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Added lint match_vec_item 
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‎CHANGELOG.md‎

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@@ -1352,6 +1352,7 @@ Released 2018-09-13
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[`match_ref_pats`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_ref_pats
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[`match_same_arms`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_same_arms
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[`match_single_binding`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_single_binding
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[`match_vec_item`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_vec_item
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[`match_wild_err_arm`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_wild_err_arm
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[`maybe_infinite_iter`]: https://rust-lang.github.io/rust-clippy/master/index.html#maybe_infinite_iter
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[`mem_discriminant_non_enum`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_discriminant_non_enum

‎clippy_lints/src/lib.rs‎

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@@ -249,6 +249,7 @@ mod macro_use;
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mod main_recursion;
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mod map_clone;
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mod map_unit_fn;
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mod match_vec_item;
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mod matches;
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mod mem_discriminant;
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mod mem_forget;
@@ -629,6 +630,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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&map_clone::MAP_CLONE,
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&map_unit_fn::OPTION_MAP_UNIT_FN,
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&map_unit_fn::RESULT_MAP_UNIT_FN,
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&match_vec_item::MATCH_VEC_ITEM,
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&matches::INFALLIBLE_DESTRUCTURING_MATCH,
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&matches::MATCH_AS_REF,
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&matches::MATCH_BOOL,
@@ -1060,6 +1062,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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store.register_late_pass(|| box future_not_send::FutureNotSend);
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store.register_late_pass(|| box utils::internal_lints::CollapsibleCalls);
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store.register_late_pass(|| box if_let_mutex::IfLetMutex);
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store.register_late_pass(|| box match_vec_item::MatchVecItem);
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store.register_group(true, "clippy::restriction", Some("clippy_restriction"), vec![
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LintId::of(&arithmetic::FLOAT_ARITHMETIC),
@@ -1277,6 +1280,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&map_clone::MAP_CLONE),
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LintId::of(&map_unit_fn::OPTION_MAP_UNIT_FN),
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LintId::of(&map_unit_fn::RESULT_MAP_UNIT_FN),
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LintId::of(&match_vec_item::MATCH_VEC_ITEM),
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LintId::of(&matches::INFALLIBLE_DESTRUCTURING_MATCH),
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LintId::of(&matches::MATCH_AS_REF),
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LintId::of(&matches::MATCH_BOOL),
@@ -1469,6 +1473,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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LintId::of(&loops::WHILE_LET_ON_ITERATOR),
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LintId::of(&main_recursion::MAIN_RECURSION),
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LintId::of(&map_clone::MAP_CLONE),
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LintId::of(&match_vec_item::MATCH_VEC_ITEM),
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LintId::of(&matches::INFALLIBLE_DESTRUCTURING_MATCH),
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LintId::of(&matches::MATCH_BOOL),
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LintId::of(&matches::MATCH_OVERLAPPING_ARM),

‎clippy_lints/src/match_vec_item.rs‎

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@@ -0,0 +1,111 @@
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use crate::utils::{is_wild, span_lint_and_help};
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use if_chain::if_chain;
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use rustc_hir::{Arm, Expr, ExprKind, MatchSource};
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use rustc_lint::{LateContext, LateLintPass, LintContext};
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty::{self, AdtDef};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// **What it does:** Checks for `match vec[idx]` or `match vec[n..m]`.
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///
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/// **Why is this bad?** This can panic at runtime.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust, no_run
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/// let arr = vec![0, 1, 2, 3];
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/// let idx = 1;
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///
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/// // Bad
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/// match arr[idx] {
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/// 0 => println!("{}", 0),
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/// 1 => println!("{}", 3),
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/// _ => {},
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/// }
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/// ```
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/// Use instead:
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/// ```rust, no_run
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/// let arr = vec![0, 1, 2, 3];
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/// let idx = 1;
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///
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/// // Good
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/// match arr.get(idx) {
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/// Some(0) => println!("{}", 0),
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/// Some(1) => println!("{}", 3),
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/// _ => {},
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/// }
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/// ```
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pub MATCH_VEC_ITEM,
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style,
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"match vector by indexing can panic"
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}
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declare_lint_pass!(MatchVecItem => [MATCH_VEC_ITEM]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MatchVecItem {
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fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) {
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if_chain! {
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if !in_external_macro(cx.sess(), expr.span);
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if let ExprKind::Match(ref ex, ref arms, MatchSource::Normal) = expr.kind;
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if contains_wild_arm(arms);
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if is_vec_indexing(cx, ex);
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then {
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span_lint_and_help(
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cx,
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MATCH_VEC_ITEM,
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expr.span,
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"indexing vector may panic",
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None,
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"consider using `get(..)` instead.",
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);
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}
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}
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}
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}
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fn contains_wild_arm(arms: &[Arm<'_>]) -> bool {
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arms.iter().any(|arm| is_wild(&arm.pat) && is_unit_expr(arm.body))
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}
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fn is_vec_indexing<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
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if_chain! {
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if let ExprKind::Index(ref array, _) = expr.kind;
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let ty = cx.tables.expr_ty(array);
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if let ty::Adt(def, _) = ty.kind;
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if is_vec(cx, def);
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then {
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return true;
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}
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}
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false
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}
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fn is_vec<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, def: &'a AdtDef) -> bool {
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if_chain! {
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let def_path = cx.tcx.def_path(def.did);
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if def_path.data.len() == 2;
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if let Some(module) = def_path.data.get(0);
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if module.data.as_symbol() == sym!(vec);
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if let Some(name) = def_path.data.get(1);
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if name.data.as_symbol() == sym!(Vec);
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then {
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return true;
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}
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}
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false
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}
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fn is_unit_expr(expr: &Expr<'_>) -> bool {
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match expr.kind {
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ExprKind::Tup(ref v) if v.is_empty() => true,
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ExprKind::Block(ref b, _) if b.stmts.is_empty() && b.expr.is_none() => true,
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_ => false,
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}
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}

