Merge #4743

4743: Add tracking of packed repr, use it to highlight unsafe refs r=matklad a=Nashenas88

Taking a reference to a misaligned field on a packed struct is an
unsafe operation. Highlight that behavior. Currently, the misaligned
part isn't tracked, so this highlight is a bit too aggressive.

Fixes #4600

Co-authored-by: Paul Daniel Faria <Nashenas88@users.noreply.github.com>
Co-authored-by: Paul Daniel Faria <nashenas88@users.noreply.github.com>
Co-authored-by: Paul Daniel Faria <paulf@pop-os.localdomain>

crates/ra_hir/src/code_model.rs

@@ -4,6 +4,7 @@ use std::{iter, sync::Arc};
 use arrayvec::ArrayVec;
 use either::Either;
 use hir_def::{
+    adt::ReprKind,
     adt::StructKind,
     adt::VariantData,
     builtin_type::BuiltinType,
@@ -431,6 +432,10 @@ impl Struct {
         Type::from_def(db, self.id.lookup(db.upcast()).container.module(db.upcast()).krate, self.id)
     }
 
+    pub fn repr(self, db: &dyn HirDatabase) -> Option<ReprKind> {
+        db.struct_data(self.id).repr.clone()
+    }
+
     fn variant_data(self, db: &dyn HirDatabase) -> Arc<VariantData> {
         db.struct_data(self.id).variant_data.clone()
     }
@@ -1253,6 +1258,19 @@ impl Type {
         )
     }
 
+    pub fn is_packed(&self, db: &dyn HirDatabase) -> bool {
+        let adt_id = match self.ty.value {
+            Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(adt_id), .. }) => adt_id,
+            _ => return false,
+        };
+
+        let adt = adt_id.into();
+        match adt {
+            Adt::Struct(s) => matches!(s.repr(db), Some(ReprKind::Packed)),
+            _ => false,
+        }
+    }
+
     pub fn is_raw_ptr(&self) -> bool {
         matches!(&self.ty.value, Ty::Apply(ApplicationTy { ctor: TypeCtor::RawPtr(..), .. }))
     }

crates/ra_hir/src/lib.rs

@@ -49,7 +49,7 @@ pub use hir_def::{
     docs::Documentation,
     nameres::ModuleSource,
     path::{ModPath, Path, PathKind},
-    type_ref::Mutability,
+    type_ref::{Mutability, TypeRef},
 };
 pub use hir_expand::{
     hygiene::Hygiene, name::Name, HirFileId, InFile, MacroCallId, MacroCallLoc,

crates/ra_hir/src/semantics.rs

@@ -25,7 +25,8 @@ use crate::{
     semantics::source_to_def::{ChildContainer, SourceToDefCache, SourceToDefCtx},
     source_analyzer::{resolve_hir_path, resolve_hir_path_qualifier, SourceAnalyzer},
     AssocItem, Callable, Crate, Field, Function, HirFileId, ImplDef, InFile, Local, MacroDef,
-    Module, ModuleDef, Name, Origin, Path, ScopeDef, Trait, Type, TypeAlias, TypeParam, VariantDef,
+    Module, ModuleDef, Name, Origin, Path, ScopeDef, Trait, Type, TypeAlias, TypeParam, TypeRef,
+    VariantDef,
 };
 use resolver::TypeNs;
 
@@ -279,6 +280,18 @@ impl<'db, DB: HirDatabase> Semantics<'db, DB> {
     pub fn assert_contains_node(&self, node: &SyntaxNode) {
         self.imp.assert_contains_node(node)
     }
+
+    pub fn is_unsafe_method_call(&self, method_call_expr: ast::MethodCallExpr) -> bool {
+        self.imp.is_unsafe_method_call(method_call_expr)
+    }
+
+    pub fn is_unsafe_ref_expr(&self, ref_expr: &ast::RefExpr) -> bool {
+        self.imp.is_unsafe_ref_expr(ref_expr)
+    }
+
+    pub fn is_unsafe_ident_pat(&self, ident_pat: &ast::IdentPat) -> bool {
+        self.imp.is_unsafe_ident_pat(ident_pat)
+    }
 }
 
