From 0b48a451dd61ac0b6bd4c1078a301b5e19e92275 Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Sun, 17 May 2026 21:22:16 +0300
Subject: [PATCH 1/7] new lint: bufreader_stdin

---
 clippy_lints/src/bufreader_stdin.rs | 82 +++++++++++++++++++++++++++++
 clippy_lints/src/declared_lints.rs  |  1 +
 clippy_lints/src/lib.rs             |  1 +
 tests/ui/bufreader_stdin.fixed      | 12 +++++
 tests/ui/bufreader_stdin.rs         | 12 +++++
 tests/ui/bufreader_stdin.stderr     | 22 ++++++++
 6 files changed, 130 insertions(+)
 create mode 100644 clippy_lints/src/bufreader_stdin.rs
 create mode 100644 tests/ui/bufreader_stdin.fixed
 create mode 100644 tests/ui/bufreader_stdin.rs
 create mode 100644 tests/ui/bufreader_stdin.stderr

diff --git a/clippy_lints/src/bufreader_stdin.rs b/clippy_lints/src/bufreader_stdin.rs
new file mode 100644
index 000000000000..4fed4f13d2cd
--- /dev/null
+++ b/clippy_lints/src/bufreader_stdin.rs
@@ -0,0 +1,82 @@
+use clippy_utils::{diagnostics::span_lint_and_sugg, source::snippet};
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, QPath, TyKind};
+use rustc_lint::{LateContext, LateLintPass};
+use clippy_utils::{sym};
+use rustc_session::impl_lint_pass;
+
+declare_clippy_lint! {
+    /// ### What it does
+    /// Checks for usage of `BufReader::new` with `Stdin` or `StdinLock`.
+    ///
+    /// ### Why is this bad?
+    /// `Stdin` is already buffered. Re-buffering it only increase the memcpy calls.
+    ///
+    /// ### Example
+    ///
+    /// ```ignore
+    /// let reader = std::io::BufReader::new(std::io::stdin());
+    /// ```
+    /// Use instead:
+    /// ```ignore
+    /// let stdin = std::io::stdin();
+    /// let reader = stdin.lock();
+    /// ```
+
+    #[clippy::version = "1.97.0"]
+    pub BUFREADER_STDIN,
+    perf,
+    "using `BufReader::new` with `Stdin` or `StdinLock` is unnecessary and less efficient"
+}
+
+impl_lint_pass!(BufreaderStdin => [BUFREADER_STDIN]);
+
+pub struct BufreaderStdin {
+}
+
+impl BufreaderStdin { 
+    pub fn new() -> Self {
+        Self {}
+    }
+}
+
+impl<'tcx> LateLintPass<'tcx> for BufreaderStdin {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if expr.span.from_expansion(){
+            return;
+        }
+
+        if let ExprKind::Call(func, [arg]) = expr.kind
+        && let ExprKind::Path(QPath::TypeRelative(ty, segment)) = func.kind
+        && segment.ident.name == sym::new
+        && let TyKind::Path(ref qpath) = ty.kind
+        && let Some(did) = cx.qpath_res(qpath, ty.hir_id).opt_def_id()
+        && cx.tcx.def_path_str(did).ends_with("std::io::BufReader")
+        && let arg_ty = cx.typeck_results().expr_ty(arg)
+        && let Some(arg_did) = arg_ty.ty_adt_def().map(rustc_middle::ty::AdtDef::did)
+        {
+            if cx.tcx.is_diagnostic_item(sym::Stdin, arg_did) {
+                span_lint_and_sugg(
+                    cx,
+                    BUFREADER_STDIN,
+                    expr.span,
+                    "using `BufReader::new` with `Stdin`",
+                    "instead of wrapping `Stdin` in `BufReader`, use the `lock` method directly",
+                    format!("{}.lock()", snippet(cx, arg.span, "..")),
+                    Applicability::MachineApplicable,
+                );
+            }
+            else if cx.tcx.def_path_str(arg_did).ends_with("std::io::StdinLock"){
+                span_lint_and_sugg(
+                    cx,
