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Add new lint shadow_type_generic
Add a new restriction lint `shadow_type_generic` that checks for generic parameters that shadow types in scope. Signed-off-by: Alexandre Barone <[email protected]>
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‎CHANGELOG.md‎

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@@ -6851,6 +6851,7 @@ Released 2018-09-13
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[`set_contains_or_insert`]: https://rust-lang.github.io/rust-clippy/master/index.html#set_contains_or_insert
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[`shadow_reuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_reuse
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[`shadow_same`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_same
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[`shadow_type_generic`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_type_generic
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[`shadow_unrelated`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_unrelated
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[`short_circuit_statement`]: https://rust-lang.github.io/rust-clippy/master/index.html#short_circuit_statement
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[`should_assert_eq`]: https://rust-lang.github.io/rust-clippy/master/index.html#should_assert_eq

‎clippy_lints/src/declared_lints.rs‎

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@@ -672,6 +672,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
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crate::shadow::SHADOW_REUSE_INFO,
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crate::shadow::SHADOW_SAME_INFO,
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crate::shadow::SHADOW_UNRELATED_INFO,
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crate::shadow_type::SHADOW_TYPE_GENERIC_INFO,
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crate::significant_drop_tightening::SIGNIFICANT_DROP_TIGHTENING_INFO,
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crate::single_call_fn::SINGLE_CALL_FN_INFO,
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crate::single_char_lifetime_names::SINGLE_CHAR_LIFETIME_NAMES_INFO,

‎clippy_lints/src/lib.rs‎

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@@ -323,6 +323,7 @@ mod semicolon_if_nothing_returned;
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mod serde_api;
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mod set_contains_or_insert;
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mod shadow;
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mod shadow_type;
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mod significant_drop_tightening;
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mod single_call_fn;
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mod single_char_lifetime_names;
@@ -819,5 +820,6 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
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store.register_late_pass(|_| Box::new(toplevel_ref_arg::ToplevelRefArg));
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store.register_late_pass(|_| Box::new(volatile_composites::VolatileComposites));
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store.register_late_pass(|_| Box::new(replace_box::ReplaceBox));
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store.register_late_pass(|_| Box::<shadow_type::ShadowTypeGeneric>::default());
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// add lints here, do not remove this comment, it's used in `new_lint`
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}

‎clippy_lints/src/shadow_type.rs‎

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use clippy_utils::diagnostics::span_lint_and_then;
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use rustc_data_structures::fx::FxHashMap;
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use rustc_hir::{GenericParamKind, Generics, HirId, Item, ItemKind, Mod};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_session::impl_lint_pass;
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use rustc_span::{Ident, Span, Symbol};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for generic parameters that shadow types in scope.
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///
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/// ### Why restrict this?
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/// To avoid confusion and potential bugs, as it can lead to
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/// misunderstandings about which type is being referred to.
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///
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/// ### Example
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/// ```no_run
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/// struct Foo;
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/// struct Bar<Foo> { f: Foo }
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/// ```
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///
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/// Use instead:
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/// ```no_run
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/// struct Foo;
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/// struct Bar<F> { f: F } // use different generic parameter name
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/// ```
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#[clippy::version = "1.89.0"]
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pub SHADOW_TYPE_GENERIC,
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restriction,
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"shadowing of type in scope by generic parameter"
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}
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#[derive(Default)]
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pub(crate) struct ShadowTypeGeneric {
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module_types: FxHashMap<Symbol, Span>,
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}
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impl_lint_pass!(ShadowTypeGeneric => [SHADOW_TYPE_GENERIC]);
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impl<'tcx> LateLintPass<'tcx> for ShadowTypeGeneric {
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fn check_mod(&mut self, cx: &LateContext<'tcx>, module: &'tcx Mod<'tcx>, _: HirId) {
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self.module_types.clear();
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let items = module.item_ids.iter().map(|&id| cx.tcx.hir_item(id));
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for item in items {
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if item.span.in_external_macro(cx.sess().source_map()) || item.span.from_expansion() {
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continue;
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}
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if let ItemKind::Enum(ident, _, _) | ItemKind::Struct(ident, _, _) = item.kind {
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self.module_types.insert(ident.name, ident.span);
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}
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}
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}
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fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
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if item.span.in_external_macro(cx.sess().source_map()) || item.span.from_expansion() {
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return;
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}
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if let ItemKind::Enum(ident, generics, _) | ItemKind::Struct(ident, generics, _) = item.kind {
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self.check(cx, ident, generics);
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}
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}
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}
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impl ShadowTypeGeneric {
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fn check(&self, cx: &LateContext<'_>, ident: Ident, generics: &Generics<'_>) {
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// Look for generic parameters such as `T`.
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let generic_params = generics
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.params
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.iter()
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.filter(|gen_param| matches!(gen_param.kind, GenericParamKind::Type { .. }));
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// Match generic parameters with module types and split into spans lists.
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let (gen_param_spans, type_spans): (Vec<_>, Vec<_>) = generic_params
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.filter_map(|gen_param| {
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self.module_types
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.get(&gen_param.name.ident().name)
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.map(|type_span| (gen_param.span, type_span))
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})
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.unzip();
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let (msg, help) = match gen_param_spans.len() {
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0 => {
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// No generic parameters shadowing types in scope
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return;
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},
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1 => (
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format!("generic parameter in `{ident}` shadows type in scope"),
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"consider using a different name for the generic parameter",
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),
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_ => (
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format!("generic parameters in `{ident}` shadow types in scope"),
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"consider using different names for the generic parameters",
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),
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};
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span_lint_and_then(cx, SHADOW_TYPE_GENERIC, gen_param_spans, msg, |diag| {
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diag.span_labels(
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type_spans,
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&format!("this type is being shadowed by a generic parameter in `{ident}`"),
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);
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diag.help(help);
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});
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}
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}

