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

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_hir_typeck/src/intrinsicck.rs

@@ -122,7 +122,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     format!("generic size {size}")
                 }
             }
-            Err(LayoutError::Unknown(bad)) => {
+            Err(LayoutError::TooGeneric(bad)) => {
                 if *bad == ty {
                     "this type does not have a fixed size".to_owned()
                 } else {

compiler/rustc_middle/messages.ftl

@@ -100,6 +100,8 @@ 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 =
@@ -107,4 +109,5 @@ middle_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(_),
@@ -413,10 +420,9 @@ impl<'tcx> SizeSkeleton<'tcx> {
                             // Alignment is unchanged by arrays.
                             return Ok(SizeSkeleton::Known(Size::from_bytes(size), a));
                         }
-                        Err(tcx.arena.alloc(LayoutError::Unknown(ty)))
+                        Err(err)
                     }
-                    SizeSkeleton::Pointer { .. } => Err(err),
+                    SizeSkeleton::Pointer { .. } | SizeSkeleton::Generic(_) => Err(err),
-                    SizeSkeleton::Generic(_) => Err(tcx.arena.alloc(LayoutError::Unknown(ty))),
                 }
             }
 

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) {
+            if cx.typing_env.param_env.caller_bounds().is_empty() {
-                let guar = cx.tcx().dcx().delayed_bug(format!(
+                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.
@@ -146,6 +144,35 @@ fn univariant_uninterned<'tcx>(
     cx.calc.univariant(fields, repr, kind).map_err(|err| map_error(cx, ty, err))
 }
 
+fn validate_const_with_value<'tcx>(
+    const_: ty::Const<'tcx>,
+    ty: Ty<'tcx>,
+    cx: &LayoutCx<'tcx>,
+) -> Result<ty::Const<'tcx>, &'tcx LayoutError<'tcx>> {
+    match const_.kind() {
+        ty::ConstKind::Value(..) => Ok(const_),
+        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::Infer(_) | ty::ConstKind::Bound(..) | ty::ConstKind::Placeholder(_) => {
+            bug!("unexpected type: {ty:?}");
+        }
+    }
+}
+
 fn layout_of_uncached<'tcx>(
     cx: &LayoutCx<'tcx>,
     ty: Ty<'tcx>,
@@ -182,12 +209,13 @@ fn layout_of_uncached<'tcx>(
                         &mut layout.backend_repr
                     {
                         if let Some(start) = start {
-                            scalar.valid_range_mut().start = start
+                            scalar.valid_range_mut().start =
+                                validate_const_with_value(start, ty, cx)?
                                     .try_to_bits(tcx, cx.typing_env)
                                     .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
                         }
                         if let Some(end) = end {
-                            let mut end = end
+                            let mut end = validate_const_with_value(end, ty, cx)?
                                 .try_to_bits(tcx, cx.typing_env)
                                 .ok_or_else(|| error(cx, LayoutError::Unknown(ty)))?;
                             if !include_end {
@@ -319,17 +347,13 @@ fn layout_of_uncached<'tcx>(
         }
 
         // Arrays and slices.
-        ty::Array(element, mut count) => {
+        ty::Array(element, count) => {
-            if count.has_aliases() {
+            let count = validate_const_with_value(count, ty, cx)?
-                count = tcx.normalize_erasing_regions(cx.typing_env, count);
+                .to_valtree()
-                if count.has_aliases() {
+                .0
-                    return Err(error(cx, LayoutError::Unknown(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 +711,9 @@ 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 +723,11 @@ 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 @@
         {% endfor %}
     </ul>
     {% endif %}
-    {# This kind of layout error can occur with valid code, e.g. if you try to
+        {# This kind of layout error can occur with valid code, for example
-    get the layout of a generic type such as `Vec<T>`. #}
+        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, {#+ #}
+            <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>
         {# 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 @@
             <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

@@ -1,11 +0,0 @@
-//@ known-bug: #135020
-
-pub fn problem_thingy(items: &mut impl Iterator<Item = str>) {
-    let mut peeker = items.peekable();
-    match peeker.peek() {
-        Some(_) => (),
-        None => return (),
-    }
-}
-
-pub fn main() {}

tests/rustdoc/type-layout.rs

@@ -37,7 +37,8 @@ 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 'Unable to compute type layout, possibly due to this type having generic parameters.'
+//@ hasraw type_layout/struct.Generic.html 'Layout can only be computed for concrete, fully-instantiated types.'
 //@ !hasraw - 'Size: '
 pub struct Generic<T>(T);
 
