From 3106219e24c9d52a739ffaf38c10f0c1357f30f3 Mon Sep 17 00:00:00 2001
From: Bruno Andreotti <bandreotti@proton.me>
Date: Tue, 30 Jan 2024 16:17:02 -0300
Subject: [PATCH] Don't lint slice type annotations for byte strings

---
 clippy_lints/src/redundant_type_annotations.rs | 11 ++++++++++-
 tests/ui/redundant_type_annotations.rs         |  7 ++++++-
 tests/ui/redundant_type_annotations.stderr     |  4 ++--
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/clippy_lints/src/redundant_type_annotations.rs b/clippy_lints/src/redundant_type_annotations.rs
index 07fcb69afbc..c8352c05265 100644
--- a/clippy_lints/src/redundant_type_annotations.rs
+++ b/clippy_lints/src/redundant_type_annotations.rs
@@ -188,7 +188,6 @@ fn check_local<'tcx>(&mut self, cx: &LateContext<'tcx>, local: &'tcx rustc_hir::
                     match init_lit.node {
                         // In these cases the annotation is redundant
                         LitKind::Str(..)
-                        | LitKind::ByteStr(..)
                         | LitKind::Byte(..)
                         | LitKind::Char(..)
                         | LitKind::Bool(..)
@@ -202,6 +201,16 @@ fn check_local<'tcx>(&mut self, cx: &LateContext<'tcx>, local: &'tcx rustc_hir::
                             }
                         },
                         LitKind::Err => (),
+                        LitKind::ByteStr(..) => {
+                            // We only lint if the type annotation is an array type (e.g. &[u8; 4]).
+                            // If instead it is a slice (e.g. &[u8]) it may not be redundant, so we
+                            // don't lint.
+                            if let hir::TyKind::Ref(_, mut_ty) = ty.kind
+                                && matches!(mut_ty.ty.kind, hir::TyKind::Array(..))
+                            {
+                                span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
+                            }
+                        },
                     }
                 },
                 _ => (),
diff --git a/tests/ui/redundant_type_annotations.rs b/tests/ui/redundant_type_annotations.rs
index acf53fea2bb..dc9b073ffba 100644
--- a/tests/ui/redundant_type_annotations.rs
+++ b/tests/ui/redundant_type_annotations.rs
@@ -196,13 +196,18 @@ fn test_simple_types() {
     let _var: &str = "test";
     //~^ ERROR: redundant type annotation
 
-    let _var: &[u8] = b"test";
+    let _var: &[u8; 4] = b"test";
     //~^ ERROR: redundant type annotation
 
     let _var: bool = false;
     //~^ ERROR: redundant type annotation
 }
 
+fn issue12212() {
+    // This should not be linted
+    let _var: &[u8] = b"test";
+}
+
 fn issue11190() {}
 
 fn main() {}
diff --git a/tests/ui/redundant_type_annotations.stderr b/tests/ui/redundant_type_annotations.stderr
index d1f26f1832e..48df465ad49 100644
--- a/tests/ui/redundant_type_annotations.stderr
+++ b/tests/ui/redundant_type_annotations.stderr
@@ -94,8 +94,8 @@ LL |     let _var: &str = "test";
 error: redundant type annotation
   --> $DIR/redundant_type_annotations.rs:199:5
    |
-LL |     let _var: &[u8] = b"test";
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     let _var: &[u8; 4] = b"test";
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: redundant type annotation
   --> $DIR/redundant_type_annotations.rs:202:5