fail if ui asks for input without a terminal

This commit attempts to fix the issue where
`get` stalls if an annex remote tries to ask for
credentials in a process that has no terminal
attached.

datalad/ui/dialog.py

@@ -31,6 +31,7 @@
 from ..utils import auto_repr
 from ..utils import on_windows
 from .base import InteractiveUI
+from .utils import has_terminal
 from datalad.support.exceptions import CapturedException
 
 # Example APIs which might be useful to look for "inspiration"
@@ -357,6 +358,31 @@ def get_progressbar(self, *args, **kwargs):
         return super(UnderAnnexUI, self).get_progressbar(
                 *args, **kwargs)
 
+    def input(self, prompt, hidden=False):
+        if not has_terminal():
+            # we are not interactive
+            raise RuntimeError('Interactive input not available for `ui.input()` in annex remotes')
+        return super(UnderAnnexUI, self).input(prompt, hidden)
+
+    def question(self,
+                 text,
+                 title=None,
+                 choices=None,
+                 default=None,
+                 hidden=False,
+                 repeat=None):
+        if not has_terminal():
+            # we are not interactive
+            raise RuntimeError('Interactive input not available for `ui.question()` in annex remotes')
+        return super(UnderAnnexUI, self).question(
+            text,
+            title=title,
+            choices=choices,
+            default=default,
+            hidden=hidden,
+            repeat=repeat
+        )
+
 
 @auto_repr
 class UnderTestsUI(DialogUI):

datalad/ui/utils.py

@@ -73,4 +73,16 @@ def show_hint(msg):
     ui.message("{}".format(
             ansi_colors.color_word(
                 msg,
-                ansi_colors.YELLOW)))
+                ansi_colors.YELLOW)))
+
+
+def has_terminal():
+    """Return True if the process has a controlling terminal
+
+    This checks for a controlling terminal on Linux
+    """
+    try:
+        open('/dev/tty', 'r').close()
+        return True
+    except IOError as exc:
+        return False