src/tools/clippy/clippy_lints/src/match_str_case_mismatch.rs

   1 use clippy_utils::diagnostics::span_lint_and_sugg;
   2 use clippy_utils::ty::is_type_diagnostic_item;
   3 use rustc_ast::ast::LitKind;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::intravisit::{walk_expr, Visitor};
   6 use rustc_hir::{Arm, Expr, ExprKind, MatchSource, PatKind};
   7 use rustc_lint::{LateContext, LateLintPass};
   8 use rustc_middle::lint::in_external_macro;
   9 use rustc_middle::ty;
  10 use rustc_session::{declare_lint_pass, declare_tool_lint};
  11 use rustc_span::symbol::Symbol;
  12 use rustc_span::{sym, Span};
  13
  14 declare_clippy_lint! {
  15     /// ### What it does
  16     /// Checks for `match` expressions modifying the case of a string with non-compliant arms
  17     ///
  18     /// ### Why is this bad?
  19     /// The arm is unreachable, which is likely a mistake
  20     ///
  21     /// ### Example
  22     /// ```rust
  23     /// # let text = "Foo";
  24     ///
  25     /// match &*text.to_ascii_lowercase() {
  26     ///     "foo" => {},
  27     ///     "Bar" => {},
  28     ///     _ => {},
  29     /// }
  30     /// ```
  31     /// Use instead:
  32     /// ```rust
  33     /// # let text = "Foo";
  34     ///
  35     /// match &*text.to_ascii_lowercase() {
  36     ///     "foo" => {},
  37     ///     "bar" => {},
  38     ///     _ => {},
  39     /// }
  40     /// ```
  41     #[clippy::version = "1.58.0"]
  42     pub MATCH_STR_CASE_MISMATCH,
  43     correctness,
  44     "creation of a case altering match expression with non-compliant arms"
  45 }
  46
  47 declare_lint_pass!(MatchStrCaseMismatch => [MATCH_STR_CASE_MISMATCH]);
  48
  49 #[derive(Debug)]
  50 enum CaseMethod {
  51     LowerCase,
  52     AsciiLowerCase,
  53     UpperCase,
  54     AsciiUppercase,
  55 }
  56
  57 impl<'tcx> LateLintPass<'tcx> for MatchStrCaseMismatch {
  58     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  59         if_chain! {
  60             if !in_external_macro(cx.tcx.sess, expr.span);
  61             if let ExprKind::Match(match_expr, arms, MatchSource::Normal) = expr.kind;
  62             if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty(match_expr).kind();
  63             if let ty::Str = ty.kind();
  64             then {
  65                 let mut visitor = MatchExprVisitor {
  66                     cx,
  67                     case_method: None,
  68                 };
  69
  70                 visitor.visit_expr(match_expr);
  71
  72                 if let Some(case_method) = visitor.case_method {
  73                     if let Some((bad_case_span, bad_case_sym)) = verify_case(&case_method, arms) {
  74                         lint(cx, &case_method, bad_case_span, bad_case_sym.as_str());
  75                     }
  76                 }
  77             }
  78         }
  79     }
  80 }
  81
  82 struct MatchExprVisitor<'a, 'tcx> {
  83     cx: &'a LateContext<'tcx>,
  84     case_method: Option<CaseMethod>,
  85 }
  86
  87 impl<'a, 'tcx> Visitor<'tcx> for MatchExprVisitor<'a, 'tcx> {
  88     fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
  89         match ex.kind {
  90             ExprKind::MethodCall(segment, [receiver], _) if self.case_altered(segment.ident.as_str(), receiver) => {},
  91             _ => walk_expr(self, ex),
  92         }
  93     }
  94 }
  95
  96 impl<'a, 'tcx> MatchExprVisitor<'a, 'tcx> {
  97     fn case_altered(&mut self, segment_ident: &str, receiver: &Expr<'_>) -> bool {
  98         if let Some(case_method) = get_case_method(segment_ident) {
  99             let ty = self.cx.typeck_results().expr_ty(receiver).peel_refs();
 100
 101             if is_type_diagnostic_item(self.cx, ty, sym::String) || ty.kind() == &ty::Str {
 102                 self.case_method = Some(case_method);
 103                 return true;
 104             }
 105         }
 106
 107         false
 108     }
 109 }
 110
 111 fn get_case_method(segment_ident_str: &str) -> Option<CaseMethod> {
 112     match segment_ident_str {
 113         "to_lowercase" => Some(CaseMethod::LowerCase),
 114         "to_ascii_lowercase" => Some(CaseMethod::AsciiLowerCase),
 115         "to_uppercase" => Some(CaseMethod::UpperCase),
 116         "to_ascii_uppercase" => Some(CaseMethod::AsciiUppercase),
 117         _ => None,
 118     }
 119 }
 120
 121 fn verify_case<'a>(case_method: &'a CaseMethod, arms: &'a [Arm<'_>]) -> Option<(Span, Symbol)> {
 122     let case_check = match case_method {
 123         CaseMethod::LowerCase => |input: &str| -> bool { input.chars().all(|c| c.to_lowercase().next() == Some(c)) },
 124         CaseMethod::AsciiLowerCase => |input: &str| -> bool { !input.chars().any(|c| c.is_ascii_uppercase()) },
 125         CaseMethod::UpperCase => |input: &str| -> bool { input.chars().all(|c| c.to_uppercase().next() == Some(c)) },
 126         CaseMethod::AsciiUppercase => |input: &str| -> bool { !input.chars().any(|c| c.is_ascii_lowercase()) },
 127     };
 128
 129     for arm in arms {
 130         if_chain! {
 131             if let PatKind::Lit(Expr {
 132                                 kind: ExprKind::Lit(lit),
 133                                 ..
 134                             }) = arm.pat.kind;
 135             if let LitKind::Str(symbol, _) = lit.node;
 136             let input = symbol.as_str();
 137             if !case_check(input);
 138             then {
 139                 return Some((lit.span, symbol));
 140             }
 141         }
 142     }
 143
 144     None
 145 }
 146
 147 fn lint(cx: &LateContext<'_>, case_method: &CaseMethod, bad_case_span: Span, bad_case_str: &str) {
 148     let (method_str, suggestion) = match case_method {
 149         CaseMethod::LowerCase => ("to_lowercase", bad_case_str.to_lowercase()),
 150         CaseMethod::AsciiLowerCase => ("to_ascii_lowercase", bad_case_str.to_ascii_lowercase()),
 151         CaseMethod::UpperCase => ("to_uppercase", bad_case_str.to_uppercase()),
 152         CaseMethod::AsciiUppercase => ("to_ascii_uppercase", bad_case_str.to_ascii_uppercase()),
 153     };
 154
 155     span_lint_and_sugg(
 156         cx,
 157         MATCH_STR_CASE_MISMATCH,
 158         bad_case_span,
 159         "this `match` arm has a differing case than its expression",
 160         &*format!("consider changing the case of this arm to respect `{}`", method_str),
 161         format!("\"{}\"", suggestion),
 162         Applicability::MachineApplicable,
 163     );
 164 }