 impl<'db> SemanticsImpl<'db> {
@@ -574,6 +587,90 @@ impl<'db> SemanticsImpl<'db> {
         });
         InFile::new(file_id, node)
     }
+
+    pub fn is_unsafe_method_call(&self, method_call_expr: ast::MethodCallExpr) -> bool {
+        method_call_expr
+            .expr()
+            .and_then(|expr| {
+                let field_expr = if let ast::Expr::FieldExpr(field_expr) = expr {
+                    field_expr
+                } else {
+                    return None;
+                };
+                let ty = self.type_of_expr(&field_expr.expr()?)?;
+                if !ty.is_packed(self.db) {
+                    return None;
+                }
+
+                let func = self.resolve_method_call(&method_call_expr).map(Function::from)?;
+                let is_unsafe = func.has_self_param(self.db)
+                    && matches!(func.params(self.db).first(), Some(TypeRef::Reference(..)));
+                Some(is_unsafe)
+            })
+            .unwrap_or(false)
+    }
+
+    pub fn is_unsafe_ref_expr(&self, ref_expr: &ast::RefExpr) -> bool {
+        ref_expr
+            .expr()
+            .and_then(|expr| {
+                let field_expr = match expr {
+                    ast::Expr::FieldExpr(field_expr) => field_expr,
+                    _ => return None,
+                };
+                let expr = field_expr.expr()?;
+                self.type_of_expr(&expr)
+            })
+            // Binding a reference to a packed type is possibly unsafe.
+            .map(|ty| ty.is_packed(self.db))
+            .unwrap_or(false)
+
+        // FIXME This needs layout computation to be correct. It will highlight
+        // more than it should with the current implementation.
+    }
+
+    pub fn is_unsafe_ident_pat(&self, ident_pat: &ast::IdentPat) -> bool {
+        if !ident_pat.ref_token().is_some() {
+            return false;
+        }
+
+        ident_pat
+            .syntax()
+            .parent()
+            .and_then(|parent| {
+                // `IdentPat` can live under `RecordPat` directly under `RecordPatField` or
+                // `RecordPatFieldList`. `RecordPatField` also lives under `RecordPatFieldList`,
+                // so this tries to lookup the `IdentPat` anywhere along that structure to the
+                // `RecordPat` so we can get the containing type.
+                let record_pat = ast::RecordPatField::cast(parent.clone())
+                    .and_then(|record_pat| record_pat.syntax().parent())
+                    .or_else(|| Some(parent.clone()))
+                    .and_then(|parent| {
+                        ast::RecordPatFieldList::cast(parent)?
+                            .syntax()
+                            .parent()
+                            .and_then(ast::RecordPat::cast)
+                    });
+
+                // If this doesn't match a `RecordPat`, fallback to a `LetStmt` to see if
+                // this is initialized from a `FieldExpr`.
+                if let Some(record_pat) = record_pat {
+                    self.type_of_pat(&ast::Pat::RecordPat(record_pat))
+                } else if let Some(let_stmt) = ast::LetStmt::cast(parent) {
+                    let field_expr = match let_stmt.initializer()? {
+                        ast::Expr::FieldExpr(field_expr) => field_expr,
+                        _ => return None,
+                    };
+
+                    self.type_of_expr(&field_expr.expr()?)
+                } else {
+                    None
+                }
+            })
+            // Binding a reference to a packed type is possibly unsafe.
+            .map(|ty| ty.is_packed(self.db))
+            .unwrap_or(false)
+    }
 }
 
 pub trait ToDef: AstNode + Clone {

crates/ra_hir_def/src/adt.rs

@@ -9,11 +9,12 @@ use hir_expand::{
 };
 use ra_arena::{map::ArenaMap, Arena};
 use ra_syntax::ast::{self, NameOwner, VisibilityOwner};
+use tt::{Delimiter, DelimiterKind, Leaf, Subtree, TokenTree};
 
 use crate::{
     body::{CfgExpander, LowerCtx},
     db::DefDatabase,
-    item_tree::{Field, Fields, ItemTree},
+    item_tree::{AttrOwner, Field, Fields, ItemTree, ModItem},
     src::HasChildSource,
     src::HasSource,
     trace::Trace,
@@ -29,6 +30,7 @@ use ra_cfg::CfgOptions;
 pub struct StructData {
     pub name: Name,
     pub variant_data: Arc<VariantData>,
+    pub repr: Option<ReprKind>,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -58,26 +60,58 @@ pub struct FieldData {
     pub visibility: RawVisibility,
 }
 
