Stop using <DefId as Ord> in various diagnostic situations

Cargo.lock

@@ -4236,6 +4236,7 @@ name = "rustc_middle"
 version = "0.0.0"
 dependencies = [
  "bitflags 2.4.2",
+ "derivative",
  "either",
  "field-offset",
  "gsgdt",

compiler/rustc_middle/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 [dependencies]
 # tidy-alphabetical-start
 bitflags = "2.4.1"
+derivative = "2.2.0"
 either = "1.5.0"
 field-offset = "0.3.5"
 gsgdt = "0.1.2"

compiler/rustc_middle/src/mir/consts.rs

@@ -456,7 +456,7 @@ impl<'tcx> Const<'tcx> {
 }
 
 /// An unevaluated (potentially generic) constant used in MIR.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, TyEncodable, TyDecodable)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, TyEncodable, TyDecodable)]
 #[derive(Hash, HashStable, TypeFoldable, TypeVisitable, Lift)]
 pub struct UnevaluatedConst<'tcx> {
     pub def: DefId,

compiler/rustc_middle/src/mir/query.rs

@@ -284,8 +284,15 @@ rustc_data_structures::static_assert_size!(ConstraintCategory<'_>, 16);
 /// order of the category, thereby influencing diagnostic output.
 ///
 /// See also `rustc_const_eval::borrow_check::constraints`.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash)]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, Hash)]
 #[derive(TyEncodable, TyDecodable, HashStable, TypeVisitable, TypeFoldable)]
+#[derive(derivative::Derivative)]
+#[derivative(
+    PartialOrd,
+    Ord,
+    PartialOrd = "feature_allow_slow_enum",
+    Ord = "feature_allow_slow_enum"
+)]
 pub enum ConstraintCategory<'tcx> {
     Return(ReturnConstraint),
     Yield,
@@ -295,6 +302,7 @@ pub enum ConstraintCategory<'tcx> {
     Cast {
         /// Whether this is an unsizing cast and if yes, this contains the target type.
         /// Region variables are erased to ReErased.
+        #[derivative(PartialOrd = "ignore", Ord = "ignore")]
         unsize_to: Option<Ty<'tcx>>,
     },
 
@@ -304,7 +312,7 @@ pub enum ConstraintCategory<'tcx> {
     ClosureBounds,
 
     /// Contains the function type if available.
-    CallArgument(Option<Ty<'tcx>>),
+    CallArgument(#[derivative(PartialOrd = "ignore", Ord = "ignore")] Option<Ty<'tcx>>),
     CopyBound,
     SizedBound,
     Assignment,

compiler/rustc_middle/src/ty/layout.rs

@@ -2,7 +2,7 @@ use crate::error::UnsupportedFnAbi;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrFlags;
 use crate::query::TyCtxtAt;
 use crate::ty::normalize_erasing_regions::NormalizationError;
-use crate::ty::{self, ConstKind, Ty, TyCtxt, TypeVisitableExt};
+use crate::ty::{self, Ty, TyCtxt, TypeVisitableExt};
 use rustc_error_messages::DiagMessage;
 use rustc_errors::{
     Diag, DiagArgValue, DiagCtxt, Diagnostic, EmissionGuarantee, IntoDiagArg, Level,
@@ -356,21 +356,10 @@ impl<'tcx> SizeSkeleton<'tcx> {
                                 .ok_or_else(|| &*tcx.arena.alloc(LayoutError::SizeOverflow(ty)))?;
                             return Ok(SizeSkeleton::Known(Size::from_bytes(size)));
                         }
-                        let len = tcx.expand_abstract_consts(len);
-                        let prev = ty::Const::from_target_usize(tcx, s.bytes());
-                        let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, prev) else {
-                            return Err(tcx.arena.alloc(LayoutError::SizeOverflow(ty)));
-                        };
-                        Ok(SizeSkeleton::Generic(gen_size))
+                        Err(tcx.arena.alloc(LayoutError::Unknown(ty)))
                     }
                     SizeSkeleton::Pointer { .. } => Err(err),
-                    SizeSkeleton::Generic(g) => {
-                        let len = tcx.expand_abstract_consts(len);
-                        let Some(gen_size) = mul_sorted_consts(tcx, param_env, len, g) else {
-                            return Err(tcx.arena.alloc(LayoutError::SizeOverflow(ty)));
-                        };
-                        Ok(SizeSkeleton::Generic(gen_size))
-                    }
+                    SizeSkeleton::Generic(_) => Err(tcx.arena.alloc(LayoutError::Unknown(ty))),
                 }
             }
 
