5 files changed, 65 insertions, 15 deletions
diff --git a/compiler/rustc_middle/src/mir/interpret/error.rs b/compiler/rustc_middle/src/mir/interpret/error.rs
index 7e3be0b5d5f..0a7296e7c78 100644
--- a/compiler/rustc_middle/src/mir/interpret/error.rs
+++ b/compiler/rustc_middle/src/mir/interpret/error.rs
@@ -11,7 +11,7 @@ use rustc_errors::{
 };
 use rustc_macros::HashStable;
 use rustc_session::CtfeBacktrace;
-use rustc_span::def_id::DefId;
+use rustc_span::{def_id::DefId, Span, DUMMY_SP};
 use rustc_target::abi::{call, Align, Size, VariantIdx, WrappingRange};
 
 use std::borrow::Cow;
@@ -21,16 +21,25 @@ use std::{any::Any, backtrace::Backtrace, fmt};
 pub enum ErrorHandled {
     /// Already reported an error for this evaluation, and the compilation is
     /// *guaranteed* to fail. Warnings/lints *must not* produce `Reported`.
-    Reported(ReportedErrorInfo),
+    Reported(ReportedErrorInfo, Span),
     /// Don't emit an error, the evaluation failed because the MIR was generic
     /// and the args didn't fully monomorphize it.
-    TooGeneric,
+    TooGeneric(Span),
 }
 
 impl From<ErrorGuaranteed> for ErrorHandled {
     #[inline]
     fn from(error: ErrorGuaranteed) -> ErrorHandled {
-        ErrorHandled::Reported(error.into())
+        ErrorHandled::Reported(error.into(), DUMMY_SP)
+    }
+}
+
+impl ErrorHandled {
+    pub fn with_span(self, span: Span) -> Self {
+        match self {
+            ErrorHandled::Reported(err, _span) => ErrorHandled::Reported(err, span),
+            ErrorHandled::TooGeneric(_span) => ErrorHandled::TooGeneric(span),
+        }
     }
 }
 
@@ -162,6 +171,16 @@ impl From<ErrorGuaranteed> for InterpErrorInfo<'_> {
     }
 }
 
+impl From<ErrorHandled> for InterpErrorInfo<'_> {
+    fn from(err: ErrorHandled) -> Self {
+        InterpError::InvalidProgram(match err {
+            ErrorHandled::Reported(r, _span) => InvalidProgramInfo::AlreadyReported(r),
+            ErrorHandled::TooGeneric(_span) => InvalidProgramInfo::TooGeneric,
+        })
+        .into()
+    }
+}
+
 impl<'tcx> From<InterpError<'tcx>> for InterpErrorInfo<'tcx> {
     fn from(kind: InterpError<'tcx>) -> Self {
         InterpErrorInfo(Box::new(InterpErrorInfoInner {
diff --git a/compiler/rustc_middle/src/mir/interpret/queries.rs b/compiler/rustc_middle/src/mir/interpret/queries.rs
index fc659ce18a4..71e648bab6a 100644
--- a/compiler/rustc_middle/src/mir/interpret/queries.rs
+++ b/compiler/rustc_middle/src/mir/interpret/queries.rs
@@ -61,8 +61,8 @@ impl<'tcx> TyCtxt<'tcx> {
                 let cid = GlobalId { instance, promoted: ct.promoted };
                 self.const_eval_global_id(param_env, cid, span)
             }
-            Ok(None) => Err(ErrorHandled::TooGeneric),
-            Err(err) => Err(ErrorHandled::Reported(err.into())),
+            Ok(None) => Err(ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))),
+            Err(err) => Err(ErrorHandled::Reported(err.into(), span.unwrap_or(DUMMY_SP))),
         }
     }
 
@@ -117,8 +117,8 @@ impl<'tcx> TyCtxt<'tcx> {
                     }
                 })
             }
-            Ok(None) => Err(ErrorHandled::TooGeneric),
-            Err(err) => Err(ErrorHandled::Reported(err.into())),
+            Ok(None) => Err(ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))),
+            Err(err) => Err(ErrorHandled::Reported(err.into(), span.unwrap_or(DUMMY_SP))),
         }
     }
 
