1 files changed, 86 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/case_sensitive_file_extension_comparisons.rs b/src/tools/clippy/clippy_lints/src/case_sensitive_file_extension_comparisons.rs
new file mode 100644
index 000000000..7eff71d50
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/case_sensitive_file_extension_comparisons.rs
@@ -0,0 +1,86 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use if_chain::if_chain;
+use rustc_ast::ast::LitKind;
+use rustc_hir::{Expr, ExprKind, PathSegment};
+use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
+use rustc_session::{declare_lint_pass, declare_tool_lint};
+use rustc_span::{source_map::Spanned, symbol::sym, Span};
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for calls to `ends_with` with possible file extensions
+    /// and suggests to use a case-insensitive approach instead.
+    ///
+    /// ### Why is this bad?
+    /// `ends_with` is case-sensitive and may not detect files with a valid extension.
+    ///
+    /// ### Example
+    /// ```rust
+    /// fn is_rust_file(filename: &str) -> bool {
+    ///     filename.ends_with(".rs")
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// fn is_rust_file(filename: &str) -> bool {
+    ///     let filename = std::path::Path::new(filename);
+    ///     filename.extension()
+    ///         .map(|ext| ext.eq_ignore_ascii_case("rs"))
+    ///         .unwrap_or(false)
+    /// }
+    /// ```
+    #[clippy::version = "1.51.0"]
+    pub CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS,
+    pedantic,
+    "Checks for calls to ends_with with case-sensitive file extensions"
+}
+
+declare_lint_pass!(CaseSensitiveFileExtensionComparisons => [CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS]);
+
+fn check_case_sensitive_file_extension_comparison(ctx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Span> {
+    if_chain! {
+        if let ExprKind::MethodCall(PathSegment { ident, .. }, [obj, extension, ..], span) = expr.kind;
+        if ident.as_str() == "ends_with";
+        if let ExprKind::Lit(Spanned { node: LitKind::Str(ext_literal, ..), ..}) = extension.kind;
+        if (2..=6).contains(&ext_literal.as_str().len());
+        if ext_literal.as_str().starts_with('.');
+        if ext_literal.as_str().chars().skip(1).all(|c| c.is_uppercase() || c.is_ascii_digit())
+            || ext_literal.as_str().chars().skip(1).all(|c| c.is_lowercase() || c.is_ascii_digit());
+        then {
+            let mut ty = ctx.typeck_results().expr_ty(obj);
+            ty = match ty.kind() {
+                ty::Ref(_, ty, ..) => *ty,
+                _ => ty
+            };
+
+            match ty.kind() {
+                ty::Str => {
+                    return Some(span);
+                },
+                ty::Adt(def, _) => {
+                    if ctx.tcx.is_diagnostic_item(sym::String, def.did()) {
+                        return Some(span);
+                    }
+                },
+                _ => { return None; }
+            }
+        }
+    }
+    None
+}
+
+impl<'tcx> LateLintPass<'tcx> for CaseSensitiveFileExtensionComparisons {
+    fn check_expr(&mut self, ctx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
+        if let Some(span) = check_case_sensitive_file_extension_comparison(ctx, expr) {
+            span_lint_and_help(
+                ctx,
+                CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS,
+                span,
+                "case-sensitive file extension comparison",
+                None,
+                "consider using a case-insensitive comparison instead",
+            );
+        }
+    }
+}