rustc_lint/unqualified_local_imports.rs
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use rustc_hir::def::{DefKind, Res};
use rustc_hir::{self as hir};
use rustc_session::{declare_lint, declare_lint_pass};
use rustc_span::symbol::kw;
use crate::{LateContext, LateLintPass, LintContext, lints};
declare_lint! {
/// The `unqualified_local_imports` lint checks for `use` items that import a local item using a
/// path that does not start with `self::`, `super::`, or `crate::`.
///
/// ### Example
///
/// ```rust,edition2018
/// #![warn(unqualified_local_imports)]
///
/// mod localmod {
/// pub struct S;
/// }
///
/// use localmod::S;
/// # // We have to actually use `S`, or else the `unused` warnings suppress the lint we care about.
/// # pub fn main() {
/// # let _x = S;
/// # }
/// ```
///
/// {{produces}}
///
/// ### Explanation
///
/// This lint is meant to be used with the (unstable) rustfmt setting `group_imports = "StdExternalCrate"`.
/// That setting makes rustfmt group `self::`, `super::`, and `crate::` imports separately from those
/// refering to other crates. However, rustfmt cannot know whether `use c::S;` refers to a local module `c`
/// or an external crate `c`, so it always gets categorized as an import from another crate.
/// To ensure consistent grouping of imports from the local crate, all local imports must
/// start with `self::`, `super::`, or `crate::`. This lint can be used to enforce that style.
pub UNQUALIFIED_LOCAL_IMPORTS,
Allow,
"`use` of a local item without leading `self::`, `super::`, or `crate::`",
@feature_gate = unqualified_local_imports;
}
declare_lint_pass!(UnqualifiedLocalImports => [UNQUALIFIED_LOCAL_IMPORTS]);
impl<'tcx> LateLintPass<'tcx> for UnqualifiedLocalImports {
fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
let hir::ItemKind::Use(path, _kind) = item.kind else { return };
// `path` has three resolutions for the type, module, value namespaces.
// Check if any of them qualifies: local crate, and not a macro.
// (Macros can't be imported any other way so we don't complain about them.)
let is_local_import = |res: &Res| {
matches!(
res,
hir::def::Res::Def(def_kind, def_id)
if def_id.is_local() && !matches!(def_kind, DefKind::Macro(_)),
)
};
if !path.res.iter().any(is_local_import) {
return;
}
// So this does refer to something local. Let's check whether it starts with `self`,
// `super`, or `crate`. If the path is empty, that means we have a `use *`, which is
// equivalent to `use crate::*` so we don't fire the lint in that case.
let Some(first_seg) = path.segments.first() else { return };
if matches!(first_seg.ident.name, kw::SelfLower | kw::Super | kw::Crate) {
return;
}
let encl_item_id = cx.tcx.hir().get_parent_item(item.hir_id());
let encl_item = cx.tcx.hir_node_by_def_id(encl_item_id.def_id);
if encl_item.fn_kind().is_some() {
// `use` in a method -- don't lint, that leads to too many undesirable lints
// when a function imports all variants of an enum.
return;
}
// This `use` qualifies for our lint!
cx.emit_span_lint(
UNQUALIFIED_LOCAL_IMPORTS,
first_seg.ident.span,
lints::UnqualifiedLocalImportsDiag {},
);
}
}