Auto merge of #136539 - matthewjasper:late-normalize-errors, r=compiler-errors

Emit dropck normalization errors in borrowck

Borrowck generally assumes that any queries it runs for type checking will succeed, thinking that HIR typeck will have errored first if there was a problem. However as of #98641, dropck isn't run on HIR, so there's no direct guarantee that it doesn't error. While a type being well-formed might be expected to ensure that its fields are well-formed, this is not the case for types containing a type projection:

```rust
pub trait AuthUser {
    type Id;
}

pub trait AuthnBackend {
    type User: AuthUser;
}

pub struct AuthSession<Backend: AuthnBackend> {
    data: Option<<<Backend as AuthnBackend>::User as AuthUser>::Id>,
}

pub trait Authz: Sized {
    type AuthnBackend: AuthnBackend<User = Self>;
}

pub fn run_query<User: Authz>(auth: AuthSession<User::AuthnBackend>) {}
// ^ No User: AuthUser bound is required or inferred.
```

While improvements to trait solving might fix this in the future, for now we go for a pragmatic solution of emitting an error from borrowck (by rerunning dropck outside of a query) and making drop elaboration check if an error has been emitted previously before panicking for a failed normalization.

Closes #103899
Closes #135039

r? `@compiler-errors` (feel free to re-assign)

compiler/rustc_borrowck/src/type_check/liveness/trace.rs

@@ -3,7 +3,8 @@ use rustc_index::bit_set::DenseBitSet;
 use rustc_index::interval::IntervalSet;
 use rustc_infer::infer::canonical::QueryRegionConstraints;
 use rustc_infer::infer::outlives::for_liveness;
-use rustc_middle::mir::{BasicBlock, Body, ConstraintCategory, Local, Location};
+use rustc_middle::mir::{BasicBlock, Body, ConstraintCategory, HasLocalDecls, Local, Location};
+use rustc_middle::span_bug;
 use rustc_middle::traits::query::DropckOutlivesResult;
 use rustc_middle::ty::relate::Relate;
 use rustc_middle::ty::{Ty, TyCtxt, TypeVisitable, TypeVisitableExt};
@@ -11,7 +12,10 @@ use rustc_mir_dataflow::ResultsCursor;
 use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::{HasMoveData, MoveData, MovePathIndex};
 use rustc_mir_dataflow::points::{DenseLocationMap, PointIndex};
-use rustc_span::DUMMY_SP;
+use rustc_span::{DUMMY_SP, Span};
+use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
+use rustc_trait_selection::traits::ObligationCtxt;
+use rustc_trait_selection::traits::query::dropck_outlives;
 use rustc_trait_selection::traits::query::type_op::{DropckOutlives, TypeOp, TypeOpOutput};
 use tracing::debug;
 
@@ -162,9 +166,10 @@ impl<'a, 'typeck, 'b, 'tcx> LivenessResults<'a, 'typeck, 'b, 'tcx> {
     fn dropck_boring_locals(&mut self, boring_locals: Vec<Local>) {
         for local in boring_locals {
             let local_ty = self.cx.body.local_decls[local].ty;
+            let local_span = self.cx.body.local_decls[local].source_info.span;
             let drop_data = self.cx.drop_data.entry(local_ty).or_insert_with({
                 let typeck = &self.cx.typeck;
-                move || LivenessContext::compute_drop_data(typeck, local_ty)
+                move || LivenessContext::compute_drop_data(typeck, local_ty, local_span)
             });
 
             drop_data.dropck_result.report_overflows(
@@ -522,9 +527,10 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
             values::pretty_print_points(self.location_map, live_at.iter()),
         );
 
+        let local_span = self.body.local_decls()[dropped_local].source_info.span;
         let drop_data = self.drop_data.entry(dropped_ty).or_insert_with({
             let typeck = &self.typeck;
-            move || Self::compute_drop_data(typeck, dropped_ty)
+            move || Self::compute_drop_data(typeck, dropped_ty, local_span)
         });
 
         if let Some(data) = &drop_data.region_constraint_data {
@@ -589,19 +595,44 @@ impl<'tcx> LivenessContext<'_, '_, '_, 'tcx> {
         }
     }
 
-    fn compute_drop_data(typeck: &TypeChecker<'_, 'tcx>, dropped_ty: Ty<'tcx>) -> DropData<'tcx> {
-        debug!("compute_drop_data(dropped_ty={:?})", dropped_ty,);
+    fn compute_drop_data(
+        typeck: &TypeChecker<'_, 'tcx>,
+        dropped_ty: Ty<'tcx>,
+        span: Span,
+    ) -> DropData<'tcx> {
+        debug!("compute_drop_data(dropped_ty={:?})", dropped_ty);
 
-        match typeck
-            .infcx
-            .param_env
-            .and(DropckOutlives { dropped_ty })
-            .fully_perform(typeck.infcx, DUMMY_SP)
-        {
+        let op = typeck.infcx.param_env.and(DropckOutlives { dropped_ty });
+
+        match op.fully_perform(typeck.infcx, DUMMY_SP) {
             Ok(TypeOpOutput { output, constraints, .. }) => {
                 DropData { dropck_result: output, region_constraint_data: constraints }
             }
-            Err(_) => DropData { dropck_result: Default::default(), region_constraint_data: None },
+            Err(_) => {
+                // We don't run dropck on HIR, and dropck looks inside fields of
+                // types, so there's no guarantee that it succeeds. We also
+                // can't rely on the the `ErrorGuaranteed` from `fully_perform` here
+                // because it comes from delay_span_bug.
+                let ocx = ObligationCtxt::new_with_diagnostics(&typeck.infcx);
+                let errors =
+                    match dropck_outlives::compute_dropck_outlives_with_errors(&ocx, op, span) {
+                        Ok(_) => ocx.select_all_or_error(),
+                        Err(e) => {
+                            if e.is_empty() {
+                                ocx.select_all_or_error()
+                            } else {
+                                e
+                            }
+                        }
+                    };
+
+                if !errors.is_empty() {
+                    typeck.infcx.err_ctxt().report_fulfillment_errors(errors);
+                } else {
+                    span_bug!(span, "Rerunning drop data query produced no error.");
+                }
+                DropData { dropck_result: Default::default(), region_constraint_data: None }
+            }
         }
     }
 }