Add TooGeneric variant to LayoutError and emit Unknown one

- `check-pass` test for a MRE of #135020
- fail test for #135138
- switch to `TooGeneric` for checking CMSE fn signatures
- switch to `TooGeneric` for compute `SizeSkeleton` (for transmute)
- fix broken tests

Author: FedericoBruzzone

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -140,7 +140,7 @@ where
         // Don't emit a new diagnostic for these errors, they are already reported elsewhere or
         // should remain silent.
         err_inval!(AlreadyReported(info)) => ErrorHandled::Reported(info, span),
-        err_inval!(Layout(LayoutError::Unknown(_))) | err_inval!(TooGeneric) => {
+        err_inval!(Layout(LayoutError::TooGeneric(_))) | err_inval!(TooGeneric) => {
             ErrorHandled::TooGeneric(span)
         }
         err_inval!(Layout(LayoutError::ReferencesError(guar))) => {

compiler/rustc_hir_analysis/src/hir_ty_lowering/cmse.rs

@@ -201,7 +201,7 @@ fn should_emit_generic_error<'tcx>(abi: ExternAbi, layout_err: &'tcx LayoutError
     use LayoutError::*;
 
     match layout_err {
-        Unknown(ty) => {
+        TooGeneric(ty) => {
             match abi {
                 ExternAbi::CCmseNonSecureCall => {
                     // prevent double reporting of this error
@@ -211,7 +211,11 @@ fn should_emit_generic_error<'tcx>(abi: ExternAbi, layout_err: &'tcx LayoutError
                 _ => bug!("invalid ABI: {abi}"),
             }
         }
-        SizeOverflow(..) | NormalizationFailure(..) | ReferencesError(..) | Cycle(..) => {
+        Unknown(..)
+        | SizeOverflow(..)
+        | NormalizationFailure(..)
+        | ReferencesError(..)
+        | Cycle(..) => {
             false // not our job to report these
         }
     }

compiler/rustc_middle/messages.ftl

@@ -100,11 +100,14 @@ 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_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

@@ -129,6 +129,9 @@ pub enum LayoutError<'tcx> {
     #[diag(middle_unknown_layout)]
     Unknown { ty: Ty<'tcx> },
 
+    #[diag(middle_too_generic)]
+    TooGeneric { ty: Ty<'tcx> },
+
     #[diag(middle_values_too_big)]
     Overflow { ty: Ty<'tcx> },
 

compiler/rustc_middle/src/ty/layout.rs

@@ -231,6 +231,7 @@ impl fmt::Display for ValidityRequirement {
 pub enum LayoutError<'tcx> {
     Unknown(Ty<'tcx>),
     SizeOverflow(Ty<'tcx>),
+    TooGeneric(Ty<'tcx>),
     NormalizationFailure(Ty<'tcx>, NormalizationError<'tcx>),
     ReferencesError(ErrorGuaranteed),
     Cycle(ErrorGuaranteed),
@@ -244,6 +245,7 @@ impl<'tcx> LayoutError<'tcx> {
         match self {
             Unknown(_) => middle_unknown_layout,
             SizeOverflow(_) => middle_values_too_big,
+            TooGeneric(_) => middle_too_generic,
             NormalizationFailure(_, _) => middle_cannot_be_normalized,
             Cycle(_) => middle_cycle,
             ReferencesError(_) => middle_layout_references_error,
@@ -257,6 +259,7 @@ impl<'tcx> LayoutError<'tcx> {
         match self {
             Unknown(ty) => E::Unknown { ty },
             SizeOverflow(ty) => E::Overflow { ty },
+            TooGeneric(ty) => E::TooGeneric { ty },
             NormalizationFailure(ty, e) => {
                 E::NormalizationFailure { ty, failure_ty: e.get_type_for_failure() }
             }
@@ -272,6 +275,9 @@ impl<'tcx> fmt::Display for LayoutError<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         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")
+            }
             LayoutError::SizeOverflow(ty) => {
                 write!(f, "values of the type `{ty}` are too big for the target architecture")
             }
@@ -350,10 +356,11 @@ impl<'tcx> SizeSkeleton<'tcx> {
                     return Err(tcx.arena.alloc(LayoutError::Unknown(ty)));
                 }
             }
-            Err(err @ LayoutError::Unknown(_)) => err,
+            Err(err @ LayoutError::TooGeneric(_)) => err,
             // We can't extract SizeSkeleton info from other layout errors
             Err(
                 e @ LayoutError::Cycle(_)
+                | e @ LayoutError::Unknown(_)
                 | e @ LayoutError::SizeOverflow(_)
                 | e @ LayoutError::NormalizationFailure(..)
                 | e @ LayoutError::ReferencesError(_),

compiler/rustc_transmute/src/layout/tree.rs

@@ -197,6 +197,7 @@ pub(crate) mod rustc {
             match err {
                 LayoutError::Unknown(..)
                 | LayoutError::ReferencesError(..)
+                | LayoutError::TooGeneric(..)
                 | LayoutError::NormalizationFailure(..) => Self::UnknownLayout,
                 LayoutError::SizeOverflow(..) => Self::SizeOverflow,
                 LayoutError::Cycle(err) => Self::TypeError(*err),

compiler/rustc_ty_utils/src/layout.rs

@@ -104,14 +104,12 @@ fn map_error<'tcx>(
             // This is sometimes not a compile error if there are trivially false where clauses.
             // See `tests/ui/layout/trivial-bounds-sized.rs` for an example.
             assert!(field.layout.is_unsized(), "invalid layout error {err:#?}");
-            if !field.ty.is_sized(cx.tcx(), cx.typing_env) {
-                let guar = cx.tcx().dcx().delayed_bug(format!(
+            if cx.typing_env.param_env.caller_bounds().is_empty() {
+                cx.tcx().dcx().delayed_bug(format!(
                     "encountered unexpected unsized field in layout of {ty:?}: {field:#?}"
                 ));
-                LayoutError::ReferencesError(guar)
-            } else {
-                LayoutError::Unknown(ty)
             }
+            LayoutError::Unknown(ty)
         }
         LayoutCalculatorError::EmptyUnion => {
             // This is always a compile error.
@@ -319,17 +317,32 @@ fn layout_of_uncached<'tcx>(
         }
 