‎tests/ui/shadow_type.rs‎

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#![warn(clippy::shadow_type_generic)]
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pub mod structs {
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struct Foo;
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enum Bar {}
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//~v shadow_type_generic
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struct Struct1<Foo> {
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foo: Foo,
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}
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//~v shadow_type_generic
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struct Struct2<Bar> {
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bar: Bar,
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}
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//~v shadow_type_generic
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struct Struct3<Foo, Bar> {
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foo: Foo,
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bar: Bar,
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}
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//~v shadow_type_generic
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struct Struct4<Foo, B, Bar> {
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foo: Foo,
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b: B,
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bar: Bar,
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}
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struct Struct5 {
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foo: Foo,
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}
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struct Struct6 {
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bar: Bar,
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}
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}
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pub mod enums {
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struct Foo;
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enum Bar {}
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//~v shadow_type_generic
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enum Enum1<Foo> {
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Foo(Foo),
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}
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//~v shadow_type_generic
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enum Enum2<Bar> {
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Bar(Bar),
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}
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//~v shadow_type_generic
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enum Enum3<Foo, Bar> {
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Foo(Foo),
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Bar(Bar),
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}
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//~v shadow_type_generic
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enum Enum4<Foo, B, Bar> {
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Foo(Foo),
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B(B),
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Bar(Bar),
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}
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enum Enum5 {
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Foo(Foo),
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}
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enum Enum6 {
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Bar(Bar),
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}
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}
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fn main() {}

‎tests/ui/shadow_type.stderr‎

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error: generic parameter in `Struct1` shadows type in scope
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--> tests/ui/shadow_type.rs:8:20
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|
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LL | struct Foo;
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| --- this type is being shadowed by a generic parameter in `Struct1`
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...
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LL | struct Struct1<Foo> {
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| ^^^
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|
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= help: consider using a different name for the generic parameter
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= note: `-D clippy::shadow-type-generic` implied by `-D warnings`
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= help: to override `-D warnings` add `#[allow(clippy::shadow_type_generic)]`
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error: generic parameter in `Struct2` shadows type in scope
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--> tests/ui/shadow_type.rs:12:20
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|
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LL | enum Bar {}
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| --- this type is being shadowed by a generic parameter in `Struct2`
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...
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LL | struct Struct2<Bar> {
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| ^^^
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|
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= help: consider using a different name for the generic parameter
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error: generic parameters in `Struct3` shadow types in scope
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--> tests/ui/shadow_type.rs:16:20
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|
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LL | struct Foo;
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| --- this type is being shadowed by a generic parameter in `Struct3`
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LL | enum Bar {}
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| --- this type is being shadowed by a generic parameter in `Struct3`
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...
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LL | struct Struct3<Foo, Bar> {
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| ^^^ ^^^
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|
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= help: consider using different names for the generic parameters
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error: generic parameters in `Struct4` shadow types in scope
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--> tests/ui/shadow_type.rs:21:20
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|
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LL | struct Foo;
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| --- this type is being shadowed by a generic parameter in `Struct4`
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LL | enum Bar {}
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| --- this type is being shadowed by a generic parameter in `Struct4`
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...
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LL | struct Struct4<Foo, B, Bar> {
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| ^^^ ^^^
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|
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= help: consider using different names for the generic parameters
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error: generic parameter in `Enum1` shadows type in scope
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--> tests/ui/shadow_type.rs:39:16
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|
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LL | struct Foo;
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| --- this type is being shadowed by a generic parameter in `Enum1`
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...
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LL | enum Enum1<Foo> {
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| ^^^
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|
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= help: consider using a different name for the generic parameter
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error: generic parameter in `Enum2` shadows type in scope
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--> tests/ui/shadow_type.rs:43:16
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|
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LL | enum Bar {}
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| --- this type is being shadowed by a generic parameter in `Enum2`
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...
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LL | enum Enum2<Bar> {
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| ^^^
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|
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= help: consider using a different name for the generic parameter
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error: generic parameters in `Enum3` shadow types in scope
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--> tests/ui/shadow_type.rs:47:16
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|
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LL | struct Foo;
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| --- this type is being shadowed by a generic parameter in `Enum3`
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LL | enum Bar {}
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| --- this type is being shadowed by a generic parameter in `Enum3`
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...
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LL | enum Enum3<Foo, Bar> {
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| ^^^ ^^^
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|
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= help: consider using different names for the generic parameters
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error: generic parameters in `Enum4` shadow types in scope
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--> tests/ui/shadow_type.rs:52:16
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|
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LL | struct Foo;
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| --- this type is being shadowed by a generic parameter in `Enum4`
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LL | enum Bar {}
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| --- this type is being shadowed by a generic parameter in `Enum4`
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...
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LL | enum Enum4<Foo, B, Bar> {
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| ^^^ ^^^
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|
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= help: consider using different names for the generic parameters
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error: aborting due to 8 previous errors
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