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Implement RFC 3373: Avoid non-local definitions in functions This PR implements [RFC 3373: Avoid non-local definitions in functions](#120363).
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,222 @@ | ||
| use rustc_hir::{def::DefKind, Body, Item, ItemKind, Node, Path, QPath, TyKind}; | ||
| use rustc_span::def_id::{DefId, LOCAL_CRATE}; | ||
| use rustc_span::{sym, symbol::kw, ExpnKind, MacroKind}; | ||
|
|
||
| use smallvec::{smallvec, SmallVec}; | ||
|
|
||
| use crate::lints::{NonLocalDefinitionsCargoUpdateNote, NonLocalDefinitionsDiag}; | ||
| use crate::{LateContext, LateLintPass, LintContext}; | ||
|
|
||
| declare_lint! { | ||
| /// The `non_local_definitions` lint checks for `impl` blocks and `#[macro_export]` | ||
| /// macro inside bodies (functions, enum discriminant, ...). | ||
| /// | ||
| /// ### Example | ||
| /// | ||
| /// ```rust | ||
| /// trait MyTrait {} | ||
| /// struct MyStruct; | ||
| /// | ||
| /// fn foo() { | ||
| /// impl MyTrait for MyStruct {} | ||
| /// } | ||
| /// ``` | ||
| /// | ||
| /// {{produces}} | ||
| /// | ||
| /// ### Explanation | ||
| /// | ||
| /// Creating non-local definitions go against expectation and can create discrepancies | ||
| /// in tooling. It should be avoided. It may become deny-by-default in edition 2024 | ||
| /// and higher, see see the tracking issue <https://github.com/rust-lang/rust/issues/120363>. | ||
| /// | ||
| /// An `impl` definition is non-local if it is nested inside an item and neither | ||
| /// the type nor the trait are at the same nesting level as the `impl` block. | ||
| /// | ||
| /// All nested bodies (functions, enum discriminant, array length, consts) (expect for | ||
| /// `const _: Ty = { ... }` in top-level module, which is still undecided) are checked. | ||
| pub NON_LOCAL_DEFINITIONS, | ||
| Warn, | ||
| "checks for non-local definitions", | ||
| report_in_external_macro | ||
| } | ||
|
|
||
| #[derive(Default)] | ||
| pub struct NonLocalDefinitions { | ||
| body_depth: u32, | ||
| } | ||
|
|
||
| impl_lint_pass!(NonLocalDefinitions => [NON_LOCAL_DEFINITIONS]); | ||
|
|
||
| // FIXME(Urgau): Figure out how to handle modules nested in bodies. | ||
| // It's currently not handled by the current logic because modules are not bodies. | ||
| // They don't even follow the correct order (check_body -> check_mod -> check_body_post) | ||
| // instead check_mod is called after every body has been handled. | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions { | ||
| fn check_body(&mut self, _cx: &LateContext<'tcx>, _body: &'tcx Body<'tcx>) { | ||
| self.body_depth += 1; | ||
| } | ||
|
|
||
| fn check_body_post(&mut self, _cx: &LateContext<'tcx>, _body: &'tcx Body<'tcx>) { | ||
| self.body_depth -= 1; | ||
| } | ||
|
|
||
| fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) { | ||
| if self.body_depth == 0 { | ||
| return; | ||
| } | ||
|
|
||
| let parent = cx.tcx.parent(item.owner_id.def_id.into()); | ||
| let parent_def_kind = cx.tcx.def_kind(parent); | ||
| let parent_opt_item_name = cx.tcx.opt_item_name(parent); | ||
|
|
||
| // Per RFC we (currently) ignore anon-const (`const _: Ty = ...`) in top-level module. | ||
| if self.body_depth == 1 | ||
| && parent_def_kind == DefKind::Const | ||
| && parent_opt_item_name == Some(kw::Underscore) | ||
| { | ||
| return; | ||
| } | ||
|
|
||
| let cargo_update = || { | ||
| let oexpn = item.span.ctxt().outer_expn_data(); | ||
| if let Some(def_id) = oexpn.macro_def_id | ||
| && let ExpnKind::Macro(macro_kind, macro_name) = oexpn.kind | ||
| && def_id.krate != LOCAL_CRATE | ||
| && std::env::var_os("CARGO").is_some() | ||
| { | ||
| Some(NonLocalDefinitionsCargoUpdateNote { | ||
| macro_kind: macro_kind.descr(), | ||
| macro_name, | ||
| crate_name: cx.tcx.crate_name(def_id.krate), | ||
| }) | ||
| } else { | ||
| None | ||
| } | ||
| }; | ||
|
|
||
| match item.kind { | ||
| ItemKind::Impl(impl_) => { | ||
| // The RFC states: | ||
| // | ||
| // > An item nested inside an expression-containing item (through any | ||
| // > level of nesting) may not define an impl Trait for Type unless | ||
| // > either the **Trait** or the **Type** is also nested inside the | ||