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ReprKind {
+    Packed,
+    Other,
+}
+
+fn repr_from_value(item_tree: &ItemTree, of: AttrOwner) -> Option<ReprKind> {
+    item_tree.attrs(of).by_key("repr").tt_values().find_map(parse_repr_tt)
+}
+
+fn parse_repr_tt(tt: &Subtree) -> Option<ReprKind> {
+    match tt.delimiter {
+        Some(Delimiter { kind: DelimiterKind::Parenthesis, .. }) => {}
+        _ => return None,
+    }
+
+    let mut it = tt.token_trees.iter();
+    match it.next()? {
+        TokenTree::Leaf(Leaf::Ident(ident)) if ident.text == "packed" => Some(ReprKind::Packed),
+        _ => Some(ReprKind::Other),
+    }
+}
+
 impl StructData {
     pub(crate) fn struct_data_query(db: &dyn DefDatabase, id: StructId) -> Arc<StructData> {
         let loc = id.lookup(db);
         let item_tree = db.item_tree(loc.id.file_id);
+        let repr = repr_from_value(&item_tree, ModItem::from(loc.id.value).into());
         let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
 
         let strukt = &item_tree[loc.id.value];
         let variant_data = lower_fields(&item_tree, &cfg_options, &strukt.fields);
-
-        Arc::new(StructData { name: strukt.name.clone(), variant_data: Arc::new(variant_data) })
+        Arc::new(StructData {
+            name: strukt.name.clone(),
+            variant_data: Arc::new(variant_data),
+            repr,
+        })
     }
     pub(crate) fn union_data_query(db: &dyn DefDatabase, id: UnionId) -> Arc<StructData> {
         let loc = id.lookup(db);
         let item_tree = db.item_tree(loc.id.file_id);
+        let repr = repr_from_value(&item_tree, ModItem::from(loc.id.value).into());
         let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
 
         let union = &item_tree[loc.id.value];
         let variant_data = lower_fields(&item_tree, &cfg_options, &union.fields);
 
-        Arc::new(StructData { name: union.name.clone(), variant_data: Arc::new(variant_data) })
+        Arc::new(StructData {
+            name: union.name.clone(),
+            variant_data: Arc::new(variant_data),
+            repr,
+        })
     }
 }
 

crates/ra_ide/src/syntax_highlighting.rs

@@ -497,9 +497,9 @@ fn highlight_element(
             match name_kind {
                 Some(NameClass::ExternCrate(_)) => HighlightTag::Module.into(),
                 Some(NameClass::Definition(def)) => {
-                    highlight_name(db, def, false) | HighlightModifier::Definition
+                    highlight_name(sema, db, def, None, false) | HighlightModifier::Definition
                 }
-                Some(NameClass::ConstReference(def)) => highlight_name(db, def, false),
+                Some(NameClass::ConstReference(def)) => highlight_name(sema, db, def, None, false),
                 Some(NameClass::FieldShorthand { field, .. }) => {
                     let mut h = HighlightTag::Field.into();
                     if let Definition::Field(field) = field {
@@ -532,7 +532,7 @@ fn highlight_element(
                                 binding_hash = Some(calc_binding_hash(&name, *shadow_count))
                             }
                         };
-                        highlight_name(db, def, possibly_unsafe)
+                        highlight_name(sema, db, def, Some(name_ref), possibly_unsafe)
                     }
                     NameRefClass::FieldShorthand { .. } => HighlightTag::Field.into(),
                 },
@@ -566,9 +566,20 @@ fn highlight_element(
             }
         }
         p if p.is_punct() => match p {
-            T![::] | T![->] | T![=>] | T![&] | T![..] | T![=] | T![@] => {
-                HighlightTag::Operator.into()
+            T![&] => {
+                let h = HighlightTag::Operator.into();
+                let is_unsafe = element
+                    .parent()
+                    .and_then(ast::RefExpr::cast)
+                    .map(|ref_expr| sema.is_unsafe_ref_expr(&ref_expr))
+                    .unwrap_or(false);
+                if is_unsafe {
+                    h | HighlightModifier::Unsafe
+                } else {
+                    h
                 }
+            }
+            T![::] | T![->] | T![=>] | T![..] | T![=] | T![@] => HighlightTag::Operator.into(),
             T![!] if element.parent().and_then(ast::MacroCall::cast).is_some() => {
                 HighlightTag::Macro.into()
             }
@@ -649,6 +660,18 @@ fn highlight_element(
                         HighlightTag::SelfKeyword.into()
                     }
                 }
+                T![ref] => element
+                    .parent()
+                    .and_then(ast::IdentPat::cast)
+                    .and_then(|ident_pat| {
+                        if sema.is_unsafe_ident_pat(&ident_pat) {
+                            Some(HighlightModifier::Unsafe)
+                        } else {
+                            None
+                        }
+                    })
+                    .map(|modifier| h | modifier)
+                    .unwrap_or(h),
                 _ => h,
             }
         }
@@ -678,7 +701,13 @@ fn is_child_of_impl(element: &SyntaxElement) -> bool {
     }
 }
 
