More precise CFG for for cycles by using updated evaluator (PY-19856)

python/src/com/jetbrains/python/codeInsight/controlflow/PyControlFlowBuilder.java

@@ -32,7 +32,6 @@ import com.jetbrains.python.psi.impl.PyAugAssignmentStatementNavigator;
 import com.jetbrains.python.psi.impl.PyEvaluator;
 import com.jetbrains.python.psi.impl.PyImportStatementNavigator;
 import org.jetbrains.annotations.NotNull;
-import org.jetbrains.annotations.Nullable;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -476,7 +475,7 @@ public class PyControlFlowBuilder extends PyRecursiveElementVisitor {
     }
     final Instruction head = myBuilder.prevInstruction;
     final PyElsePart elsePart = node.getElsePart();
-    if (elsePart == null && !nonEmptyIterationSource(source)) {
+    if (elsePart == null && !PyEvaluator.evaluateAsBoolean(source, false)) {
       myBuilder.addPendingEdge(node, myBuilder.prevInstruction);
     }
     final PyStatementList list = forPart.getStatementList();
@@ -511,13 +510,6 @@ public class PyControlFlowBuilder extends PyRecursiveElementVisitor {
     myBuilder.flowAbrupted();
   }
 
-  private static boolean nonEmptyIterationSource(@Nullable PyExpression source) {
-    return
-      source instanceof PySequenceExpression && !((PySequenceExpression)source).isEmpty() ||
-      source instanceof PyStringLiteralExpression && !((PyStringLiteralExpression)source).getStringValue().isEmpty() ||
-      source instanceof PyParenthesizedExpression && nonEmptyIterationSource(((PyParenthesizedExpression)source).getContainedExpression());
-  }
-
   @Override
   public void visitPyBreakStatement(final PyBreakStatement node) {
     myBuilder.startNode(node);

python/testData/codeInsight/controlflow/fortrycontinue.txt

@@ -2,7 +2,7 @@
 1(2) element: PyAssignmentStatement
 2(3) WRITE ACCESS: tests
 3(4) element: PyForStatement
-4(5,17) READ ACCESS: tests
+4(5) READ ACCESS: tests
 5(6) element: PyTargetExpression: t
 6(7) WRITE ACCESS: t
 7(8) element: PyTryExceptStatement