rustc_lint/non_local_def.rs
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use rustc_errors::MultiSpan;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::{Body, HirId, Item, ItemKind, Node, Path, TyKind};
use rustc_middle::ty::TyCtxt;
use rustc_session::{declare_lint, impl_lint_pass};
use rustc_span::def_id::{DefId, LOCAL_CRATE};
use rustc_span::symbol::kw;
use rustc_span::{ExpnKind, MacroKind, Span, sym};
use crate::lints::{NonLocalDefinitionsCargoUpdateNote, NonLocalDefinitionsDiag};
use crate::{LateContext, LateLintPass, LintContext, fluent_generated as fluent};
declare_lint! {
/// The `non_local_definitions` lint checks for `impl` blocks and `#[macro_export]`
/// macro inside bodies (functions, enum discriminant, ...).
///
/// ### Example
///
/// ```rust
/// #![warn(non_local_definitions)]
/// 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 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(crate) 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: &Body<'tcx>) {
self.body_depth += 1;
}
fn check_body_post(&mut self, _cx: &LateContext<'tcx>, _body: &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 def_id = item.owner_id.def_id.into();
let parent = cx.tcx.parent(def_id);
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
&& rustc_session::utils::was_invoked_from_cargo()
{
Some(NonLocalDefinitionsCargoUpdateNote {
macro_kind: macro_kind.descr(),
macro_name,
crate_name: cx.tcx.crate_name(def_id.krate),
})
} else {
None
}
};
// determining if we are in a doctest context can't currently be determined
// by the code itself (there are no specific attributes), but fortunately rustdoc
// sets a perma-unstable env var for libtest so we just reuse that for now
let is_at_toplevel_doctest =
|| self.body_depth == 2 && std::env::var("UNSTABLE_RUSTDOC_TEST_PATH").is_ok();
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 those 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.
// 1. We collect all the `hir::Path` from the `Self` type and `Trait` ref
// of the `impl` definition
let mut collector = PathCollector { paths: Vec::new() };
collector.visit_ty(&impl_.self_ty);
if let Some(of_trait) = &impl_.of_trait {
collector.visit_trait_ref(of_trait);
}
// 1.5. Remove any path that doesn't resolve to a `DefId` or if it resolve to a
// type-param (e.g. `T`).
collector.paths.retain(
|p| matches!(p.res, Res::Def(def_kind, _) if def_kind != DefKind::TyParam),
);
// 1.9. We retrieve the parent def id of the impl item, ...
//
// ... modulo const-anons items, for enhanced compatibility with the ecosystem
// as that pattern is common with `serde`, `bevy`, ...
//
// For this example we want the `DefId` parent of the outermost const-anon items.
// ```
// const _: () = { // the parent of this const-anon
// const _: () = {
// impl Foo {}
// };
// };
// ```
//
// It isn't possible to mix a impl in a module with const-anon, but an item can
// be put inside a module and referenced by a impl so we also have to treat the
// item parent as transparent to module and for consistency we have to do the same
// for impl, otherwise the item-def and impl-def won't have the same parent.
let outermost_impl_parent = peel_parent_while(cx.tcx, parent, |tcx, did| {
tcx.def_kind(did) == DefKind::Mod
|| (tcx.def_kind(did) == DefKind::Const
&& tcx.opt_item_name(did) == Some(kw::Underscore))
});
// 2. We check if any of the paths reference a the `impl`-parent.
//
// If that the case we bail out, as was asked by T-lang, even though this isn't
// correct from a type-system point of view, as inference exists and one-impl-rule
// make its so that we could still leak the impl.
if collector
.paths
.iter()
.any(|path| path_has_local_parent(path, cx, parent, outermost_impl_parent))
{
return;
}
// Get the span of the parent const item ident (if it's a not a const anon).
//
// Used to suggest changing the const item to a const anon.
let span_for_const_anon_suggestion = if 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
};
let const_anon = matches!(parent_def_kind, DefKind::Const | DefKind::Static { .. })
.then_some(span_for_const_anon_suggestion);
let impl_span = item.span.shrink_to_lo().to(impl_.self_ty.span);
let mut ms = MultiSpan::from_span(impl_span);
for path in &collector.paths {
// FIXME: While a translatable diagnostic message can have an argument
// we (currently) have no way to set different args per diag msg with
// `MultiSpan::push_span_label`.
