R raymond/fix/issue 107165

compiler/rustc_resolve/src/diagnostics.rs

@@ -1896,13 +1896,16 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
             }
             // Final step in the import chain, point out if the ADT is `non_exhaustive`
             // which is probably why this privacy violation occurred.
+            let mut err_help = None;
             if next_binding.is_none()
                 && let Some(span) = non_exhaustive
             {
                 note_span.push_span_label(
                     span,
                     "cannot be constructed because it is `#[non_exhaustive]`",
                 );
+                err_help =
+                    Some(format!("consider using a struct pattern instead: `{ident} {{ .. }}`"));
             }
             let note = errors::NoteAndRefersToTheItemDefinedHere {
                 span: note_span,
@@ -1912,6 +1915,9 @@ impl<'a, 'tcx> Resolver<'a, 'tcx> {
                 dots: next_binding.is_some(),
             };
             err.subdiagnostic(self.tcx.dcx(), note);
+            if let Some(err_help) = err_help {
+                err.span_help(ident.span, err_help);
+            }
         }
         // We prioritize shorter paths, non-core imports and direct imports over the alternatives.
         sugg_paths.sort_by_key(|(p, reexport)| (p.len(), p[0] == "core", *reexport));

tests/ui/match/auxiliary/non_exhaustive_structs_and_variants_lib.rs

@@ -0,0 +1,7 @@
+pub enum Elibrary {
+    #[non_exhaustive]
+    Unit,
+
+    #[non_exhaustive]
+    Tuple(i64),
+}

tests/ui/match/non-exhaustive-variant-hint-issue-107165.rs

@@ -0,0 +1,49 @@
+//@ aux-build:non_exhaustive_structs_and_variants_lib.rs
+
+/* Provide a hint to the user that a match of a non-exhaustive variant might
+ * fail because of a missing struct pattern (issue #107165).
+ */
+
+// Ignore non_exhaustive in the same crate
+enum Elocal {
+    #[non_exhaustive]
+    Unit,
+
+    #[non_exhaustive]
+    Tuple(i64),
+}
+
+extern crate non_exhaustive_structs_and_variants_lib;
+use non_exhaustive_structs_and_variants_lib::Elibrary;
+
+fn local() -> Elocal {
+    todo!()
+}
+
+fn library() -> Elibrary {
+    todo!()
+}
+
+fn main() {
+    let loc = local();
+    // No error for enums defined in this crate
+    match loc {
+        Elocal::Unit => (),
+        Elocal::Tuple(_) => (),
+    };
+
+    // Elibrary is externally defined
+    let lib = library();
+
+    match lib {
+        Elibrary::Unit => (),
+        //~^ ERROR unit variant `Unit` is private [E0603]
+        _ => (),
+    };
+
+    match lib {
+        Elibrary::Tuple(_) => (),
+        //~^ ERROR tuple variant `Tuple` is private [E0603]
+        _ => (),
+    };
+}

tests/ui/match/non-exhaustive-variant-hint-issue-107165.stderr

@@ -0,0 +1,41 @@
+error[E0603]: unit variant `Unit` is private
+  --> $DIR/non-exhaustive-variant-hint-issue-107165.rs:39:19
+   |
+LL |         Elibrary::Unit => (),
+   |                   ^^^^ private unit variant
+   |
+note: the unit variant `Unit` is defined here
+  --> $DIR/auxiliary/non_exhaustive_structs_and_variants_lib.rs:3:5
+   |
+LL |     #[non_exhaustive]
+   |     ----------------- cannot be constructed because it is `#[non_exhaustive]`
+LL |     Unit,
+   |     ^^^^
+help: consider using a struct pattern instead: `Unit { .. }`
+  --> $DIR/non-exhaustive-variant-hint-issue-107165.rs:39:19
+   |
+LL |         Elibrary::Unit => (),
+   |                   ^^^^
+
+error[E0603]: tuple variant `Tuple` is private
+  --> $DIR/non-exhaustive-variant-hint-issue-107165.rs:45:19
+   |
+LL |         Elibrary::Tuple(_) => (),
+   |                   ^^^^^ private tuple variant
+   |
+note: the tuple variant `Tuple` is defined here
+  --> $DIR/auxiliary/non_exhaustive_structs_and_variants_lib.rs:6:5
+   |
+LL |     #[non_exhaustive]
+   |     ----------------- cannot be constructed because it is `#[non_exhaustive]`
+LL |     Tuple(i64),
+   |     ^^^^^
+help: consider using a struct pattern instead: `Tuple { .. }`
+  --> $DIR/non-exhaustive-variant-hint-issue-107165.rs:45:19
+   |
+LL |         Elibrary::Tuple(_) => (),
+   |                   ^^^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0603`.

