PY-21244 Fix type annotations for the built-in function "map"

python/helpers/python-skeletons/__builtin__.py

@@ -202,9 +202,9 @@ def map(function, sequence, *sequence_1):
     """Return a list of the results of applying the function to the items of
     the argument sequence(s).
 
-    :type function: ((T) -> V) | None
+    :type function: None | (T) -> V
     :type sequence: collections.Iterable[T]
-    :rtype: list[V] | bytes | unicode
+    :rtype: list[V]
     """
     pass
 

python/helpers/python-skeletons/builtins.py

@@ -195,16 +195,28 @@ def max(*args, key=None, default=None):
     pass
 
 
-def map(function, sequence, *sequence_1):
-    """Return a list of the results of applying the function to the items of
-    the argument sequence(s).
+class map(object):
+    def __init__(self, function, sequence, *sequence_1):
+        """Return an iterable of the results of applying the function to the items of
+        the argument sequence(s).
 
-    :type function: ((T) -> V) | None
-    :type sequence: collections.Iterable[T]
-    :rtype: list[V] | bytes | str
-    """
-    pass
+        :type function: None | (T) -> V
+        :type sequence: collections.Iterable[T]
+        :rtype: map[T, V]
+        """
+        pass
 
+    def __iter__(self):
+        """
+        :rtype: collections.Iterator[V]
+        """
+        return self
+
+    def __next__(self):
+        """
+        :rtype: V
+        """
+        pass
 
 def min(*args, key=None, default=None):
     """Return the smallest item in an iterable or the smallest of two or more

python/testData/inspections/PyTypeCheckerInspection/MapArgumentsInOppositeOrder.py

@@ -0,0 +1 @@
+map(<weak_warning descr="Expected type 'Optional[(Any) -> Any]' (matched generic type 'Optional[(TypeVar('T')) -> TypeVar('V')]'), got 'str' instead">'foo'</weak_warning>, <weak_warning descr="Expected type 'Iterable' (matched generic type 'Iterable[TypeVar('T')]'), got '(c: Any) -> int' instead">lambda c: 42</weak_warning>)

python/testData/inspections/PyTypeCheckerInspection/MapReturnElementType.py

@@ -1,5 +1,5 @@
 def test():
     xs = map(lambda x: x + 1, [1, 2, 3])
-    print('foo' + xs[0])  # Can be a str since map returns list[V] | str | unicode
+    print('foo' + <warning descr="Expected type 'Union[str, unicode]', got 'int' instead">xs[0]</warning>)
     ys = map(tuple, iter([1, 2, 3]))
-    print(1 + <warning descr="Expected type 'Number', got 'Union[tuple, str, unicode]' instead">ys[0]</warning>, 'bar' + ys[1])
+    print(1 + <warning descr="Expected type 'Number', got 'tuple' instead">ys[0]</warning>, 'bar' + <warning descr="Expected type 'Union[str, unicode]', got 'tuple' instead">ys[1]</warning>)

python/testSrc/com/jetbrains/python/Py3TypeTest.java

@@ -441,6 +441,13 @@ public class Py3TypeTest extends PyTestCase {
            "expr = float.fromhex(\"0.5\")");
   }
 
+  // PY-20073
+  public void testMapReturnType() {
+    doTest("int", 
+           "for x in map(lambda x: 42, 'foo'):\n" +
+           "    expr = x");
+  }
+
   private void doTest(final String expectedType, final String text) {
     myFixture.configureByText(PythonFileType.INSTANCE, text);
     final PyExpression expr = myFixture.findElementByText("expr", PyExpression.class);

python/testSrc/com/jetbrains/python/inspections/Py3TypeCheckerInspectionTest.java

@@ -168,4 +168,9 @@ public class Py3TypeCheckerInspectionTest extends PyTestCase {
   public void testFloatFromhex() {
     doTest();
   }
+
+  // PY-20073
+  public void testMapArgumentsInOppositeOrder() {
+    doTest();
+  }
 }

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

@@ -341,4 +341,9 @@ public class PyTypeCheckerInspectionTest extends PyTestCase {
   public void testFloatFromhex() {
     doTest();
   }
+
+  // PY-20073
+  public void testMapArgumentsInOppositeOrder() {
+    doTest();
+  }
 }