Check structs and enums for use_self (rust-lang#15566)

Closes rust-lang/rust-clippy#15555

changelog: [`use_self`]: Check structs and enums

Author: blyxyas

CHANGELOG.md

@@ -7052,6 +7052,7 @@ Released 2018-09-13
 [`msrv`]: https://doc.rust-lang.org/clippy/lint_configuration.html#msrv
 [`pass-by-value-size-limit`]: https://doc.rust-lang.org/clippy/lint_configuration.html#pass-by-value-size-limit
 [`pub-underscore-fields-behavior`]: https://doc.rust-lang.org/clippy/lint_configuration.html#pub-underscore-fields-behavior
+[`recursive-self-in-type-definitions`]: https://doc.rust-lang.org/clippy/lint_configuration.html#recursive-self-in-type-definitions
 [`semicolon-inside-block-ignore-singleline`]: https://doc.rust-lang.org/clippy/lint_configuration.html#semicolon-inside-block-ignore-singleline
 [`semicolon-outside-block-ignore-multiline`]: https://doc.rust-lang.org/clippy/lint_configuration.html#semicolon-outside-block-ignore-multiline
 [`single-char-binding-names-threshold`]: https://doc.rust-lang.org/clippy/lint_configuration.html#single-char-binding-names-threshold

book/src/lint_configuration.md

@@ -927,6 +927,16 @@ exported visibility, or whether they are marked as "pub".
 * [`pub_underscore_fields`](https://rust-lang.github.io/rust-clippy/master/index.html#pub_underscore_fields)
 
 
+## `recursive-self-in-type-definitions`
+Whether the type itself in a struct or enum should be replaced with `Self` when encountering recursive types.
+
+**Default Value:** `true`
+
+---
+**Affected lints:**
+* [`use_self`](https://rust-lang.github.io/rust-clippy/master/index.html#use_self)
+
+
 ## `semicolon-inside-block-ignore-singleline`
 Whether to lint only if it's multiline.
 

clippy_config/src/conf.rs

@@ -809,6 +809,9 @@ define_Conf! {
     /// exported visibility, or whether they are marked as "pub".
     #[lints(pub_underscore_fields)]
     pub_underscore_fields_behavior: PubUnderscoreFieldsBehaviour = PubUnderscoreFieldsBehaviour::PubliclyExported,
+    /// Whether the type itself in a struct or enum should be replaced with `Self` when encountering recursive types.
+    #[lints(use_self)]
+    recursive_self_in_type_definitions: bool = true,
     /// Whether to lint only if it's multiline.
     #[lints(semicolon_inside_block)]
     semicolon_inside_block_ignore_singleline: bool = false,

clippy_lints/src/matches/single_match.rs

@@ -224,7 +224,7 @@ enum PatState<'a> {
     /// A std enum we know won't be extended. Tracks the states of each variant separately.
     ///
     /// This is not used for `Option` since it uses the current pattern to track its state.
-    StdEnum(&'a mut [PatState<'a>]),
+    StdEnum(&'a mut [Self]),
     /// Either the initial state for a pattern or a non-std enum. There is currently no need to
     /// distinguish these cases.
     ///

clippy_lints/src/use_self.rs

@@ -58,13 +58,15 @@ declare_clippy_lint! {
 pub struct UseSelf {
     msrv: Msrv,
     stack: Vec<StackItem>,
+    recursive_self_in_type_definitions: bool,
 }
 
 impl UseSelf {
     pub fn new(conf: &'static Conf) -> Self {
         Self {
             msrv: conf.msrv,
             stack: Vec::new(),
+            recursive_self_in_type_definitions: conf.recursive_self_in_type_definitions,
         }
     }
 }
@@ -84,10 +86,10 @@ const SEGMENTS_MSG: &str = "segments should be composed of at least 1 element";
 
