Try to elide long completion based on user input.

If what the user has typed is already in the completion and the
completion is really long, try to elide what the user has already typed
from the displayed text of the completion.

Keep the first 3 and last 3 of what is already present.

This will behave weirdly if all the completion have a common prefix as I
believe prompt toolkit will insert the common prefix (or do we?). I'll
have to check how to consider the common prefix as being typed.

IPython/terminal/ptutils.py

@@ -1,168 +1,190 b''
 """prompt-toolkit utilities
 
 Everything in this module is a private API,
 not to be used outside IPython.
 """
 
 # Copyright (c) IPython Development Team.
 # Distributed under the terms of the Modified BSD License.
 
 import unicodedata
 from wcwidth import wcwidth
 
 from IPython.core.completer import (
     provisionalcompleter, cursor_to_position,
     _deduplicate_completions)
 from prompt_toolkit.completion import Completer, Completion
 from prompt_toolkit.lexers import Lexer
 from prompt_toolkit.lexers import PygmentsLexer
 from prompt_toolkit.patch_stdout import patch_stdout
 
 import pygments.lexers as pygments_lexers
 import os
 
 _completion_sentinel = object()
 
-def _elide(string, *, min_elide=30):
+def _elide_point(string, *, min_elide=30):
     """
     If a string is long enough, and has at least 3 dots,
     replace the middle part with ellipses.
 
     If a string naming a file is long enough, and has at least 3 slashes,
     replace the middle part with ellipses.
 
     If three consecutive dots, or two consecutive dots are encountered these are
     replaced by the equivalents HORIZONTAL ELLIPSIS or TWO DOT LEADER unicode
     equivalents
     """
     string = string.replace('...','\N{HORIZONTAL ELLIPSIS}')
     string = string.replace('..','\N{TWO DOT LEADER}')
     if len(string) < min_elide:
         return string
 
     object_parts = string.split('.')
     file_parts = string.split(os.sep)
     if file_parts[-1] == '':
         file_parts.pop()
 
     if len(object_parts) > 3:
         return '{}.{}\N{HORIZONTAL ELLIPSIS}{}.{}'.format(object_parts[0], object_parts[1][0], object_parts[-2][-1], object_parts[-1])
 
     elif len(file_parts) > 3:
         return ('{}' + os.sep + '{}\N{HORIZONTAL ELLIPSIS}{}' + os.sep + '{}').format(file_parts[0], file_parts[1][0], file_parts[-2][-1], file_parts[-1])
 
     return string
 
+def _elide_typed(string, typed, *, min_elide=30):
+    """
+    Elide the middle of a long string if the beginning has already been typed.
+    """
+
+    if len(string) < min_elide:
+        return string
+    cut_how_much = len(typed)-3
+    if string.startswith(typed) and len(string)> len(typed):
+        return f"{string[:3]}\N{HORIZONTAL ELLIPSIS}{string[cut_how_much:]}"
+    return string
+
+def _elide(string, typed, min_elide=30):
+    return _elide_typed(
+        _elide_point(string, min_elide=min_elide),
+        typed, min_elide=min_elide)
+
+
 
 def _adjust_completion_text_based_on_context(text, body, offset):
     if text.endswith('=') and len(body) > offset and body[offset] == '=':
         return text[:-1]
     else:
         return text
 
 
 class IPythonPTCompleter(Completer):
     """Adaptor to provide IPython completions to prompt_toolkit"""
     def __init__(self, ipy_completer=None, shell=None):
         if shell is None and ipy_completer is None:
             raise TypeError("Please pass shell=an InteractiveShell instance.")
         self._ipy_completer = ipy_completer
         self.shell = shell
 
     @property
     def ipy_completer(self):
         if self._ipy_completer:
             return self._ipy_completer
         else:
             return self.shell.Completer
 
     def get_completions(self, document, complete_event):
         if not document.current_line.strip():
             return
         # Some bits of our completion system may print stuff (e.g. if a module
         # is imported). This context manager ensures that doesn't interfere with
         # the prompt.
 
         with patch_stdout(), provisionalcompleter():
             body = document.text
             cursor_row = document.cursor_position_row
             cursor_col = document.cursor_position_col
             cursor_position = document.cursor_position
             offset = cursor_to_position(body, cursor_row, cursor_col)
+            try:
             yield from self._get_completions(body, offset, cursor_position, self.ipy_completer)
+            except Exception as e:
+                from traceback import print_tb
+                print_tb(e)
 
     @staticmethod
     def _get_completions(body, offset, cursor_position, ipyc):
         """
         Private equivalent of get_completions() use only for unit_testing.
         """
         debug = getattr(ipyc, 'debug', False)
         completions = _deduplicate_completions(
             body, ipyc.completions(body, offset))
         for c in completions:
             if not c.text:
                 # Guard against completion machinery giving us an empty string.
                 continue
             text = unicodedata.normalize('NFC', c.text)
             # When the first character of the completion has a zero length,
             # then it's probably a decomposed unicode character. E.g. caused by
             # the "\dot" completion. Try to compose again with the previous
             # character.
             if wcwidth(text[0]) == 0:
                 if cursor_position + c.start > 0:
                     char_before = body[c.start - 1]
                     fixed_text = unicodedata.normalize(
                         'NFC', char_before + text)
 
                     # Yield the modified completion instead, if this worked.
                     if wcwidth(text[0:1]) == 1:
                         yield Completion(fixed_text, start_position=c.start - offset - 1)
                         continue
 
             # TODO: Use Jedi to determine meta_text
             # (Jedi currently has a bug that results in incorrect information.)
             # meta_text = ''
             # yield Completion(m, start_position=start_pos,
             #                  display_meta=meta_text)
             display_text = c.text
 
             adjusted_text = _adjust_completion_text_based_on_context(c.text, body, offset)
             if c.type == 'function':
-                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text+'()'), display_meta=c.type+c.signature)
+                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text+'()', body[c.start:c.end]), display_meta=c.type+c.signature)
             else:
-                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text), display_meta=c.type)
+                yield Completion(adjusted_text, start_position=c.start - offset, display=_elide(display_text,  body[c.start:c.end]), display_meta=c.type)
 
 class IPythonPTLexer(Lexer):
     """
     Wrapper around PythonLexer and BashLexer.
     """
     def __init__(self):
         l = pygments_lexers
         self.python_lexer = PygmentsLexer(l.Python3Lexer)
         self.shell_lexer = PygmentsLexer(l.BashLexer)
 
         self.magic_lexers = {
             'HTML': PygmentsLexer(l.HtmlLexer),
             'html': PygmentsLexer(l.HtmlLexer),
             'javascript': PygmentsLexer(l.JavascriptLexer),
             'js': PygmentsLexer(l.JavascriptLexer),
             'perl': PygmentsLexer(l.PerlLexer),
             'ruby': PygmentsLexer(l.RubyLexer),
             'latex': PygmentsLexer(l.TexLexer),
         }
 
     def lex_document(self, document):
         text = document.text.lstrip()
 
         lexer = self.python_lexer
 
         if text.startswith('!') or text.startswith('%%bash'):
             lexer = self.shell_lexer
 
         elif text.startswith('%%'):
             for magic, l in self.magic_lexers.items():
                 if text.startswith('%%' + magic):
                     lexer = l
                     break
 
         return lexer.lex_document(document)