Extend byte_char_slices to cover arrays (#16770)

samueltardieu · web-flow · commit c0adb72b3a0a · 2026-04-15T16:21:17.000Z
Closes rust-lang/rust-clippy#16759 changelog: [`byte_char_slices`] enhance to cover arrays
diff --git a/clippy_lints/src/byte_char_slices.rs b/clippy_lints/src/byte_char_slices.rs
@@ -1,9 +1,15 @@
-use clippy_utils::diagnostics::span_lint_and_sugg;
-use rustc_ast::ast::{BorrowKind, Expr, ExprKind, Mutability};
-use rustc_ast::token::{Lit, LitKind};
+use std::borrow::Cow;
+
+use clippy_utils::diagnostics::span_lint_and_then;
+use clippy_utils::source::snippet_with_applicability;
+use clippy_utils::sugg::Sugg;
+use clippy_utils::{get_parent_expr, span_contains_cfg, span_contains_comment};
+use rustc_ast::LitKind;
 use rustc_errors::Applicability;
-use rustc_lint::{EarlyContext, EarlyLintPass};
+use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability};
+use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::declare_lint_pass;
+use rustc_span::Span;
 
 declare_clippy_lint! {
     /// ### What it does
@@ -30,47 +36,73 @@ declare_clippy_lint! {
 
 declare_lint_pass!(ByteCharSlice => [BYTE_CHAR_SLICES]);
 
-impl EarlyLintPass for ByteCharSlice {
-    fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
+impl<'tcx> LateLintPass<'tcx> for ByteCharSlice {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
         if !expr.span.from_expansion()
-            && let Some(slice) = is_byte_char_slices(expr)
+            && let Some((has_ref, slice)) = is_byte_char_slices(cx, expr)
         {
-            span_lint_and_sugg(
+            span_lint_and_then(
                 cx,
                 BYTE_CHAR_SLICES,
                 expr.span,
                 "can be more succinctly written as a byte str",
-                "try",
-                format!("b\"{slice}\""),
-                Applicability::MachineApplicable,
+                |diag| {
+                    let mut app = Applicability::MachineApplicable;
+                    let mut sugg = Sugg::hir_from_snippet(cx, expr, |_| {
+                        let mut slice = slice.iter().fold("b\"".to_owned(), |mut acc, span| {
+                            let snippet = snippet_with_applicability(cx, *span, "b'?'", &mut app);
+                            acc.push_str(match &snippet[2..snippet.len() - 1] {
+                                "\"" => "\\\"",
+                                "\\'" => "'",
+                                other => other,
+                            });
+                            acc
+                        });
+                        slice.push('"');
+                        Cow::Owned(slice)
+                    });
+                    if !has_ref && !cx.typeck_results().expr_ty_adjusted(expr).is_array_slice() {
+                        sugg = sugg.deref();
+                    }
+
+                    diag.span_suggestion(expr.span, "try", sugg, app);
+                },
             );
         }
     }
 }
 
