Support positive iterations in control flow (PY-14840, PY-22003)

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

@@ -32,6 +32,7 @@ import com.jetbrains.python.psi.impl.PyAugAssignmentStatementNavigator;
 import com.jetbrains.python.psi.impl.PyConstantExpressionEvaluator;
 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;
@@ -455,7 +456,7 @@ public class PyControlFlowBuilder extends PyRecursiveElementVisitor {
     }
     final Instruction head = myBuilder.prevInstruction;
     final PyElsePart elsePart = node.getElsePart();
-    if (elsePart == null) {
+    if (elsePart == null && !nonEmptyIterationSource(source)) {
       myBuilder.addPendingEdge(node, myBuilder.prevInstruction);
     }
     final PyStatementList list = forPart.getStatementList();
@@ -490,6 +491,13 @@ 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/positiveiteration.py

@@ -0,0 +1,3 @@
+for i in "abc":
+    j = 1
+print(j)

python/testData/codeInsight/controlflow/positiveiteration.txt

@@ -0,0 +1,9 @@
+0(1) element: null
+1(2) element: PyForStatement
+2(3) element: PyTargetExpression: i
+3(4) WRITE ACCESS: i
+4(5) element: PyAssignmentStatement
+5(2,6) WRITE ACCESS: j
+6(7) element: PyPrintStatement
+7(8) READ ACCESS: j
+8() element: null

python/testData/codeInsight/controlflow/trytry.txt

@@ -5,7 +5,7 @@
 4(5,55) element: PyTryPart
 5(6,55) element: PyAssignmentStatement
 6(7,55) WRITE ACCESS: b
-7(8,53,55) element: PyForStatement
+7(8,55) element: PyForStatement
 8(9,55) element: PyTargetExpression: x
 9(10,55) WRITE ACCESS: x
 10(11,55) element: PyTryExceptStatement

python/testData/inspections/PyUnboundLocalVariableInspection/PositiveIteration.py

@@ -0,0 +1,16 @@
+def test1():
+    for i in "abc":
+        j = 1
+    print(j)
+
+
+def test2():
+    for i in (1, 2):
+        j = 1
+    print(j)
+
+
+def test3():
+    for i in [1, 2]:
+        j = 1
+    print(j)

python/testData/inspections/PyUnusedLocalInspection/py2.py

@@ -20,7 +20,7 @@ def boo():
   for i in [1,2]:
     print(i)
 
-  j = 1 #pass
+  <weak_warning descr="Local variable 'j' value is not used">j</weak_warning> = 1 #fail
   for j in [-2, -1]:
     print(j)
   print (j)

python/testSrc/com/jetbrains/python/PyControlFlowBuilderTest.java

@@ -238,6 +238,12 @@ public class PyControlFlowBuilderTest extends LightMarkedTestCase {
     doTest();
   }
 
+  // PY-14840
+  // PY-22003
+  public void testPositiveIteration() {
+    doTest();
+  }
+
   private void doTestFirstStatement() {
     final String testName = getTestName(false).toLowerCase();
     configureByFile(testName + ".py");

python/testSrc/com/jetbrains/python/inspections/PyUnboundLocalVariableInspectionTest.java

@@ -191,6 +191,12 @@ public class PyUnboundLocalVariableInspectionTest extends PyInspectionTestCase {
     doTest();
   }
 
+  // PY-14840
+  // PY-22003
+  public void testPositiveIteration() {
+    doTest();
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {