Fix applying @needs_global_scope to cell magics.

There was some side effect in some magic to allow passing
needs_local_scope. We know pass the global_scope to cell magice when
using @needs_local_scope, but at the same time this means that we can't
rely on the existance of local_ns from within the magic to know wheter
we are cell-called or line called.

Fixes  #11659

IPython/core/interactiveshell.py

@@ -2345,7 +2345,7 b' class InteractiveShell(SingletonConfigurable):'
                 magic_arg_s = self.var_expand(line, stack_depth)
             kwargs = {}
             if getattr(fn, "needs_local_scope", False):
-                kwargs['local_ns'] = sys._getframe(stack_depth).f_locals
+                kwargs['local_ns'] = self.user_ns
 
             with self.builtin_trap:
                 args = (magic_arg_s, cell)

IPython/core/magics/execution.py

@@ -1127,8 +1127,8 b' python-profiler package from non-free.""")'
         ns = {}
         glob = self.shell.user_ns
         # handles global vars with same name as local vars. We store them in conflict_globs.
-        if local_ns is not None:
-            conflict_globs = {}
+        conflict_globs = {}
+        if local_ns and cell is None:
             for var_name, var_val in glob.items():
                 if var_name in local_ns:
                     conflict_globs[var_name] = var_val
@@ -1154,9 +1154,8 b' python-profiler package from non-free.""")'
         timeit_result = TimeitResult(number, repeat, best, worst, all_runs, tc, precision)
 
         # Restore global vars from conflict_globs
-        if local_ns is not None:
-            if len(conflict_globs) > 0:
-                glob.update(conflict_globs)
+        if conflict_globs:
+           glob.update(conflict_globs)
                 
         if not quiet :
             # Check best timing is greater than zero to avoid a

IPython/core/tests/test_magic.py

@@ -419,6 +419,16 b' def test_time3():'
                     "run = 0\n"
                     "run += 1")
 
+def test_time_local_ns():
+    """
+    Test that local_ns is actually global_ns when running a cell magic
+    """
+    ip = get_ipython()
+    ip.run_cell("%%time\n"
+                "myvar = 1")
+    nt.assert_equal(ip.user_ns['myvar'], 1)
+    del ip.user_ns['myvar']
+
 def test_doctest_mode():
     "Toggle doctest_mode twice, it should be a no-op and run without error"
     _ip.magic('doctest_mode')