Rollup merge of #122820 - oli-obk:no_ord_def_id, r=estebank

Stop using `<DefId as Ord>` in various diagnostic situations

work towards https://github.com/rust-lang/rust/issues/90317

Reverts part of https://github.com/rust-lang/rust/pull/106281, as it sorts constants and that's problematic since it can contain `ParamConst`, which contains `DefId`s

4 files changed, 15 insertions, 67 deletions

diff --git a/compiler/rustc_middle/Cargo.toml b/compiler/rustc_middle/Cargo.toml
index 96c58ef411b..9e8ee92b5d9 100644
--- a/compiler/rustc_middle/Cargo.toml
+++ b/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"
diff --git a/compiler/rustc_middle/src/mir/consts.rs b/compiler/rustc_middle/src/mir/consts.rs
index 214297b9869..02185cbeacf 100644
--- a/compiler/rustc_middle/src/mir/consts.rs
+++ b/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,
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index 8bd872c1b19..731e050ca9b 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/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,
diff --git a/compiler/rustc_middle/src/ty/layout.rs b/compiler/rustc_middle/src/ty/layout.rs
index 11fd73c9094..595ef71cc32 100644
--- a/compiler/rustc_middle/src/ty/layout.rs
+++ b/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>;
 }