misc layout_of cleanup

compiler/rustc_middle/messages.ftl

@@ -37,9 +37,6 @@ middle_autodiff_unsafe_inner_const_ref = reading from a `Duplicated` const {$ty}
 middle_bounds_check =
     index out of bounds: the length is {$len} but the index is {$index}
 
-middle_cannot_be_normalized =
-    unable to determine layout for `{$ty}` because `{$failure_ty}` cannot be normalized
-
 middle_conflict_types =
     this expression supplies two conflicting concrete types for the same opaque type
 
@@ -52,9 +49,6 @@ middle_const_eval_non_int =
 middle_const_not_used_in_type_alias =
     const parameter `{$ct}` is part of concrete type but not used in parameter list for the `impl Trait` type alias
 
-middle_cycle =
-    a cycle occurred during layout computation
-
 middle_deprecated = use of deprecated {$kind} `{$path}`{$has_note ->
         [true] : {$note}
         *[other] {""}
@@ -78,9 +72,23 @@ middle_erroneous_constant = erroneous constant encountered
 middle_failed_writing_file =
     failed to write file {$path}: {$error}"
 
+middle_layout_cycle =
+    a cycle occurred during layout computation
+
+middle_layout_normalization_failure =
+    unable to determine layout for `{$ty}` because `{$failure_ty}` cannot be normalized
+
 middle_layout_references_error =
     the type has an unknown layout
 
+middle_layout_size_overflow =
+    values of the type `{$ty}` are too big for the target architecture
+
+middle_layout_too_generic = the type `{$ty}` does not have a fixed layout
+
+middle_layout_unknown =
+    the type `{$ty}` has an unknown layout
+
 middle_opaque_hidden_type_mismatch =
     concrete type differs from previous defining opaque type use
     .label = expected `{$self_ty}`, got `{$other_ty}`
@@ -98,16 +106,8 @@ middle_strict_coherence_needs_negative_coherence =
     to use `strict_coherence` on this trait, the `with_negative_coherence` feature must be enabled
     .label = due to this attribute
 
-middle_too_generic = `{$ty}` does not have a fixed size
-
 middle_type_length_limit = reached the type-length limit while instantiating `{$shrunk}`
 
-middle_unknown_layout =
-    the type `{$ty}` has an unknown layout
-
 middle_unsupported_union = we don't support unions yet: '{$ty_name}'
 
-middle_values_too_big =
-    values of the type `{$ty}` are too big for the target architecture
-
 middle_written_to_path = the full type name has been written to '{$path}'

compiler/rustc_middle/src/error.rs

@@ -132,19 +132,19 @@ impl fmt::Debug for CustomSubdiagnostic<'_> {
 
 #[derive(Diagnostic)]
 pub enum LayoutError<'tcx> {
-    #[diag(middle_unknown_layout)]
+    #[diag(middle_layout_unknown)]
     Unknown { ty: Ty<'tcx> },
 
-    #[diag(middle_too_generic)]
+    #[diag(middle_layout_too_generic)]
     TooGeneric { ty: Ty<'tcx> },
 
-    #[diag(middle_values_too_big)]
+    #[diag(middle_layout_size_overflow)]
     Overflow { ty: Ty<'tcx> },
 
-    #[diag(middle_cannot_be_normalized)]
+    #[diag(middle_layout_normalization_failure)]
     NormalizationFailure { ty: Ty<'tcx>, failure_ty: String },
 
-    #[diag(middle_cycle)]
+    #[diag(middle_layout_cycle)]
     Cycle,
 
     #[diag(middle_layout_references_error)]

