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clippy_lints/src/trailing_zero_sized_array_without_repr_c.rs

@@ -26,7 +26,7 @@ declare_clippy_lint! {
     /// Use instead:
     /// ```rust
     /// #[repr(C)]
-    /// struct MakesSense {
+    /// struct MoreOftenUseful {
     ///     some_field: usize,
     ///     last: [SomeType; 0],
     /// }
@@ -45,15 +45,13 @@ declare_lint_pass!(TrailingZeroSizedArrayWithoutReprC => [TRAILING_ZERO_SIZED_AR
 
 impl<'tcx> LateLintPass<'tcx> for TrailingZeroSizedArrayWithoutReprC {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) {
-        dbg!(item.ident);
-
         if is_struct_with_trailing_zero_sized_array(cx, item) && !has_repr_c(cx, item.def_id) {
             span_lint_and_sugg(
                 cx,
                 TRAILING_ZERO_SIZED_ARRAY_WITHOUT_REPR_C,
                 item.span,
                 "trailing zero-sized array in a struct which is not marked `#[repr(C)]`",
-                "try",
+                "try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):",
                 format!("#[repr(C)]\n{}", snippet(cx, item.span, "..")),
                 Applicability::MaybeIncorrect,
             );
@@ -62,46 +60,40 @@ impl<'tcx> LateLintPass<'tcx> for TrailingZeroSizedArrayWithoutReprC {
 }
 
 fn is_struct_with_trailing_zero_sized_array(cx: &LateContext<'tcx>, item: &'tcx Item<'tcx>) -> bool {
-    if let ItemKind::Struct(data, _generics) = &item.kind {
+    if_chain! {
-        if let VariantData::Struct(field_defs, _) = data {
+        if let ItemKind::Struct(data, _generics) = &item.kind;
-            if let Some(last_field) = field_defs.last() {
+        if let VariantData::Struct(field_defs, _) = data;
-                if let TyKind::Array(_, aconst) = last_field.ty.kind {
+        if let Some(last_field) = field_defs.last();
-                    let aconst_def_id = cx.tcx.hir().body_owner_def_id(aconst.body).to_def_id();
+        if let TyKind::Array(_, aconst) = last_field.ty.kind;
-                    let ty = cx.tcx.type_of(aconst_def_id);
+        let aconst_def_id = cx.tcx.hir().body_owner_def_id(aconst.body).to_def_id();
-                    let constant = cx
+        let ty = cx.tcx.type_of(aconst_def_id);
-                        .tcx
+        let constant = cx
-                        // NOTE: maybe const_eval_resolve? seems especially cursed to be using a const expr which
+            .tcx
-                        // resolves to 0 to create a zero-sized array, tho
+            // NOTE: maybe const_eval_resolve?
-                        .const_eval_poly(aconst_def_id)
+            .const_eval_poly(aconst_def_id)
-                        .ok()
+            .ok()
-                        .map(|val| rustc_middle::ty::Const::from_value(cx.tcx, val, ty));
+            .map(|val| rustc_middle::ty::Const::from_value(cx.tcx, val, ty));
-                    if let Some(Constant::Int(val)) = constant.and_then(miri_to_const) {
+        if let Some(Constant::Int(val)) = constant.and_then(miri_to_const);
-                        if val == 0 {
+        if val == 0;
-                            // eprintln!("trailing: true");
+        then {
-                            return true;
+            true
-                        }
+        } else {
-                    }
+            false
-                }
-            }
         }
     }
-    // dbg!(aconst);
-    // eprintln!("trailing: false");
-    false
 }
 
 fn has_repr_c(cx: &LateContext<'tcx>, def_id: LocalDefId) -> bool {
-    let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
+    let hir_map = cx.tcx.hir();
-    let attrs = cx.tcx.hir().attrs(hir_id);
+    let hir_id = hir_map.local_def_id_to_hir_id(def_id);
+    let attrs = hir_map.attrs(hir_id);
 
     // NOTE: Can there ever be more than one `repr` attribute?
     // other `repr` syms: repr, repr128, repr_align, repr_align_enum, repr_no_niche, repr_packed,
     // repr_simd, repr_transparent
-    if let Some(_repr_attr) = attrs.iter().find(|attr| attr.has_name(sym::repr)) {
+    if let Some(_attr) = attrs.iter().find(|attr| attr.has_name(sym::repr)) {
-        // eprintln!("repr: true");
         true
     } else {
-        // eprintln!("repr: false");
         false
     }
 }

tests/ui/trailing_zero_sized_array_without_repr_c.rs

@@ -1,6 +1,5 @@
 #![warn(clippy::trailing_zero_sized_array_without_repr_c)]
-
+// #![feature(const_generics_defaults)] // see below
-// #![feature(const_generics_defaults)]
 
 struct RarelyUseful {
     field: i32,
@@ -48,6 +47,9 @@ struct UsingFunction {
     last: [usize; compute_zero()],
 }
 