tests/ui/rfcs/rfc-2008-non-exhaustive/struct.stderr

@@ -17,6 +17,11 @@ LL | #[non_exhaustive]
    | ----------------- cannot be constructed because it is `#[non_exhaustive]`
 LL | pub struct TupleStruct(pub u16, pub u16);
    | ^^^^^^^^^^^^^^^^^^^^^^
+help: consider using a struct pattern instead: `TupleStruct { .. }`
+  --> $DIR/struct.rs:23:32
+   |
+LL |     let ts_explicit = structs::TupleStruct(640, 480);
+   |                                ^^^^^^^^^^^
 
 error[E0603]: unit struct `UnitStruct` is private
   --> $DIR/struct.rs:32:32
@@ -31,6 +36,11 @@ LL | #[non_exhaustive]
    | ----------------- cannot be constructed because it is `#[non_exhaustive]`
 LL | pub struct UnitStruct;
    | ^^^^^^^^^^^^^^^^^^^^^
+help: consider using a struct pattern instead: `UnitStruct { .. }`
+  --> $DIR/struct.rs:32:32
+   |
+LL |     let us_explicit = structs::UnitStruct;
+   |                                ^^^^^^^^^^
 
 error[E0639]: cannot create non-exhaustive struct using struct expression
   --> $DIR/struct.rs:7:14

tests/ui/rfcs/rfc-2008-non-exhaustive/variant.stderr

@@ -11,6 +11,11 @@ LL |     #[non_exhaustive] Tuple(u32),
    |     ----------------- ^^^^^
    |     |
    |     cannot be constructed because it is `#[non_exhaustive]`
+help: consider using a struct pattern instead: `Tuple { .. }`
+  --> $DIR/variant.rs:11:48
+   |
+LL |     let variant_tuple = NonExhaustiveVariants::Tuple(640);
+   |                                                ^^^^^
 
 error[E0603]: unit variant `Unit` is private
   --> $DIR/variant.rs:14:47
@@ -25,6 +30,11 @@ LL |     #[non_exhaustive] Unit,
    |     ----------------- ^^^^
    |     |
    |     cannot be constructed because it is `#[non_exhaustive]`
+help: consider using a struct pattern instead: `Unit { .. }`
+  --> $DIR/variant.rs:14:47
+   |
+LL |     let variant_unit = NonExhaustiveVariants::Unit;
+   |                                               ^^^^
 
 error[E0603]: unit variant `Unit` is private
   --> $DIR/variant.rs:18:32
@@ -39,6 +49,11 @@ LL |     #[non_exhaustive] Unit,
    |     ----------------- ^^^^
    |     |
    |     cannot be constructed because it is `#[non_exhaustive]`
+help: consider using a struct pattern instead: `Unit { .. }`
+  --> $DIR/variant.rs:18:32
+   |
+LL |         NonExhaustiveVariants::Unit => "",
+   |                                ^^^^
 
 error[E0603]: tuple variant `Tuple` is private
   --> $DIR/variant.rs:20:32
@@ -53,6 +68,11 @@ LL |     #[non_exhaustive] Tuple(u32),
    |     ----------------- ^^^^^
    |     |
    |     cannot be constructed because it is `#[non_exhaustive]`
+help: consider using a struct pattern instead: `Tuple { .. }`
+  --> $DIR/variant.rs:20:32
+   |
+LL |         NonExhaustiveVariants::Tuple(fe_tpl) => "",
+   |                                ^^^^^
 
 error[E0603]: tuple variant `Tuple` is private
   --> $DIR/variant.rs:26:35
@@ -67,6 +87,11 @@ LL |     #[non_exhaustive] Tuple(u32),
    |     ----------------- ^^^^^
    |     |
    |     cannot be constructed because it is `#[non_exhaustive]`
+help: consider using a struct pattern instead: `Tuple { .. }`
+  --> $DIR/variant.rs:26:35
+   |
+LL |     if let NonExhaustiveVariants::Tuple(fe_tpl) = variant_struct {
+   |                                   ^^^^^
 
 error[E0639]: cannot create non-exhaustive variant using struct expression
   --> $DIR/variant.rs:8:26