+                    BUFREADER_STDIN,
+                    expr.span,
+                    "using `BufReader::new` with `StdinLock`",
+                    "instead of wrapping `StdinLock` in `BufReader`, use it directly",
+                    snippet(cx, arg.span, "..").to_string(),
+                    Applicability::MachineApplicable,
+                );
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/clippy_lints/src/declared_lints.rs b/clippy_lints/src/declared_lints.rs
index b14ee7f3de90..c58f69b1d7f6 100644
--- a/clippy_lints/src/declared_lints.rs
+++ b/clippy_lints/src/declared_lints.rs
@@ -44,6 +44,7 @@ pub static LINTS: &[&::declare_clippy_lint::LintInfo] = &[
     crate::booleans::OVERLY_COMPLEX_BOOL_EXPR_INFO,
     crate::borrow_deref_ref::BORROW_DEREF_REF_INFO,
     crate::box_default::BOX_DEFAULT_INFO,
+    crate::bufreader_stdin::BUFREADER_STDIN_INFO,
     crate::byte_char_slices::BYTE_CHAR_SLICES_INFO,
     crate::cargo::CARGO_COMMON_METADATA_INFO,
     crate::cargo::LINT_GROUPS_PRIORITY_INFO,
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index 7a233e09e800..f1c2c2ae93b5 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -84,6 +84,7 @@ mod bool_to_int_with_if;
 mod booleans;
 mod borrow_deref_ref;
 mod box_default;
+mod bufreader_stdin;
 mod byte_char_slices;
 mod cargo;
 mod casts;
diff --git a/tests/ui/bufreader_stdin.fixed b/tests/ui/bufreader_stdin.fixed
new file mode 100644
index 000000000000..8b61d51509af
--- /dev/null
+++ b/tests/ui/bufreader_stdin.fixed
@@ -0,0 +1,12 @@
+#![warn(clippy::bufreader_stdin)]
+
+use std::io::{self, BufReader};
+
+fn main() {
+    let a = io::stdin();
+    let reader = a.lock();
+    //~^ bufreader_stdin
+    let b = io::stdin().lock();
+    let reader = b;
+    //~^ bufreader_stdin
+}
\ No newline at end of file
diff --git a/tests/ui/bufreader_stdin.rs b/tests/ui/bufreader_stdin.rs
new file mode 100644
index 000000000000..badfb31e5a3f
--- /dev/null
+++ b/tests/ui/bufreader_stdin.rs
@@ -0,0 +1,12 @@
+#![warn(clippy::bufreader_stdin)]
+
+use std::io::{self, BufReader};
+
+fn main() {
+    let a = io::stdin();
+    let reader = BufReader::new(a);
+    //~^ bufreader_stdin
+    let b = io::stdin().lock();
+    let reader = BufReader::new(b);
+    //~^ bufreader_stdin
+}
\ No newline at end of file
diff --git a/tests/ui/bufreader_stdin.stderr b/tests/ui/bufreader_stdin.stderr
new file mode 100644
index 000000000000..6190cd892453
--- /dev/null
+++ b/tests/ui/bufreader_stdin.stderr
@@ -0,0 +1,22 @@
+error: using `BufReader::new` with `Stdin`
+  --> tests/ui/bufreader_stdin.rs:7:18
+   |
+LL |     let reader = BufReader::new(a);
+   |                  ^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::bufreader-stdin` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::bufreader_stdin)]`
+help: instead of wrapping `Stdin` in `BufReader`, use the `lock` method directly
+   |
+LL -     let reader = BufReader::new(a);
+LL +     let reader = a.lock();
+   |
+
+error: using `BufReader::new` with `StdinLock`
+  --> tests/ui/bufreader_stdin.rs:10:18
+   |
+LL |     let reader = BufReader::new(b);
+   |                  ^^^^^^^^^^^^^^^^^ help: instead of wrapping `StdinLock` in `BufReader`, use it directly: `b`
+
+error: aborting due to 2 previous errors
+

From 6ff18aade12c19c5a289e5e9d2779d5c7fbf8349 Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Sun, 17 May 2026 21:29:31 +0300
Subject: [PATCH 2/7] fixed change log