@@ -91,3 +92,9 @@ 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;

tests/ui/enum-discriminant/eval-error.rs

@@ -6,7 +6,7 @@ union Foo {
 
 enum Bar {
     Boo = {
-        let _: Option<Foo> = None;
+        let _: Option<Foo> = None; //~ ERROR evaluation of constant value failed
         0
     },
 }

tests/ui/enum-discriminant/eval-error.stderr

@@ -45,7 +45,13 @@ help: wrap the field type in `ManuallyDrop<...>`
 LL |     a: std::mem::ManuallyDrop<str>,
    |        +++++++++++++++++++++++   +
 
-error: aborting due to 4 previous errors
+error[E0080]: evaluation of constant value failed
+  --> $DIR/eval-error.rs:9:30
+   |
+LL |         let _: Option<Foo> = None;
+   |                              ^^^^ the type `Foo` has an unknown layout
 
-Some errors have detailed explanations: E0277, E0517, E0740.
+error: aborting due to 5 previous errors
-For more information about an error, try `rustc --explain E0277`.
+
+Some errors have detailed explanations: E0080, E0277, E0517, E0740.
+For more information about an error, try `rustc --explain E0080`.

tests/ui/layout/base-layout-is-sized-ice-123078.rs

@@ -8,6 +8,7 @@ struct S {
 }
 
 const C: S = unsafe { std::mem::transmute(()) };
+//~^ ERROR cannot transmute between types of different sizes, or dependently-sized types
 const _: [(); {
     C;
     0

tests/ui/layout/base-layout-is-sized-ice-123078.stderr

@@ -16,6 +16,16 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL |     a: Box<[u8]>,
    |        ++++    +
 
-error: aborting due to 1 previous error
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/base-layout-is-sized-ice-123078.rs:10:23
+   |
+LL | const C: S = unsafe { std::mem::transmute(()) };
+   |                       ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `()` (0 bits)
+   = note: target type: `S` (the type `S` has an unknown layout)
 
-For more information about this error, try `rustc --explain E0277`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0277, E0512.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/layout/invalid-unsized-const-eval.rs

@@ -10,5 +10,6 @@ struct LazyLock {
 }
 
 static EMPTY_SET: LazyLock = todo!();
+//~^ ERROR could not evaluate static initializer
 
 fn main() {}

tests/ui/layout/invalid-unsized-const-eval.stderr

@@ -7,6 +7,13 @@ LL |     data: (dyn Sync, ()),
    = help: the trait `Sized` is not implemented for `(dyn Sync + 'static)`
    = note: only the last element of a tuple may have a dynamically sized type
 
-error: aborting due to 1 previous error
+error[E0080]: could not evaluate static initializer
+  --> $DIR/invalid-unsized-const-eval.rs:12:1
+   |
+LL | static EMPTY_SET: LazyLock = todo!();
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^ the type `(dyn Sync, ())` has an unknown layout
 
-For more information about this error, try `rustc --explain E0277`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0080, E0277.
+For more information about an error, try `rustc --explain E0080`.

tests/ui/layout/invalid-unsized-in-always-sized-tail.stderr

@@ -18,6 +18,20 @@ LL | struct MySlice<T>(T);
    |                |
    |                this could be changed to `T: ?Sized`...
 
-error: aborting due to 1 previous error
+error[E0080]: could not evaluate static initializer
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
+   |
+   = note: the type `MySlice<[bool]>` has an unknown layout
+   |
+note: inside `align_of::<P2>`
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
+note: inside `CHECK`
+  --> $DIR/invalid-unsized-in-always-sized-tail.rs:15:28
+   |
+LL | static CHECK: () = assert!(align_of::<P2>() == 1);
+   |                            ^^^^^^^^^^^^^^^^
 
-For more information about this error, try `rustc --explain E0277`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0080, E0277.
+For more information about an error, try `rustc --explain E0080`.