 /// Checks whether the slice is that of byte chars, and if so, builds a byte-string out of it
-fn is_byte_char_slices(expr: &Expr) -> Option<String> {
-    if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, expr) = &expr.kind
-        && let ExprKind::Array(members) = &expr.kind
+fn is_byte_char_slices<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> Option<(bool, Vec<Span>)> {
+    let (has_ref, expr) = if let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, inner) = expr.kind {
+        (true, inner)
+    } else if let Some(parent) = get_parent_expr(cx, expr) // Already checked by the parent expr.
+        && let ExprKind::AddrOf(BorrowKind::Ref, Mutability::Not, _) = parent.kind
+    {
+        return None;
+    } else {
+        (false, expr)
+    };
+
+    if let ExprKind::Array(members) = expr.kind
         && !members.is_empty()
+        && !span_contains_comment(cx, expr.span)
+        && !span_contains_cfg(cx, expr.span)
     {
-        members
+        return members
             .iter()
-            .map(|member| match &member.kind {
-                ExprKind::Lit(Lit {
-                    kind: LitKind::Byte,
-                    symbol,
-                    ..
-                }) => Some(symbol.as_str()),
-                _ => None,
-            })
-            .map(|maybe_quote| match maybe_quote {
-                Some("\"") => Some("\\\""),
-                Some("\\'") => Some("'"),
-                other => other,
+            .try_fold(Vec::new(), |mut acc, member| {
+                if let ExprKind::Lit(lit) = member.kind
+                    && let LitKind::Byte(_) = lit.node
+                    && expr.span.eq_ctxt(member.span)
+                {
+                    acc.push(lit.span);
+                    return Some(acc);
+                }
+                None
             })
-            .collect::<Option<String>>()
-    } else {
-        None
+            .map(|s| (has_ref, s));
     }
+
+    None
 }
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
@@ -515,7 +515,6 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
         Box::new(|| Box::new(visibility::Visibility)),
         Box::new(|| Box::new(multiple_bound_locations::MultipleBoundLocations)),
         Box::new(|| Box::new(field_scoped_visibility_modifiers::FieldScopedVisibilityModifiers)),
-        Box::new(|| Box::new(byte_char_slices::ByteCharSlice)),
         Box::new(|| Box::new(cfg_not_test::CfgNotTest)),
         Box::new(|| Box::new(empty_line_after::EmptyLineAfter::new())),
         // add early passes here, used by `cargo dev new_lint`
@@ -867,6 +866,7 @@ pub fn register_lint_passes(store: &mut rustc_lint::LintStore, conf: &'static Co
         Box::new(|_| Box::new(manual_checked_ops::ManualCheckedOps)),
         Box::new(move |tcx| Box::new(manual_pop_if::ManualPopIf::new(tcx, conf))),
         Box::new(move |_| Box::new(manual_noop_waker::ManualNoopWaker::new(conf))),
+        Box::new(|_| Box::new(byte_char_slices::ByteCharSlice)),
         // add late passes here, used by `cargo dev new_lint`
     ];
     store.late_passes.extend(late_lints);
diff --git a/clippy_lints/src/returns/needless_return.rs b/clippy_lints/src/returns/needless_return.rs
@@ -259,7 +259,7 @@ fn emit_return_lint(
 // Go backwards while encountering whitespace and extend the given Span to that point.
 fn extend_span_to_previous_non_ws(cx: &LateContext<'_>, sp: Span) -> Span {
     if let Ok(prev_source) = cx.sess().source_map().span_to_prev_source(sp) {
-        let ws = [b' ', b'\t', b'\n'];
+        let ws = *b" \t\n";
         if let Some(non_ws_pos) = prev_source.bytes().rposition(|c| !ws.contains(&c)) {
             let len = prev_source.len() - non_ws_pos - 1;
             return sp.with_lo(sp.lo() - BytePos::from_usize(len));
diff --git a/tests/ui/byte_char_slices.fixed b/tests/ui/byte_char_slices.fixed
@@ -1,4 +1,5 @@
 #![warn(clippy::byte_char_slices)]
+#![allow(clippy::useless_vec)]
 
 fn main() {
     let bad = b"abc";
@@ -11,7 +12,40 @@ fn main() {
     //~^ byte_char_slices
 
     let good = &[b'a', 0x42];
-    let good = [b'a', b'a'];
-    //~^ useless_vec
-    let good: u8 = [b'a', b'c'].into_iter().sum();
+    let good = vec![b'a', b'a'];
+}
+
+fn takes_array_ref(_: &[u8; 2]) {}
+
+fn takes_array_ref_ref(_: &&[u8; 2]) {}
+
+fn issue16759(bytes: [u32; 3]) {
+    const START: u32 = u32::from_le_bytes(*b"WORK");
+    //~^ byte_char_slices
+
+    let auto_deref_to_slice: u8 = b"ac".iter().copied().sum();
+    //~^ byte_char_slices
+
+    let with_comment = [
+        // 1     2     3
+        b'a', b'b', b'c', //   x
+        b'd', b'e', b'f', //  2x
+        b'g', b'h', b'i', //  3x
+    ];
+    let with_cfg = [
+        b'a',
+        b'b',
+        b'c',
+        #[cfg(feature = "foo")]
+        b'd',
+    ];
+
+    let with_escape: u8 = b"'\"\x00\n\\".iter().copied().sum();
+    //~^ byte_char_slices
+
+    takes_array_ref(b"ab");
+    //~^ byte_char_slices
+
+    takes_array_ref_ref(&b"ab");
+    //~^ byte_char_slices
 }
diff --git a/tests/ui/byte_char_slices.rs b/tests/ui/byte_char_slices.rs
@@ -1,4 +1,5 @@
 #![warn(clippy::byte_char_slices)]
+#![allow(clippy::useless_vec)]
 