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 8df3a79b4d4..95d27a017fe 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -565,6 +565,37 @@ impl<'tcx> Body<'tcx> {
     pub fn is_custom_mir(&self) -> bool {
         self.injection_phase.is_some()
     }
+
+    /// *Must* be called once the full substitution for this body is known, to ensure that the body
+    /// is indeed fit for code generation or consumption more generally.
+    ///
+    /// Sadly there's no nice way to represent an "arbitrary normalizer", so we take one for
+    /// constants specifically. (`Option<GenericArgsRef>` could be used for that, but the fact
+    /// that `Instance::args_for_mir_body` is private and instead instance exposes normalization
+    /// functions makes it seem like exposing the generic args is not the intended strategy.)
+    ///
+    /// Also sadly, CTFE doesn't even know whether it runs on MIR that is already polymorphic or still monomorphic,
+    /// so we cannot just immediately ICE on TooGeneric.
+    ///
+    /// Returns Ok(()) if everything went fine, and `Err` if a problem occurred and got reported.
+    pub fn post_mono_checks(
+        &self,
+        tcx: TyCtxt<'tcx>,
+        param_env: ty::ParamEnv<'tcx>,
+        normalize_const: impl Fn(ConstantKind<'tcx>) -> Result<ConstantKind<'tcx>, ErrorHandled>,
+    ) -> Result<(), ErrorHandled> {
+        // For now, the only thing we have to check is is to ensure that all the constants used in
+        // the body successfully evaluate.
+        for &const_ in &self.required_consts {
+            let c = normalize_const(const_.literal)?;
+            c.eval(tcx, param_env, Some(const_.span)).map_err(|e| {
+                // The query results don't always have the span we want.
+                e.with_span(const_.span)
+            })?;
+        }
+
+        Ok(())
+    }
 }
 
 #[derive(Copy, Clone, PartialEq, Eq, Debug, TyEncodable, TyDecodable, HashStable)]
@@ -2397,10 +2428,10 @@ impl<'tcx> ConstantKind<'tcx> {
     pub fn normalize(self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> Self {
         match self.eval(tcx, param_env, None) {
             Ok(val) => Self::Val(val, self.ty()),
-            Err(ErrorHandled::Reported(guar)) => {
+            Err(ErrorHandled::Reported(guar, _span)) => {
                 Self::Ty(ty::Const::new_error(tcx, guar.into(), self.ty()))
             }
-            Err(ErrorHandled::TooGeneric) => self,
+            Err(ErrorHandled::TooGeneric(_span)) => self,
         }
     }
 
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index b4c6e0d970a..219927f5ab4 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -478,8 +478,8 @@ impl<'tcx> AdtDef<'tcx> {
             }
             Err(err) => {
                 let msg = match err {
-                    ErrorHandled::Reported(_) => "enum discriminant evaluation failed",
-                    ErrorHandled::TooGeneric => "enum discriminant depends on generics",
+                    ErrorHandled::Reported(..) => "enum discriminant evaluation failed",
+                    ErrorHandled::TooGeneric(..) => "enum discriminant depends on generics",
                 };
                 tcx.sess.delay_span_bug(tcx.def_span(expr_did), msg);
                 None
diff --git a/compiler/rustc_middle/src/ty/consts.rs b/compiler/rustc_middle/src/ty/consts.rs
index 629f9f8cd7d..ba871d6478b 100644
--- a/compiler/rustc_middle/src/ty/consts.rs
+++ b/compiler/rustc_middle/src/ty/consts.rs
@@ -300,7 +300,7 @@ impl<'tcx> Const<'tcx> {
             | ConstKind::Infer(_)
             | ConstKind::Bound(_, _)
             | ConstKind::Placeholder(_)
-            | ConstKind::Expr(_) => Err(ErrorHandled::TooGeneric),
+            | ConstKind::Expr(_) => Err(ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))),
         }
     }
 
@@ -309,8 +309,8 @@ impl<'tcx> Const<'tcx> {
     pub fn normalize(self, tcx: TyCtxt<'tcx>, param_env: ParamEnv<'tcx>) -> Self {
         match self.eval(tcx, param_env, None) {
             Ok(val) => Self::new_value(tcx, val, self.ty()),
-            Err(ErrorHandled::Reported(r)) => Self::new_error(tcx, r.into(), self.ty()),
-            Err(ErrorHandled::TooGeneric) => self,
+            Err(ErrorHandled::Reported(r, _span)) => Self::new_error(tcx, r.into(), self.ty()),
+            Err(ErrorHandled::TooGeneric(_span)) => self,
         }
     }