tests/ui/layout/issue-unsized-tail-restatic-ice-122488.rs

@@ -6,5 +6,6 @@ struct ArenaSet<U: Deref, V: ?Sized = <U as Deref>::Target>(V, U);
 //~^ ERROR the size for values of type `V` cannot be known at compilation time
 
 const DATA: *const ArenaSet<Vec<u8>> = std::ptr::null_mut();
+//~^ ERROR evaluation of constant value failed
 
 pub fn main() {}

tests/ui/layout/issue-unsized-tail-restatic-ice-122488.stderr

@@ -22,6 +22,13 @@ help: the `Box` type always has a statically known size and allocates its conten
 LL | struct ArenaSet<U: Deref, V: ?Sized = <U as Deref>::Target>(Box<V>, U);
    |                                                             ++++ +
 
-error: aborting due to 1 previous error
+error[E0080]: evaluation of constant value failed
+  --> $DIR/issue-unsized-tail-restatic-ice-122488.rs:8:1
+   |
+LL | const DATA: *const ArenaSet<Vec<u8>> = std::ptr::null_mut();
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the type `ArenaSet<Vec<u8>, [u8]>` has an unknown layout
 
-For more information about this error, try `rustc --explain E0277`.
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0080, E0277.
+For more information about an error, try `rustc --explain E0080`.

tests/ui/layout/uncomputable-due-to-trivial-bounds-ice-135138.rs

@@ -0,0 +1,11 @@
+#![feature(trivial_bounds)]
+
+fn return_str()
+where
+    str: Sized,
+{
+    [(); { let _a: Option<str> = None; 0 }];
+    //~^ ERROR evaluation of constant value failed
+}
+
+fn main() {}

tests/ui/layout/uncomputable-due-to-trivial-bounds-ice-135138.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/uncomputable-due-to-trivial-bounds-ice-135138.rs:7:16
+   |
+LL |     [(); { let _a: Option<str> = None; 0 }];
+   |                ^^ the type `Option<str>` has an unknown layout
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/layout/unexpected-unsized-field-issue-135020.rs

@@ -0,0 +1,7 @@
+//@ check-pass
+
+fn problem_thingy(items: &mut impl Iterator<Item = str>) {
+    items.peekable();
+}
+
+fn main() {}

tests/ui/layout/unknown-when-no-type-parameter.rs

@@ -0,0 +1,14 @@
+#![feature(trivial_bounds)]
+
+//@ error-pattern: error[E0080]: evaluation of constant value failed
+//@ error-pattern: the type `<() as Project>::Assoc` has an unknown layout
+
+trait Project {
+    type Assoc;
+}
+
+fn foo() where (): Project {
+    [(); size_of::<<() as Project>::Assoc>()];
+}
+
+fn main() {}

tests/ui/layout/unknown-when-no-type-parameter.stderr

@@ -0,0 +1,16 @@
+error[E0080]: evaluation of constant value failed
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
+   |
+   = note: the type `<() as Project>::Assoc` has an unknown layout
+   |
+note: inside `std::mem::size_of::<<() as Project>::Assoc>`
+  --> $SRC_DIR/core/src/mem/mod.rs:LL:COL
+note: inside `foo::{constant#0}`
+  --> $DIR/unknown-when-no-type-parameter.rs:11:10
+   |
+LL |     [(); size_of::<<() as Project>::Assoc>()];
+   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/layout/unknown-when-ptr-metadata-is-DST.rs

@@ -0,0 +1,12 @@
+#![feature(ptr_metadata)]
+#![feature(trivial_bounds)]
+
+fn return_str()
+where
+    str: std::ptr::Pointee<Metadata = str>,
+{
+    [(); { let _a: Option<&str> = None; 0 }];
+    //~^ ERROR evaluation of constant value failed
+}
+
+fn main() {}

tests/ui/layout/unknown-when-ptr-metadata-is-DST.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/unknown-when-ptr-metadata-is-DST.rs:8:16
+   |
+LL |     [(); { let _a: Option<&str> = None; 0 }];
+   |                ^^ the type `str` has an unknown layout
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0080`.

tests/ui/structs/ice-struct-tail-normalization-113272.rs

@@ -13,6 +13,6 @@ struct Other {
 fn main() {
     unsafe {
         std::mem::transmute::<Option<()>, Option<&Other>>(None);
-        //~^ ERROR cannot transmute
+        //~^ ERROR cannot transmute between types of different sizes, or dependently-sized types
     }
 }