Better detection of repr packed and align

Fixes issue #43317.

Author: bitshifter

src/librustc/diagnostics.rs

@@ -2025,5 +2025,4 @@ register_diagnostics! {
     E0490, // a value of type `..` is borrowed for too long
     E0495, // cannot infer an appropriate lifetime due to conflicting requirements
     E0566, // conflicting representation hints
-    E0587, // conflicting packed and align representation hints
 }

src/librustc/hir/check_attr.rs

@@ -76,8 +76,6 @@ impl<'a> CheckAttrVisitor<'a> {
         };
 
         let mut conflicting_reprs = 0;
-        let mut found_packed = false;
-        let mut found_align = false;
 
         for word in words {
 
@@ -106,7 +104,6 @@ impl<'a> CheckAttrVisitor<'a> {
                                 ("attribute should be applied to struct or union",
                                  "a struct or union")
                     } else {
-                        found_packed = true;
                         continue
                     }
                 }
@@ -120,7 +117,6 @@ impl<'a> CheckAttrVisitor<'a> {
                     }
                 }
                 "align" => {
-                    found_align = true;
                     if target != Target::Struct &&
                             target != Target::Union {
                         ("attribute should be applied to struct or union",
@@ -150,10 +146,6 @@ impl<'a> CheckAttrVisitor<'a> {
             span_warn!(self.sess, attr.span, E0566,
                        "conflicting representation hints");
         }
-        if found_align && found_packed {
-            struct_span_err!(self.sess, attr.span, E0587,
-                             "conflicting packed and align representation hints").emit();
-        }
     }
 }
 

src/librustc_typeck/check/mod.rs

@@ -1063,11 +1063,7 @@ fn check_struct<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         check_simd(tcx, span, def_id);
     }
 
-    // if struct is packed and not aligned, check fields for alignment.
-    // Checks for combining packed and align attrs on single struct are done elsewhere.
-    if tcx.adt_def(def_id).repr.packed() && tcx.adt_def(def_id).repr.align == 0 {
-        check_packed(tcx, span, def_id);
-    }
+    check_packed(tcx, span, def_id);
 }
 
 fn check_union<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
@@ -1478,9 +1474,15 @@ pub fn check_simd<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span, def_id: DefId
 }
 
 fn check_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, sp: Span, def_id: DefId) {
-    if check_packed_inner(tcx, def_id, &mut Vec::new()) {
-        struct_span_err!(tcx.sess, sp, E0588,
-            "packed struct cannot transitively contain a `[repr(align)]` struct").emit();
+    if tcx.adt_def(def_id).repr.packed() {
+        if tcx.adt_def(def_id).repr.align > 0 {
+            struct_span_err!(tcx.sess, sp, E0587,
+                             "struct has conflicting packed and align representation hints").emit();
+        }
+        else if check_packed_inner(tcx, def_id, &mut Vec::new()) {
+            struct_span_err!(tcx.sess, sp, E0588,
+                "packed struct cannot transitively contain a `[repr(align)]` struct").emit();
+        }
     }
 }
 

src/librustc_typeck/diagnostics.rs

@@ -4663,6 +4663,7 @@ register_diagnostics! {
            // but `{}` was found in the type `{}`
     E0567, // auto traits can not have type parameters
     E0568, // auto-traits can not have predicates,
+    E0587, // struct has conflicting packed and align representation hints
     E0588, // packed struct cannot transitively contain a `[repr(align)]` struct
     E0592, // duplicate definitions with name `{}`
 //  E0613, // Removed (merged with E0609)

src/test/compile-fail/conflicting-repr-hints.rs

@@ -27,7 +27,15 @@ enum D { D }
 #[repr(C, packed)]
 struct E(i32);
 
-#[repr(packed, align(8))] //~ ERROR conflicting packed and align representation hints
-struct F(i32);
+#[repr(packed, align(8))]
+struct F(i32); //~ ERROR struct has conflicting packed and align representation hints
+
+#[repr(packed)]
+#[repr(align(8))]
+struct G(i32); //~ ERROR struct has conflicting packed and align representation hints
+
+#[repr(align(8))]
+#[repr(packed)]
+struct H(i32); //~ ERROR struct has conflicting packed and align representation hints
 
 fn main() {}