Allow more deriving on packed structs.

[rust.git] / compiler / rustc_lint_defs / src / builtin.rs

diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index b6481d70bc8898fe2de912d9f382e90233fa28bd..4438639d635283aa27119116e5d66689749adfdb 100644 (file)
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -3381,6 +3381,7 @@
         REPR_TRANSPARENT_EXTERNAL_PRIVATE_FIELDS,
         NAMED_ARGUMENTS_USED_POSITIONALLY,
         IMPLIED_BOUNDS_ENTAILMENT,
+        BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
     ]
 }
 
@@ -4109,3 +4110,35 @@
         reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
     };
 }
+
+declare_lint! {
+    /// The `byte_slice_in_packed_struct_with_derive` lint detects cases where a byte slice field
+    /// (`[u8]`) is used in a `packed` struct that derives one or more built-in traits.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// #[repr(packed)]
+    /// #[derive(Hash)]
+    /// struct FlexZeroSlice {
+    ///     width: u8,
+    ///     data: [u8],
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// This was previously accepted but is being phased out, because fields in packed structs are
+    /// now required to implement `Copy` for `derive` to work. Byte slices are a temporary
+    /// exception because certain crates depended on them.
+    pub BYTE_SLICE_IN_PACKED_STRUCT_WITH_DERIVE,
+    Warn,
+    "`[u8]` slice used in a packed struct with `derive`",
+    @future_incompatible = FutureIncompatibleInfo {
+        reference: "issue #107457 <https://github.com/rust-lang/rust/issues/107457>",
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
+    };
+    report_in_external_macro
+}