| // > same expression-containing item. | ||
| // | ||
| // To achieve this we get try to get the paths of the _Trait_ and | ||
| // _Type_, and we look inside thoses paths to try a find in one | ||
| // of them a type whose parent is the same as the impl definition. | ||
| // | ||
| // If that's the case this means that this impl block declaration | ||
| // is using local items and so we don't lint on it. | ||
|
|
||
| // We also ignore anon-const in item by including the anon-const | ||
| // parent as well; and since it's quite uncommon, we use smallvec | ||
| // to avoid unnecessary heap allocations. | ||
| let local_parents: SmallVec<[DefId; 1]> = if parent_def_kind == DefKind::Const | ||
| && parent_opt_item_name == Some(kw::Underscore) | ||
| { | ||
| smallvec![parent, cx.tcx.parent(parent)] | ||
| } else { | ||
| smallvec![parent] | ||
| }; | ||
|
|
||
| let self_ty_has_local_parent = match impl_.self_ty.kind { | ||
| TyKind::Path(QPath::Resolved(_, ty_path)) => { | ||
| path_has_local_parent(ty_path, cx, &*local_parents) | ||
| } | ||
| TyKind::TraitObject([principle_poly_trait_ref, ..], _, _) => { | ||
| path_has_local_parent( | ||
| principle_poly_trait_ref.trait_ref.path, | ||
| cx, | ||
| &*local_parents, | ||
| ) | ||
| } | ||
| TyKind::TraitObject([], _, _) | ||
| | TyKind::InferDelegation(_, _) | ||
| | TyKind::Slice(_) | ||
| | TyKind::Array(_, _) | ||
| | TyKind::Ptr(_) | ||
| | TyKind::Ref(_, _) | ||
| | TyKind::BareFn(_) | ||
| | TyKind::Never | ||
| | TyKind::Tup(_) | ||
| | TyKind::Path(_) | ||
| | TyKind::AnonAdt(_) | ||
| | TyKind::OpaqueDef(_, _, _) | ||
| | TyKind::Typeof(_) | ||
| | TyKind::Infer | ||
| | TyKind::Err(_) => false, | ||
| }; | ||
|
|
||
| let of_trait_has_local_parent = impl_ | ||
| .of_trait | ||
| .map(|of_trait| path_has_local_parent(of_trait.path, cx, &*local_parents)) | ||
| .unwrap_or(false); | ||
|
|
||
| // If none of them have a local parent (LOGICAL NOR) this means that | ||
| // this impl definition is a non-local definition and so we lint on it. | ||
| if !(self_ty_has_local_parent || of_trait_has_local_parent) { | ||
| let const_anon = if self.body_depth == 1 | ||
| && parent_def_kind == DefKind::Const | ||
| && parent_opt_item_name != Some(kw::Underscore) | ||
| && let Some(parent) = parent.as_local() | ||
| && let Node::Item(item) = cx.tcx.hir_node_by_def_id(parent) | ||
| && let ItemKind::Const(ty, _, _) = item.kind | ||
| && let TyKind::Tup(&[]) = ty.kind | ||
| { | ||
| Some(item.ident.span) | ||
| } else { | ||
| None | ||
| }; | ||
|
|
||
| cx.emit_span_lint( | ||
| NON_LOCAL_DEFINITIONS, | ||
| item.span, | ||
| NonLocalDefinitionsDiag::Impl { | ||
| depth: self.body_depth, | ||
| body_kind_descr: cx.tcx.def_kind_descr(parent_def_kind, parent), | ||
| body_name: parent_opt_item_name | ||
| .map(|s| s.to_ident_string()) | ||
| .unwrap_or_else(|| "<unnameable>".to_string()), | ||
| cargo_update: cargo_update(), | ||
| const_anon, | ||
| }, | ||
| ) | ||
| } | ||
| } | ||
| ItemKind::Macro(_macro, MacroKind::Bang) | ||
| if cx.tcx.has_attr(item.owner_id.def_id, sym::macro_export) => | ||
| { | ||
| cx.emit_span_lint( | ||
| NON_LOCAL_DEFINITIONS, | ||
| item.span, | ||
| NonLocalDefinitionsDiag::MacroRules { | ||
| depth: self.body_depth, | ||
| body_kind_descr: cx.tcx.def_kind_descr(parent_def_kind, parent), | ||
| body_name: parent_opt_item_name | ||
| .map(|s| s.to_ident_string()) | ||
| .unwrap_or_else(|| "<unnameable>".to_string()), | ||
| cargo_update: cargo_update(), | ||
| }, | ||
| ) | ||
| } | ||
| _ => {} | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /// Given a path and a parent impl def id, this checks if the if parent resolution | ||
| /// def id correspond to the def id of the parent impl definition. | ||
| /// | ||
| /// Given this path, we will look at the path (and ignore any generic args): | ||
| /// | ||
| /// ```text | ||
| /// std::convert::PartialEq<Foo<Bar>> | ||
| /// ^^^^^^^^^^^^^^^^^^^^^^^ | ||
| /// ``` | ||
| fn path_has_local_parent(path: &Path<'_>, cx: &LateContext<'_>, local_parents: &[DefId]) -> bool { | ||
| path.res.opt_def_id().is_some_and(|did| local_parents.contains(&cx.tcx.parent(did))) | ||
| } |
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