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Add match_str_case_mismatch lint
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‎CHANGELOG.md

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@@ -2837,6 +2837,7 @@ Released 2018-09-13
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[`match_result_ok`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_result_ok
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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_str_case_mismatch`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_str_case_mismatch
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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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[`match_wildcard_for_single_variants`]: https://rust-lang.github.io/rust-clippy/master/index.html#match_wildcard_for_single_variants
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[`maybe_infinite_iter`]: https://rust-lang.github.io/rust-clippy/master/index.html#maybe_infinite_iter

‎clippy_lints/src/lib.register_all.rs

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@@ -118,6 +118,7 @@ store.register_group(true, "clippy::all", Some("clippy_all"), vec![
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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_result_ok::MATCH_RESULT_OK),
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LintId::of(match_str_case_mismatch::MATCH_STR_CASE_MISMATCH),
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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_LIKE_MATCHES_MACRO),

‎clippy_lints/src/lib.register_correctness.rs

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@@ -36,6 +36,7 @@ store.register_group(true, "clippy::correctness", Some("clippy_correctness"), ve
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LintId::of(loops::ITER_NEXT_LOOP),
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LintId::of(loops::NEVER_LOOP),
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LintId::of(loops::WHILE_IMMUTABLE_CONDITION),
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LintId::of(match_str_case_mismatch::MATCH_STR_CASE_MISMATCH),
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LintId::of(mem_discriminant::MEM_DISCRIMINANT_NON_ENUM),
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LintId::of(mem_replace::MEM_REPLACE_WITH_UNINIT),
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LintId::of(methods::CLONE_DOUBLE_REF),

‎clippy_lints/src/lib.register_lints.rs

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@@ -226,6 +226,7 @@ store.register_lints(&[
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map_unit_fn::RESULT_MAP_UNIT_FN,
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match_on_vec_items::MATCH_ON_VEC_ITEMS,
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match_result_ok::MATCH_RESULT_OK,
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match_str_case_mismatch::MATCH_STR_CASE_MISMATCH,
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matches::INFALLIBLE_DESTRUCTURING_MATCH,
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matches::MATCH_AS_REF,
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matches::MATCH_BOOL,

‎clippy_lints/src/lib.rs

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@@ -265,6 +265,7 @@ mod map_err_ignore;
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mod map_unit_fn;
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mod match_on_vec_items;
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mod match_result_ok;
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mod match_str_case_mismatch;
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mod matches;
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mod mem_discriminant;
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mod mem_forget;
@@ -771,6 +772,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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let enable_raw_pointer_heuristic_for_send = conf.enable_raw_pointer_heuristic_for_send;
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store.register_late_pass(move || Box::new(non_send_fields_in_send_ty::NonSendFieldInSendTy::new(enable_raw_pointer_heuristic_for_send)));
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store.register_late_pass(move || Box::new(undocumented_unsafe_blocks::UndocumentedUnsafeBlocks::default()));
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store.register_late_pass(|| Box::new(match_str_case_mismatch::MatchStrCaseMismatch));
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}
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#[rustfmt::skip]

