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Auto merge of rust-lang#120393 - Urgau:rfc3373-non-local-defs, r=<try>
Implement RFC 3373: Avoid non-local definitions in functions This PR implements [RFC 3373: Avoid non-local definitions in functions](rust-lang#120363).
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,198 @@ | ||
| use rustc_hir::{def::DefKind, Body, Item, ItemKind, Path, QPath, TyKind}; | ||
| use rustc_span::{def_id::DefId, sym, symbol::kw, MacroKind}; | ||
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|
||
| use smallvec::{smallvec, SmallVec}; | ||
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| use crate::{lints::NonLocalDefinitionsDiag, LateContext, LateLintPass, LintContext}; | ||
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| 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 | ||
| } | ||
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||
| #[derive(Default)] | ||
| pub struct NonLocalDefinitions { | ||
| body_depth: u32, | ||
| } | ||
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| impl_lint_pass!(NonLocalDefinitions => [NON_LOCAL_DEFINITIONS]); | ||
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| // 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. | ||
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| impl<'tcx> LateLintPass<'tcx> for NonLocalDefinitions { | ||
| fn check_body(&mut self, _cx: &LateContext<'tcx>, _body: &'tcx Body<'tcx>) { | ||
| self.body_depth += 1; | ||
| } | ||
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||
| fn check_body_post(&mut self, _cx: &LateContext<'tcx>, _body: &'tcx Body<'tcx>) { | ||
| self.body_depth -= 1; | ||
| } | ||
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| fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) { | ||
| if self.body_depth == 0 { | ||
| return; | ||
| } | ||
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| let parent_impl = cx.tcx.parent(item.owner_id.def_id.into()); | ||
| let parent_impl_def_kind = cx.tcx.def_kind(parent_impl); | ||
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| // Per RFC we (currently) ignore anon-const (`const _: Ty = ...`) in top-level module. | ||
| if self.body_depth == 1 | ||
| && parent_impl_def_kind == DefKind::Const | ||
| && cx.tcx.opt_item_name(parent_impl) == Some(kw::Underscore) | ||
| { | ||
| return; | ||
| } | ||
|
|
||
| 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 decleration | ||
| // is using local items and so we don't lint on it. | ||
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| // 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_impl_def_kind == DefKind::Const | ||
| && cx.tcx.opt_item_name(parent_impl) == Some(kw::Underscore) | ||
| { | ||
| smallvec![parent_impl, cx.tcx.parent(parent_impl)] | ||
| } else { | ||
| smallvec![parent_impl] | ||
| }; | ||
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| 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(poly_trait_refs, _, _) => { | ||
| poly_trait_refs.iter().any(|poly_trait_ref| { | ||
| path_has_local_parent( | ||
| poly_trait_ref.trait_ref.path, | ||
| cx, | ||
| &*local_parents, | ||
| ) | ||
| }) | ||
| } | ||
| TyKind::InferDelegation(_, _) | ||
| | TyKind::Slice(_) | ||
| | TyKind::Array(_, _) | ||
| | TyKind::Ptr(_) | ||
| | TyKind::Ref(_, _) | ||
| | TyKind::BareFn(_) | ||
| | TyKind::Never | ||
| | TyKind::Tup(_) | ||
| | TyKind::Path(_) | ||
| | TyKind::OpaqueDef(_, _, _) | ||
| | TyKind::Typeof(_) | ||
| | TyKind::Infer | ||
| | TyKind::Err(_) => false, | ||
| }; | ||
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| 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); | ||
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| // 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) { | ||
| cx.emit_span_lint( | ||
| NON_LOCAL_DEFINITIONS, | ||
| item.span, | ||
| NonLocalDefinitionsDiag::Impl { | ||
| depth: self.body_depth, | ||
| body_kind_descr: cx | ||
| .tcx | ||
| .def_kind_descr(parent_impl_def_kind, parent_impl), | ||
| body_name: cx | ||
| .tcx | ||
| .opt_item_name(parent_impl) | ||
| .map(|s| s.to_ident_string()) | ||
| .unwrap_or_else(|| "<unnameable>".to_string()), | ||
| }, | ||
| ) | ||
| } | ||
| } | ||
| 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_impl_def_kind, parent_impl), | ||
| body_name: cx | ||
| .tcx | ||
| .opt_item_name(parent_impl) | ||
| .map(|s| s.to_ident_string()) | ||
| .unwrap_or_else(|| "<unnameable>".to_string()), | ||
| }, | ||
| ) | ||
| } | ||
| _ => {} | ||
| } | ||
| } | ||
| } | ||
|
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| /// 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 { | ||
| if let Some(did) = path.res.opt_def_id() | ||
| && local_parents.contains(&cx.tcx.parent(did)) | ||
| { | ||
| return true; | ||
| } | ||
|
|
||
| false | ||
| } |
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