Auto merge of #81055 - matthewjasper:non-fatal-overflow, r=nikomatsakis

Make hitting the recursion limit in projection non-fatal

This change was originally made in #80246 to avoid future (effectively) infinite loop bugs in projections,
but wundergraph relies on rustc recovering here.

cc #80953

r? `@nikomatsakis`

compiler/rustc_trait_selection/src/traits/project.rs

@@ -736,14 +736,9 @@ fn project_type<'cx, 'tcx>(
 
     if !selcx.tcx().sess.recursion_limit().value_within_limit(obligation.recursion_depth) {
         debug!("project: overflow!");
-        match selcx.query_mode() {
-            super::TraitQueryMode::Standard => {
-                selcx.infcx().report_overflow_error(&obligation, true);
-            }
-            super::TraitQueryMode::Canonical => {
-                return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
-            }
-        }
+        // This should really be an immediate error, but some existing code
+        // relies on being able to recover from this.
+        return Err(ProjectionTyError::TraitSelectionError(SelectionError::Overflow));
     }
 
     let obligation_trait_ref = &obligation.predicate.trait_ref(selcx.tcx());

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -291,10 +291,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         self.infcx.tcx
     }
 
-    pub(super) fn query_mode(&self) -> TraitQueryMode {
-        self.query_mode
-    }
-
     ///////////////////////////////////////////////////////////////////////////
     // Selection
     //