‎src/lintlist/mod.rs‎

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@@ -1172,6 +1172,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
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deprecation: None,
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module: "matches",
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},
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Lint {
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name: "match_vec_item",
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group: "style",
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desc: "match vector by indexing can panic",
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deprecation: None,
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module: "match_vec_item",
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},
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Lint {
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name: "match_wild_err_arm",
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group: "style",

‎tests/ui/match_vec_item.rs‎

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#![warn(clippy::match_vec_item)]
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fn main() {
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match_with_wildcard();
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match_without_wildcard();
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match_wildcard_and_action();
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match_with_get();
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match_with_array();
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}
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fn match_with_wildcard() {
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let arr = vec![0, 1, 2, 3];
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let range = 1..3;
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let idx = 1;
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// Lint, may panic
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match arr[idx] {
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0 => println!("0"),
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1 => println!("1"),
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_ => {},
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}
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// Lint, may panic
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match arr[range] {
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[0, 1] => println!("0 1"),
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[1, 2] => println!("1 2"),
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_ => {},
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}
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}
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fn match_without_wildcard() {
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let arr = vec![0, 1, 2, 3];
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let range = 1..3;
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let idx = 2;
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// Ok
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match arr[idx] {
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0 => println!("0"),
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1 => println!("1"),
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num => {},
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}
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// Ok
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match arr[range] {
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[0, 1] => println!("0 1"),
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[1, 2] => println!("1 2"),
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[ref sub @ ..] => {},
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}
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}
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fn match_wildcard_and_action() {
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let arr = vec![0, 1, 2, 3];
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let range = 1..3;
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let idx = 3;
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// Ok
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match arr[idx] {
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0 => println!("0"),
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1 => println!("1"),
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_ => println!("Hello, World!"),
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}
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// Ok
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match arr[range] {
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[0, 1] => println!("0 1"),
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[1, 2] => println!("1 2"),
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_ => println!("Hello, World!"),
68+
}
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}
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fn match_with_get() {
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let arr = vec![0, 1, 2, 3];
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let range = 1..3;
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let idx = 3;
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// Ok
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match arr.get(idx) {
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Some(0) => println!("0"),
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Some(1) => println!("1"),
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_ => {},
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}
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// Ok
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match arr.get(range) {
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Some(&[0, 1]) => println!("0 1"),
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Some(&[1, 2]) => println!("1 2"),
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_ => {},
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}
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}
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fn match_with_array() {
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let arr = [0, 1, 2, 3];
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let range = 1..3;
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let idx = 3;
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// Ok
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match arr[idx] {
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0 => println!("0"),
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1 => println!("1"),
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_ => {},
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}
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// Ok
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match arr[range] {
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[0, 1] => println!("0 1"),
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[1, 2] => println!("1 2"),
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_ => {},
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}
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}

‎tests/ui/match_vec_item.stderr‎

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error: indexing vector may panic
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--> $DIR/match_vec_item.rs:17:5
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|
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LL | / match arr[idx] {
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LL | | 0 => println!("0"),
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LL | | 1 => println!("1"),
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LL | | _ => {},
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LL | | }
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| |_____^
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|
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= note: `-D clippy::match-vec-item` implied by `-D warnings`
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= help: consider using `get(..)` instead.
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error: indexing vector may panic
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--> $DIR/match_vec_item.rs:24:5
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|
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LL | / match arr[range] {
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LL | | [0, 1] => println!("0 1"),
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LL | | [1, 2] => println!("1 2"),
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LL | | _ => {},
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LL | | }
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| |_____^
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|
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= help: consider using `get(..)` instead.
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error: aborting due to 2 previous errors
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