[analyzer][cfe] Share left-FutureOr constraint gathering

Part of #54902

Change-Id: I825e522f370ac7fd39466b5f6aa6571fea5b5633
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/394501
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

pkg/_fe_analyzer_shared/lib/src/type_inference/type_analyzer_operations.dart

@@ -1270,7 +1270,7 @@ abstract class TypeConstraintGenerator<
   /// schema (in other words, may contain the unknown type `_`); the other must
   /// be simply a type. If [leftSchema] is `true`, [p] may contain `_`; if it is
   /// `false`, [q] may contain `_`.
-  bool performSubtypeConstraintGenerationForFutureOr(
+  bool performSubtypeConstraintGenerationForRightFutureOr(
       TypeStructure p, TypeStructure q,
       {required bool leftSchema, required AstNode? astNodeForTesting}) {
     // If `Q` is `FutureOr<Q0>` the match holds under constraint set `C`:
@@ -1316,6 +1316,43 @@ abstract class TypeConstraintGenerator<
     return false;
   }
 
+  /// Matches [p] against [q].
+  ///
+  /// If [p] is of the form `FutureOr<p0>` for some `p0`, and [p] is a subtype
+  /// of [q] under some constraints, the constraints making the relation
+  /// possible are recorded, and `true` is returned. Otherwise, the constraint
+  /// state is unchanged (or rolled back using [restoreState]), and `false` is
+  /// returned.
+  ///
+  /// An invariant of the type inference is that only [p] or [q] may be a
+  /// schema (in other words, may contain the unknown type `_`); the other must
+  /// be simply a type. If [leftSchema] is `true`, [p] may contain `_`; if it is
+  /// `false`, [q] may contain `_`.
+  bool performSubtypeConstraintGenerationForLeftFutureOr(
+      TypeStructure p, TypeStructure q,
+      {required bool leftSchema, required AstNode? astNodeForTesting}) {
+    // If `P` is `FutureOr<P0>` the match holds under constraint set `C1 + C2`:
+    NullabilitySuffix pNullability = p.nullabilitySuffix;
+    if (typeAnalyzerOperations.matchFutureOrInternal(p) case var p0?
+        when pNullability == NullabilitySuffix.none) {
+      final TypeConstraintGeneratorState state = currentState;
+
+      // If `Future<P0>` is a subtype match for `Q` under constraint set `C1`.
+      // And if `P0` is a subtype match for `Q` under constraint set `C2`.
+      TypeStructure futureP0 = typeAnalyzerOperations.futureTypeInternal(p0);
+      if (performSubtypeConstraintGenerationInternal(futureP0, q,
+              leftSchema: leftSchema, astNodeForTesting: astNodeForTesting) &&
+          performSubtypeConstraintGenerationInternal(p0, q,
+              leftSchema: leftSchema, astNodeForTesting: astNodeForTesting)) {
+        return true;
+      }
+
+      restoreState(state);
+    }
+
+    return false;
+  }
+
   /// Matches [p] against [q] as a subtype against supertype.
   ///
   /// If [p] and [q] are both type declaration types, then:

pkg/_fe_analyzer_shared/test/type_inference/type_constraint_gatherer_test.dart

@@ -385,7 +385,7 @@ main() {
     test('FutureOr matches FutureOr with constraints based on arguments', () {
       // `FutureOr<T> <# FutureOr<int>` reduces to `T <# int`
       var tcg = _TypeConstraintGatherer({'T'});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('FutureOr<T>'), Type('FutureOr<int>'),
               leftSchema: false, astNodeForTesting: Node.placeholder()))
           .isTrue();
@@ -396,7 +396,7 @@ main() {
         () {
       // `FutureOr<int> <# FutureOr<String>` reduces to `int <# String`
       var tcg = _TypeConstraintGatherer({});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('FutureOr<int>'), Type('FutureOr<String>'),
               leftSchema: false, astNodeForTesting: Node.placeholder()))
           .isFalse();
@@ -412,7 +412,7 @@ main() {
       // In cases where both branches produce a constraint, the "Future" branch
       // is favored.
       var tcg = _TypeConstraintGatherer({'T'});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('Future<int>'), Type('FutureOr<T>'),
               leftSchema: false, astNodeForTesting: Node.placeholder()))
           .isTrue();
@@ -428,7 +428,7 @@ main() {
       // In cases where only one branch produces a constraint, that branch is
       // favored.
       var tcg = _TypeConstraintGatherer({'T'});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('Future<_>'), Type('FutureOr<T>'),
               leftSchema: true, astNodeForTesting: Node.placeholder()))
           .isTrue();
@@ -444,18 +444,48 @@ main() {
       // In cases where both branches produce a constraint, the "Future" branch
       // is favored.
       var tcg = _TypeConstraintGatherer({'T'});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('T'), Type('FutureOr<int>'),
               leftSchema: false, astNodeForTesting: Node.placeholder()))
           .isTrue();
       check(tcg._constraints).deepEquals(['T <: Future<int>']);
     });
 
