Auto merge of rust-lang#10250 - tylerjw:issue_7419, r=xFrednet

wildcard_enum_match_arm lint takes the enum origin into account

fixes rust-lang#7419

---

changelog: Enhancement: [`wildcard_enum_match_arm`]: Now lints missing private variants, for local enums
[rust-lang#10250](rust-lang#10250)
<!-- changelog_checked -->

Author: bors

clippy_lints/src/matches/match_wild_enum.rs

@@ -45,8 +45,13 @@ pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
 
     // Accumulate the variants which should be put in place of the wildcard because they're not
     // already covered.
-    let has_hidden = adt_def.variants().iter().any(|x| is_hidden(cx, x));
-    let mut missing_variants: Vec<_> = adt_def.variants().iter().filter(|x| !is_hidden(cx, x)).collect();
+    let is_external = adt_def.did().as_local().is_none();
+    let has_external_hidden = is_external && adt_def.variants().iter().any(|x| is_hidden(cx, x));
+    let mut missing_variants: Vec<_> = adt_def
+        .variants()
+        .iter()
+        .filter(|x| !(is_external && is_hidden(cx, x)))
+        .collect();
 
     let mut path_prefix = CommonPrefixSearcher::None;
     for arm in arms {
@@ -133,7 +138,7 @@ pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
 
     match missing_variants.as_slice() {
         [] => (),
-        [x] if !adt_def.is_variant_list_non_exhaustive() && !has_hidden => span_lint_and_sugg(
+        [x] if !adt_def.is_variant_list_non_exhaustive() && !has_external_hidden => span_lint_and_sugg(
             cx,
             MATCH_WILDCARD_FOR_SINGLE_VARIANTS,
             wildcard_span,
@@ -144,7 +149,7 @@ pub(crate) fn check(cx: &LateContext<'_>, ex: &Expr<'_>, arms: &[Arm<'_>]) {
         ),
         variants => {
             let mut suggestions: Vec<_> = variants.iter().copied().map(format_suggestion).collect();
-            let message = if adt_def.is_variant_list_non_exhaustive() || has_hidden {
+            let message = if adt_def.is_variant_list_non_exhaustive() || has_external_hidden {
                 suggestions.push("_".into());
                 "wildcard matches known variants and will also match future added variants"
             } else {

tests/ui/match_wildcard_for_single_variants.fixed

@@ -123,7 +123,7 @@ fn main() {
             Enum::A => (),
             Enum::B => (),
             Enum::C => (),
-            _ => (),
+            Enum::__Private => (),
         }
         match Enum::A {
             Enum::A => (),

tests/ui/match_wildcard_for_single_variants.stderr

@@ -48,11 +48,17 @@ error: wildcard matches only a single variant and will also match any future add
 LL |         _ => (),
    |         ^ help: try this: `Color::Blue`
 
+error: wildcard matches only a single variant and will also match any future added variants
+  --> $DIR/match_wildcard_for_single_variants.rs:126:13
+   |
+LL |             _ => (),
+   |             ^ help: try this: `Enum::__Private`
+
 error: wildcard matches only a single variant and will also match any future added variants
   --> $DIR/match_wildcard_for_single_variants.rs:153:13
    |
 LL |             _ => 2,
    |             ^ help: try this: `Foo::B`
 
-error: aborting due to 9 previous errors
+error: aborting due to 10 previous errors
 

tests/ui/wildcard_enum_match_arm.fixed

@@ -96,7 +96,7 @@ fn main() {
         }
         match Enum::A {
             Enum::A => (),
-            Enum::B | _ => (),
+            Enum::B | Enum::__Private => (),
         }
     }
 }

tests/ui/wildcard_enum_match_arm.stderr

@@ -34,11 +34,11 @@ error: wildcard matches known variants and will also match future added variants
 LL |         _ => {},
    |         ^ help: try this: `ErrorKind::PermissionDenied | _`
 
-error: wildcard matches known variants and will also match future added variants
+error: wildcard match will also match any future added variants
   --> $DIR/wildcard_enum_match_arm.rs:99:13
    |
 LL |             _ => (),
-   |             ^ help: try this: `Enum::B | _`
+   |             ^ help: try this: `Enum::B | Enum::__Private`
 
 error: aborting due to 6 previous errors