‎clippy_lints/src/match_str_case_mismatch.rs

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use clippy_utils::diagnostics::span_lint_and_help;
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use clippy_utils::ty::is_type_diagnostic_item;
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use rustc_ast::ast::LitKind;
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use rustc_hir::intravisit::{walk_expr, NestedVisitorMap, Visitor};
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use rustc_hir::{Arm, Expr, ExprKind, MatchSource, PatKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_middle::hir::map::Map;
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use rustc_middle::lint::in_external_macro;
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use rustc_middle::ty;
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::{sym, Span};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for `match` expressions modifying the case of a string with non-compliant arms
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///
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/// ### Why is this bad?
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/// The arm is unreachable, which is likely a mistake
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///
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/// ### Example
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/// ```rust
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/// match &*text.to_ascii_lowercase() {
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/// "foo" => {},
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/// "Bar" => {},
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/// _ => {},
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/// }
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/// ```
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/// Use instead:
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/// ```rust
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/// match &*text.to_ascii_lowercase() {
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/// "foo" => {},
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/// "bar" => {},
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/// _ => {},
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/// }
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/// ```
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pub MATCH_STR_CASE_MISMATCH,
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correctness,
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"creation of a case altering match expression with non-compliant arms"
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}
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declare_lint_pass!(MatchStrCaseMismatch => [MATCH_STR_CASE_MISMATCH]);
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#[derive(Debug)]
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enum CaseMethod {
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LowerCase,
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AsciiLowerCase,
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UpperCase,
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AsciiUppercase,
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}
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impl LateLintPass<'_> for MatchStrCaseMismatch {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if_chain! {
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if !in_external_macro(cx.tcx.sess, expr.span);
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if let ExprKind::Match(match_expr, arms, MatchSource::Normal) = expr.kind;
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if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty(match_expr).kind();
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if let ty::Str = ty.kind();
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then {
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let mut visitor = MatchExprVisitor {
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cx,
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case_method: None,
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};
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visitor.visit_expr(match_expr);
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if let Some(case_method) = visitor.case_method {
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if let Some(bad_case) = verify_case(&case_method, arms) {
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lint(cx, expr.span, &case_method, bad_case);
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}
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}
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}
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}
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}
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}
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struct MatchExprVisitor<'a, 'tcx> {
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cx: &'a LateContext<'tcx>,
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case_method: Option<CaseMethod>,
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}
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impl<'a, 'tcx> Visitor<'tcx> for MatchExprVisitor<'a, 'tcx> {
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type Map = Map<'tcx>;
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fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
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NestedVisitorMap::None
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}
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fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
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match ex.kind {
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ExprKind::MethodCall(segment, _, [receiver], _)
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if self.case_altered(&*segment.ident.as_str(), receiver) => {},
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_ => walk_expr(self, ex),
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}
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}
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}
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impl<'a, 'tcx> MatchExprVisitor<'a, 'tcx> {
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fn case_altered(&mut self, segment_ident: &str, receiver: &Expr<'_>) -> bool {
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if let Some(case_method) = get_case_method(segment_ident) {
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let ty = self.cx.typeck_results().expr_ty(receiver).peel_refs();
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if is_type_diagnostic_item(self.cx, ty, sym::String) || ty.kind() == &ty::Str {
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self.case_method = Some(case_method);
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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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}
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fn get_case_method(segment_ident_str: &str) -> Option<CaseMethod> {
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match segment_ident_str {
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"to_lowercase" => Some(CaseMethod::LowerCase),
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"to_ascii_lowercase" => Some(CaseMethod::AsciiLowerCase),
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"to_uppercase" => Some(CaseMethod::UpperCase),
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"to_ascii_uppercase" => Some(CaseMethod::AsciiUppercase),
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_ => None,
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}
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}
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fn verify_case(case_method: &CaseMethod, arms: &'_ [Arm<'_>]) -> Option<Span> {
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let mut bad_case = None;
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let case_check = match case_method {
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CaseMethod::LowerCase => |input: &str| -> bool { input.chars().all(char::is_lowercase) },
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CaseMethod::AsciiLowerCase => |input: &str| -> bool { input.chars().all(|c| matches!(c, 'a'..='z')) },
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CaseMethod::UpperCase => |input: &str| -> bool { input.chars().all(char::is_uppercase) },
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CaseMethod::AsciiUppercase => |input: &str| -> bool { input.chars().all(|c| matches!(c, 'A'..='Z')) },
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};
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for arm in arms {
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if_chain! {
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if let PatKind::Lit(Expr {
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kind: ExprKind::Lit(lit),
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..
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}) = arm.pat.kind;
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if let LitKind::Str(symbol, _) = lit.node;
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if !case_check(&symbol.as_str());
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then {
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bad_case = Some(lit.span);
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break;
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}
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}
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}
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bad_case
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}
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fn lint(cx: &LateContext<'_>, expr_span: Span, case_method: &CaseMethod, bad_case_span: Span) {
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let method_str = match case_method {
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CaseMethod::LowerCase => "to_lower_case",
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CaseMethod::AsciiLowerCase => "to_ascii_lowercase",
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CaseMethod::UpperCase => "to_uppercase",
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CaseMethod::AsciiUppercase => "to_ascii_uppercase",
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};
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span_lint_and_help(
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cx,
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MATCH_STR_CASE_MISMATCH,
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expr_span,
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"this `match` expression alters case, but has non-compliant arms",
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Some(bad_case_span),
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&*format!("consider changing the case of this arm to respect `{}`", method_str),
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);
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}

