[dart2js] Fix nested conditions in global inference

A bug in global inference made the analysis accidentally carry over
the state of a nested condition in a subexpression and conclude
that it was part of the state of the outer condition.

This was due to the fact that we didn't clear the state when
popping out of the context and reentering the conition state.

Fixes #48571

Change-Id: I4e8294bb1a05bb3b910b6aec374357d75acb67cb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240321
Reviewed-by: Stephen Adams <[email protected]>
Commit-Queue: Sigmund Cherem <[email protected]>

Author: sigmundch

pkg/compiler/lib/src/inferrer/builder_kernel.dart

@@ -99,6 +99,12 @@ class KernelTypeGraphBuilder extends ir.Visitor<TypeInformation>
     _stateAfterWhenFalseInternal = whenFalse;
   }
 
+  /// Removes from the current [_state] any data from the boolean value of the
+  /// most recently visited node.
+  void _clearConditionalStateAfter() {
+    _stateAfterWhenTrueInternal = _stateAfterWhenFalseInternal = null;
+  }
+
   final SideEffectsBuilder _sideEffectsBuilder;
   final Map<JumpTarget, List<LocalState>> _breaksFor =
       <JumpTarget, List<LocalState>>{};
@@ -257,15 +263,16 @@ class KernelTypeGraphBuilder extends ir.Visitor<TypeInformation>
     var oldAccumulateIsChecks = _accumulateIsChecks;
     _accumulateIsChecks = conditionContext;
     var result = node?.accept(this);
+
+    // Clear the conditional state to ensure we don't accidentally carry over
+    // conclusions from a nested condition into an outer condition. For example:
+    //
+    //   if (methodCall(x is T && true)) { /* don't assume x is T here. */ }
+    if (!conditionContext) _clearConditionalStateAfter();
     _accumulateIsChecks = oldAccumulateIsChecks;
     return result;
   }
 
-  void visitList(List<ir.Node> nodes) {
-    if (nodes == null) return;
-    nodes.forEach(visit);
-  }
-
   void handleParameter(ir.VariableDeclaration node, {bool isOptional}) {
     Local local = _localsMap.getLocalVariable(node);
     DartType type = _localsMap.getLocalType(_elementMap, local);
@@ -1696,11 +1703,7 @@ class KernelTypeGraphBuilder extends ir.Visitor<TypeInformation>
   }
 
   TypeInformation handleCondition(ir.Node node) {
-    bool oldAccumulateIsChecks = _accumulateIsChecks;
-    _accumulateIsChecks = true;
-    TypeInformation result = visit(node, conditionContext: true);
-    _accumulateIsChecks = oldAccumulateIsChecks;
-    return result;
+    return visit(node, conditionContext: true);
   }
 
   void _potentiallyAddIsCheck(ir.IsExpression node) {

pkg/compiler/test/inference/data/issue_48571.dart

@@ -21,35 +21,35 @@ Base either = DateTime.now()
     ? Child2()
     : Child1();
 
-/*member: test1:[null|exact=Child1]*/
+/*member: test1:Union(null, [exact=Child1], [exact=Child2])*/
 test1() {
   Base child = either;
   if (trivial(child is Child1 && true)) return child;
   return null;
 }
 
-/*member: test2:[null|exact=Child1]*/
+/*member: test2:Union(null, [exact=Child1], [exact=Child2])*/
 test2() {
   Base child = either;
   if (child is Child1 || trivial(child is Child1 && true)) return child;
   return null;
 }
 
-/*member: test3:[null]*/
+/*member: test3:[null|exact=Child2]*/
 test3() {
   Base child = either;
   if (trivial(child is Child1 && true) && child is Child2) return child;
   return null;
 }
 
-/*member: test4:[null]*/
+/*member: test4:[null|exact=Child2]*/
 test4() {
   Base child = either;
   if (child is Child2 && trivial(child is Child1 && true)) return child;
   return null;
 }
 
-/*member: test5:[null|exact=Child1]*/
+/*member: test5:Union(null, [exact=Child1], [exact=Child2])*/
 test5() {
   Base child = either;
   if ((child is Child1 && true) /*invoke: [exact=JSBool]*/ == false)
@@ -64,7 +64,7 @@ test6() {
   return null;
 }
 
-/*member: test7:[null|exact=Child1]*/
+/*member: test7:Union(null, [exact=Child1], [exact=Child2])*/
 test7() {
   Base child = either;
   if (trivial(trivial(child is Child1 && true))) return child;