src/tools/clippy/clippy_lints/src/case_sensitive_file_extension_comparisons.rs

   1 use clippy_utils::diagnostics::span_lint_and_help;
   2 use if_chain::if_chain;
   3 use rustc_ast::ast::LitKind;
   4 use rustc_hir::{Expr, ExprKind, PathSegment};
   5 use rustc_lint::{LateContext, LateLintPass};
   6 use rustc_middle::ty;
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::{source_map::Spanned, symbol::sym, Span};
   9
  10 declare_clippy_lint! {
  11     /// **What it does:**
  12     /// Checks for calls to `ends_with` with possible file extensions
  13     /// and suggests to use a case-insensitive approach instead.
  14     ///
  15     /// **Why is this bad?**
  16     /// `ends_with` is case-sensitive and may not detect files with a valid extension.
  17     ///
  18     /// **Known problems:** None.
  19     ///
  20     /// **Example:**
  21     ///
  22     /// ```rust
  23     /// fn is_rust_file(filename: &str) -> bool {
  24     ///     filename.ends_with(".rs")
  25     /// }
  26     /// ```
  27     /// Use instead:
  28     /// ```rust
  29     /// fn is_rust_file(filename: &str) -> bool {
  30     ///     filename.rsplit('.').next().map(|ext| ext.eq_ignore_ascii_case("rs")) == Some(true)
  31     /// }
  32     /// ```
  33     pub CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS,
  34     pedantic,
  35     "Checks for calls to ends_with with case-sensitive file extensions"
  36 }
  37
  38 declare_lint_pass!(CaseSensitiveFileExtensionComparisons => [CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS]);
  39
  40 fn check_case_sensitive_file_extension_comparison(ctx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Span> {
  41     if_chain! {
  42         if let ExprKind::MethodCall(PathSegment { ident, .. }, _, [obj, extension, ..], span) = expr.kind;
  43         if ident.as_str() == "ends_with";
  44         if let ExprKind::Lit(Spanned { node: LitKind::Str(ext_literal, ..), ..}) = extension.kind;
  45         if (2..=6).contains(&ext_literal.as_str().len());
  46         if ext_literal.as_str().starts_with('.');
  47         if ext_literal.as_str().chars().skip(1).all(|c| c.is_uppercase() || c.is_digit(10))
  48             || ext_literal.as_str().chars().skip(1).all(|c| c.is_lowercase() || c.is_digit(10));
  49         then {
  50             let mut ty = ctx.typeck_results().expr_ty(obj);
  51             ty = match ty.kind() {
  52                 ty::Ref(_, ty, ..) => ty,
  53                 _ => ty
  54             };
  55
  56             match ty.kind() {
  57                 ty::Str => {
  58                     return Some(span);
  59                 },
  60                 ty::Adt(&ty::AdtDef { did, .. }, _) => {
  61                     if ctx.tcx.is_diagnostic_item(sym::string_type, did) {
  62                         return Some(span);
  63                     }
  64                 },
  65                 _ => { return None; }
  66             }
  67         }
  68     }
  69     None
  70 }
  71
  72 impl LateLintPass<'tcx> for CaseSensitiveFileExtensionComparisons {
  73     fn check_expr(&mut self, ctx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
  74         if let Some(span) = check_case_sensitive_file_extension_comparison(ctx, expr) {
  75             span_lint_and_help(
  76                 ctx,
  77                 CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS,
  78                 span,
  79                 "case-sensitive file extension comparison",
  80                 None,
  81                 "consider using a case-insensitive comparison instead",
  82             );
  83         }
  84     }
  85 }