Rollup merge of #115340 - RalfJung:more_is_1zst, r=oli-obk

some more is_zst that should be is_1zst

Follow-up to #115277

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -195,8 +195,8 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
                     let ty_b = field.ty(tcx, args_b);
 
                     if let Ok(layout) = tcx.layout_of(param_env.and(ty_a)) {
-                        if layout.is_zst() && layout.align.abi.bytes() == 1 {
-                            // ignore ZST fields with alignment of 1 byte
+                        if layout.is_1zst() {
+                            // ignore 1-ZST fields
                             return false;
                         }
                     }

compiler/rustc_lint/src/types.rs

@@ -804,7 +804,7 @@ pub(crate) fn nonnull_optimization_guaranteed<'tcx>(
     tcx.has_attr(def.did(), sym::rustc_nonnull_optimization_guaranteed)
 }
 
-/// `repr(transparent)` structs can have a single non-ZST field, this function returns that
+/// `repr(transparent)` structs can have a single non-1-ZST field, this function returns that
 /// field.
 pub fn transparent_newtype_field<'a, 'tcx>(
     tcx: TyCtxt<'tcx>,
@@ -813,8 +813,8 @@ pub fn transparent_newtype_field<'a, 'tcx>(
     let param_env = tcx.param_env(variant.def_id);
     variant.fields.iter().find(|field| {
         let field_ty = tcx.type_of(field.did).instantiate_identity();
-        let is_zst = tcx.layout_of(param_env.and(field_ty)).is_ok_and(|layout| layout.is_zst());
-        !is_zst
+        let is_1zst = tcx.layout_of(param_env.and(field_ty)).is_ok_and(|layout| layout.is_1zst());
+        !is_1zst
     })
 }
 

compiler/rustc_ty_utils/src/abi.rs

@@ -592,13 +592,13 @@ fn make_thin_self_ptr<'tcx>(
             for i in 0..fat_pointer_layout.fields.count() {
                 let field_layout = fat_pointer_layout.field(cx, i);
 
-                if !field_layout.is_zst() {
+                if !field_layout.is_1zst() {
                     fat_pointer_layout = field_layout;
                     continue 'descend_newtypes;
                 }
             }
 
-            bug!("receiver has no non-zero-sized fields {:?}", fat_pointer_layout);
+            bug!("receiver has no non-1-ZST fields {:?}", fat_pointer_layout);
         }
 
         fat_pointer_layout.ty

compiler/rustc_ty_utils/src/layout.rs

@@ -192,7 +192,7 @@ fn layout_of_uncached<'tcx>(
 
                 let metadata_layout = cx.layout_of(metadata_ty)?;
                 // If the metadata is a 1-zst, then the pointer is thin.
-                if metadata_layout.is_zst() && metadata_layout.align.abi.bytes() == 1 {
+                if metadata_layout.is_1zst() {
                     return Ok(tcx.mk_layout(LayoutS::scalar(cx, data_ptr)));
                 }