         // Arrays and slices.
-        ty::Array(element, mut count) => {
-            if count.has_aliases() {
-                count = tcx.normalize_erasing_regions(cx.typing_env, count);
-                if count.has_aliases() {
-                    return Err(error(cx, LayoutError::Unknown(ty)));
+        ty::Array(element, count) => {
+            let count = match count.kind() {
+                ty::ConstKind::Value(_, valtree) => valtree
+                    .try_to_target_usize(tcx)
+                    .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?,
+                ty::ConstKind::Error(guar) => {
+                    return Err(error(cx, LayoutError::ReferencesError(guar)));
                 }
-            }
+                ty::ConstKind::Param(_) | ty::ConstKind::Expr(_) => {
+                    if !count.has_param() {
+                        bug!("no generic type found in count of array type: {ty:?}");
+                    }
+                    return Err(error(cx, LayoutError::TooGeneric(ty)));
+                }
+                ty::ConstKind::Unevaluated(_) => {
+                    if !count.has_param() {
+                        return Err(error(cx, LayoutError::Unknown(ty)));
+                    } else {
+                        return Err(error(cx, LayoutError::TooGeneric(ty)));
+                    }
+                }
+                ty::ConstKind::Infer(_)
+                | ty::ConstKind::Bound(..)
+                | ty::ConstKind::Placeholder(_) => bug!("unexpected count in array type: {ty:?}"),
+            };
 
-            let count = count
-                .try_to_target_usize(tcx)
-                .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
             let element = cx.layout_of(element)?;
             let size = element
                 .size
@@ -687,6 +700,9 @@ fn layout_of_uncached<'tcx>(
 
         // Types with no meaningful known layout.
         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)));
@@ -696,7 +712,11 @@ fn layout_of_uncached<'tcx>(
             bug!("Layout::compute: unexpected type `{}`", ty)
         }
 
-        ty::Placeholder(..) | ty::Param(_) => {
+        ty::Param(_) => {
+            return Err(error(cx, LayoutError::TooGeneric(ty)));
+        }
+
+        ty::Placeholder(..) => {
             return Err(error(cx, LayoutError::Unknown(ty)));
         }
     })

src/librustdoc/html/templates/type_layout.html

@@ -28,13 +28,11 @@ <h2 id="layout" class="section-header"> {# #}
         {% endfor %}
     </ul>
     {% endif %}
-    {# This kind of layout error can occur with valid code, e.g. if you try to
-    get the layout of a generic type such as `Vec<T>`. #}
+        {# This kind of layout error can occur with valid code, for example
+        if there are trivial bounds: `struct Foo(str, str) where str: Sized;`. #}
         {% when Err(LayoutError::Unknown(_)) %}
         <p> {# #}
-            <strong>Note:</strong> Unable to compute type layout, {#+ #}
-            possibly due to this type having generic parameters. {#+ #}
-            Layout can only be computed for concrete, fully-instantiated types. {# #}
+            <strong>Note:</strong> Unable to compute type layout. {# #}
         </p>
         {# This kind of error probably can't happen with valid code, but we don't
         want to panic and prevent the docs from building, so we just let the
@@ -44,6 +42,14 @@ <h2 id="layout" class="section-header"> {# #}
             <strong>Note:</strong> Encountered an error during type layout; {#+ #}
             the type was too big. {# #}
         </p>
+        {# This kind of layout error can occur with valid code, e.g. if you try to
+        get the layout of a generic type such as `Vec<T>`. #}
+        {% when Err(LayoutError::TooGeneric(_)) %}
+        <p> {# #}
+            <strong>Note:</strong> Unable to compute type layout, {#+ #}
+            possibly due to this type having generic parameters. {#+ #}
+            Layout can only be computed for concrete, fully-instantiated types. {# #}
+        </p>
         {% when Err(LayoutError::ReferencesError(_)) %}
         <p> {# #}
             <strong>Note:</strong> Encountered an error during type layout; {#+ #}

tests/crashes/135020.rs

@@ -37,7 +37,7 @@ pub struct Y(u8);
 pub struct Z;
 
 // We can't compute layout for generic types.
-//@ hasraw type_layout/struct.Generic.html 'Unable to compute type layout, possibly due to this type having generic parameters'
+//@ hasraw type_layout/struct.Generic.html 'Encountered an error during type layout; the type was too generic.'
 //@ !hasraw - 'Size: '
 pub struct Generic<T>(T);
 
@@ -91,3 +91,9 @@ pub enum Uninhabited {}
 //@ hasraw type_layout/struct.Uninhabited2.html 'Size: '
 //@ hasraw - '8 bytes (<a href="https://doc.rust-lang.org/stable/reference/glossary.html#uninhabited">uninhabited</a>)'
 pub struct Uninhabited2(std::convert::Infallible, u64);
+
+pub trait Project { type Assoc; }
+// We can't compute layout. A `LayoutError::Unknown` is returned.
+//@ hasraw type_layout/struct.Unknown.html 'Unable to compute type layout.'
+//@ !hasraw - 'Size: '
+pub struct Unknown(<() as Project>::Assoc) where for<'a> (): Project;