Properly check for builtin derived code

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -761,8 +761,7 @@ impl<'a> TraitDef<'a> {
         let path = cx.path_all(self.span, false, vec![type_ident], self_params);
         let self_type = cx.ty_path(path);
 
-        let attr = cx.attr_word(sym::automatically_derived, self.span);
-        let attrs = thin_vec![attr];
+        let attrs = thin_vec![cx.attr_word(sym::automatically_derived, self.span),];
         let opt_trait_ref = Some(trait_ref);
 
         cx.item(

compiler/rustc_middle/src/ty/mod.rs

@@ -46,7 +46,7 @@ use rustc_serialize::{Decodable, Encodable};
 use rustc_session::cstore::Untracked;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{ExpnId, Span};
+use rustc_span::{ExpnId, ExpnKind, Span};
 use rustc_target::abi::{Align, Integer, IntegerType, VariantIdx};
 pub use rustc_target::abi::{ReprFlags, ReprOptions};
 use rustc_type_ir::WithCachedTypeInfo;
@@ -2436,8 +2436,23 @@ impl<'tcx> TyCtxt<'tcx> {
         None
     }
 
-    /// If the given `DefId` belongs to a trait that was automatically derived, returns `true`.
-    pub fn is_builtin_derive(self, def_id: DefId) -> bool {
+    /// Check if the given `DefId` is `#\[automatically_derived\], *and*
+    /// whether it was produced by expanding a builtin derive macro.
+    pub fn is_builtin_derived(self, def_id: DefId) -> bool {
+        if self.is_automatically_derived(def_id)
+            && let Some(def_id) = def_id.as_local()
+            && let outer = self.def_span(def_id).ctxt().outer_expn_data()
+            && matches!(outer.kind, ExpnKind::Macro(MacroKind::Derive, _))
+            && self.has_attr(outer.macro_def_id.unwrap(), sym::rustc_builtin_macro)
+        {
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Check if the given `DefId` is `#\[automatically_derived\]`.
+    pub fn is_automatically_derived(self, def_id: DefId) -> bool {
         self.has_attr(def_id, sym::automatically_derived)
     }
 

compiler/rustc_mir_transform/src/check_packed_ref.rs

@@ -42,12 +42,12 @@ impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
                 let def_id = self.body.source.instance.def_id();
                 if let Some(impl_def_id) = self.tcx.impl_of_method(def_id)
-                    && self.tcx.is_builtin_derive(impl_def_id)
+                    && self.tcx.is_builtin_derived(impl_def_id)
                 {
                     // If we ever reach here it means that the generated derive
                     // code is somehow doing an unaligned reference, which it
                     // shouldn't do.
-                    unreachable!();
+                    span_bug!(self.source_info.span, "builtin derive created an unaligned reference");
                 } else {
                     struct_span_err!(
                         self.tcx.sess,

compiler/rustc_passes/src/dead.rs

@@ -259,7 +259,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
     /// for discussion).
     fn should_ignore_item(&mut self, def_id: DefId) -> bool {
         if let Some(impl_of) = self.tcx.impl_of_method(def_id) {
-            if !self.tcx.has_attr(impl_of, sym::automatically_derived) {
+            if !self.tcx.is_automatically_derived(impl_of) {
                 return false;
             }
 

compiler/rustc_passes/src/stability.rs

@@ -537,7 +537,7 @@ impl<'tcx> MissingStabilityAnnotations<'tcx> {
         // then it would be "stable" at least for the impl.
         // We gate usages of it using `feature(const_trait_impl)` anyways
         // so there is no unstable leakage
-        if self.tcx.is_builtin_derive(def_id.to_def_id()) {
+        if self.tcx.is_automatically_derived(def_id.to_def_id()) {
             return;
         }
 

