PY-19825 Fixed: Tuple sub-assignment typing broken

Find the highest ancestor of tuple, calculate its type and then extract type of its subtuples and their elements

python/src/com/jetbrains/python/psi/impl/PyTargetExpressionImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2014 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -176,16 +176,18 @@ public class PyTargetExpressionImpl extends PyBaseElementImpl<PyTargetExpression
       }
       if (parent instanceof PyTupleExpression) {
         PsiElement nextParent = parent.getParent();
-        while (nextParent instanceof PyParenthesizedExpression) {
+        while (nextParent instanceof PyParenthesizedExpression || nextParent instanceof PyTupleExpression) {
           nextParent = nextParent.getParent();
         }
         if (nextParent instanceof PyAssignmentStatement) {
           final PyAssignmentStatement assignment = (PyAssignmentStatement)nextParent;
           final PyExpression value = assignment.getAssignedValue();
-          if (value != null) {
+          final PyExpression lhs = assignment.getLeftHandSideExpression();
+          final PyTupleExpression targetTuple = PsiTreeUtil.findChildOfType(lhs, PyTupleExpression.class, false);
+          if (value != null && targetTuple != null) {
             final PyType assignedType = PyTypeChecker.toNonWeakType(context.getType(value), context);
             if (assignedType instanceof PyTupleType) {
-              final PyType t = PyTypeChecker.getTargetTypeFromTupleAssignment(this, (PyTupleExpression)parent, (PyTupleType)assignedType);
+              final PyType t = PyTypeChecker.getTargetTypeFromTupleAssignment(this, targetTuple, (PyTupleType)assignedType);
               if (t != null) {
                 return t;
               }

python/testSrc/com/jetbrains/python/PyTypeTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2000-2013 JetBrains s.r.o.
+ * Copyright 2000-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -834,6 +834,30 @@ public class PyTypeTest extends PyTestCase {
            "expr = (1, False) * 2");
   }
 
+
+  public void testTupleDestructuring() {
+    doTest("str",
+           "_, expr = (1, 'val') ");
+  }
+
+  public void testParensTupleDestructuring() {
+    doTest("str",
+           "(_, expr) = (1, 'val') ");
+  }
+
+  // PY-19825
+  public void testSubTupleDestructuring() {
+    doTest("str",
+           "(a, (_, expr)) = (1, (2,'val')) ");
+  }
+
+  // PY-19825
+  public void testSubTupleIndirectDestructuring() {
+    doTest("str",
+           "xs = (2,'val')\n" +
+           "(a, (_, expr)) = (1, xs) ");
+  }
+
   public void testConstructorUnification() {
     doTest("C[int]",
            "class C(object):\n" +