Issue 39667. Use flow analysis in IfElement.

Bug: #39667
Change-Id: I4528869a8d39d1b27c0cdf21ab20173bdb0efbc4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127482
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

pkg/_fe_analyzer_shared/test/flow_analysis/nullability/data/if_element.dart

@@ -0,0 +1,109 @@
+// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+void list_if_notNull_then_else_left(int? x) {
+  [if (null != x) /*nonNullable*/ x else x];
+}
+
+void list_if_notNull_then_else_right(int? x) {
+  [if (x != null) /*nonNullable*/ x else x];
+}
+
+void list_if_notNull_thenExit_left(int? x) {
+  [if (null != x) throw 42, x];
+}
+
+void list_if_notNull_thenExit_right(int? x) {
+  [if (x != null) throw 42, x];
+}
+
+void list_if_null_then_else_left(int? x) {
+  [if (null == x) x else /*nonNullable*/ x ];
+}
+
+void list_if_null_then_else_right(int? x) {
+  [if (x == null) x else /*nonNullable*/ x ];
+}
+
+void list_if_null_thenExit_left(int? x) {
+  [if (null == x) throw 42, /*nonNullable*/ x];
+}
+
+void list_if_null_thenExit_right(int? x) {
+  [if (x == null) throw 42, /*nonNullable*/ x];
+}
+
+map_if_notNull_then_else_left(int? x) {
+  return {if (null != x) /*nonNullable*/ x: /*nonNullable*/ x else x: x};
+}
+
+map_if_notNull_then_else_right(int? x) {
+  return {if (x != null) /*nonNullable*/ x: /*nonNullable*/ x else x: x};
+}
+
+map_if_notNull_thenExit_left(int? x) {
+  return {if (null != x) throw 42: 0, x: x};
+}
+
+map_if_notNull_thenExit_right(int? x) {
+  return {if (x != null) throw 42: 0, x: x};
+}
+
+map_if_null_then_else_left(int? x) {
+  return {if (null == x) x: x else /*nonNullable*/ x: /*nonNullable*/ x };
+}
+
+map_if_null_then_else_right(int? x) {
+  return {if (x == null) x: x else /*nonNullable*/ x: /*nonNullable*/ x };
+}
+
+map_if_null_thenExit_left(int? x) {
+  return {if (null == x) throw 42: 0, /*nonNullable*/ x: /*nonNullable*/ x };
+}
+
+map_if_null_thenExit_right(int? x) {
+  return {if (x == null) throw 42: 0, /*nonNullable*/ x: /*nonNullable*/ x };
+}
+
+set_if_notNull_then_else_left(int? x) {
+  return {if (null != x) /*nonNullable*/ x else x};
+}
+
+set_if_notNull_then_else_right(int? x) {
+  return {if (x != null) /*nonNullable*/ x else x};
+}
+
+set_if_notNull_thenExit_left(int? x) {
+  return {if (null != x) throw 42, x};
+}
+
+set_if_notNull_thenExit_right(int? x) {
+  return {if (x != null) throw 42, x};
+}
+
+set_if_null_then_else_left(int? x) {
+  return {if (null == x) x else /*nonNullable*/ x };
+}
+
+set_if_null_then_else_right(int? x) {
+  return {if (x == null) x else /*nonNullable*/ x };
+}
+
+set_if_null_thenExit_left(int? x) {
+  return {if (null == x) throw 42, /*nonNullable*/ x};
+}
+
+set_if_null_thenExit_right(int? x) {
+  return {if (x == null) throw 42, /*nonNullable*/ x};
+}
+
+class C {
+  C.constructor_if_then_else(int? x) {
+    [if (x == null) x else /*nonNullable*/ x ];
+  }
+
+  void method_if_then_else(int? x) {
+    [if (x == null) x else /*nonNullable*/ x ];
+  }
+}

pkg/analyzer/lib/src/generated/resolver.dart

@@ -1625,15 +1625,28 @@ class ResolverVisitor extends ScopedVisitor {
     InferenceContext.setType(condition, typeProvider.boolType);
     // TODO(scheglov) Do we need these checks for null?
     condition?.accept(this);
+
     CollectionElement thenElement = node.thenElement;
-    _promoteManager.visitIfElement_thenElement(
-      condition,
-      thenElement,
-      () {
-        thenElement.accept(this);
-      },
-    );
-    node.elseElement?.accept(this);
+    if (_flowAnalysis != null) {
+      _flowAnalysis.flow.ifStatement_thenBegin(condition);
+      thenElement.accept(this);
+    } else {
+      _promoteManager.visitIfElement_thenElement(
+        condition,
+        thenElement,
+        () {
+          thenElement.accept(this);
+        },
+      );
+    }
+
+    var elseElement = node.elseElement;
+    if (elseElement != null) {
+      _flowAnalysis?.flow?.ifStatement_elseBegin();
+      elseElement.accept(this);
+    }
+
+    _flowAnalysis?.flow?.ifStatement_end(elseElement != null);
 
     node.accept(elementResolver);
     node.accept(typeAnalyzer);

pkg/front_end/test/id_tests/nullability_test.dart

@@ -19,7 +19,11 @@ main(List<String> args) async {
       createUriForFileName: createUriForFileName,
       onFailure: onFailure,
       runTest: runTestFor(
-          const NullabilityDataComputer(), [cfeNonNullableOnlyConfig]));
+          const NullabilityDataComputer(), [cfeNonNullableOnlyConfig]),
+      skipList: [
+        // TODO(dmitryas): Run all nullability tests.
+        'if_element.dart',
+      ]);
 }
 
 class NullabilityDataComputer extends DataComputer<String> {