---
 CHANGELOG.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dc308285319f..6a697f1e2fcf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6778,6 +6778,7 @@ Released 2018-09-13
 [`box_vec`]: https://rust-lang.github.io/rust-clippy/master/index.html#box_vec
 [`boxed_local`]: https://rust-lang.github.io/rust-clippy/master/index.html#boxed_local
 [`branches_sharing_code`]: https://rust-lang.github.io/rust-clippy/master/index.html#branches_sharing_code
+[`bufreader_stdin`]: https://rust-lang.github.io/rust-clippy/master/index.html#bufreader_stdin
 [`builtin_type_shadow`]: https://rust-lang.github.io/rust-clippy/master/index.html#builtin_type_shadow
 [`by_ref_peekable_peek`]: https://rust-lang.github.io/rust-clippy/master/index.html#by_ref_peekable_peek
 [`byte_char_slices`]: https://rust-lang.github.io/rust-clippy/master/index.html#byte_char_slices

From fc21fd796914d3305f72b1ae46fbeaabea8e3556 Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Sun, 17 May 2026 21:30:55 +0300
Subject: [PATCH 3/7] ran `cargo dev fmt`

---
 clippy_lints/src/bufreader_stdin.rs | 31 ++++++++++++++---------------
 tests/ui/bufreader_stdin.rs         |  2 +-
 2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/clippy_lints/src/bufreader_stdin.rs b/clippy_lints/src/bufreader_stdin.rs
index 4fed4f13d2cd..c26ca737b293 100644
--- a/clippy_lints/src/bufreader_stdin.rs
+++ b/clippy_lints/src/bufreader_stdin.rs
@@ -1,8 +1,9 @@
-use clippy_utils::{diagnostics::span_lint_and_sugg, source::snippet};
+use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::source::snippet;
+use clippy_utils::sym;
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, ExprKind, QPath, TyKind};
 use rustc_lint::{LateContext, LateLintPass};
-use clippy_utils::{sym};
 use rustc_session::impl_lint_pass;
 
 declare_clippy_lint! {
@@ -31,10 +32,9 @@ declare_clippy_lint! {
 
 impl_lint_pass!(BufreaderStdin => [BUFREADER_STDIN]);
 
-pub struct BufreaderStdin {
-}
+pub struct BufreaderStdin {}
 
-impl BufreaderStdin { 
+impl BufreaderStdin {
     pub fn new() -> Self {
         Self {}
     }
@@ -42,18 +42,18 @@ impl BufreaderStdin {
 
 impl<'tcx> LateLintPass<'tcx> for BufreaderStdin {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if expr.span.from_expansion(){
+        if expr.span.from_expansion() {
             return;
         }
 
         if let ExprKind::Call(func, [arg]) = expr.kind
-        && let ExprKind::Path(QPath::TypeRelative(ty, segment)) = func.kind
-        && segment.ident.name == sym::new
-        && let TyKind::Path(ref qpath) = ty.kind
-        && let Some(did) = cx.qpath_res(qpath, ty.hir_id).opt_def_id()
-        && cx.tcx.def_path_str(did).ends_with("std::io::BufReader")
-        && let arg_ty = cx.typeck_results().expr_ty(arg)
-        && let Some(arg_did) = arg_ty.ty_adt_def().map(rustc_middle::ty::AdtDef::did)
+            && let ExprKind::Path(QPath::TypeRelative(ty, segment)) = func.kind
+            && segment.ident.name == sym::new
+            && let TyKind::Path(ref qpath) = ty.kind
+            && let Some(did) = cx.qpath_res(qpath, ty.hir_id).opt_def_id()
+            && cx.tcx.def_path_str(did).ends_with("std::io::BufReader")
+            && let arg_ty = cx.typeck_results().expr_ty(arg)
+            && let Some(arg_did) = arg_ty.ty_adt_def().map(rustc_middle::ty::AdtDef::did)
         {
             if cx.tcx.is_diagnostic_item(sym::Stdin, arg_did) {
                 span_lint_and_sugg(
@@ -65,8 +65,7 @@ impl<'tcx> LateLintPass<'tcx> for BufreaderStdin {
                     format!("{}.lock()", snippet(cx, arg.span, "..")),
                     Applicability::MachineApplicable,
                 );
-            }
-            else if cx.tcx.def_path_str(arg_did).ends_with("std::io::StdinLock"){
+            } else if cx.tcx.def_path_str(arg_did).ends_with("std::io::StdinLock") {
                 span_lint_and_sugg(
                     cx,
                     BUFREADER_STDIN,
@@ -79,4 +78,4 @@ impl<'tcx> LateLintPass<'tcx> for BufreaderStdin {
             }
         }
     }
-}
\ No newline at end of file
+}
diff --git a/tests/ui/bufreader_stdin.rs b/tests/ui/bufreader_stdin.rs
index badfb31e5a3f..41d6cbd564cd 100644
--- a/tests/ui/bufreader_stdin.rs
+++ b/tests/ui/bufreader_stdin.rs
@@ -9,4 +9,4 @@ fn main() {
     let b = io::stdin().lock();
     let reader = BufReader::new(b);
     //~^ bufreader_stdin
-}
\ No newline at end of file
+}

