[iter_without_into_iter]: fix papercuts in suggestion and restrict linting to exported types

clippy_lints/src/iter_without_into_iter.rs

@@ -19,6 +19,11 @@ declare_clippy_lint! {
     /// It's not bad, but having them is idiomatic and allows the type to be used in for loops directly
     /// (`for val in &iter {}`), without having to first call `iter()` or `iter_mut()`.
     ///
+    /// ### Limitations
+    /// This lint focuses on providing an idiomatic API. Therefore, it will only
+    /// lint on types which are accessible outside of the crate. For internal types,
+    /// the `IntoIterator` trait can be implemented on demand if it is actually needed.
+    ///
     /// ### Example
     /// ```rust
     /// struct MySlice<'a>(&'a [u8]);
@@ -61,6 +66,14 @@ declare_clippy_lint! {
     /// by just calling `.iter()`, instead of the more awkward `<&Type>::into_iter` or `(&val).into_iter()` syntax
     /// in case of ambiguity with another `IntoIterator` impl.
     ///
+    /// ### Limitations
+    /// This lint focuses on providing an idiomatic API. Therefore, it will only
+    /// lint on types which are accessible outside of the crate. For internal types,
+    /// these methods can be added on demand if they are actually needed. Otherwise,
+    /// it would trigger the [`dead_code`] lint for the unused method.
+    ///
+    /// [`dead_code`]: https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#dead-code
+    ///
     /// ### Example
     /// ```rust
     /// struct MySlice<'a>(&'a [u8]);
@@ -104,6 +117,12 @@ fn is_nameable_in_impl_trait(ty: &rustc_hir::Ty<'_>) -> bool {
     !matches!(ty.kind, TyKind::OpaqueDef(..))
 }
 
+fn is_ty_exported(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
+    ty.ty_adt_def()
+        .and_then(|adt| adt.did().as_local())
+        .is_some_and(|did| cx.effective_visibilities.is_exported(did))
+}
+
 /// Returns the deref chain of a type, starting with the type itself.
 fn deref_chain<'cx, 'tcx>(cx: &'cx LateContext<'tcx>, ty: Ty<'tcx>) -> impl Iterator<Item = Ty<'tcx>> + 'cx {
     iter::successors(Some(ty), |&ty| {
@@ -154,6 +173,7 @@ impl LateLintPass<'_> for IterWithoutIntoIter {
                     None
                 }
             })
+            && is_ty_exported(cx, ty)
         {
             span_lint_and_then(
                 cx,
@@ -226,6 +246,7 @@ impl {self_ty_without_ref} {{
             )
             // Only lint if the `IntoIterator` impl doesn't actually exist
             && !implements_trait(cx, ref_ty, into_iter_did, &[])
+            && is_ty_exported(cx, ref_ty.peel_refs())
         {
             let self_ty_snippet = format!("{borrow_prefix}{}", snippet(cx, imp.self_ty.span, ".."));
 
@@ -247,8 +268,8 @@ impl {self_ty_without_ref} {{
 "
 impl IntoIterator for {self_ty_snippet} {{
     type IntoIter = {ret_ty};
-    type Iter = {iter_ty};
-    fn into_iter() -> Self::IntoIter {{
+    type Item = {iter_ty};
+    fn into_iter(self) -> Self::IntoIter {{
         self.iter()
     }}
 }}

tests/ui/into_iter_without_iter.rs

@@ -3,127 +3,117 @@
 
 use std::iter::IntoIterator;
 
-fn main() {
-    {
-        struct S;
-
-        impl<'a> IntoIterator for &'a S {
-            //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter` method
-            type IntoIter = std::slice::Iter<'a, u8>;
-            type Item = &'a u8;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
-        impl<'a> IntoIterator for &'a mut S {
-            //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter_mut` method
-            type IntoIter = std::slice::IterMut<'a, u8>;
-            type Item = &'a mut u8;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+pub struct S1;
+impl<'a> IntoIterator for &'a S1 {
+    //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter` method
+    type IntoIter = std::slice::Iter<'a, u8>;
+    type Item = &'a u8;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
     }
-    {
-        struct S<T>(T);
-        impl<'a, T> IntoIterator for &'a S<T> {
-            //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter` method
-            type IntoIter = std::slice::Iter<'a, T>;
-            type Item = &'a T;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
-        impl<'a, T> IntoIterator for &'a mut S<T> {
-            //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter_mut` method
-            type IntoIter = std::slice::IterMut<'a, T>;
-            type Item = &'a mut T;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+}
+impl<'a> IntoIterator for &'a mut S1 {
+    //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter_mut` method
+    type IntoIter = std::slice::IterMut<'a, u8>;
+    type Item = &'a mut u8;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
     }
-    {
-        // Both iter and iter_mut methods exist, don't lint
-        struct S<'a, T>(&'a T);
-
-        impl<'a, T> S<'a, T> {
-            fn iter(&self) -> std::slice::Iter<'a, T> {
-                todo!()
-            }
-            fn iter_mut(&mut self) -> std::slice::IterMut<'a, T> {
-                todo!()
-            }
-        }
+}
 