 fn main() {
     let bad = &[b'a', b'b', b'c'];
@@ -12,6 +13,39 @@ fn main() {
 
     let good = &[b'a', 0x42];
     let good = vec![b'a', b'a'];
-    //~^ useless_vec
-    let good: u8 = [b'a', b'c'].into_iter().sum();
+}
+
+fn takes_array_ref(_: &[u8; 2]) {}
+
+fn takes_array_ref_ref(_: &&[u8; 2]) {}
+
+fn issue16759(bytes: [u32; 3]) {
+    const START: u32 = u32::from_le_bytes([b'W', b'O', b'R', b'K']);
+    //~^ byte_char_slices
+
+    let auto_deref_to_slice: u8 = [b'a', b'c'].iter().copied().sum();
+    //~^ byte_char_slices
+
+    let with_comment = [
+        // 1     2     3
+        b'a', b'b', b'c', //   x
+        b'd', b'e', b'f', //  2x
+        b'g', b'h', b'i', //  3x
+    ];
+    let with_cfg = [
+        b'a',
+        b'b',
+        b'c',
+        #[cfg(feature = "foo")]
+        b'd',
+    ];
+
+    let with_escape: u8 = [b'\'', b'"', b'\x00', b'\n', b'\\'].iter().copied().sum();
+    //~^ byte_char_slices
+
+    takes_array_ref(&[b'a', b'b']);
+    //~^ byte_char_slices
+
+    takes_array_ref_ref(&&[b'a', b'b']);
+    //~^ byte_char_slices
 }
diff --git a/tests/ui/byte_char_slices.stderr b/tests/ui/byte_char_slices.stderr
@@ -1,5 +1,5 @@
 error: can be more succinctly written as a byte str
-  --> tests/ui/byte_char_slices.rs:4:15
+  --> tests/ui/byte_char_slices.rs:5:15
    |
 LL |     let bad = &[b'a', b'b', b'c'];
    |               ^^^^^^^^^^^^^^^^^^^ help: try: `b"abc"`
@@ -8,31 +8,52 @@ LL |     let bad = &[b'a', b'b', b'c'];
    = help: to override `-D warnings` add `#[allow(clippy::byte_char_slices)]`
 
 error: can be more succinctly written as a byte str
-  --> tests/ui/byte_char_slices.rs:6:18
+  --> tests/ui/byte_char_slices.rs:7:18
    |
 LL |     let quotes = &[b'"', b'H', b'i'];
    |                  ^^^^^^^^^^^^^^^^^^^ help: try: `b"\"Hi"`
 
 error: can be more succinctly written as a byte str
-  --> tests/ui/byte_char_slices.rs:8:18
+  --> tests/ui/byte_char_slices.rs:9:18
    |
 LL |     let quotes = &[b'\'', b'S', b'u', b'p'];
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b"'Sup"`
 
 error: can be more succinctly written as a byte str
-  --> tests/ui/byte_char_slices.rs:10:19
+  --> tests/ui/byte_char_slices.rs:11:19
    |
 LL |     let escapes = &[b'\x42', b'E', b's', b'c'];
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b"\x42Esc"`
 
-error: useless use of `vec!`
-  --> tests/ui/byte_char_slices.rs:14:16
+error: can be more succinctly written as a byte str
+  --> tests/ui/byte_char_slices.rs:23:43
+   |
+LL |     const START: u32 = u32::from_le_bytes([b'W', b'O', b'R', b'K']);
+   |                                           ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `*b"WORK"`
+
+error: can be more succinctly written as a byte str
+  --> tests/ui/byte_char_slices.rs:26:35
+   |
+LL |     let auto_deref_to_slice: u8 = [b'a', b'c'].iter().copied().sum();
+   |                                   ^^^^^^^^^^^^ help: try: `b"ac"`
+
+error: can be more succinctly written as a byte str
+  --> tests/ui/byte_char_slices.rs:43:27
+   |
+LL |     let with_escape: u8 = [b'\'', b'"', b'\x00', b'\n', b'\\'].iter().copied().sum();
+   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b"'\"\x00\n\\"`
+
+error: can be more succinctly written as a byte str
+  --> tests/ui/byte_char_slices.rs:46:21
    |
-LL |     let good = vec![b'a', b'a'];
-   |                ^^^^^^^^^^^^^^^^ help: you can use an array directly: `[b'a', b'a']`
+LL |     takes_array_ref(&[b'a', b'b']);
+   |                     ^^^^^^^^^^^^^ help: try: `b"ab"`
+
+error: can be more succinctly written as a byte str
+  --> tests/ui/byte_char_slices.rs:49:26
    |
-   = note: `-D clippy::useless-vec` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::useless_vec)]`
+LL |     takes_array_ref_ref(&&[b'a', b'b']);
+   |                          ^^^^^^^^^^^^^ help: try: `b"ab"`
 
-error: aborting due to 5 previous errors
+error: aborting due to 9 previous errors
 
diff --git a/tests/ui/ptr_offset_by_literal.fixed b/tests/ui/ptr_offset_by_literal.fixed
@@ -1,5 +1,5 @@
 #![warn(clippy::ptr_offset_by_literal)]
-#![allow(clippy::inconsistent_digit_grouping)]
+#![allow(clippy::inconsistent_digit_grouping, clippy::byte_char_slices)]
 
 fn main() {
     let arr = [b'a', b'b', b'c'];
diff --git a/tests/ui/ptr_offset_by_literal.rs b/tests/ui/ptr_offset_by_literal.rs
@@ -1,5 +1,5 @@
 #![warn(clippy::ptr_offset_by_literal)]
-#![allow(clippy::inconsistent_digit_grouping)]
+#![allow(clippy::inconsistent_digit_grouping, clippy::byte_char_slices)]
 
 fn main() {
     let arr = [b'a', b'b', b'c'];