From 75d8e79676803137a37c437c9fadb52ee46e220b Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Sun, 17 May 2026 21:38:15 +0300
Subject: [PATCH 4/7] removed extra space in test

---
 tests/ui/bufreader_stdin.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/ui/bufreader_stdin.rs b/tests/ui/bufreader_stdin.rs
index 41d6cbd564cd..badfb31e5a3f 100644
--- a/tests/ui/bufreader_stdin.rs
+++ b/tests/ui/bufreader_stdin.rs
@@ -9,4 +9,4 @@ fn main() {
     let b = io::stdin().lock();
     let reader = BufReader::new(b);
     //~^ bufreader_stdin
-}
+}
\ No newline at end of file

From 346b56ac4ba3816fd5edc905cc4749bc4a2cb058 Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Sun, 17 May 2026 21:42:50 +0300
Subject: [PATCH 5/7] made sure test and output match

---
 tests/ui/bufreader_stdin.fixed | 2 +-
 tests/ui/bufreader_stdin.rs    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/ui/bufreader_stdin.fixed b/tests/ui/bufreader_stdin.fixed
index 8b61d51509af..2984af523388 100644
--- a/tests/ui/bufreader_stdin.fixed
+++ b/tests/ui/bufreader_stdin.fixed
@@ -9,4 +9,4 @@ fn main() {
     let b = io::stdin().lock();
     let reader = b;
     //~^ bufreader_stdin
-}
\ No newline at end of file
+}
diff --git a/tests/ui/bufreader_stdin.rs b/tests/ui/bufreader_stdin.rs
index badfb31e5a3f..41d6cbd564cd 100644
--- a/tests/ui/bufreader_stdin.rs
+++ b/tests/ui/bufreader_stdin.rs
@@ -9,4 +9,4 @@ fn main() {
     let b = io::stdin().lock();
     let reader = BufReader::new(b);
     //~^ bufreader_stdin
-}
\ No newline at end of file
+}

From e0e52523d29534163943f2e927bf2f9f5651051b Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Wed, 22 Jul 2026 02:15:46 +0300
Subject: [PATCH 6/7] addressed PR comments

---
 clippy_lints/src/bufreader_stdin.rs | 64 ++++++++++++++++-------------
 clippy_lints/src/lib.rs             |  1 +
 tests/ui/bufreader_stdin.fixed      |  7 ++++
 tests/ui/bufreader_stdin.rs         |  7 ++++
 tests/ui/bufreader_stdin.stderr     |  8 ++--
 5 files changed, 55 insertions(+), 32 deletions(-)

diff --git a/clippy_lints/src/bufreader_stdin.rs b/clippy_lints/src/bufreader_stdin.rs
index c26ca737b293..f95fa0cdfaa4 100644
--- a/clippy_lints/src/bufreader_stdin.rs
+++ b/clippy_lints/src/bufreader_stdin.rs
@@ -1,4 +1,4 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
+use clippy_utils::diagnostics::{span_lint, span_lint_and_sugg};
 use clippy_utils::source::snippet;
 use clippy_utils::sym;
 use rustc_errors::Applicability;
@@ -11,14 +11,16 @@ declare_clippy_lint! {
     /// Checks for usage of `BufReader::new` with `Stdin` or `StdinLock`.
     ///
     /// ### Why is this bad?
-    /// `Stdin` is already buffered. Re-buffering it only increase the memcpy calls.
+    /// `Stdin` is already buffered. Re-buffering it only increases the memcpy calls.
     ///
     /// ### Example
     ///
     /// ```ignore
     /// let reader = std::io::BufReader::new(std::io::stdin());
     /// ```
+    ///
     /// Use instead:
+    ///
     /// ```ignore
     /// let stdin = std::io::stdin();
     /// let reader = stdin.lock();
@@ -26,7 +28,7 @@ declare_clippy_lint! {
 
