borrowck: move error tainting earlier

Author: lcnr

compiler/rustc_borrowck/src/handle_placeholders.rs

@@ -216,22 +216,11 @@ pub(crate) fn compute_sccs_applying_placeholder_outlives_constraints<'tcx>(
         placeholder_index_to_region: _,
         liveness_constraints,
         mut outlives_constraints,
-        mut member_constraints,
+        member_constraints,
         universe_causes,
         type_tests,
     } = constraints;
 
-    if let Some(guar) = universal_regions.tainted_by_errors() {
-        debug!("Universal regions tainted by errors; removing constraints!");
-        // Suppress unhelpful extra errors in `infer_opaque_types` by clearing out all
-        // outlives bounds that we may end up checking.
-        outlives_constraints = Default::default();
-        member_constraints = Default::default();
-
-        // Also taint the entire scope.
-        infcx.set_tainted_by_errors(guar);
-    }
-
     let fr_static = universal_regions.fr_static;
     let compute_sccs =
         |constraints: &OutlivesConstraintSet<'tcx>,

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -182,6 +182,17 @@ pub(crate) fn type_check<'tcx>(
         )
     });
 
+    // In case type check encountered an error region, we suppress unhelpful extra
+    // errors in by clearing out all outlives bounds that we may end up checking.
+    if let Some(guar) = universal_region_relations.universal_regions.encountered_re_error() {
+        debug!("encountered an error region; removing constraints!");
+        constraints.outlives_constraints = Default::default();
+        constraints.member_constraints = Default::default();
+        constraints.type_tests = Default::default();
+        root_cx.set_tainted_by_errors(guar);
+        infcx.set_tainted_by_errors(guar);
+    }
+
     MirTypeckResults {
         constraints,
         universal_region_relations,

compiler/rustc_borrowck/src/universal_regions.rs

@@ -217,7 +217,7 @@ struct UniversalRegionIndices<'tcx> {
 
     /// Whether we've encountered an error region. If we have, cancel all
     /// outlives errors, as they are likely bogus.
-    pub tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
+    pub encountered_re_error: Cell<Option<ErrorGuaranteed>>,
 }
 
 #[derive(Debug, PartialEq)]
@@ -442,8 +442,8 @@ impl<'tcx> UniversalRegions<'tcx> {
         self.fr_fn_body
     }
 
-    pub(crate) fn tainted_by_errors(&self) -> Option<ErrorGuaranteed> {
-        self.indices.tainted_by_errors.get()
+    pub(crate) fn encountered_re_error(&self) -> Option<ErrorGuaranteed> {
+        self.indices.encountered_re_error.get()
     }
 }
 
@@ -706,7 +706,7 @@ impl<'cx, 'tcx> UniversalRegionsBuilder<'cx, 'tcx> {
         UniversalRegionIndices {
             indices: global_mapping.chain(arg_mapping).collect(),
             fr_static,
-            tainted_by_errors: Cell::new(None),
+            encountered_re_error: Cell::new(None),
         }
     }
 
@@ -916,7 +916,7 @@ impl<'tcx> UniversalRegionIndices<'tcx> {
         match r.kind() {
             ty::ReVar(..) => r.as_var(),
             ty::ReError(guar) => {
-                self.tainted_by_errors.set(Some(guar));
+                self.encountered_re_error.set(Some(guar));
                 // We use the `'static` `RegionVid` because `ReError` doesn't actually exist in the
                 // `UniversalRegionIndices`. This is fine because 1) it is a fallback only used if
                 // errors are being emitted and 2) it leaves the happy path unaffected.