 impl<'tcx> LateLintPass<'tcx> for UseSelf {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &Item<'tcx>) {
-        // We push the self types of `impl`s on a stack here. Only the top type on the stack is
-        // relevant for linting, since this is the self type of the `impl` we're currently in. To
-        // avoid linting on nested items, we push `StackItem::NoCheck` on the stack to signal, that
-        // we're in an `impl` or nested item, that we don't want to lint
+        // We push the self types of items on a stack here. Only the top type on the stack is
+        // relevant for linting, since this is the self type of the item we're currently in. To
+        // avoid linting on nested items, we push `StackItem::NoCheck` on the stack to signal that
+        // we're in an item or nested item that we don't want to lint
         let stack_item = if let ItemKind::Impl(Impl { self_ty, generics, .. }) = item.kind
             && let TyKind::Path(QPath::Resolved(_, item_path)) = self_ty.kind
             && let parameters = &item_path.segments.last().expect(SEGMENTS_MSG).args
@@ -112,6 +114,15 @@ impl<'tcx> LateLintPass<'tcx> for UseSelf {
                 impl_id: item.owner_id.def_id,
                 types_to_skip,
             }
+        } else if let ItemKind::Struct(..) | ItemKind::Enum(..) = item.kind
+            && self.recursive_self_in_type_definitions
+            && !item.span.from_expansion()
+            && !is_from_proc_macro(cx, item)
+        {
+            StackItem::Check {
+                impl_id: item.owner_id.def_id,
+                types_to_skip: FxHashSet::default(),
+            }
         } else {
             StackItem::NoCheck
         };

clippy_utils/src/consts.rs

@@ -50,15 +50,15 @@ pub enum Constant {
     /// `true` or `false`.
     Bool(bool),
     /// An array of constants.
-    Vec(Vec<Constant>),
+    Vec(Vec<Self>),
     /// Also an array, but with only one constant, repeated N times.
-    Repeat(Box<Constant>, u64),
+    Repeat(Box<Self>, u64),
     /// A tuple of constants.
-    Tuple(Vec<Constant>),
+    Tuple(Vec<Self>),
     /// A raw pointer.
     RawPtr(u128),
     /// A reference
-    Ref(Box<Constant>),
+    Ref(Box<Self>),
     /// A literal with syntax error.
     Err,
 }

clippy_utils/src/sugg.rs

@@ -33,7 +33,7 @@ pub enum Sugg<'a> {
     /// or `-`, but only if the type with and without the operator is kept identical.
     /// It means that doubling the operator can be used to remove it instead, in
     /// order to provide better suggestions.
-    UnOp(UnOp, Box<Sugg<'a>>),
+    UnOp(UnOp, Box<Self>),
 }
 
 /// Literal constant `0`, for convenience.

tests/ui-toml/toml_unknown_key/conf_unknown_key.stderr

@@ -66,6 +66,7 @@ error: error reading Clippy's configuration file: unknown field `foobar`, expect
            msrv
            pass-by-value-size-limit
            pub-underscore-fields-behavior
+           recursive-self-in-type-definitions
            semicolon-inside-block-ignore-singleline
            semicolon-outside-block-ignore-multiline
            single-char-binding-names-threshold
@@ -161,6 +162,7 @@ error: error reading Clippy's configuration file: unknown field `barfoo`, expect
            msrv
            pass-by-value-size-limit
            pub-underscore-fields-behavior
+           recursive-self-in-type-definitions
            semicolon-inside-block-ignore-singleline
            semicolon-outside-block-ignore-multiline
            single-char-binding-names-threshold
@@ -256,6 +258,7 @@ error: error reading Clippy's configuration file: unknown field `allow_mixed_uni
            msrv
            pass-by-value-size-limit
            pub-underscore-fields-behavior
+           recursive-self-in-type-definitions
            semicolon-inside-block-ignore-singleline
            semicolon-outside-block-ignore-multiline
            single-char-binding-names-threshold

tests/ui-toml/use_self/default/clippy.toml

@@ -0,0 +1 @@
+recursive-self-in-type-definitions = false