‎tests/ui/match_str_case_mismatch.rs

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@@ -0,0 +1,98 @@
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#![warn(clippy::match_str_case_mismatch)]
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// Valid
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fn as_str_match() {
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let var = "BAR";
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match var.to_ascii_lowercase().as_str() {
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"foo" => {},
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"bar" => {},
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_ => {},
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}
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}
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fn addrof_unary_match() {
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let var = "BAR";
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match &*var.to_ascii_lowercase() {
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"foo" => {},
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"bar" => {},
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_ => {},
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}
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}
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fn alternating_chain() {
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let var = "BAR";
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match &*var
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.to_ascii_lowercase()
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.to_uppercase()
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.to_lowercase()
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.to_ascii_uppercase()
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{
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"FOO" => {},
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"BAR" => {},
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_ => {},
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}
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}
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fn unrelated_method() {
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struct Item {
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a: String,
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}
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impl Item {
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#[allow(clippy::wrong_self_convention)]
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fn to_lowercase(self) -> String {
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self.a
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}
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}
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let item = Item { a: String::from("BAR") };
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match &*item.to_lowercase() {
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"FOO" => {},
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"BAR" => {},
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_ => {},
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}
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}
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// Invalid
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fn as_str_match_mismatch() {
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let var = "BAR";
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match var.to_ascii_lowercase().as_str() {
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"foo" => {},
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"Bar" => {},
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_ => {},
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}
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}
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fn addrof_unary_match_mismatch() {
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let var = "BAR";
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match &*var.to_ascii_lowercase() {
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"foo" => {},
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"Bar" => {},
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_ => {},
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}
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}
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fn alternating_chain_mismatch() {
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let var = "BAR";
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match &*var
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.to_ascii_lowercase()
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.to_uppercase()
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.to_lowercase()
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.to_ascii_uppercase()
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{
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"FOO" => {},
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"bAR" => {},
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_ => {},
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}
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}
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fn main() {}

‎tests/ui/match_str_case_mismatch.stderr

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error: this `match` expression alters case, but has non-compliant arms
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--> $DIR/match_str_case_mismatch.rs:66:5
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|
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LL | / match var.to_ascii_lowercase().as_str() {
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LL | | "foo" => {},
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LL | | "Bar" => {},
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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-str-case-mismatch` implied by `-D warnings`
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help: consider changing the case of this arm to respect `to_ascii_lowercase`
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--> $DIR/match_str_case_mismatch.rs:68:9
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|
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LL | "Bar" => {},
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| ^^^^^
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error: this `match` expression alters case, but has non-compliant arms
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--> $DIR/match_str_case_mismatch.rs:76:5
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|
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LL | / match &*var.to_ascii_lowercase() {
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LL | | "foo" => {},
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LL | | "Bar" => {},
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LL | | _ => {},
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LL | | }
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| |_____^
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|
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help: consider changing the case of this arm to respect `to_ascii_lowercase`
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--> $DIR/match_str_case_mismatch.rs:78:9
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|
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LL | "Bar" => {},
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| ^^^^^
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error: this `match` expression alters case, but has non-compliant arms
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--> $DIR/match_str_case_mismatch.rs:86:5
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|
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LL | / match &*var
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LL | | .to_ascii_lowercase()
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LL | | .to_uppercase()
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LL | | .to_lowercase()
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... |
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LL | | _ => {},
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LL | | }
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| |_____^
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|
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help: consider changing the case of this arm to respect `to_ascii_uppercase`
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--> $DIR/match_str_case_mismatch.rs:93:9
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|
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LL | "bAR" => {},
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| ^^^^^
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error: aborting due to 3 previous errors
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