-fn highlight_name(db: &RootDatabase, def: Definition, possibly_unsafe: bool) -> Highlight {
+fn highlight_name(
+    sema: &Semantics<RootDatabase>,
+    db: &RootDatabase,
+    def: Definition,
+    name_ref: Option<ast::NameRef>,
+    possibly_unsafe: bool,
+) -> Highlight {
     match def {
         Definition::Macro(_) => HighlightTag::Macro,
         Definition::Field(field) => {
@@ -697,6 +726,15 @@ fn highlight_name(db: &RootDatabase, def: Definition, possibly_unsafe: bool) ->
                 let mut h = HighlightTag::Function.into();
                 if func.is_unsafe(db) {
                     h |= HighlightModifier::Unsafe;
+                } else {
+                    let is_unsafe = name_ref
+                        .and_then(|name_ref| name_ref.syntax().parent())
+                        .and_then(ast::MethodCallExpr::cast)
+                        .map(|method_call_expr| sema.is_unsafe_method_call(method_call_expr))
+                        .unwrap_or(false);
+                    if is_unsafe {
+                        h |= HighlightModifier::Unsafe;
+                    }
                 }
                 return h;
             }
@@ -768,8 +806,18 @@ fn highlight_name_ref_by_syntax(name: ast::NameRef, sema: &Semantics<RootDatabas
         _ => return default.into(),
     };
 
-    let tag = match parent.kind() {
-        METHOD_CALL_EXPR => HighlightTag::Function,
+    match parent.kind() {
+        METHOD_CALL_EXPR => {
+            let mut h = Highlight::new(HighlightTag::Function);
+            let is_unsafe = ast::MethodCallExpr::cast(parent)
+                .map(|method_call_expr| sema.is_unsafe_method_call(method_call_expr))
+                .unwrap_or(false);
+            if is_unsafe {
+                h |= HighlightModifier::Unsafe;
+            }
+
+            h
+        }
         FIELD_EXPR => {
             let h = HighlightTag::Field;
             let is_union = ast::FieldExpr::cast(parent)
@@ -782,7 +830,11 @@ fn highlight_name_ref_by_syntax(name: ast::NameRef, sema: &Semantics<RootDatabas
                     })
                 })
                 .unwrap_or(false);
-            return if is_union { h | HighlightModifier::Unsafe } else { h.into() };
+            if is_union {
+                h | HighlightModifier::Unsafe
+            } else {
+                h.into()
+            }
         }
         PATH_SEGMENT => {
             let path = match parent.parent().and_then(ast::Path::cast) {
@@ -807,18 +859,15 @@ fn highlight_name_ref_by_syntax(name: ast::NameRef, sema: &Semantics<RootDatabas
             };
 
             match parent.kind() {
-                CALL_EXPR => HighlightTag::Function,
-                _ => {
-                    if name.text().chars().next().unwrap_or_default().is_uppercase() {
-                        HighlightTag::Struct
+                CALL_EXPR => HighlightTag::Function.into(),
+                _ => if name.text().chars().next().unwrap_or_default().is_uppercase() {
+                    HighlightTag::Struct.into()
                 } else {
                     HighlightTag::Constant
                 }
+                .into(),
             }
         }
+        _ => default.into(),
     }
-        _ => default,
-    };
-
-    tag.into()
 }

crates/ra_ide/src/syntax_highlighting/tests.rs

@@ -292,10 +292,24 @@ struct TypeForStaticMut {
 
 static mut global_mut: TypeForStaticMut = TypeForStaticMut { a: 0 };
 
