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Add new lint unneeded_struct_pattern 
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‎CHANGELOG.md

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@@ -6133,6 +6133,7 @@ Released 2018-09-13
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[`unnecessary_unwrap`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_unwrap
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[`unnecessary_wraps`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_wraps
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[`unneeded_field_pattern`]: https://rust-lang.github.io/rust-clippy/master/index.html#unneeded_field_pattern
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[`unneeded_struct_pattern`]: https://rust-lang.github.io/rust-clippy/master/index.html#unneeded_struct_pattern
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[`unneeded_wildcard_pattern`]: https://rust-lang.github.io/rust-clippy/master/index.html#unneeded_wildcard_pattern
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[`unnested_or_patterns`]: https://rust-lang.github.io/rust-clippy/master/index.html#unnested_or_patterns
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[`unreachable`]: https://rust-lang.github.io/rust-clippy/master/index.html#unreachable

‎clippy_lints/src/declared_lints.rs

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@@ -753,6 +753,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
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crate::unnecessary_self_imports::UNNECESSARY_SELF_IMPORTS_INFO,
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crate::unnecessary_struct_initialization::UNNECESSARY_STRUCT_INITIALIZATION_INFO,
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crate::unnecessary_wraps::UNNECESSARY_WRAPS_INFO,
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crate::unneeded_struct_pattern::UNNEEDED_STRUCT_PATTERN_INFO,
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crate::unnested_or_patterns::UNNESTED_OR_PATTERNS_INFO,
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crate::unsafe_removed_from_name::UNSAFE_REMOVED_FROM_NAME_INFO,
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crate::unused_async::UNUSED_ASYNC_INFO,

‎clippy_lints/src/lib.rs

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@@ -374,6 +374,7 @@ mod unnecessary_owned_empty_strings;
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mod unnecessary_self_imports;
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mod unnecessary_struct_initialization;
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mod unnecessary_wraps;
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mod unneeded_struct_pattern;
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mod unnested_or_patterns;
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mod unsafe_removed_from_name;
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mod unused_async;
@@ -967,5 +968,6 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
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store.register_late_pass(|_| Box::new(manual_ignore_case_cmp::ManualIgnoreCaseCmp));
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store.register_late_pass(|_| Box::new(unnecessary_literal_bound::UnnecessaryLiteralBound));
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store.register_late_pass(move |_| Box::new(arbitrary_source_item_ordering::ArbitrarySourceItemOrdering::new(conf)));
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store.register_late_pass(|_| Box::new(unneeded_struct_pattern::UnneededStructPattern));
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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/unneeded_struct_pattern.rs

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@@ -0,0 +1,76 @@
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use clippy_utils::diagnostics::span_lint_and_sugg;
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use clippy_utils::is_from_proc_macro;
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use rustc_errors::Applicability;
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use rustc_hir::def::{DefKind, Res};
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use rustc_hir::{Pat, PatKind, QPath};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::declare_lint_pass;
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for struct patterns that match against unit variant.
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///
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/// ### Why is this bad?
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/// Struct pattern `{ }` or `{ .. }` is not needed for unit variant.
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///
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/// ### Example
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/// ```no_run
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/// match Some(42) {
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/// Some(v) => v,
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/// None { .. } => 0,
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/// };
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/// // Or
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/// match Some(42) {
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/// Some(v) => v,
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/// None { } => 0,
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/// };
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/// ```
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/// Use instead:
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/// ```no_run
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/// match Some(42) {
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/// Some(v) => v,
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/// None => 0,
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/// };
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/// ```
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#[clippy::version = "1.83.0"]
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pub UNNEEDED_STRUCT_PATTERN,
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style,
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"using struct pattern to match against unit variant"
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}
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declare_lint_pass!(UnneededStructPattern => [UNNEEDED_STRUCT_PATTERN]);
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impl LateLintPass<'_> for UnneededStructPattern {
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fn check_pat(&mut self, cx: &LateContext<'_>, pat: &Pat<'_>) {
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if !pat.span.from_expansion()
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&& let PatKind::Struct(path, [], _) = &pat.kind
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&& let QPath::Resolved(_, path) = path
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&& let Res::Def(DefKind::Variant, did) = path.res
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{
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let enum_did = cx.tcx.parent(did);
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let variant = cx.tcx.adt_def(enum_did).variant_with_id(did);
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let has_only_fields_brackets = variant.ctor.is_some() && variant.fields.is_empty();
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let non_exhaustive_activated = !variant.def_id.is_local() && variant.is_field_list_non_exhaustive();
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if !has_only_fields_brackets || non_exhaustive_activated {
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return;
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}
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if is_from_proc_macro(cx, *path) {
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return;
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}
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if let Some(brackets_span) = pat.span.trim_start(path.span) {
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span_lint_and_sugg(
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cx,
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UNNEEDED_STRUCT_PATTERN,
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brackets_span,
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"struct pattern is not needed for a unit variant",
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"remove the struct pattern",
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String::new(),
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Applicability::MachineApplicable,
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);
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}
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}
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}
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}

