Check for accessing unnamed field in find_field

Author: clubby789

compiler/rustc_hir_analysis/src/collect.rs

@@ -793,6 +793,10 @@ fn convert_enum_variant_types(tcx: TyCtxt<'_>, def_id: DefId) {
 fn find_field(tcx: TyCtxt<'_>, (def_id, ident): (DefId, Ident)) -> Option<FieldIdx> {
     tcx.adt_def(def_id).non_enum_variant().fields.iter_enumerated().find_map(|(idx, field)| {
         if field.is_unnamed() {
+            // Users can't write `expr._`, but derive macros can
+            if ident.name == kw::Underscore {
+                return Some(idx);
+            }
             let field_ty = tcx.type_of(field.did).instantiate_identity();
             let adt_def = field_ty.ty_adt_def().expect("expect Adt for unnamed field");
             tcx.find_field((adt_def.did(), ident)).map(|_| idx)

compiler/rustc_middle/src/query/mod.rs

@@ -2225,6 +2225,8 @@ rustc_queries! {
         separate_provide_extern
     }
 
+    /// Find a field with a given name on the given def (must be a struct or union). Will
+    /// recurse into unnamed fields if present.
     query find_field((def_id, ident): (DefId, rustc_span::symbol::Ident)) -> Option<rustc_target::abi::FieldIdx> {
         desc { |tcx| "find the index of maybe nested field `{ident}` in `{}`", tcx.def_path_str(def_id) }
     }

tests/ui/union/unnamed-fields/restrict_type_hir.rs

@@ -18,6 +18,7 @@ enum BadEnum {
 }
 
 #[repr(C)]
+#[derive(Debug)]
 enum BadEnum2 {
     A,
     B,
@@ -26,7 +27,9 @@ enum BadEnum2 {
 type MyStruct = A;
 type MyI32 = i32;
 
+// Derive to check if accessing fields will ICE (#121263)
 #[repr(C)]
+#[derive(Debug)]
 struct L {
     _: i32, //~ ERROR unnamed fields can only have struct or union types
     _: MyI32, //~ ERROR unnamed fields can only have struct or union types

tests/ui/union/unnamed-fields/restrict_type_hir.stderr

@@ -1,29 +1,29 @@
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:31:5
+  --> $DIR/restrict_type_hir.rs:34:5
    |
 LL |     _: i32,
    |     ^^^^^^
 
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:32:5
+  --> $DIR/restrict_type_hir.rs:35:5
    |
 LL |     _: MyI32,
    |     ^^^^^^^^
 
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:33:5
+  --> $DIR/restrict_type_hir.rs:36:5
    |
 LL |     _: BadEnum,
    |     ^^^^^^^^^^
 
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:34:5
+  --> $DIR/restrict_type_hir.rs:37:5
    |
 LL |     _: BadEnum2,
    |     ^^^^^^^^^^^
 
 error: named type of unnamed field must have `#[repr(C)]` representation
-  --> $DIR/restrict_type_hir.rs:36:5
+  --> $DIR/restrict_type_hir.rs:39:5
    |
 LL |     _: dep::BadStruct,
    |     ^^^^^^^^^^^^^^^^^ unnamed field defined here
@@ -41,19 +41,19 @@ LL | pub struct BadStruct(());
    |
 
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:37:5
+  --> $DIR/restrict_type_hir.rs:40:5
    |
 LL |     _: dep::BadEnum,
    |     ^^^^^^^^^^^^^^^
 
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:38:5
+  --> $DIR/restrict_type_hir.rs:41:5
    |
 LL |     _: dep::BadEnum2,
    |     ^^^^^^^^^^^^^^^^
 
 error: unnamed fields can only have struct or union types
-  --> $DIR/restrict_type_hir.rs:39:5
+  --> $DIR/restrict_type_hir.rs:42:5
    |
 LL |     _: dep::BadAlias,
    |     ^^^^^^^^^^^^^^^^