     #[clippy::version = "1.97.0"]
     pub BUFREADER_STDIN,
-    perf,
+    pedantic,
     "using `BufReader::new` with `Stdin` or `StdinLock` is unnecessary and less efficient"
 }
 
@@ -42,39 +44,45 @@ impl BufreaderStdin {
 
 impl<'tcx> LateLintPass<'tcx> for BufreaderStdin {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if expr.span.from_expansion() {
-            return;
-        }
-
         if let ExprKind::Call(func, [arg]) = expr.kind
             && let ExprKind::Path(QPath::TypeRelative(ty, segment)) = func.kind
             && segment.ident.name == sym::new
             && let TyKind::Path(ref qpath) = ty.kind
             && let Some(did) = cx.qpath_res(qpath, ty.hir_id).opt_def_id()
-            && cx.tcx.def_path_str(did).ends_with("std::io::BufReader")
-            && let arg_ty = cx.typeck_results().expr_ty(arg)
-            && let Some(arg_did) = arg_ty.ty_adt_def().map(rustc_middle::ty::AdtDef::did)
+            && cx.tcx.is_diagnostic_item(sym::IoBufReader, did)
+            && let Some(arg_did) = cx
+                .typeck_results()
+                .expr_ty(arg)
+                .ty_adt_def()
+                .map(rustc_middle::ty::AdtDef::did)
         {
-            if cx.tcx.is_diagnostic_item(sym::Stdin, arg_did) {
-                span_lint_and_sugg(
-                    cx,
-                    BUFREADER_STDIN,
-                    expr.span,
-                    "using `BufReader::new` with `Stdin`",
+            let snip = snippet(cx, arg.span, "..");
+            let applicability = if snip == ".." {
+                Applicability::HasPlaceholders
+            } else {
+                Applicability::MaybeIncorrect
+            };
+
+            let (msg, help, sugg) = if cx.tcx.is_diagnostic_item(sym::Stdin, arg_did) {
+                (
+                    "wrapping already buffered `Stdin` into a `BufReader`",
                     "instead of wrapping `Stdin` in `BufReader`, use the `lock` method directly",
-                    format!("{}.lock()", snippet(cx, arg.span, "..")),
-                    Applicability::MachineApplicable,
-                );
-            } else if cx.tcx.def_path_str(arg_did).ends_with("std::io::StdinLock") {
-                span_lint_and_sugg(
-                    cx,
-                    BUFREADER_STDIN,
-                    expr.span,
-                    "using `BufReader::new` with `StdinLock`",
+                    format!("{snip}.lock()"),
+                )
+            } else if cx.tcx.is_diagnostic_item(sym::StdinLock, arg_did) {
+                (
+                    "wrapping already buffered `StdinLock` into a `BufReader`",
                     "instead of wrapping `StdinLock` in `BufReader`, use it directly",
-                    snippet(cx, arg.span, "..").to_string(),
-                    Applicability::MachineApplicable,
-                );
+                    snip.to_string(),
+                )
+            } else {
+                return;
+            };
+
+            if arg.span.from_expansion() {
+                span_lint(cx, BUFREADER_STDIN, expr.span, msg);
+            } else {
+                span_lint_and_sugg(cx, BUFREADER_STDIN, expr.span, msg, help, sugg, applicability);
             }
         }
     }
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index f1c2c2ae93b5..66b3fa9014cd 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -869,6 +869,7 @@ rustc_lint::late_lint_methods!(
         RedundantElse: redundant_else::RedundantElse = redundant_else::RedundantElse,
         RestWhenDestructuringStruct: rest_when_destructuring_struct::RestWhenDestructuringStruct = rest_when_destructuring_struct::RestWhenDestructuringStruct,
         BlockScrutinee: block_scrutinee::BlockScrutinee = block_scrutinee::BlockScrutinee,
+        BufreaderStdin: bufreader_stdin::BufreaderStdin = bufreader_stdin::BufreaderStdin::new(),
         // add late passes here, used by `cargo dev new_lint`
     ]]
 );
diff --git a/tests/ui/bufreader_stdin.fixed b/tests/ui/bufreader_stdin.fixed
index 2984af523388..ebf94ec9187d 100644
--- a/tests/ui/bufreader_stdin.fixed
+++ b/tests/ui/bufreader_stdin.fixed
@@ -2,10 +2,17 @@
 
 use std::io::{self, BufReader};
 