+#[repr(packed)]
+struct Packed {
+    a: u16,
+}
+
+trait DoTheAutoref {
+    fn calls_autoref(&self);
+}
+
+impl DoTheAutoref for u16 {
+    fn calls_autoref(&self) {}
+}
+
 fn main() {
-    let x = &5 as *const usize;
+    let x = &5 as *const _ as *const usize;
     let u = Union { b: 0 };
     unsafe {
+        // unsafe fn and method calls
         unsafe_fn();
         let b = u.b;
         match u {
@@ -303,9 +317,22 @@ fn main() {
             Union { a } => (),
         }
         HasUnsafeFn.unsafe_method();
-        let y = *(x);
-        let z = -x;
+
+        // unsafe deref
+        let y = *x;
+
+        // unsafe access to a static mut
         let a = global_mut.a;
+
+        // unsafe ref of packed fields
+        let packed = Packed { a: 0 };
+        let a = &packed.a;
+        let ref a = packed.a;
+        let Packed { ref a } = packed;
+        let Packed { a: ref _a } = packed;
+
+        // unsafe auto ref of packed field
+        packed.a.calls_autoref();
     }
 }
 "#

crates/ra_ide/test_data/highlight_unsafe.html

@@ -54,10 +54,24 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
 
 <span class="keyword">static</span> <span class="keyword">mut</span> <span class="static declaration mutable unsafe">global_mut</span><span class="punctuation">:</span> <span class="struct">TypeForStaticMut</span> <span class="operator">=</span> <span class="struct">TypeForStaticMut</span> <span class="punctuation">{</span> <span class="field">a</span><span class="punctuation">:</span> <span class="numeric_literal">0</span> <span class="punctuation">}</span><span class="punctuation">;</span>
 