+    test('Testing FutureOr as the lower bound of the constraint', () {
+      var tcg = _TypeConstraintGatherer({'T'});
+      check(tcg.performSubtypeConstraintGenerationForLeftFutureOr(
+              Type('FutureOr<T>'), Type('dynamic'),
+              leftSchema: false, astNodeForTesting: Node.placeholder()))
+          .isTrue();
+      check(tcg._constraints).deepEquals(['T <: dynamic']);
+    });
+
+    test('FutureOr does not match Future in general', () {
+      // `FutureOr<P0> <# Q` if `Future<P0> <# Q` and `P0 <# Q`. This test case
+      // verifies that if `Future<P0> <# Q` matches but `P0 <# Q` does not, then
+      // the match fails.
+      var tcg = _TypeConstraintGatherer({'T'});
+      check(tcg.performSubtypeConstraintGenerationForLeftFutureOr(
+              Type('FutureOr<(T,)>'), Type('Future<(int,)>'),
+              leftSchema: false, astNodeForTesting: Node.placeholder()))
+          .isFalse();
+      check(tcg._constraints).isEmpty();
+    });
+
+    test('Testing nested FutureOr as the lower bound of the constraint', () {
+      var tcg = _TypeConstraintGatherer({'T'});
+      check(tcg.performSubtypeConstraintGenerationForLeftFutureOr(
+              Type('FutureOr<FutureOr<T>>'), Type('FutureOr<dynamic>'),
+              leftSchema: false, astNodeForTesting: Node.placeholder()))
+          .isTrue();
+      check(tcg._constraints).deepEquals(['T <: dynamic', 'T <: dynamic']);
+    });
+
     test('Future matches FutureOr with no constraints', () {
       // `Future<int> <# FutureOr<int>` matches (taking the "Future" branch of
       // the FutureOr) without generating any constraints.
       var tcg = _TypeConstraintGatherer({});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('Future<int>'), Type('FutureOr<int>'),
               leftSchema: false, astNodeForTesting: Node.placeholder()))
           .isTrue();
@@ -467,7 +497,7 @@ main() {
       // "non-Future" branch of the FutureOr, so the constraint `T <: int` is
       // produced.
       var tcg = _TypeConstraintGatherer({'T'});
-      check(tcg.performSubtypeConstraintGenerationForFutureOr(
+      check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
               Type('List<T>'), Type('FutureOr<List<int>>'),
               leftSchema: false, astNodeForTesting: Node.placeholder()))
           .isTrue();
@@ -477,7 +507,7 @@ main() {
     group('Nullable FutureOr on RHS:', () {
       test('Does not match, according to spec', () {
         var tcg = _TypeConstraintGatherer({'T'});
-        check(tcg.performSubtypeConstraintGenerationForFutureOr(
+        check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
                 Type('FutureOr<T>'), Type('FutureOr<int>?'),
                 leftSchema: false, astNodeForTesting: Node.placeholder()))
             .isFalse();
@@ -487,7 +517,7 @@ main() {
       test('Matches, according to CFE discrepancy', () {
         var tcg = _TypeConstraintGatherer({'T'},
             enableDiscrepantObliviousnessOfNullabilitySuffixOfFutureOr: true);
-        check(tcg.performSubtypeConstraintGenerationForFutureOr(
+        check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
                 Type('FutureOr<T>'), Type('FutureOr<int>?'),
                 leftSchema: false, astNodeForTesting: Node.placeholder()))
             .isTrue();
@@ -498,7 +528,7 @@ main() {
     group('Nullable FutureOr on LHS:', () {
       test('Does not match, according to spec', () {
         var tcg = _TypeConstraintGatherer({'T'});
-        check(tcg.performSubtypeConstraintGenerationForFutureOr(
+        check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
                 Type('FutureOr<T>?'), Type('FutureOr<int>'),
                 leftSchema: false, astNodeForTesting: Node.placeholder()))
             .isFalse();
@@ -508,7 +538,7 @@ main() {
       test('Matches, according to CFE discrepancy', () {
         var tcg = _TypeConstraintGatherer({'T'},
             enableDiscrepantObliviousnessOfNullabilitySuffixOfFutureOr: true);
-        check(tcg.performSubtypeConstraintGenerationForFutureOr(
+        check(tcg.performSubtypeConstraintGenerationForRightFutureOr(
                 Type('FutureOr<T>?'), Type('FutureOr<int>'),
                 leftSchema: false, astNodeForTesting: Node.placeholder()))
             .isTrue();
@@ -844,6 +874,7 @@ class _TypeConstraintGatherer extends TypeConstraintGenerator<Type,
       case (PrimaryType(name: 'int'), 'String'):
       case (PrimaryType(name: 'List'), 'Future'):
       case (PrimaryType(name: 'String'), 'int'):
+      case (PrimaryType(name: 'Future'), 'String'):
         // Unrelated types
         return null;
       default:
@@ -891,16 +922,32 @@ class _TypeConstraintGatherer extends TypeConstraintGenerator<Type,
       return true;
     }
 
+    if (performSubtypeConstraintGenerationForRightFutureOr(p, q,
+        leftSchema: leftSchema, astNodeForTesting: astNodeForTesting)) {
+      return true;
+    }
+
     if (performSubtypeConstraintGenerationForRightNullableType(p, q,
         leftSchema: leftSchema, astNodeForTesting: astNodeForTesting)) {
       return true;
     }
 