+macro_rules! stdin_macro {
+    () => {
+        io::stdin()
+    };
+}
+
 fn main() {
     let a = io::stdin();
     let reader = a.lock();
     //~^ bufreader_stdin
+
     let b = io::stdin().lock();
     let reader = b;
     //~^ bufreader_stdin
diff --git a/tests/ui/bufreader_stdin.rs b/tests/ui/bufreader_stdin.rs
index 41d6cbd564cd..1f16b4a3b7ef 100644
--- a/tests/ui/bufreader_stdin.rs
+++ b/tests/ui/bufreader_stdin.rs
@@ -2,10 +2,17 @@
 
 use std::io::{self, BufReader};
 
+macro_rules! stdin_macro {
+    () => {
+        io::stdin()
+    };
+}
+
 fn main() {
     let a = io::stdin();
     let reader = BufReader::new(a);
     //~^ bufreader_stdin
+
     let b = io::stdin().lock();
     let reader = BufReader::new(b);
     //~^ bufreader_stdin
diff --git a/tests/ui/bufreader_stdin.stderr b/tests/ui/bufreader_stdin.stderr
index 6190cd892453..cde280ae7182 100644
--- a/tests/ui/bufreader_stdin.stderr
+++ b/tests/ui/bufreader_stdin.stderr
@@ -1,5 +1,5 @@
-error: using `BufReader::new` with `Stdin`
-  --> tests/ui/bufreader_stdin.rs:7:18
+error: wrapping already buffered `Stdin` into a `BufReader`
+  --> tests/ui/bufreader_stdin.rs:13:18
    |
 LL |     let reader = BufReader::new(a);
    |                  ^^^^^^^^^^^^^^^^^
@@ -12,8 +12,8 @@ LL -     let reader = BufReader::new(a);
 LL +     let reader = a.lock();
    |
 
-error: using `BufReader::new` with `StdinLock`
-  --> tests/ui/bufreader_stdin.rs:10:18
+error: wrapping already buffered `StdinLock` into a `BufReader`
+  --> tests/ui/bufreader_stdin.rs:17:18
    |
 LL |     let reader = BufReader::new(b);
    |                  ^^^^^^^^^^^^^^^^^ help: instead of wrapping `StdinLock` in `BufReader`, use it directly: `b`

From 0a8061712dccb1c482791501c19eecbb51562d80 Mon Sep 17 00:00:00 2001
From: JafarTano <81587305+JaafarTanoukhi@users.noreply.github.com>
Date: Wed, 22 Jul 2026 12:54:14 +0300
Subject: [PATCH 7/7] optimized get_diagnostic_item usage

---
 clippy_lints/src/bufreader_stdin.rs | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/clippy_lints/src/bufreader_stdin.rs b/clippy_lints/src/bufreader_stdin.rs
index f95fa0cdfaa4..090e41fe6e01 100644
--- a/clippy_lints/src/bufreader_stdin.rs
+++ b/clippy_lints/src/bufreader_stdin.rs
@@ -63,20 +63,19 @@ impl<'tcx> LateLintPass<'tcx> for BufreaderStdin {
                 Applicability::MaybeIncorrect
             };
 
-            let (msg, help, sugg) = if cx.tcx.is_diagnostic_item(sym::Stdin, arg_did) {
-                (
+            let arg_did_name = cx.tcx.get_diagnostic_name(arg_did);
+            let (msg, help, sugg) = match arg_did_name {
+                Some(sym::Stdin) => (
                     "wrapping already buffered `Stdin` into a `BufReader`",
                     "instead of wrapping `Stdin` in `BufReader`, use the `lock` method directly",
                     format!("{snip}.lock()"),
-                )
-            } else if cx.tcx.is_diagnostic_item(sym::StdinLock, arg_did) {
-                (
+                ),
+                Some(sym::StdinLock) => (
                     "wrapping already buffered `StdinLock` into a `BufReader`",
                     "instead of wrapping `StdinLock` in `BufReader`, use it directly",
                     snip.to_string(),
-                )
-            } else {
-                return;
+                ),
+                _ => return,
             };
 
             if arg.span.from_expansion() {