include docstring in detail_level=1 if no source is found

We currently display source for ?? and docstring for ?,
which means less info is displayed if no source is found (e.g. compiled functions).

This displays docstring for ?? as a fallback when no Source is found.

This is a regression in 5.x

IPython/core/oinspect.py

@@ -645,7 +645,7 b' class Inspector(Colorable):'
             # Functions, methods, classes
             append_field(_mime, 'Signature', 'definition', code_formatter)
             append_field(_mime, 'Init signature', 'init_definition', code_formatter)
-            if detail_level > 0:
+            if detail_level > 0 and info['source']:
                 append_field(_mime, 'Source', 'source', code_formatter)
             else:
                 append_field(_mime, 'Docstring', 'docstring', formatter)

IPython/core/tests/test_oinspect.py

@@ -18,7 +18,7 b' from IPython.core.magic import (Magics, magics_class, line_magic,'
                                 register_line_cell_magic)
 from decorator import decorator
 from IPython.testing.decorators import skipif
-from IPython.testing.tools import AssertPrints
+from IPython.testing.tools import AssertPrints, AssertNotPrints
 from IPython.utils.path import compress_user
 from IPython.utils import py3compat
 from IPython.utils.signatures import Signature, Parameter
@@ -406,12 +406,12 b' def test_property_docstring_is_in_info_for_detail_level_0():'
             pass
 
     ip.user_ns['a_obj'] = A()
-    nt.assert_equals(
+    nt.assert_equal(
         'This is `foobar` property.',
         ip.object_inspect('a_obj.foobar', detail_level=0)['docstring'])
 
     ip.user_ns['a_cls'] = A
-    nt.assert_equals(
+    nt.assert_equal(
         'This is `foobar` property.',
         ip.object_inspect('a_cls.foobar', detail_level=0)['docstring'])
 
@@ -429,6 +429,29 b' def test_pinfo_nonascii():'
     ip._inspect('pinfo', 'nonascii2', detail_level=1)
 
 
+def test_pinfo_docstring_no_source():
+    """Docstring should be included with detail_level=1 if there is no source"""
+    with AssertPrints('Docstring:'):
+        ip._inspect('pinfo', 'str.format', detail_level=0)
+    with AssertPrints('Docstring:'):
+        ip._inspect('pinfo', 'str.format', detail_level=1)
+
+
+def test_pinfo_no_docstring_if_source():
+    """Docstring should not be included with detail_level=1 if source is found"""
+    def foo():
+        """foo has a docstring"""
+
+    ip.user_ns['foo'] = foo
+
+    with AssertPrints('Docstring:'):
+        ip._inspect('pinfo', 'foo', detail_level=0)
+    with AssertPrints('Source:'):
+        ip._inspect('pinfo', 'foo', detail_level=1)
+    with AssertNotPrints('Docstring:'):
+        ip._inspect('pinfo', 'foo', detail_level=1)
+
+
 def test_pinfo_magic():
     with AssertPrints('Docstring:'):
         ip._inspect('pinfo', 'lsmagic', detail_level=0)