+<span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">repr</span><span class="punctuation">(</span><span class="attribute">packed</span><span class="punctuation">)</span><span class="attribute">]</span>
+<span class="keyword">struct</span> <span class="struct declaration">Packed</span> <span class="punctuation">{</span>
+    <span class="field declaration">a</span><span class="punctuation">:</span> <span class="builtin_type">u16</span><span class="punctuation">,</span>
+<span class="punctuation">}</span>
+
+<span class="keyword">trait</span> <span class="trait declaration">DoTheAutoref</span> <span class="punctuation">{</span>
+    <span class="keyword">fn</span> <span class="function declaration">calls_autoref</span><span class="punctuation">(</span><span class="operator">&</span><span class="self_keyword">self</span><span class="punctuation">)</span><span class="punctuation">;</span>
+<span class="punctuation">}</span>
+
+<span class="keyword">impl</span> <span class="trait">DoTheAutoref</span> <span class="keyword">for</span> <span class="builtin_type">u16</span> <span class="punctuation">{</span>
+    <span class="keyword">fn</span> <span class="function declaration">calls_autoref</span><span class="punctuation">(</span><span class="operator">&</span><span class="self_keyword">self</span><span class="punctuation">)</span> <span class="punctuation">{</span><span class="punctuation">}</span>
+<span class="punctuation">}</span>
+
 <span class="keyword">fn</span> <span class="function declaration">main</span><span class="punctuation">(</span><span class="punctuation">)</span> <span class="punctuation">{</span>
-    <span class="keyword">let</span> <span class="variable declaration">x</span> <span class="operator">=</span> <span class="operator">&</span><span class="numeric_literal">5</span> <span class="keyword">as</span> <span class="keyword">*</span><span class="keyword">const</span> <span class="builtin_type">usize</span><span class="punctuation">;</span>
+    <span class="keyword">let</span> <span class="variable declaration">x</span> <span class="operator">=</span> <span class="operator">&</span><span class="numeric_literal">5</span> <span class="keyword">as</span> <span class="keyword">*</span><span class="keyword">const</span> <span class="punctuation">_</span> <span class="keyword">as</span> <span class="keyword">*</span><span class="keyword">const</span> <span class="builtin_type">usize</span><span class="punctuation">;</span>
     <span class="keyword">let</span> <span class="variable declaration">u</span> <span class="operator">=</span> <span class="union">Union</span> <span class="punctuation">{</span> <span class="field">b</span><span class="punctuation">:</span> <span class="numeric_literal">0</span> <span class="punctuation">}</span><span class="punctuation">;</span>
     <span class="keyword unsafe">unsafe</span> <span class="punctuation">{</span>
+        <span class="comment">// unsafe fn and method calls</span>
         <span class="function unsafe">unsafe_fn</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
         <span class="keyword">let</span> <span class="variable declaration">b</span> <span class="operator">=</span> <span class="variable">u</span><span class="punctuation">.</span><span class="field unsafe">b</span><span class="punctuation">;</span>
         <span class="keyword control">match</span> <span class="variable">u</span> <span class="punctuation">{</span>
@@ -65,8 +79,21 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
             <span class="union">Union</span> <span class="punctuation">{</span> <span class="field unsafe">a</span> <span class="punctuation">}</span> <span class="operator">=&gt;</span> <span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">,</span>
         <span class="punctuation">}</span>
         <span class="struct">HasUnsafeFn</span><span class="punctuation">.</span><span class="function unsafe">unsafe_method</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
-        <span class="keyword">let</span> <span class="variable declaration">y</span> <span class="operator">=</span> <span class="operator unsafe">*</span><span class="punctuation">(</span><span class="variable">x</span><span class="punctuation">)</span><span class="punctuation">;</span>
-        <span class="keyword">let</span> <span class="variable declaration">z</span> <span class="operator">=</span> <span class="numeric_literal">-</span><span class="variable">x</span><span class="punctuation">;</span>
+
+        <span class="comment">// unsafe deref</span>
+        <span class="keyword">let</span> <span class="variable declaration">y</span> <span class="operator">=</span> <span class="operator unsafe">*</span><span class="variable">x</span><span class="punctuation">;</span>
+
+        <span class="comment">// unsafe access to a static mut</span>
         <span class="keyword">let</span> <span class="variable declaration">a</span> <span class="operator">=</span> <span class="static mutable unsafe">global_mut</span><span class="punctuation">.</span><span class="field">a</span><span class="punctuation">;</span>
+
+        <span class="comment">// unsafe ref of packed fields</span>
+        <span class="keyword">let</span> <span class="variable declaration">packed</span> <span class="operator">=</span> <span class="struct">Packed</span> <span class="punctuation">{</span> <span class="field">a</span><span class="punctuation">:</span> <span class="numeric_literal">0</span> <span class="punctuation">}</span><span class="punctuation">;</span>
+        <span class="keyword">let</span> <span class="variable declaration">a</span> <span class="operator">=</span> <span class="operator unsafe">&</span><span class="variable">packed</span><span class="punctuation">.</span><span class="field">a</span><span class="punctuation">;</span>
+        <span class="keyword">let</span> <span class="keyword unsafe">ref</span> <span class="variable declaration">a</span> <span class="operator">=</span> <span class="variable">packed</span><span class="punctuation">.</span><span class="field">a</span><span class="punctuation">;</span>
+        <span class="keyword">let</span> <span class="struct">Packed</span> <span class="punctuation">{</span> <span class="keyword unsafe">ref</span> <span class="field">a</span> <span class="punctuation">}</span> <span class="operator">=</span> <span class="variable">packed</span><span class="punctuation">;</span>
+        <span class="keyword">let</span> <span class="struct">Packed</span> <span class="punctuation">{</span> <span class="field">a</span><span class="punctuation">:</span> <span class="keyword unsafe">ref</span> <span class="variable declaration">_a</span> <span class="punctuation">}</span> <span class="operator">=</span> <span class="variable">packed</span><span class="punctuation">;</span>
+
+        <span class="comment">// unsafe auto ref of packed field</span>
+        <span class="variable">packed</span><span class="punctuation">.</span><span class="field">a</span><span class="punctuation">.</span><span class="function unsafe">calls_autoref</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="punctuation">}</span>
 <span class="punctuation">}</span></code></pre>