@@ -468,56 +457,6 @@ impl<'tcx> SizeSkeleton<'tcx> {
     }
 }
 
-/// When creating the layout for types with abstract consts in their size (i.e. [usize; 4 * N]),
-/// to ensure that they have a canonical order and can be compared directly we combine all
-/// constants, and sort the other terms. This allows comparison of expressions of sizes,
-/// allowing for things like transmuting between types that depend on generic consts.
-/// This returns `None` if multiplication of constants overflows.
-fn mul_sorted_consts<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    param_env: ty::ParamEnv<'tcx>,
-    a: ty::Const<'tcx>,
-    b: ty::Const<'tcx>,
-) -> Option<ty::Const<'tcx>> {
-    use crate::mir::BinOp::Mul;
-
-    let mut work = vec![a, b];
-    let mut done = vec![];
-    while let Some(n) = work.pop() {
-        if let ConstKind::Expr(ty::Expr::Binop(Mul, l, r)) = n.kind() {
-            work.push(l);
-            work.push(r)
-        } else {
-            done.push(n);
-        }
-    }
-    let mut k = 1;
-    let mut overflow = false;
-    done.retain(|c| {
-        let Some(c) = c.try_eval_target_usize(tcx, param_env) else {
-            return true;
-        };
-        let Some(next) = c.checked_mul(k) else {
-            overflow = true;
-            return false;
-        };
-        k = next;
-        false
-    });
-    if overflow {
-        return None;
-    }
-    if k != 1 {
-        done.push(ty::Const::from_target_usize(tcx, k));
-    } else if k == 0 {
-        return Some(ty::Const::from_target_usize(tcx, 0));
-    }
-    done.sort_unstable();
-
-    // create a single tree from the buffer
-    done.into_iter().reduce(|acc, n| ty::Const::new_expr(tcx, ty::Expr::Binop(Mul, n, acc), n.ty()))
-}
-
 pub trait HasTyCtxt<'tcx>: HasDataLayout {
     fn tcx(&self) -> TyCtxt<'tcx>;
 }

tests/ui/const-generics/transmute-fail.rs

@@ -32,4 +32,79 @@ fn overflow(v: [[[u32; 8888888]; 9999999]; 777777777]) -> [[[u32; 9999999]; 7777
   }
 }
 
+fn transpose<const W: usize, const H: usize>(v: [[u32;H]; W]) -> [[u32; W]; H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn ident<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [[u32; H]; W] {
+  unsafe {
+    std::mem::transmute(v)
+  }
+}
+
+fn flatten<const W: usize, const H: usize>(v: [[u32; H]; W]) -> [u32; W * H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn coagulate<const W: usize, const H: usize>(v: [u32; H*W]) -> [[u32; W];H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn flatten_3d<const W: usize, const H: usize, const D: usize>(
+  v: [[[u32; D]; H]; W]
+) -> [u32; D * W * H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn flatten_somewhat<const W: usize, const H: usize, const D: usize>(
+  v: [[[u32; D]; H]; W]
+) -> [[u32; D * W]; H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn known_size<const L: usize>(v: [u16; L]) -> [u8; L * 2] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn condense_bytes<const L: usize>(v: [u8; L * 2]) -> [u16; L] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn singleton_each<const L: usize>(v: [u8; L]) -> [[u8;1]; L] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
+fn transpose_with_const<const W: usize, const H: usize>(
+  v: [[u32; 2 * H]; W + W]
+) -> [[u32; W + W]; 2 * H] {
+  unsafe {
+    std::mem::transmute(v)
+    //~^ ERROR: cannot transmute between types of different sizes, or dependently-sized types
+  }
+}
+
 fn main() {}