+// NOTE: including these (along with the required feature) triggers an ICE. Should make sure the
+// const generics people are aware of that if they weren't already.
+
 // #[repr(C)]
 // struct ConstParamOk<const N: usize = 0> {
 //     field: i32,
@@ -59,8 +61,7 @@ struct UsingFunction {
 //     last: [usize; N]
 // }
 
-
+// TODO: actually, uh,, no idea what behavior here would be
-// TODO: actually, uh,,
 #[repr(packed)]
 struct ReprPacked {
     small: u8,
@@ -68,20 +69,21 @@ struct ReprPacked {
     weird: [u64; 0],
 }
 
-// same
+// TODO: clarify expected behavior
 #[repr(align(64))]
 struct ReprAlign {
     field: i32,
     last: [usize; 0],
 }
 
-// same
+// TODO: clarify expected behavior
 #[repr(C, align(64))]
 struct ReprCAlign {
     field: i32,
     last: [usize; 0],
 }
 
+// NOTE: because of https://doc.rust-lang.org/stable/reference/type-layout.html#primitive-representation-of-enums-with-fields and I'm not sure when in the compilation pipeline that would happen
 #[repr(C)]
 enum DontLintAnonymousStructsFromDesuraging {
     A(u32),
@@ -109,5 +111,4 @@ struct LotsOfFields {
     last: [usize; 0],
 }
 
-fn main() {
+fn main() {}
-}

tests/ui/trailing_zero_sized_array_without_repr_c.stderr

@@ -0,0 +1,113 @@
+error: trailing zero-sized array in a struct which is not marked `#[repr(C)]`
+  --> $DIR/trailing_zero_sized_array_without_repr_c.rs:4:1
+   |
+LL | / struct RarelyUseful {
+LL | |     field: i32,
+LL | |     last: [usize; 0],
+LL | | }
+   | |_^
+   |
+   = note: `-D clippy::trailing-zero-sized-array-without-repr-c` implied by `-D warnings`
+help: try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):
+   |
+LL + #[repr(C)]
+LL + struct RarelyUseful {
+LL +     field: i32,
+LL +     last: [usize; 0],
+LL + }
+   |
+
+error: trailing zero-sized array in a struct which is not marked `#[repr(C)]`
+  --> $DIR/trailing_zero_sized_array_without_repr_c.rs:15:1
+   |
+LL | / struct OnlyFieldIsZeroSizeArray {
+LL | |     first_and_last: [usize; 0],
+LL | | }
+   | |_^
+   |
+help: try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):
+   |
+LL + #[repr(C)]
+LL + struct OnlyFieldIsZeroSizeArray {
+LL +     first_and_last: [usize; 0],
+LL + }
+   |
+
+error: trailing zero-sized array in a struct which is not marked `#[repr(C)]`
+  --> $DIR/trailing_zero_sized_array_without_repr_c.rs:19:1
+   |
+LL | / struct GenericArrayType<T> {
+LL | |     field: i32,
+LL | |     last: [T; 0],
+LL | | }
+   | |_^
+   |
+help: try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):
+   |
+LL + #[repr(C)]
+LL + struct GenericArrayType<T> {
+LL +     field: i32,
+LL +     last: [T; 0],
+LL + }
+   |
+
+error: trailing zero-sized array in a struct which is not marked `#[repr(C)]`
+  --> $DIR/trailing_zero_sized_array_without_repr_c.rs:30:1
+   |
+LL | / struct ZeroSizedFromExternalConst {
+LL | |     field: i32,
+LL | |     last: [usize; ZERO],
+LL | | }
+   | |_^
+   |
+help: try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):
+   |
+LL + #[repr(C)]
+LL + struct ZeroSizedFromExternalConst {
+LL +     field: i32,
+LL +     last: [usize; ZERO],
+LL + }
+   |
+
+error: trailing zero-sized array in a struct which is not marked `#[repr(C)]`
+  --> $DIR/trailing_zero_sized_array_without_repr_c.rs:45:1
+   |
+LL | / struct UsingFunction {
+LL | |     field: i32,
+LL | |     last: [usize; compute_zero()],
+LL | | }
+   | |_^
+   |
+help: try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):
+   |
+LL + #[repr(C)]
+LL + struct UsingFunction {
+LL +     field: i32,
+LL +     last: [usize; compute_zero()],
+LL + }
+   |
+
+error: trailing zero-sized array in a struct which is not marked `#[repr(C)]`
+  --> $DIR/trailing_zero_sized_array_without_repr_c.rs:94:1
+   |
+LL | / struct LotsOfFields {
+LL | |     f1: u32,
+LL | |     f2: u32,
+LL | |     f3: u32,
+...  |
+LL | |     last: [usize; 0],
+LL | | }
+   | |_^
+   |
+help: try annotating the struct definition with `#[repr(C)]` (or another `repr` attribute):
+   |
+LL + #[repr(C)]
+LL + struct LotsOfFields {
+LL +     f1: u32,
+LL +     f2: u32,
+LL +     f3: u32,
+LL +     f4: u32,
+ ...
+
+error: aborting due to 6 previous errors
+