compiler/rustc_middle/src/ty/layout.rs

@@ -229,11 +229,32 @@ impl fmt::Display for ValidityRequirement {
 
 #[derive(Copy, Clone, Debug, HashStable, TyEncodable, TyDecodable)]
 pub enum LayoutError<'tcx> {
+    /// A type doesn't have a sensible layout.
+    ///
+    /// This variant is used for layout errors that don't necessarily cause
+    /// compile errors.
+    ///
+    /// For example, this can happen if a struct contains an unsized type in a
+    /// non-tail field, but has an unsatisfiable bound like `str: Sized`.
     Unknown(Ty<'tcx>),
+    /// The size of a type exceeds [`TargetDataLayout::obj_size_bound`].
     SizeOverflow(Ty<'tcx>),
+    /// The layout can vary due to a generic parameter.
+    ///
+    /// Unlike `Unknown`, this variant is a "soft" error and indicates that the layout
+    /// may become computable after further instantiating the generic parameter(s).
     TooGeneric(Ty<'tcx>),
+    /// An alias failed to normalize.
+    ///
+    /// This variant is necessary, because, due to trait solver incompleteness, it is
+    /// possible than an alias that was rigid during analysis fails to normalize after
+    /// revealing opaque types.
+    ///
+    /// See `tests/ui/layout/normalization-failure.rs` for an example.
     NormalizationFailure(Ty<'tcx>, NormalizationError<'tcx>),
+    /// A non-layout error is reported elsewhere.
     ReferencesError(ErrorGuaranteed),
+    /// A type has cyclic layout, i.e. the type contains itself without indirection.
     Cycle(ErrorGuaranteed),
 }
 
@@ -243,11 +264,11 @@ impl<'tcx> LayoutError<'tcx> {
 
         use crate::fluent_generated::*;
         match self {
-            Unknown(_) => middle_unknown_layout,
-            SizeOverflow(_) => middle_values_too_big,
-            TooGeneric(_) => middle_too_generic,
-            NormalizationFailure(_, _) => middle_cannot_be_normalized,
-            Cycle(_) => middle_cycle,
+            Unknown(_) => middle_layout_unknown,
+            SizeOverflow(_) => middle_layout_size_overflow,
+            TooGeneric(_) => middle_layout_too_generic,
+            NormalizationFailure(_, _) => middle_layout_normalization_failure,
+            Cycle(_) => middle_layout_cycle,
             ReferencesError(_) => middle_layout_references_error,
         }
     }
@@ -276,7 +297,7 @@ impl<'tcx> fmt::Display for LayoutError<'tcx> {
         match *self {
             LayoutError::Unknown(ty) => write!(f, "the type `{ty}` has an unknown layout"),
             LayoutError::TooGeneric(ty) => {
-                write!(f, "`{ty}` does not have a fixed size")
+                write!(f, "the type `{ty}` does not have a fixed layout")
             }
             LayoutError::SizeOverflow(ty) => {
                 write!(f, "values of the type `{ty}` are too big for the target architecture")

compiler/rustc_ty_utils/src/layout.rs

@@ -134,42 +134,32 @@ fn univariant_uninterned<'tcx>(
     cx: &LayoutCx<'tcx>,
     ty: Ty<'tcx>,
     fields: &IndexSlice<FieldIdx, TyAndLayout<'tcx>>,
-    repr: &ReprOptions,
     kind: StructKind,
 ) -> Result<LayoutData<FieldIdx, VariantIdx>, &'tcx LayoutError<'tcx>> {
-    let pack = repr.pack;
-    if pack.is_some() && repr.align.is_some() {
-        cx.tcx().dcx().bug("struct cannot be packed and aligned");
-    }
-
-    cx.calc.univariant(fields, repr, kind).map_err(|err| map_error(cx, ty, err))
+    let repr = ReprOptions::default();
+    cx.calc.univariant(fields, &repr, kind).map_err(|err| map_error(cx, ty, err))
 }
 
 fn extract_const_value<'tcx>(
-    const_: ty::Const<'tcx>,
-    ty: Ty<'tcx>,
     cx: &LayoutCx<'tcx>,
+    ty: Ty<'tcx>,
+    ct: ty::Const<'tcx>,
 ) -> Result<ty::Value<'tcx>, &'tcx LayoutError<'tcx>> {
-    match const_.kind() {
+    match ct.kind() {
         ty::ConstKind::Value(cv) => Ok(cv),
-        ty::ConstKind::Error(guar) => {
-            return Err(error(cx, LayoutError::ReferencesError(guar)));
-        }
-        ty::ConstKind::Param(_) | ty::ConstKind::Expr(_) => {
-            if !const_.has_param() {
-                bug!("no generic type found in the type: {ty:?}");
-            }
-            return Err(error(cx, LayoutError::TooGeneric(ty)));
-        }
-        ty::ConstKind::Unevaluated(_) => {
-            if !const_.has_param() {
-                return Err(error(cx, LayoutError::Unknown(ty)));
-            } else {
-                return Err(error(cx, LayoutError::TooGeneric(ty)));
+        ty::ConstKind::Param(_) | ty::ConstKind::Expr(_) | ty::ConstKind::Unevaluated(_) => {
+            if !ct.has_param() {
+                bug!("failed to normalize const, but it is not generic: {ct:?}");
             }
+            Err(error(cx, LayoutError::TooGeneric(ty)))
         }
-        ty::ConstKind::Infer(_) | ty::ConstKind::Bound(..) | ty::ConstKind::Placeholder(_) => {
-            bug!("unexpected type: {ty:?}");
+        ty::ConstKind::Infer(_)
+        | ty::ConstKind::Bound(..)
+        | ty::ConstKind::Placeholder(_)
+        | ty::ConstKind::Error(_) => {
+            // `ty::ConstKind::Error` is handled at the top of `layout_of_uncached`
+            // (via `ty.error_reported()`).
+            bug!("layout_of: unexpected const: {ct:?}");
         }
     }
 }
@@ -194,10 +184,9 @@ fn layout_of_uncached<'tcx>(
     };
     let scalar = |value: Primitive| tcx.mk_layout(LayoutData::scalar(cx, scalar_unit(value)));
 
