Rollup merge of rust-lang#111951 - cjgillot:uninh-comment, r=Nadrieril

Correct comment on privately uninhabited pattern.

Follow-up to rust-lang#111624 (comment)

r? `@Nadrieril`

Author: matthiaskrgr

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

@@ -491,8 +491,8 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
             AdtDefinedHere { adt_def_span, ty, variants }
         };
 
-        // Emit an extra note if the first uncovered witness is
-        // visibly uninhabited anywhere in the current crate.
+        // Emit an extra note if the first uncovered witness would be uninhabited
+        // if we disregard visibility.
         let witness_1_is_privately_uninhabited =
             if cx.tcx.features().exhaustive_patterns
                 && let Some(witness_1) = witnesses.get(0)

tests/ui/pattern/usefulness/empty-match.exhaustive_patterns.stderr

@@ -1,5 +1,5 @@
 error: unreachable pattern
-  --> $DIR/empty-match.rs:37:9
+  --> $DIR/empty-match.rs:58:9
    |
 LL |         _ => {},
    |         ^
@@ -11,37 +11,52 @@ LL | #![deny(unreachable_patterns)]
    |         ^^^^^^^^^^^^^^^^^^^^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:40:9
+  --> $DIR/empty-match.rs:61:9
    |
 LL |         _ if false => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:47:9
+  --> $DIR/empty-match.rs:68:9
    |
 LL |         _ => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:50:9
+  --> $DIR/empty-match.rs:71:9
    |
 LL |         _ if false => {},
    |         ^
 
+error[E0005]: refutable pattern in local binding
+  --> $DIR/empty-match.rs:76:9
+   |
+LL |     let None = x;
+   |         ^^^^ pattern `Some(_)` not covered
+   |
+   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
+   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
+   = note: pattern `Some(_)` is currently uninhabited, but this variant contains private fields which may become inhabited in the future
+   = note: the matched value is of type `Option<SecretlyUninhabitedForeignStruct>`
+help: you might want to use `if let` to ignore the variant that isn't matched
+   |
+LL |     if let None = x { todo!() };
+   |     ++              +++++++++++
+
 error: unreachable pattern
-  --> $DIR/empty-match.rs:57:9
+  --> $DIR/empty-match.rs:88:9
    |
 LL |         _ => {},
    |         ^
 
 error: unreachable pattern
-  --> $DIR/empty-match.rs:60:9
+  --> $DIR/empty-match.rs:91:9
    |
 LL |         _ if false => {},
    |         ^
 
