From 390246c8e11a28f2087ac25cc419300f03bde693 Mon Sep 17 00:00:00 2001
From: Boxy <supbscripter@gmail.com>
Date: Sun, 26 Feb 2023 20:49:08 +0000
Subject: [PATCH] use `ObligationCtxt` not `QueryNormalizer`

---
 .../src/traits/query/normalize.rs             | 12 ++---
 src/librustdoc/clean/mod.rs                   | 50 ++++++++++++++-----
 2 files changed, 41 insertions(+), 21 deletions(-)

diff --git a/compiler/rustc_trait_selection/src/traits/query/normalize.rs b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
index a986a9b6a71b1..af6c4049029a6 100644
--- a/compiler/rustc_trait_selection/src/traits/query/normalize.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/normalize.rs
@@ -284,14 +284,10 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                 let result = tcx.normalize_projection_ty(c_data)?;
                 // We don't expect ambiguity.
                 if result.is_ambiguous() {
-                    // Rustdoc normalizes possibly not well-formed types, so only
-                    // treat this as a bug if we're not in rustdoc.
-                    if !tcx.sess.opts.actually_rustdoc {
-                        tcx.sess.delay_span_bug(
-                            DUMMY_SP,
-                            format!("unexpected ambiguity: {:?} {:?}", c_data, result),
-                        );
-                    }
+                    tcx.sess.delay_span_bug(
+                        DUMMY_SP,
+                        format!("unexpected ambiguity: {:?} {:?}", c_data, result),
+                    );
                     return Err(NoSolution);
                 }
                 let InferOk { value: result, obligations } =
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 2d247bd537bdf..191f89ebe0583 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -1666,22 +1666,46 @@ fn normalize<'tcx>(
     }
 
     use crate::rustc_trait_selection::infer::TyCtxtInferExt;
-    use crate::rustc_trait_selection::traits::query::normalize::QueryNormalizeExt;
+    use crate::rustc_trait_selection::traits::ObligationCtxt;
     use rustc_middle::traits::ObligationCause;
 
-    // Try to normalize `<X as Y>::T` to a type
+    assert!(
+        !ty.has_non_region_infer(),
+        "`ty`: {:?} has pre existing infer vars before `InferCtxt` creation",
+        ty
+    );
+
     let infcx = cx.tcx.infer_ctxt().build();
-    let normalized = infcx
-        .at(&ObligationCause::dummy(), cx.param_env)
-        .query_normalize(ty)
-        .map(|resolved| infcx.resolve_vars_if_possible(resolved.value));
-    match normalized {
-        Ok(normalized_value) => {
-            debug!("normalized {:?} to {:?}", ty, normalized_value);
-            Some(normalized_value)
-        }
-        Err(err) => {
-            debug!("failed to normalize {:?}: {:?}", ty, err);
+    // use an `ObligationCtxt` as it has a nice API for dealing with returned obligations from normalization
+    // and does not expect us to be inside of typeck. It also does not ICE when the projection could not be
+    // normalized like some other normalization routines (`QueryNormalizer`, `normalize_erasing_regions`, etc)
+    let ocx = ObligationCtxt::new(&infcx);
+
+    // Try to normalize `<X as Y>::T` to a type
+    let normalized = ocx.normalize(&ObligationCause::dummy(), cx.param_env, ty);
+    // We have to ensure that we deal with nested obligations from attempting to normalize as `ty`
+    // normalizing to `normalized` is only the case if the nested obligations hold.
+    let errs = ocx.select_all_or_error();
+    // Evaluating nested obligations might constrain infer vars that were created during normalization
+    // so we should resolve any infer vars in `normalized` to their new values.
+    let normalized = infcx.resolve_vars_if_possible(normalized);
+
+    match errs.as_slice() {
+        [] if normalized == ty => {
+            debug!("normalizing {:?} did not make progress", ty);
+            None
+        }
+        [] => {
+            debug!("normalized {:?} to {:?}", ty, normalized);
+
+            assert!(
+                !normalized.has_non_region_infer(),
+                "`normalized` has infer vars which would escape the `InferCtxt` they were created in"
+            );
+            Some(normalized)
+        }
+        errs => {
+            debug!("failed to normalize {:?}: {:?}", ty, errs);
             None
         }
     }