tests/ui/const-generics/transmute-fail.stderr

@@ -4,8 +4,8 @@ error[E0512]: cannot transmute between types of different sizes, or dependently-
 LL |     std::mem::transmute(v)
    |     ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[[u32; H+1]; W]` (generic size (H + 1) * 4 * W)
-   = note: target type: `[[u32; W+1]; H]` (generic size (W + 1) * 4 * H)
+   = note: source type: `[[u32; H+1]; W]` (size can vary because of [u32; H+1])
+   = note: target type: `[[u32; W+1]; H]` (size can vary because of [u32; W+1])
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
   --> $DIR/transmute-fail.rs:16:5
@@ -22,8 +22,8 @@ error[E0512]: cannot transmute between types of different sizes, or dependently-
 LL |     std::mem::transmute(v)
    |     ^^^^^^^^^^^^^^^^^^^
    |
-   = note: source type: `[[u32; H]; W]` (generic size 4 * H * W)
-   = note: target type: `[u32; W * H * H]` (generic size 4 * H * H * W)
+   = note: source type: `[[u32; H]; W]` (size can vary because of [u32; H])
+   = note: target type: `[u32; W * H * H]` (this type does not have a fixed size)
 
 error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
   --> $DIR/transmute-fail.rs:30:5
@@ -34,6 +34,87 @@ LL |     std::mem::transmute(v)
    = note: source type: `[[[u32; 8888888]; 9999999]; 777777777]` (values of the type `[[u32; 8888888]; 9999999]` are too big for the current architecture)
    = note: target type: `[[[u32; 9999999]; 777777777]; 8888888]` (values of the type `[[u32; 9999999]; 777777777]` are too big for the current architecture)
 
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:37:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[u32; H]; W]` (size can vary because of [u32; H])
+   = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W])
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:50:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[u32; H]; W]` (size can vary because of [u32; H])
+   = note: target type: `[u32; W * H]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:57:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u32; H*W]` (this type does not have a fixed size)
+   = note: target type: `[[u32; W]; H]` (size can vary because of [u32; W])
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:66:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[[u32; D]; H]; W]` (size can vary because of [u32; D])
+   = note: target type: `[u32; D * W * H]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:75:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[[u32; D]; H]; W]` (size can vary because of [u32; D])
+   = note: target type: `[[u32; D * W]; H]` (size can vary because of [u32; D * W])
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:82:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u16; L]` (this type does not have a fixed size)
+   = note: target type: `[u8; L * 2]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:89:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; L * 2]` (this type does not have a fixed size)
+   = note: target type: `[u16; L]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:96:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[u8; L]` (this type does not have a fixed size)
+   = note: target type: `[[u8; 1]; L]` (this type does not have a fixed size)
+
+error[E0512]: cannot transmute between types of different sizes, or dependently-sized types
+  --> $DIR/transmute-fail.rs:105:5
+   |
+LL |     std::mem::transmute(v)
+   |     ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: source type: `[[u32; 2 * H]; W + W]` (size can vary because of [u32; 2 * H])
+   = note: target type: `[[u32; W + W]; 2 * H]` (size can vary because of [u32; W + W])
+
 error[E0308]: mismatched types
   --> $DIR/transmute-fail.rs:12:53
    |
@@ -46,7 +127,7 @@ error[E0308]: mismatched types
 LL | fn bar<const W: bool, const H: usize>(v: [[u32; H]; W]) -> [[u32; W]; H] {
    |                                                                   ^ expected `usize`, found `bool`
 
-error: aborting due to 6 previous errors
+error: aborting due to 15 previous errors
 
 Some errors have detailed explanations: E0308, E0512.
 For more information about an error, try `rustc --explain E0308`.