 error[E0004]: non-exhaustive patterns: type `u8` is non-empty
-  --> $DIR/empty-match.rs:78:20
+  --> $DIR/empty-match.rs:109:20
    |
 LL |     match_no_arms!(0u8);
    |                    ^^^
@@ -50,69 +65,69 @@ LL |     match_no_arms!(0u8);
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyStruct1` is non-empty
-  --> $DIR/empty-match.rs:79:20
+  --> $DIR/empty-match.rs:111:20
    |
 LL |     match_no_arms!(NonEmptyStruct1);
    |                    ^^^^^^^^^^^^^^^
    |
 note: `NonEmptyStruct1` defined here
-  --> $DIR/empty-match.rs:14:8
+  --> $DIR/empty-match.rs:15:8
    |
 LL | struct NonEmptyStruct1;
    |        ^^^^^^^^^^^^^^^
    = note: the matched value is of type `NonEmptyStruct1`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyStruct2` is non-empty
-  --> $DIR/empty-match.rs:80:20
+  --> $DIR/empty-match.rs:113:20
    |
 LL |     match_no_arms!(NonEmptyStruct2(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyStruct2` defined here
-  --> $DIR/empty-match.rs:15:8
+  --> $DIR/empty-match.rs:18:8
    |
 LL | struct NonEmptyStruct2(bool);
    |        ^^^^^^^^^^^^^^^
    = note: the matched value is of type `NonEmptyStruct2`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyUnion1` is non-empty
-  --> $DIR/empty-match.rs:81:20
+  --> $DIR/empty-match.rs:115:20
    |
 LL |     match_no_arms!((NonEmptyUnion1 { foo: () }));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyUnion1` defined here
-  --> $DIR/empty-match.rs:16:7
+  --> $DIR/empty-match.rs:21:7
    |
 LL | union NonEmptyUnion1 {
    |       ^^^^^^^^^^^^^^
    = note: the matched value is of type `NonEmptyUnion1`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: type `NonEmptyUnion2` is non-empty
-  --> $DIR/empty-match.rs:82:20
+  --> $DIR/empty-match.rs:117:20
    |
 LL |     match_no_arms!((NonEmptyUnion2 { foo: () }));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: `NonEmptyUnion2` defined here
-  --> $DIR/empty-match.rs:19:7
+  --> $DIR/empty-match.rs:26:7
    |
 LL | union NonEmptyUnion2 {
    |       ^^^^^^^^^^^^^^
    = note: the matched value is of type `NonEmptyUnion2`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum1::Foo(_)` not covered
-  --> $DIR/empty-match.rs:83:20
+  --> $DIR/empty-match.rs:119:20
    |
 LL |     match_no_arms!(NonEmptyEnum1::Foo(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyEnum1::Foo(_)` not covered
    |
 note: `NonEmptyEnum1` defined here
-  --> $DIR/empty-match.rs:24:5
+  --> $DIR/empty-match.rs:33:5
    |
 LL | enum NonEmptyEnum1 {
    |      -------------
@@ -122,39 +137,40 @@ LL |     Foo(bool),
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
-  --> $DIR/empty-match.rs:84:20
+  --> $DIR/empty-match.rs:122:20
    |
 LL |     match_no_arms!(NonEmptyEnum2::Foo(true));
    |                    ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
    |
 note: `NonEmptyEnum2` defined here
-  --> $DIR/empty-match.rs:27:5
+  --> $DIR/empty-match.rs:40:5
    |
 LL | enum NonEmptyEnum2 {
    |      -------------
 LL |     Foo(bool),
    |     ^^^ not covered
+...
 LL |     Bar,
    |     ^^^ not covered
    = note: the matched value is of type `NonEmptyEnum2`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or multiple match arms
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
-  --> $DIR/empty-match.rs:85:20
+  --> $DIR/empty-match.rs:125:20
    |
 LL |     match_no_arms!(NonEmptyEnum5::V1);
    |                    ^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
    |
 note: `NonEmptyEnum5` defined here
-  --> $DIR/empty-match.rs:30:6
+  --> $DIR/empty-match.rs:49:6
    |
 LL | enum NonEmptyEnum5 {
    |      ^^^^^^^^^^^^^
    = note: the matched value is of type `NonEmptyEnum5`
    = help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or multiple match arms
 