-    let univariant =
-        |fields: &IndexSlice<FieldIdx, TyAndLayout<'tcx>>, repr: &ReprOptions, kind| {
-            Ok(tcx.mk_layout(univariant_uninterned(cx, ty, fields, repr, kind)?))
-        };
+    let univariant = |fields: &IndexSlice<FieldIdx, TyAndLayout<'tcx>>, kind| {
+        Ok(tcx.mk_layout(univariant_uninterned(cx, ty, fields, kind)?))
+    };
     debug_assert!(!ty.has_non_region_infer());
 
     Ok(match *ty.kind() {
@@ -210,12 +199,12 @@ fn layout_of_uncached<'tcx>(
                         &mut layout.backend_repr
                     {
                         if let Some(start) = start {
-                            scalar.valid_range_mut().start = extract_const_value(start, ty, cx)?
+                            scalar.valid_range_mut().start = extract_const_value(cx, ty, start)?
                                 .try_to_bits(tcx, cx.typing_env)
                                 .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
                         }
                         if let Some(end) = end {
-                            let mut end = extract_const_value(end, ty, cx)?
+                            let mut end = extract_const_value(cx, ty, end)?
                                 .try_to_bits(tcx, cx.typing_env)
                                 .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
                             if !include_end {
@@ -274,16 +263,11 @@ fn layout_of_uncached<'tcx>(
                 data_ptr.valid_range_mut().start = 1;
             }
 
-            let pointee = tcx.normalize_erasing_regions(cx.typing_env, pointee);
             if pointee.is_sized(tcx, cx.typing_env) {
                 return Ok(tcx.mk_layout(LayoutData::scalar(cx, data_ptr)));
             }
 
-            let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type()
-                // Projection eagerly bails out when the pointee references errors,
-                // fall back to structurally deducing metadata.
-                && !pointee.references_error()
-            {
+            let metadata = if let Some(metadata_def_id) = tcx.lang_items().metadata_type() {
                 let pointee_metadata = Ty::new_projection(tcx, metadata_def_id, [pointee]);
                 let metadata_ty =
                     match tcx.try_normalize_erasing_regions(cx.typing_env, pointee_metadata) {
@@ -354,7 +338,7 @@ fn layout_of_uncached<'tcx>(
 
         // Arrays and slices.
         ty::Array(element, count) => {
-            let count = extract_const_value(count, ty, cx)?
+            let count = extract_const_value(cx, ty, count)?
                 .try_to_target_usize(tcx)
                 .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
 
@@ -415,17 +399,10 @@ fn layout_of_uncached<'tcx>(
         }),
 
         // Odd unit types.
-        ty::FnDef(..) => {
-            univariant(IndexSlice::empty(), &ReprOptions::default(), StructKind::AlwaysSized)?
-        }
+        ty::FnDef(..) => univariant(IndexSlice::empty(), StructKind::AlwaysSized)?,
         ty::Dynamic(_, _, ty::Dyn) | ty::Foreign(..) => {
-            let mut unit = univariant_uninterned(
-                cx,
-                ty,
-                IndexSlice::empty(),
-                &ReprOptions::default(),
-                StructKind::AlwaysSized,
-            )?;
+            let mut unit =
+                univariant_uninterned(cx, ty, IndexSlice::empty(), StructKind::AlwaysSized)?;
             match unit.backend_repr {
                 BackendRepr::Memory { ref mut sized } => *sized = false,
                 _ => bug!(),
@@ -439,7 +416,6 @@ fn layout_of_uncached<'tcx>(
             let tys = args.as_closure().upvar_tys();
             univariant(
                 &tys.iter().map(|ty| cx.layout_of(ty)).try_collect::<IndexVec<_, _>>()?,
-                &ReprOptions::default(),
                 StructKind::AlwaysSized,
             )?
         }
@@ -448,7 +424,6 @@ fn layout_of_uncached<'tcx>(
             let tys = args.as_coroutine_closure().upvar_tys();
             univariant(
                 &tys.iter().map(|ty| cx.layout_of(ty)).try_collect::<IndexVec<_, _>>()?,
-                &ReprOptions::default(),
                 StructKind::AlwaysSized,
             )?
         }
@@ -457,11 +432,7 @@ fn layout_of_uncached<'tcx>(
             let kind =
                 if tys.len() == 0 { StructKind::AlwaysSized } else { StructKind::MaybeUnsized };
 
