Code Folding Occasionally Breaks

Description

What steps will reproduce the problem?

The problem is that, occasionally, the arrow for code folding collapse and expansion disappears. This renders the code there inaccessible from the editor. The editor still grays out the function name, but it will not be expandable. The arrow only seems to disappear after collapsing a code block/function/class. This doesn’t happen everytime that I collapse the code block. I don’t know the exact order of clicks and where those clicks take place that make this issue manifest.

Versions

• Spyder version: 4.0.1
• Python version: 3.7.1
• Qt version: 5.9.6
• PyQt5 version: 5.9.2
• Operating System: Windows 10

Dependencies

atomicwrites >=1.2.0         :  1.3.0 (OK)
chardet >=2.0.0              :  3.0.4 (OK)
cloudpickle >=0.5.0          :  1.2.2 (OK)
diff_match_patch >=20181111  :  20181111 (OK)
intervaltree                 :  None (OK)
IPython >=4.0                :  7.11.1 (OK)
jedi =0.14.1                 :  0.14.1 (OK)
nbconvert >=4.0              :  5.6.1 (OK)
numpydoc >=0.6.0             :  0.9.2 (OK)
pexpect >=4.4.0              :  4.7.0 (OK)
pickleshare >=0.4            :  0.7.5 (OK)
psutil >=0.3                 :  5.6.7 (OK)
pygments >=2.0               :  2.5.2 (OK)
pylint >=0.25                :  2.4.4 (OK)
pyls >=0.31.2;<0.32.0        :  0.31.2 (OK)
zmq >=17                     :  18.1.0 (OK)
qdarkstyle >=2.7             :  2.7 (OK)
qtawesome >=0.5.7            :  0.6.0 (OK)
qtconsole >=4.6.0            :  4.6.0 (OK)
qtpy >=1.5.0                 :  1.9.0 (OK)
rtree >=0.8.3                :  0.8.3 (OK)
sphinx >=0.6.6               :  2.3.1 (OK)
spyder_kernels >=1.8.1;<2.0.0:  1.8.1 (OK)
watchdog                     :  None (OK)
cython >=0.21                :  None (NOK)
matplotlib >=2.0.0           :  3.1.1 (OK)
numpy >=1.7                  :  1.18.1 (OK)
pandas >=0.13.1              :  None (NOK)
scipy >=0.17.0               :  1.3.2 (OK)
sympy >=0.7.3                :  None (NOK)

[ccordoba12]

it involves the use of the option to move a line up in the Editor

This is really cool to know. Thanks a lot @dalthviz!

[goanpeca]

@dalthviz please try to reproduce this issue. Thanks!