Remove expansion restriction + fix doc and tests naming

clippy_lints/src/methods/mod.rs

@@ -725,6 +725,7 @@
     /// **Known problems:** None.
     ///
     /// **Example:**
+    /// In an impl block:
     /// ```rust
     /// # struct Foo;
     /// # struct NotAFoo;
@@ -737,25 +738,40 @@
     ///
     /// ```rust
     /// # struct Foo;
-    /// # struct FooError;
+    /// struct Bar(Foo);
     /// impl Foo {
-    ///     // Good. Return type contains `Self`
-    ///     fn new() -> Result<Foo, FooError> {
-    ///         # Ok(Foo)
+    ///     // Bad. The type name must contain `Self`
+    ///     fn new() -> Bar {
+    /// # Bar(Foo)
     ///     }
     /// }
     /// ```
     ///
     /// ```rust
     /// # struct Foo;
-    /// struct Bar(Foo);
+    /// # struct FooError;
     /// impl Foo {
-    ///     // Bad. The type name must contain `Self`.
-    ///     fn new() -> Bar {
-    ///         # Bar(Foo)
+    ///     // Good. Return type contains `Self`
+    ///     fn new() -> Result<Foo, FooError> {
+    /// # Ok(Foo)
     ///     }
     /// }
     /// ```
+    ///
+    /// Or in a trait definition:
+    /// ```rust
+    /// pub trait Trait {
+    ///     // Bad. The type name must contain `Self`
+    ///     fn new();
+    /// }
+    /// ```
+    ///
+    /// ```rust
+    /// pub trait Trait {
+    ///     // Good. Return type contains `Self`
+    ///     fn new() -> Self;
+    /// }
+    /// ```
     pub NEW_RET_NO_SELF,
     style,
     "not returning type containing `Self` in a `new` method"
@@ -1679,8 +1695,6 @@ fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::Impl
 
     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
         if_chain! {
-            if !in_external_macro(cx.tcx.sess, item.span);
-            if !item.span.from_expansion();
             if item.ident.name == sym!(new);
             if let TraitItemKind::Fn(FnSig { decl, .. }, _) = &item.kind;
             if let FnRetTy::Return(ret_ty) = &decl.output;

tests/ui/new_ret_no_self.rs

@@ -137,9 +137,9 @@ pub fn new() -> *mut Self {
     }
 }
 
-struct MutPointerReturnerOk2;
+struct ConstPointerReturnerOk2;
 
-impl MutPointerReturnerOk2 {
+impl ConstPointerReturnerOk2 {
     // should not trigger lint
     pub fn new() -> *const Self {
         unimplemented!();
@@ -283,7 +283,7 @@ fn new() -> *mut Self
         }
     }
 
-    trait MutPointerReturnerOk2 {
+    trait ConstPointerReturnerOk2 {
         // should not trigger lint
         fn new() -> *const Self
         where