-        impl<'a, T> IntoIterator for &S<'a, T> {
-            type IntoIter = std::slice::Iter<'a, T>;
-            type Item = &'a T;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+pub struct S2<T>(T);
+impl<'a, T> IntoIterator for &'a S2<T> {
+    //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter` method
+    type IntoIter = std::slice::Iter<'a, T>;
+    type Item = &'a T;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
+    }
+}
+impl<'a, T> IntoIterator for &'a mut S2<T> {
+    //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter_mut` method
+    type IntoIter = std::slice::IterMut<'a, T>;
+    type Item = &'a mut T;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
+    }
+}
 
-        impl<'a, T> IntoIterator for &mut S<'a, T> {
-            type IntoIter = std::slice::IterMut<'a, T>;
-            type Item = &'a mut T;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+// Both iter and iter_mut methods exist, don't lint
+pub struct S3<'a, T>(&'a T);
+impl<'a, T> S3<'a, T> {
+    fn iter(&self) -> std::slice::Iter<'a, T> {
+        todo!()
+    }
+    fn iter_mut(&mut self) -> std::slice::IterMut<'a, T> {
+        todo!()
+    }
+}
+impl<'a, T> IntoIterator for &S3<'a, T> {
+    type IntoIter = std::slice::Iter<'a, T>;
+    type Item = &'a T;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
+    }
+}
+impl<'a, T> IntoIterator for &mut S3<'a, T> {
+    type IntoIter = std::slice::IterMut<'a, T>;
+    type Item = &'a mut T;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
     }
-    {
-        // Only `iter` exists, no `iter_mut`
-        struct S<'a, T>(&'a T);
+}
 
-        impl<'a, T> S<'a, T> {
-            fn iter(&self) -> std::slice::Iter<'a, T> {
-                todo!()
-            }
-        }
+// Only `iter` exists, no `iter_mut`
+pub struct S4<'a, T>(&'a T);
 
-        impl<'a, T> IntoIterator for &S<'a, T> {
-            type IntoIter = std::slice::Iter<'a, T>;
-            type Item = &'a T;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+impl<'a, T> S4<'a, T> {
+    fn iter(&self) -> std::slice::Iter<'a, T> {
+        todo!()
+    }
+}
 
-        impl<'a, T> IntoIterator for &mut S<'a, T> {
-            //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter_mut` method
-            type IntoIter = std::slice::IterMut<'a, T>;
-            type Item = &'a mut T;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+impl<'a, T> IntoIterator for &S4<'a, T> {
+    type IntoIter = std::slice::Iter<'a, T>;
+    type Item = &'a T;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
     }
-    {
-        // `iter` exists, but `IntoIterator` is implemented for an alias. inherent_impls doesn't "normalize"
-        // aliases so that `inherent_impls(Alias)` where `type Alias = S` returns nothing, so this can lead
-        // to fun FPs. Make sure it doesn't happen here (we're using type_of, which should skip the alias).
-        struct S;
+}
 
-        impl S {
-            fn iter(&self) -> std::slice::Iter<'static, u8> {
-                todo!()
-            }
-        }
+impl<'a, T> IntoIterator for &mut S4<'a, T> {
+    //~^ ERROR: `IntoIterator` implemented for a reference type without an `iter_mut` method
+    type IntoIter = std::slice::IterMut<'a, T>;
+    type Item = &'a mut T;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
+    }
+}
 
-        type Alias = S;
+// `iter` exists, but `IntoIterator` is implemented for an alias. inherent_impls doesn't "normalize"
+// aliases so that `inherent_impls(Alias)` where `type Alias = S` returns nothing, so this can lead
+// to fun FPs. Make sure it doesn't happen here (we're using type_of, which should skip the alias).
+pub struct S5;
 
-        impl IntoIterator for &Alias {
-            type IntoIter = std::slice::Iter<'static, u8>;
-            type Item = &'static u8;
-            fn into_iter(self) -> Self::IntoIter {
-                todo!()
-            }
-        }
+impl S5 {
+    fn iter(&self) -> std::slice::Iter<'static, u8> {
+        todo!()
+    }
+}
+
+pub type Alias = S5;
+
+impl IntoIterator for &Alias {
+    type IntoIter = std::slice::Iter<'static, u8>;
+    type Item = &'static u8;
+    fn into_iter(self) -> Self::IntoIter {
+        todo!()
     }
 }
 
-fn issue11635() {
+fn main() {}
+
+pub mod issue11635 {
     // A little more involved than the original repro in the issue, but this tests that it correctly
     // works for more than one deref step