 error[E0004]: non-exhaustive patterns: `_` not covered
-  --> $DIR/empty-match.rs:87:24
+  --> $DIR/empty-match.rs:129:24
    |
 LL |     match_guarded_arm!(0u8);
    |                        ^^^ pattern `_` not covered
@@ -167,13 +183,13 @@ LL +             _ => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyStruct1` not covered
-  --> $DIR/empty-match.rs:88:24
+  --> $DIR/empty-match.rs:133:24
    |
 LL |     match_guarded_arm!(NonEmptyStruct1);
    |                        ^^^^^^^^^^^^^^^ pattern `NonEmptyStruct1` not covered
    |
 note: `NonEmptyStruct1` defined here
-  --> $DIR/empty-match.rs:14:8
+  --> $DIR/empty-match.rs:15:8
    |
 LL | struct NonEmptyStruct1;
    |        ^^^^^^^^^^^^^^^
@@ -185,13 +201,13 @@ LL +             NonEmptyStruct1 => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyStruct2(_)` not covered
-  --> $DIR/empty-match.rs:89:24
+  --> $DIR/empty-match.rs:137:24
    |
 LL |     match_guarded_arm!(NonEmptyStruct2(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyStruct2(_)` not covered
    |
 note: `NonEmptyStruct2` defined here
-  --> $DIR/empty-match.rs:15:8
+  --> $DIR/empty-match.rs:18:8
    |
 LL | struct NonEmptyStruct2(bool);
    |        ^^^^^^^^^^^^^^^
@@ -203,13 +219,13 @@ LL +             NonEmptyStruct2(_) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyUnion1 { .. }` not covered
-  --> $DIR/empty-match.rs:90:24
+  --> $DIR/empty-match.rs:141:24
    |
 LL |     match_guarded_arm!((NonEmptyUnion1 { foo: () }));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyUnion1 { .. }` not covered
    |
 note: `NonEmptyUnion1` defined here
-  --> $DIR/empty-match.rs:16:7
+  --> $DIR/empty-match.rs:21:7
    |
 LL | union NonEmptyUnion1 {
    |       ^^^^^^^^^^^^^^
@@ -221,13 +237,13 @@ LL +             NonEmptyUnion1 { .. } => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyUnion2 { .. }` not covered
-  --> $DIR/empty-match.rs:91:24
+  --> $DIR/empty-match.rs:145:24
    |
 LL |     match_guarded_arm!((NonEmptyUnion2 { foo: () }));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyUnion2 { .. }` not covered
    |
 note: `NonEmptyUnion2` defined here
-  --> $DIR/empty-match.rs:19:7
+  --> $DIR/empty-match.rs:26:7
    |
 LL | union NonEmptyUnion2 {
    |       ^^^^^^^^^^^^^^
@@ -239,13 +255,13 @@ LL +             NonEmptyUnion2 { .. } => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum1::Foo(_)` not covered
-  --> $DIR/empty-match.rs:92:24
+  --> $DIR/empty-match.rs:149:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum1::Foo(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^ pattern `NonEmptyEnum1::Foo(_)` not covered
    |
 note: `NonEmptyEnum1` defined here
-  --> $DIR/empty-match.rs:24:5
+  --> $DIR/empty-match.rs:33:5
    |
 LL | enum NonEmptyEnum1 {
    |      -------------
@@ -259,18 +275,19 @@ LL +             NonEmptyEnum1::Foo(_) => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
-  --> $DIR/empty-match.rs:93:24
+  --> $DIR/empty-match.rs:153:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum2::Foo(true));
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum2::Foo(_)` and `NonEmptyEnum2::Bar` not covered
    |
 note: `NonEmptyEnum2` defined here
-  --> $DIR/empty-match.rs:27:5
+  --> $DIR/empty-match.rs:40:5
    |
 LL | enum NonEmptyEnum2 {
    |      -------------
 LL |     Foo(bool),
    |     ^^^ not covered
+...
 LL |     Bar,
    |     ^^^ not covered
    = note: the matched value is of type `NonEmptyEnum2`
@@ -281,13 +298,13 @@ LL +             NonEmptyEnum2::Foo(_) | NonEmptyEnum2::Bar => todo!()
    |
 
 error[E0004]: non-exhaustive patterns: `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
-  --> $DIR/empty-match.rs:94:24
+  --> $DIR/empty-match.rs:157:24
    |
 LL |     match_guarded_arm!(NonEmptyEnum5::V1);
    |                        ^^^^^^^^^^^^^^^^^ patterns `NonEmptyEnum5::V1`, `NonEmptyEnum5::V2`, `NonEmptyEnum5::V3` and 2 more not covered
    |
 note: `NonEmptyEnum5` defined here
-  --> $DIR/empty-match.rs:30:6
+  --> $DIR/empty-match.rs:49:6
    |
 LL | enum NonEmptyEnum5 {
    |      ^^^^^^^^^^^^^
@@ -298,6 +315,7 @@ LL ~             _ if false => {},
 LL +             _ => todo!()
    |
 
-error: aborting due to 22 previous errors
+error: aborting due to 23 previous errors
 
-For more information about this error, try `rustc --explain E0004`.
+Some errors have detailed explanations: E0004, E0005.
+For more information about an error, try `rustc --explain E0004`.