#[allow(rustc::untranslatable_diagnostic)]
ms.push_span_label(
path_span_without_args(path),
format!("`{}` is not local", path_name_to_string(path)),
);
}
let doctest = is_at_toplevel_doctest();
if !doctest {
ms.push_span_label(
cx.tcx.def_span(parent),
fluent::lint_non_local_definitions_impl_move_help,
);
}
let macro_to_change =
if let ExpnKind::Macro(kind, name) = item.span.ctxt().outer_expn_data().kind {
Some((name.to_string(), kind.descr()))
} else {
None
};
cx.emit_span_lint(NON_LOCAL_DEFINITIONS, ms, 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,
doctest,
macro_to_change,
})
}
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(),
doctest: is_at_toplevel_doctest(),
},
)
}
_ => {}
}
}
}
/// Simple hir::Path collector
struct PathCollector<'tcx> {
paths: Vec<Path<'tcx>>,
}
impl<'tcx> Visitor<'tcx> for PathCollector<'tcx> {
fn visit_path(&mut self, path: &Path<'tcx>, _id: HirId) {
self.paths.push(path.clone()); // need to clone, bc of the restricted lifetime
intravisit::walk_path(self, path)
}
}
/// Given a path, this checks if the if the parent resolution def id corresponds to
/// the def id of the parent impl definition (the direct one and the outermost one).
///
/// Given this path, we will look at the path (and ignore any generic args):
///
/// ```text
/// std::convert::PartialEq<Foo<Bar>>
/// ^^^^^^^^^^^^^^^^^^^^^^^
/// ```
#[inline]
fn path_has_local_parent(
path: &Path<'_>,
cx: &LateContext<'_>,
impl_parent: DefId,
outermost_impl_parent: Option<DefId>,
) -> bool {
path.res
.opt_def_id()
.is_some_and(|did| did_has_local_parent(did, cx.tcx, impl_parent, outermost_impl_parent))
}
/// Given a def id this checks if the parent def id (modulo modules) correspond to
/// the def id of the parent impl definition (the direct one and the outermost one).
#[inline]
fn did_has_local_parent(
did: DefId,
tcx: TyCtxt<'_>,
impl_parent: DefId,
outermost_impl_parent: Option<DefId>,
) -> bool {
if !did.is_local() {
return false;
}
let Some(parent_did) = tcx.opt_parent(did) else {
return false;
};
peel_parent_while(tcx, parent_did, |tcx, did| {
tcx.def_kind(did) == DefKind::Mod
|| (tcx.def_kind(did) == DefKind::Const
&& tcx.opt_item_name(did) == Some(kw::Underscore))
})
.map(|parent_did| parent_did == impl_parent || Some(parent_did) == outermost_impl_parent)
.unwrap_or(false)
}
/// Given a `DefId` checks if it satisfies `f` if it does check with it's parent and continue
/// until it doesn't satisfies `f` and return the last `DefId` checked.
///
/// In other word this method return the first `DefId` that doesn't satisfies `f`.
#[inline]
fn peel_parent_while(
tcx: TyCtxt<'_>,
mut did: DefId,
mut f: impl FnMut(TyCtxt<'_>, DefId) -> bool,
) -> Option<DefId> {
while !did.is_crate_root() && f(tcx, did) {
did = tcx.opt_parent(did).filter(|parent_did| parent_did.is_local())?;
}
Some(did)
}
/// Return for a given `Path` the span until the last args
fn path_span_without_args(path: &Path<'_>) -> Span {
if let Some(args) = &path.segments.last().unwrap().args {
path.span.until(args.span_ext)
} else {
path.span
}
}
/// Return a "error message-able" ident for the last segment of the `Path`
fn path_name_to_string(path: &Path<'_>) -> String {
path.segments.last().unwrap().ident.name.to_ident_string()
}