[cfe] Pass variance through in ReplacementVisitor

Change-Id: I8dc9c1a77c5dfe70ad186bbd6254aaf5353aa0ca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/180900
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Dmitry Stefantsov <[email protected]>

Author: Dmitry Stefantsov

pkg/front_end/lib/src/fasta/type_inference/type_demotion.dart

@@ -65,12 +65,16 @@ class _HasPromotedTypeVariableVisitor extends DartTypeVisitor<bool> {
 /// with legacy types.
 DartType demoteTypeInLibrary(DartType type, Library library) {
   if (library.isNonNullableByDefault) {
-    return type.accept(const _DemotionNullabilityNormalization(
-            demoteTypeVariables: true, forNonNullableByDefault: true)) ??
+    return type.accept1(
+            const _DemotionNullabilityNormalization(
+                demoteTypeVariables: true, forNonNullableByDefault: true),
+            Variance.covariant) ??
         type;
   } else {
-    return type.accept(const _DemotionNullabilityNormalization(
-            demoteTypeVariables: true, forNonNullableByDefault: false)) ??
+    return type.accept1(
+            const _DemotionNullabilityNormalization(
+                demoteTypeVariables: true, forNonNullableByDefault: false),
+            Variance.covariant) ??
         type;
   }
 }
@@ -85,8 +89,10 @@ DartType normalizeNullabilityInLibrary(DartType type, Library library) {
   if (library.isNonNullableByDefault) {
     return type;
   } else {
-    return type.accept(const _DemotionNullabilityNormalization(
-            demoteTypeVariables: false, forNonNullableByDefault: false)) ??
+    return type.accept1(
+            const _DemotionNullabilityNormalization(
+                demoteTypeVariables: false, forNonNullableByDefault: false),
+            Variance.covariant) ??
         type;
   }
 }
@@ -119,7 +125,7 @@ class _DemotionNullabilityNormalization extends ReplacementVisitor {
   }
 
   @override
-  DartType visitTypeParameterType(TypeParameterType node) {
+  DartType visitTypeParameterType(TypeParameterType node, int variance) {
     Nullability newNullability = visitNullability(node);
     if (demoteTypeVariables && node.promotedBound != null) {
       return new TypeParameterType(

pkg/front_end/lib/src/fasta/type_inference/type_schema_elimination.dart

@@ -53,17 +53,11 @@ class _TypeSchemaEliminationVisitor extends ReplacementVisitor {
   final DartType topType;
   final DartType bottomType;
 
-  bool isLeastClosure;
-
-  _TypeSchemaEliminationVisitor(
-      this.isLeastClosure, this.topType, this.bottomType);
-
-  void changeVariance() {
-    isLeastClosure = !isLeastClosure;
-  }
+  _TypeSchemaEliminationVisitor(this.topType, this.bottomType);
 
   @override
-  DartType defaultDartType(DartType node) {
+  DartType defaultDartType(DartType node, int variance) {
+    bool isLeastClosure = variance == Variance.covariant;
     if (node is UnknownType) {
       return isLeastClosure ? bottomType : topType;
     }
@@ -84,9 +78,9 @@ class _TypeSchemaEliminationVisitor extends ReplacementVisitor {
     assert(bottomType == const NeverType(Nullability.nonNullable) ||
         bottomType is NullType);
     _TypeSchemaEliminationVisitor visitor =
-        new _TypeSchemaEliminationVisitor(isLeastClosure, topType, bottomType);
-    DartType result = schema.accept(visitor);
-    assert(visitor.isLeastClosure == isLeastClosure);
+        new _TypeSchemaEliminationVisitor(topType, bottomType);
+    DartType result = schema.accept1(
+        visitor, isLeastClosure ? Variance.covariant : Variance.contravariant);
     return result ?? schema;
   }
 }

pkg/front_end/test/spell_checking_list_common.txt

@@ -878,6 +878,7 @@ discards
 discover
 discovered
 discovery
+discrepancy
 disk
 dispatch
 dispatches
@@ -1604,6 +1605,7 @@ invariantly
 inversion
 invert
 inverted
+inverter
 investigate
 invisible
 invocation