+    if (performSubtypeConstraintGenerationForLeftFutureOr(p, q,
+        leftSchema: leftSchema, astNodeForTesting: astNodeForTesting)) {
+      return true;
+    }
+
     if (performSubtypeConstraintGenerationForLeftNullableType(p, q,
         leftSchema: leftSchema, astNodeForTesting: astNodeForTesting)) {
       return true;
     }
 
+    if (q is SharedDynamicTypeStructure ||
+        q is SharedVoidTypeStructure ||
+        q == typeAnalyzerOperations.objectQuestionType.unwrapTypeView()) {
+      return true;
+    }
+
     bool? result = performSubtypeConstraintGenerationForTypeDeclarationTypes(
         p, q,
         leftSchema: leftSchema, astNodeForTesting: astNodeForTesting);

pkg/analyzer/lib/src/dart/element/type_constraint_gatherer.dart

@@ -274,7 +274,7 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     // in case [performSubtypeConstraintGenerationForFutureOr] returns false, as
     // [performSubtypeConstraintGenerationForFutureOr] handles the rewinding of
     // the state itself.
-    if (performSubtypeConstraintGenerationForFutureOr(P, Q,
+    if (performSubtypeConstraintGenerationForRightFutureOr(P, Q,
         leftSchema: leftSchema, astNodeForTesting: nodeForTesting)) {
       return true;
     }
@@ -285,20 +285,9 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     }
 
     // If `P` is `FutureOr<P0>` the match holds under constraint set `C1 + C2`:
-    if (_typeSystemOperations.matchFutureOrInternal(P) case var P0?
-        when P_nullability == NullabilitySuffix.none) {
-      var rewind = _constraints.length;
-
-      // If `Future<P0>` is a subtype match for `Q` under constraint set `C1`.
-      // And if `P0` is a subtype match for `Q` under constraint set `C2`.
-      var future_P0 = _typeSystemOperations.futureTypeInternal(P0);
-      if (trySubtypeMatch(future_P0, Q, leftSchema,
-              nodeForTesting: nodeForTesting) &&
-          trySubtypeMatch(P0, Q, leftSchema, nodeForTesting: nodeForTesting)) {
-        return true;
-      }
-
-      _constraints.length = rewind;
+    if (performSubtypeConstraintGenerationForLeftFutureOr(P, Q,
+        leftSchema: leftSchema, astNodeForTesting: nodeForTesting)) {
+      return true;
     }
 
     // If `P` is `P0?` the match holds under constraint set `C1 + C2`:

pkg/front_end/lib/src/type_inference/type_constraint_gatherer.dart

@@ -356,7 +356,7 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
       return true;
     }
 
-    if (performSubtypeConstraintGenerationForFutureOr(p, q,
+    if (performSubtypeConstraintGenerationForRightFutureOr(p, q,
         leftSchema: constrainSupertype,
         astNodeForTesting: treeNodeForTesting)) {
       return true;
@@ -380,20 +380,10 @@ class TypeConstraintGatherer extends shared.TypeConstraintGenerator<
     //
     // If Future<P0> is a subtype match for Q under constraint set C1.
     // And if P0 is a subtype match for Q under constraint set C2.
-
-    if (typeOperations.matchFutureOrInternal(p) case DartType p0?) {
-      final int baseConstraintCount = _protoConstraints.length;
-      if (_isNullabilityAwareSubtypeMatch(
-              typeOperations.futureTypeInternal(p0), q,
-              constrainSupertype: constrainSupertype,
-              treeNodeForTesting: treeNodeForTesting) &&
-          // Coverage-ignore(suite): Not run.
-          _isNullabilityAwareSubtypeMatch(p0, q,
-              constrainSupertype: constrainSupertype,
-              treeNodeForTesting: treeNodeForTesting)) {
-        return true;
-      }
-      _protoConstraints.length = baseConstraintCount;
+    if (performSubtypeConstraintGenerationForLeftFutureOr(p, q,
+        leftSchema: constrainSupertype,
+        astNodeForTesting: treeNodeForTesting)) {
+      return true;
     }
 
     // If P is P0? the match holds under constraint set C1 + C2:

pkg/front_end/test/coverage_suite_expected.dart

@@ -560,7 +560,7 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
   ),
   // 100.0%.
   "package:front_end/src/kernel/body_builder.dart": (
-    hitCount: 7121,
+    hitCount: 7128,
     missCount: 0,
   ),
   // 100.0%.
@@ -870,7 +870,7 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
   ),
   // 100.0%.
   "package:front_end/src/source/outline_builder.dart": (
-    hitCount: 2118,
+    hitCount: 2122,
     missCount: 0,
   ),
   // 100.0%.
@@ -1036,7 +1036,7 @@ const Map<String, ({int hitCount, int missCount})> _expect = {
   ),
   // 100.0%.
   "package:front_end/src/type_inference/type_constraint_gatherer.dart": (
-    hitCount: 188,
+    hitCount: 179,
     missCount: 0,
   ),
   // 100.0%.