`
`12`	`12`	`FOO => {},`
`13`	`13`	//~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
`14`	`14`	`_ => {}`
`15`		`- //~^ ERROR unreachable pattern`
`16`	`15`	`}`
`17`	`16`	`}`
Original file line number	Diff line number	Diff line change
`@@ -7,7 +7,7 @@ struct T;`
`7`	`7`
`8`	`8`	`fn main() {`
`9`	`9`	`const C: &S = &S;`
`10`		`- match C {`
	`10`	+ match C { //~ ERROR: non-exhaustive patterns: `&_` not covered
`11`	`11`	`C => {}`
`12`	`12`	//~^ ERROR must be annotated with `#[derive(PartialEq, Eq)]`
`13`	`13`	`}`
Original file line number	Diff line number	Diff line change
`@@ -2,7 +2,7 @@ const F: &'static dyn PartialEq<u32> = &7u32;`
`2`	`2`
`3`	`3`	`fn main() {`
`4`	`4`	`let a: &dyn PartialEq<u32> = &7u32;`
`5`		`- match a {`
	`5`	+ match a { //~ ERROR: non-exhaustive patterns: `&_` not covered
`6`	`6`	F => panic!(), //~ ERROR: `dyn PartialEq<u32>` cannot be used in patterns
`7`	`7`	`}`
`8`	`8`	`}`
Original file line number	Diff line number	Diff line change
`@@ -5,10 +5,10 @@`
`5`	`5`	`#![feature(inline_const_pat)]`
`6`	`6`
`7`	`7`	`fn main() {`
`8`		`- match loop {} {`
	`8`	+ match loop {} { //~ ERROR: non-exhaustive patterns: `_` not covered
`9`	`9`	`const { \|\| {} } => {}, //~ ERROR cannot be used in patterns`
`10`	`10`	`}`
`11`		`- match loop {} {`
	`11`	+ match loop {} { //~ ERROR: non-exhaustive patterns: `_` not covered
`12`	`12`	`const { async {} } => {}, //~ ERROR cannot be used in patterns`
`13`	`13`	`}`
`14`	`14`	`}`