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -2097,7 +2097,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
                 // Ignore automatically derived impls and `!Trait` impls.
                 .filter(|&def_id| {
                     self.tcx.impl_polarity(def_id) != ty::ImplPolarity::Negative
-                        || self.tcx.is_builtin_derive(def_id)
+                        || self.tcx.is_automatically_derived(def_id)
                 })
                 .filter_map(|def_id| self.tcx.impl_trait_ref(def_id))
                 .map(ty::EarlyBinder::subst_identity)

tests/ui/lint/unaligned_references.rs

@@ -13,6 +13,20 @@ pub struct Packed2 {
     z: u8,
 }
 
+trait Foo {
+    fn evil(&self);
+}
+
+// Test for #108122
+#[automatically_derived]
+impl Foo for Packed2 {
+    fn evil(&self) {
+        unsafe {
+            &self.x; //~ ERROR reference to packed field
+        }
+    }
+}
+
 fn main() {
     unsafe {
         let good = Good { data: 0, ptr: &0, data2: [0, 0], aligned: [0; 32] };
@@ -37,6 +51,7 @@ fn main() {
         let _ = &packed2.x; //~ ERROR reference to packed field
         let _ = &packed2.y; // ok, has align 2 in packed(2) struct
         let _ = &packed2.z; // ok, has align 1
+        packed2.evil();
     }
 
     unsafe {
@@ -71,22 +86,10 @@ fn main() {
         #[repr(packed)]
         struct Misalign<T>(u8, T);
 
-        let m1 = Misalign(
-            0,
-            Wrapper {
-                a: U16(10),
-                b: HasDrop,
-            },
-        );
+        let m1 = Misalign(0, Wrapper { a: U16(10), b: HasDrop });
         let _ref = &m1.1.a; //~ ERROR reference to packed field
 
-        let m2 = Misalign(
-            0,
-            Wrapper2 {
-                a: U16(10),
-                b: HasDrop,
-            },
-        );
+        let m2 = Misalign(0, Wrapper2 { a: U16(10), b: HasDrop });
         let _ref = &m2.1.a; //~ ERROR reference to packed field
     }
 }

tests/ui/lint/unaligned_references.stderr

@@ -1,5 +1,14 @@
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:20:17
+  --> $DIR/unaligned_references.rs:25:13
+   |
+LL |             &self.x;
+   |             ^^^^^^^
+   |
+   = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+
+error[E0793]: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:34:17
    |
 LL |         let _ = &good.ptr;
    |                 ^^^^^^^^^
@@ -8,7 +17,7 @@ LL |         let _ = &good.ptr;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:21:17
+  --> $DIR/unaligned_references.rs:35:17
    |
 LL |         let _ = &good.data;
    |                 ^^^^^^^^^^
@@ -17,7 +26,7 @@ LL |         let _ = &good.data;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:23:17
+  --> $DIR/unaligned_references.rs:37:17
    |
 LL |         let _ = &good.data as *const _;
    |                 ^^^^^^^^^^
@@ -26,7 +35,7 @@ LL |         let _ = &good.data as *const _;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:24:27
+  --> $DIR/unaligned_references.rs:38:27
    |
 LL |         let _: *const _ = &good.data;
    |                           ^^^^^^^^^^
@@ -35,7 +44,7 @@ LL |         let _: *const _ = &good.data;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:26:17
+  --> $DIR/unaligned_references.rs:40:17
    |
 LL |         let _ = good.data.clone();
    |                 ^^^^^^^^^^^^^^^^^
@@ -44,7 +53,7 @@ LL |         let _ = good.data.clone();
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:28:17
+  --> $DIR/unaligned_references.rs:42:17
    |
 LL |         let _ = &good.data2[0];
    |                 ^^^^^^^^^^^^^^
@@ -53,7 +62,7 @@ LL |         let _ = &good.data2[0];
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:37:17
+  --> $DIR/unaligned_references.rs:51:17
    |
 LL |         let _ = &packed2.x;
    |                 ^^^^^^^^^^
@@ -62,7 +71,7 @@ LL |         let _ = &packed2.x;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:81:20
+  --> $DIR/unaligned_references.rs:90:20
    |
 LL |         let _ref = &m1.1.a;
    |                    ^^^^^^^
@@ -71,14 +80,14 @@ LL |         let _ref = &m1.1.a;
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
 error[E0793]: reference to packed field is unaligned
-  --> $DIR/unaligned_references.rs:90:20
+  --> $DIR/unaligned_references.rs:93:20
    |
 LL |         let _ref = &m2.1.a;
    |                    ^^^^^^^
    |
    = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
    = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 
-error: aborting due to 9 previous errors
+error: aborting due to 10 previous errors
 
 For more information about this error, try `rustc --explain E0793`.