1 files changed, 41 insertions, 0 deletions
diff --git a/src/tools/clippy/clippy_lints/src/methods/case_sensitive_file_extension_comparisons.rs b/src/tools/clippy/clippy_lints/src/methods/case_sensitive_file_extension_comparisons.rs
new file mode 100644
index 000000000..b3c2c7c9a
--- /dev/null
+++ b/src/tools/clippy/clippy_lints/src/methods/case_sensitive_file_extension_comparisons.rs
@@ -0,0 +1,41 @@
+use clippy_utils::diagnostics::span_lint_and_help;
+use clippy_utils::ty::is_type_diagnostic_item;
+use if_chain::if_chain;
+use rustc_ast::ast::LitKind;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_span::{source_map::Spanned, symbol::sym, Span};
+
+use super::CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS;
+
+pub(super) fn check<'tcx>(
+    cx: &LateContext<'tcx>,
+    expr: &'tcx Expr<'_>,
+    call_span: Span,
+    recv: &'tcx Expr<'_>,
+    arg: &'tcx Expr<'_>,
+) {
+    if_chain! {
+        if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
+        if let Some(impl_id) = cx.tcx.impl_of_method(method_id);
+        if cx.tcx.type_of(impl_id).is_str();
+        if let ExprKind::Lit(Spanned { node: LitKind::Str(ext_literal, ..), ..}) = arg.kind;
+        if (2..=6).contains(&ext_literal.as_str().len());
+        let ext_str = ext_literal.as_str();
+        if ext_str.starts_with('.');
+        if ext_str.chars().skip(1).all(|c| c.is_uppercase() || c.is_ascii_digit())
+            || ext_str.chars().skip(1).all(|c| c.is_lowercase() || c.is_ascii_digit());
+        let recv_ty = cx.typeck_results().expr_ty(recv).peel_refs();
+        if recv_ty.is_str() || is_type_diagnostic_item(cx, recv_ty, sym::String);
+        then {
+            span_lint_and_help(
+                cx,
+                CASE_SENSITIVE_FILE_EXTENSION_COMPARISONS,
+                call_span,
+                "case-sensitive file extension comparison",
+                None,
+                "consider using a case-insensitive comparison instead",
+            );
+        }
+    }
+}