Backport PR #12284: Try to elide long completion based on user input.

.travis.yml

@@ -38,7 +38,7 b' install:'
   - pip install setuptools --upgrade
   - pip install -e file://$PWD#egg=ipython[test] --upgrade
   - pip install trio curio --upgrade --upgrade-strategy eager
-  - pip install pytest 'matplotlib !=3.2.0'
+  - pip install pytest 'matplotlib !=3.2.0' mypy
   - pip install codecov check-manifest --upgrade
 
 script:
@@ -50,6 +50,7 b' script:'
     fi
   - cd /tmp && iptest --coverage xml && cd -
   - pytest IPython
+  - mypy --ignore-missing-imports -m IPython.terminal.ptutils
   # On the latest Python (on Linux) only, make sure that the docs build.
   - |
     if [[ "$TRAVIS_PYTHON_VERSION" == "3.7" ]] && [[ "$TRAVIS_OS_NAME" == "linux" ]]; then

IPython/core/interactiveshell.py

@@ -2217,7 +2217,7 b' class InteractiveShell(SingletonConfigurable):'
         The position argument (defaults to 0) is the index in the completers
         list where you want the completer to be inserted."""
 
-        newcomp = types.MethodType(completer,self.Completer)
+        newcomp = types.MethodType(completer, self.Completer)
         self.Completer.custom_matchers.insert(pos,newcomp)
 
     def set_completer_frame(self, frame=None):

IPython/terminal/ptutils.py

@@ -23,7 +23,7 b' import os'
 
 _completion_sentinel = object()
 
-def _elide(string, *, min_elide=30):
+def _elide_point(string:str, *, min_elide=30)->str:
     """
     If a string is long enough, and has at least 3 dots,
     replace the middle part with ellipses.
@@ -53,6 +53,26 b' def _elide(string, *, min_elide=30):'
 
     return string
 
+def _elide_typed(string:str, typed:str, *, min_elide:int=30)->str:
+    """
+    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 cut_how_much < 7:
+        return string
+    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:str, typed:str, min_elide=30)->str:
+    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] == '=':
@@ -89,7 +109,11 b' class IPythonPTCompleter(Completer):'
             cursor_col = document.cursor_position_col
             cursor_position = document.cursor_position
             offset = cursor_to_position(body, cursor_row, cursor_col)
-            yield from self._get_completions(body, offset, cursor_position, self.ipy_completer)
+            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):
@@ -128,9 +152,9 b' class IPythonPTCompleter(Completer):'
 
             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):
     """

IPython/terminal/tests/test_interactivshell.py

@@ -17,14 +17,32 b' import nose.tools as nt'
 class TestElide(unittest.TestCase):
 
     def test_elide(self):
-        _elide('concatenate((a1, a2, ...), axis') # do not raise
-        _elide('concatenate((a1, a2, ..), . axis') # do not raise
-        nt.assert_equal(_elide('aaaa.bbbb.ccccc.dddddd.eeeee.fffff.gggggg.hhhhhh'), 'aaaa.b…g.hhhhhh')
-        
+        _elide('concatenate((a1, a2, ...), axis', '') # do not raise
+        _elide('concatenate((a1, a2, ..), . axis', '') # do not raise
+        nt.assert_equal(_elide('aaaa.bbbb.ccccc.dddddd.eeeee.fffff.gggggg.hhhhhh',''), 'aaaa.b…g.hhhhhh')
+
         test_string = os.sep.join(['', 10*'a', 10*'b', 10*'c', ''])
         expect_stirng = os.sep + 'a' + '\N{HORIZONTAL ELLIPSIS}' + 'b' + os.sep + 10*'c'
-        nt.assert_equal(_elide(test_string), expect_stirng)
-
+        nt.assert_equal(_elide(test_string, ''), expect_stirng)
+
+    def test_elide_typed_normal(self):
+        nt.assert_equal(_elide('the quick brown fox jumped over the lazy dog', 'the quick brown fox', min_elide=10), 'the…fox jumped over the lazy dog')
+
+
+    def test_elide_typed_short_match(self):
+        """
+        if the match is too short we don't elide.
+        avoid the "the...the"
+        """
+        nt.assert_equal(_elide('the quick brown fox jumped over the lazy dog', 'the', min_elide=10), 'the quick brown fox jumped over the lazy dog')
+
+    def test_elide_typed_no_match(self):
+        """
+        if the match is too short we don't elide.
+        avoid the "the...the"
+        """
+        # here we typed red instead of brown
+        nt.assert_equal(_elide('the quick brown fox jumped over the lazy dog', 'the quick red fox', min_elide=10), 'the quick brown fox jumped over the lazy dog')
 
 class TestContextAwareCompletion(unittest.TestCase):