-            univariant(
-                &tys.iter().map(|k| cx.layout_of(k)).try_collect::<IndexVec<_, _>>()?,
-                &ReprOptions::default(),
-                kind,
-            )?
+            univariant(&tys.iter().map(|k| cx.layout_of(k)).try_collect::<IndexVec<_, _>>()?, kind)?
         }
 
         // SIMD vector types.
@@ -719,25 +690,30 @@ fn layout_of_uncached<'tcx>(
         }
 
         // Types with no meaningful known layout.
+        ty::Param(_) => {
+            return Err(error(cx, LayoutError::TooGeneric(ty)));
+        }
+
         ty::Alias(..) => {
-            if ty.has_param() {
-                return Err(error(cx, LayoutError::TooGeneric(ty)));
-            }
             // NOTE(eddyb) `layout_of` query should've normalized these away,
             // if that was possible, so there's no reason to try again here.
-            return Err(error(cx, LayoutError::Unknown(ty)));
-        }
-
-        ty::Bound(..) | ty::CoroutineWitness(..) | ty::Infer(_) | ty::Error(_) => {
-            bug!("Layout::compute: unexpected type `{}`", ty)
-        }
-
-        ty::Param(_) => {
-            return Err(error(cx, LayoutError::TooGeneric(ty)));
+            let err = if ty.has_param() {
+                LayoutError::TooGeneric(ty)
+            } else {
+                // This is only reachable with unsatisfiable predicates. For example, if we have
+                // `u8: Iterator`, then we can't compute the layout of `<u8 as Iterator>::Item`.
+                LayoutError::Unknown(ty)
+            };
+            return Err(error(cx, err));
         }
 
-        ty::Placeholder(..) => {
-            return Err(error(cx, LayoutError::Unknown(ty)));
+        ty::Placeholder(..)
+        | ty::Bound(..)
+        | ty::CoroutineWitness(..)
+        | ty::Infer(_)
+        | ty::Error(_) => {
+            // `ty::Error` is handled at the top of this function.
+            bug!("layout_of: unexpected type `{ty}`")
         }
     })
 }
@@ -911,13 +887,7 @@ fn coroutine_layout<'tcx>(
         .chain(iter::once(Ok(tag_layout)))
         .chain(promoted_layouts)
         .try_collect::<IndexVec<_, _>>()?;
-    let prefix = univariant_uninterned(
-        cx,
-        ty,
-        &prefix_layouts,
-        &ReprOptions::default(),
-        StructKind::AlwaysSized,
-    )?;
+    let prefix = univariant_uninterned(cx, ty, &prefix_layouts, StructKind::AlwaysSized)?;
 
     let (prefix_size, prefix_align) = (prefix.size, prefix.align);
 
@@ -982,7 +952,6 @@ fn coroutine_layout<'tcx>(
                 cx,
                 ty,
                 &variant_only_tys.map(|ty| cx.layout_of(ty)).try_collect::<IndexVec<_, _>>()?,
-                &ReprOptions::default(),
                 StructKind::Prefixed(prefix_size, prefix_align.abi),
             )?;
             variant.variants = Variants::Single { index };

tests/ui/layout/debug.rs

@@ -82,3 +82,8 @@ type Impossible = (str, str); //~ ERROR: cannot be known at compilation time
 #[rustc_layout(debug)]
 union EmptyUnion {} //~ ERROR: has an unknown layout
 //~^ ERROR: unions cannot have zero fields
+
+// Test the error message of `LayoutError::TooGeneric`
+// (this error is never emitted to users).
+#[rustc_layout(debug)]
+type TooGeneric<T> = T; //~ ERROR: does not have a fixed layout