Crash in fallback plugin when typing character

Description

What steps will reproduce the problem?

I have an animated gif available. I have many things loaded into memory and just type a character and Spyder crashes.

Traceback

  File "C:\Users\suzbm\Anaconda3\lib\site-packages\spyder\plugins\completion\fallback\actor.py", line 155, in handle_msg
    msg['current_word'])
  File "C:\Users\suzbm\Anaconda3\lib\site-packages\spyder\plugins\completion\fallback\actor.py", line 62, in tokenize
    valid = is_prefix_valid(text, offset, language)
  File "C:\Users\suzbm\Anaconda3\lib\site-packages\spyder\plugins\completion\fallback\utils.py", line 125, in is_prefix_valid
    current_pos_text = text[offset - utf16_diff - 1]
IndexError: string index out of range

Versions

• Spyder version: 4.1.2
• Python version: 3.7.4
• Qt version: 5.12.5
• PyQt5 version: 5.12.3
• Operating System: Windows 10

Dependencies

# Mandatory:
atomicwrites >=1.2.0           :  1.3.0 (OK)
chardet >=2.0.0                :  3.0.4 (OK)
cloudpickle >=0.5.0            :  1.3.0 (OK)
diff_match_patch >=20181111    :  20181111 (OK)
intervaltree                   :  None (OK)
IPython >=4.0                  :  7.12.0 (OK)
jedi =0.15.2                   :  0.15.2 (OK)
nbconvert >=4.0                :  5.6.1 (OK)
numpydoc >=0.6.0               :  0.9.2 (OK)
paramiko >=2.4.0               :  2.7.1 (OK)
parso =0.5.2                   :  0.5.2 (OK)
pexpect >=4.4.0                :  4.8.0 (OK)
pickleshare >=0.4              :  0.7.5 (OK)
psutil >=5.3                   :  5.7.0 (OK)
pygments >=2.0                 :  2.5.2 (OK)
pylint >=0.25                  :  2.4.4 (OK)
pyls >=0.31.9;<0.32.0          :  0.31.9 (OK)
qdarkstyle >=2.8               :  2.8 (OK)
qtawesome >=0.5.7              :  0.7.0 (OK)
qtconsole >=4.6.0              :  4.6.0 (OK)
qtpy >=1.5.0                   :  1.9.0 (OK)
rtree >=0.8.3                  :  0.9.4 (OK)
sphinx >=0.6.6                 :  2.4.3 (OK)
spyder_kernels >=1.9.0;<1.10.0 :  1.9.0 (OK)
watchdog                       :  None (OK)
zmq >=17                       :  19.0.0 (OK)

# Optional:
cython >=0.21                  :  0.29.15 (OK)
matplotlib >=2.0.0             :  3.1.3 (OK)
numpy >=1.7                    :  1.18.1 (OK)
pandas >=0.13.1                :  1.0.1 (OK)
scipy >=0.17.0                 :  1.4.1 (OK)
sympy >=0.7.3                  :  1.5.1 (OK)

[atiyabzafar]

@demattox I have same issue here in spyder @ccordoba12 Please take note of the issue. It started happening just an hour ago after a restart. As per my knowledge I have not updated anything since my last start.

Spyder version 4.1.2 Python 3.7.7 64-bit | Qt 5.9.6 | PyQt5 5.9.2 | Windows 10 Using Kite for indexing

Here is the gif showing the error.

Also i tried it with horizontal splitting and the problem goes away.

[demattox]

@ccordoba12 So I made a potentially interesting and hopefully helpful observation. It seems this error does not arise when I’ve split horizontally, but after closing the split panel, the error occurs again. And I noticed the tab selector button options (not sure the name for them, the square buttons to the left and right of the tab names) are highlighted when working in a single pane, but look normal in the split pane. Might be unrelated though.

Please let me know if there’s anything else I can do.