‎tests/ui/auxiliary/non-exhaustive-enum.rs

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@@ -6,3 +6,24 @@ pub enum ErrorKind {
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#[doc(hidden)]
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Uncategorized,
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}
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#[non_exhaustive]
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pub enum ExtNonExhaustiveEnum {
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Unit,
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Tuple(i32),
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Struct { field: i32 },
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}
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pub enum ExtNonExhaustiveVariant {
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ExhaustiveUnit,
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#[non_exhaustive]
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Unit,
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#[non_exhaustive]
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Tuple(i32),
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#[non_exhaustive]
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StructNoField {},
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#[non_exhaustive]
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Struct {
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field: i32,
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},
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}

‎tests/ui/unneeded_struct_pattern.fixed

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//@aux-build:non-exhaustive-enum.rs
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#![allow(clippy::manual_unwrap_or_default, clippy::manual_unwrap_or)]
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#![warn(clippy::unneeded_struct_pattern)]
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extern crate non_exhaustive_enum;
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use non_exhaustive_enum::*;
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fn main() {
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match Some(114514) {
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Some(v) => v,
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None => 0,
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};
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match Some(1919810) {
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Some(v) => v,
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None => 0,
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};
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match Some(123456) {
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Some(v) => v,
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None => 0,
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};
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match Some(Some(123456)) {
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Some(Some(v)) => v,
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Some(None) => 0,
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None => 0,
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};
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if let None = Some(0) {}
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if let None = Some(0) {}
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if let Some(None) = Some(Some(0)) {}
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let None = Some(0) else { panic!() };
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let None = Some(0) else { panic!() };
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let Some(None) = Some(Some(0)) else { panic!() };
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enum Custom {
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HasFields {
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field: i32,
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},
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HasBracketsNoFields {},
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NoBrackets,
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#[non_exhaustive]
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NoBracketsNonExhaustive,
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Init,
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};
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match Custom::Init {
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Custom::HasFields { field: value } => value, // Should be ignored
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Custom::HasBracketsNoFields {} => 0, // Should be ignored
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Custom::NoBrackets => 0, // Should be fixed
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Custom::NoBracketsNonExhaustive => 0, // Should be fixed
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_ => 0,
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};
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match Custom::Init {
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Custom::HasFields { field: value } => value, // Should be ignored
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Custom::HasBracketsNoFields { .. } => 0, // Should be ignored
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Custom::NoBrackets => 0, // Should be fixed
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Custom::NoBracketsNonExhaustive => 0, // Should be fixed
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_ => 0,
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};
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match Custom::Init {
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Custom::NoBrackets if true => 0, // Should be fixed
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_ => 0,
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};
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match Custom::Init {
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Custom::NoBrackets | Custom::NoBracketsNonExhaustive => 0, // Should be fixed
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_ => 0,
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};
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if let Custom::HasFields { field: value } = Custom::Init {} // Should be ignored
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if let Custom::HasBracketsNoFields {} = Custom::Init {} // Should be ignored
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if let Custom::HasBracketsNoFields { .. } = Custom::Init {} // Should be ignored
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if let Custom::NoBrackets = Custom::Init {} // Should be fixed
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if let Custom::NoBrackets = Custom::Init {} // Should be fixed
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if let Custom::NoBrackets | Custom::NoBracketsNonExhaustive = Custom::Init {} // Should be fixed
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if let Custom::NoBracketsNonExhaustive = Custom::Init {} // Should be fixed
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if let Custom::NoBracketsNonExhaustive = Custom::Init {} // Should be fixed
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// Should be ignored
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let Custom::HasFields { field: value } = Custom::Init else {
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panic!()
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};
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// Should be ignored
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let Custom::HasBracketsNoFields {} = Custom::Init else {
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panic!()
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};
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// Should be ignored
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let Custom::HasBracketsNoFields { .. } = Custom::Init else {
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panic!()
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};
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let Custom::NoBrackets = Custom::Init else { panic!() }; // Should be fixed
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// Should be fixed
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let Custom::NoBrackets = Custom::Init else {
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panic!()
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};
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// Should be fixed
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let Custom::NoBracketsNonExhaustive = Custom::Init else {
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panic!()
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};
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// Should be fixed
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let Custom::NoBracketsNonExhaustive = Custom::Init else {
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panic!()
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};
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enum Refutable {
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Variant,
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}
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fn pat_in_fn_param_1(Refutable::Variant: Refutable) {} // Should be fixed
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fn pat_in_fn_param_2(Refutable::Variant: Refutable) {} // Should be fixed
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for Refutable::Variant in [] {} // Should be fixed
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for Refutable::Variant in [] {} // Should be fixed
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}
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fn external_crate() {
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use ExtNonExhaustiveVariant::*;
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match ExhaustiveUnit {
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// Expected
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ExhaustiveUnit => 0,
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_ => 0,
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};
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match ExhaustiveUnit {
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// Exhaustive variant, should be fixed
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ExhaustiveUnit => 0,
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_ => 0,
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};
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match ExhaustiveUnit {
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// Exhaustive variant, should be fixed
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ExhaustiveUnit => 0,
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_ => 0,
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};
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match ExhaustiveUnit {
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ExhaustiveUnit => 0,
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// vvvvv Non-exhaustive variants, should all be ignored
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Unit { .. } => 0,
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Tuple { 0: field, .. } => field,
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StructNoField { .. } => 0,
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Struct { field, .. } => field,
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_ => 0,
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};
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}

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