Rollup merge of #91551 - b-naber:const-eval-normalization-ice, r=oli-obk

Allow for failure of subst_normalize_erasing_regions in const_eval

Fixes https://github.com/rust-lang/rust/issues/72845

Using associated types that cannot be normalized previously resulted in an ICE. We now allow for normalization failure and return a "TooGeneric" error in that case.

r? ```@RalfJung``` maybe?

compiler/rustc_middle/src/ty/instance.rs

@@ -7,6 +7,7 @@ use rustc_hir::def::Namespace;
 use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_macros::HashStable;
+use rustc_middle::ty::normalize_erasing_regions::NormalizationError;
 
 use std::fmt;
 
@@ -575,6 +576,23 @@ impl<'tcx> Instance<'tcx> {
         }
     }
 
+    #[inline(always)]
+    pub fn try_subst_mir_and_normalize_erasing_regions<T>(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        v: T,
+    ) -> Result<T, NormalizationError<'tcx>>
+    where
+        T: TypeFoldable<'tcx> + Clone,
+    {
+        if let Some(substs) = self.substs_for_mir_body() {
+            tcx.try_subst_and_normalize_erasing_regions(substs, param_env, v)
+        } else {
+            tcx.try_normalize_erasing_regions(param_env, v)
+        }
+    }
+
     /// Returns a new `Instance` where generic parameters in `instance.substs` are replaced by
     /// identity parameters if they are determined to be unused in `instance.def`.
     pub fn polymorphize(self, tcx: TyCtxt<'tcx>) -> Self {

compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

@@ -115,6 +115,8 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Monomorphizes a type from the AST by first applying the
     /// in-scope substitutions and then normalizing any associated
     /// types.
+    /// Panics if normalization fails. In case normalization might fail
+    /// use `try_subst_and_normalize_erasing_regions` instead.
     pub fn subst_and_normalize_erasing_regions<T>(
         self,
         param_substs: SubstsRef<'tcx>,
@@ -134,6 +136,30 @@ impl<'tcx> TyCtxt<'tcx> {
         let substituted = value.subst(self, param_substs);
         self.normalize_erasing_regions(param_env, substituted)
     }
+
+    /// Monomorphizes a type from the AST by first applying the
+    /// in-scope substitutions and then trying to normalize any associated
+    /// types. Contrary to `subst_and_normalize_erasing_regions` this does
+    /// not assume that normalization succeeds.
+    pub fn try_subst_and_normalize_erasing_regions<T>(
+        self,
+        param_substs: SubstsRef<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        value: T,
+    ) -> Result<T, NormalizationError<'tcx>>
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        debug!(
+            "subst_and_normalize_erasing_regions(\
+             param_substs={:?}, \
+             value={:?}, \
+             param_env={:?})",
+            param_substs, value, param_env,
+        );
+        let substituted = value.subst(self, param_substs);
+        self.try_normalize_erasing_regions(param_env, substituted)
+    }
 }
 
 struct NormalizeAfterErasingRegionsFolder<'tcx> {