Add tracking of packed repr, use it to highlight unsafe refs

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.

2 files changed, 35 insertions, 0 deletions

diff --git a/crates/ra_ide/src/syntax_highlighting.rs b/crates/ra_ide/src/syntax_highlighting.rs
index 6b7874460..0cab684eb 100644
--- a/crates/ra_ide/src/syntax_highlighting.rs
+++ b/crates/ra_ide/src/syntax_highlighting.rs
@@ -565,6 +565,30 @@ fn highlight_element(
                 _ => h,
             }
         }
+        REF_EXPR => {
+            let ref_expr = element.into_node().and_then(ast::RefExpr::cast)?;
+            let expr = ref_expr.expr()?;
+            let field_expr = match expr {
+                ast::Expr::FieldExpr(fe) => fe,
+                _ => return None,
+            };
+
+            let expr = field_expr.expr()?;
+            let ty = match sema.type_of_expr(&expr) {
+                Some(ty) => ty,
+                None => {
+                    println!("No type :(");
+                    return None;
+                }
+            };
+            if !ty.is_packed(db) {
+                return None;
+            }
+
+            // FIXME account for alignment... somehow
+
+            Highlight::new(HighlightTag::Operator) | HighlightModifier::Unsafe
+        }
         p if p.is_punct() => match p {
             T![::] | T![->] | T![=>] | T![&] | T![..] | T![=] | T![@] => {
                 HighlightTag::Operator.into()
diff --git a/crates/ra_ide/src/syntax_highlighting/tests.rs b/crates/ra_ide/src/syntax_highlighting/tests.rs
index 09062c38e..f2c078d34 100644
--- a/crates/ra_ide/src/syntax_highlighting/tests.rs
+++ b/crates/ra_ide/src/syntax_highlighting/tests.rs
@@ -292,6 +292,13 @@ struct TypeForStaticMut {
 
 static mut global_mut: TypeForStaticMut = TypeForStaticMut { a: 0 };
 
+#[repr(packed)]
+struct Packed {
+    a: u16,
+    b: u8,
+    c: u32,
+}
+
 fn main() {
     let x = &5 as *const usize;
     let u = Union { b: 0 };
@@ -306,6 +313,10 @@ fn main() {
         let y = *(x);
         let z = -x;
         let a = global_mut.a;
+        let packed = Packed { a: 0, b: 0, c: 0 };
+        let a = &packed.a;
+        let b = &packed.b;
+        let c = &packed.c;
     }
 }
 "#