clippy_lints/src/matches/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, PatKind};
   7 use rustc_lint::LateContext;
   8 use rustc_middle::ty;
   9 use rustc_span::symbol::Symbol;
  10 use rustc_span::{sym, Span};
  11
  12 use super::MATCH_STR_CASE_MISMATCH;
  13
  14 #[derive(Debug)]
  15 enum CaseMethod {
  16     LowerCase,
  17     AsciiLowerCase,
  18     UpperCase,
  19     AsciiUppercase,
  20 }
  21
  22 pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, scrutinee: &'tcx Expr<'_>, arms: &'tcx [Arm<'_>]) {
  23     if_chain! {
  24         if let ty::Ref(_, ty, _) = cx.typeck_results().expr_ty(scrutinee).kind();
  25         if let ty::Str = ty.kind();
  26         then {
  27             let mut visitor = MatchExprVisitor {
  28                 cx,
  29                 case_method: None,
  30             };
  31
  32             visitor.visit_expr(scrutinee);
  33
  34             if let Some(case_method) = visitor.case_method {
  35                 if let Some((bad_case_span, bad_case_sym)) = verify_case(&case_method, arms) {
  36                     lint(cx, &case_method, bad_case_span, bad_case_sym.as_str());
  37                 }
  38             }
  39         }
  40     }
  41 }
  42
  43 struct MatchExprVisitor<'a, 'tcx> {
  44     cx: &'a LateContext<'tcx>,
  45     case_method: Option<CaseMethod>,
  46 }
  47
  48 impl<'a, 'tcx> Visitor<'tcx> for MatchExprVisitor<'a, 'tcx> {
  49     fn visit_expr(&mut self, ex: &'tcx Expr<'_>) {
  50         match ex.kind {
  51             ExprKind::MethodCall(segment, receiver, [], _) if self.case_altered(segment.ident.as_str(), receiver) => {},
  52             _ => walk_expr(self, ex),
  53         }
  54     }
  55 }
  56
  57 impl<'a, 'tcx> MatchExprVisitor<'a, 'tcx> {
  58     fn case_altered(&mut self, segment_ident: &str, receiver: &Expr<'_>) -> bool {
  59         if let Some(case_method) = get_case_method(segment_ident) {
  60             let ty = self.cx.typeck_results().expr_ty(receiver).peel_refs();
  61
  62             if is_type_diagnostic_item(self.cx, ty, sym::String) || ty.kind() == &ty::Str {
  63                 self.case_method = Some(case_method);
  64                 return true;
  65             }
  66         }
  67
  68         false
  69     }
  70 }
  71
  72 fn get_case_method(segment_ident_str: &str) -> Option<CaseMethod> {
  73     match segment_ident_str {
  74         "to_lowercase" => Some(CaseMethod::LowerCase),
  75         "to_ascii_lowercase" => Some(CaseMethod::AsciiLowerCase),
  76         "to_uppercase" => Some(CaseMethod::UpperCase),
  77         "to_ascii_uppercase" => Some(CaseMethod::AsciiUppercase),
  78         _ => None,
  79     }
  80 }
  81
  82 fn verify_case<'a>(case_method: &'a CaseMethod, arms: &'a [Arm<'_>]) -> Option<(Span, Symbol)> {
  83     let case_check = match case_method {
  84         CaseMethod::LowerCase => |input: &str| -> bool { input.chars().all(|c| c.to_lowercase().next() == Some(c)) },
  85         CaseMethod::AsciiLowerCase => |input: &str| -> bool { !input.chars().any(|c| c.is_ascii_uppercase()) },
  86         CaseMethod::UpperCase => |input: &str| -> bool { input.chars().all(|c| c.to_uppercase().next() == Some(c)) },
  87         CaseMethod::AsciiUppercase => |input: &str| -> bool { !input.chars().any(|c| c.is_ascii_lowercase()) },
  88     };
  89
  90     for arm in arms {
  91         if_chain! {
  92             if let PatKind::Lit(Expr {
  93                                 kind: ExprKind::Lit(lit),
  94                                 ..
  95                             }) = arm.pat.kind;
  96             if let LitKind::Str(symbol, _) = lit.node;
  97             let input = symbol.as_str();
  98             if !case_check(input);
  99             then {
 100                 return Some((lit.span, symbol));
 101             }
 102         }
 103     }
 104
 105     None
 106 }
 107
 108 fn lint(cx: &LateContext<'_>, case_method: &CaseMethod, bad_case_span: Span, bad_case_str: &str) {
 109     let (method_str, suggestion) = match case_method {
 110         CaseMethod::LowerCase => ("to_lowercase", bad_case_str.to_lowercase()),
 111         CaseMethod::AsciiLowerCase => ("to_ascii_lowercase", bad_case_str.to_ascii_lowercase()),
 112         CaseMethod::UpperCase => ("to_uppercase", bad_case_str.to_uppercase()),
 113         CaseMethod::AsciiUppercase => ("to_ascii_uppercase", bad_case_str.to_ascii_uppercase()),
 114     };
 115
 116     span_lint_and_sugg(
 117         cx,
 118         MATCH_STR_CASE_MISMATCH,
 119         bad_case_span,
 120         "this `match` arm has a differing case than its expression",
 121         &format!("consider changing the case of this arm to respect `{}`", method_str),
 122         format!("\"{}\"", suggestion),
 123         Applicability::MachineApplicable,
 124     );
 125 }