Improve error reporting when connnecting with a bad channel

[plule-ansys]

Connecting PyMAPDL to a bad channel leads to an exception cascade instead of reporting the actual failure:

import grpc
from ansys.mapdl.core import Mapdl
bad_channel = grpc.insecure_channel("willnotwork")
mapdl = Mapdl(channel=bad_channel)

AttributeError: 'NoneType' object has no attribute 'pid'

Similarly, a bad channel with an interceptor also leads to an exception cascade:

import grpc
from ansys.mapdl.core import Mapdl
from grpc import UnaryUnaryClientInterceptor

class PassThru(UnaryUnaryClientInterceptor):
   def intercept_unary_unary(continuation, client_call_details, request):
     return continuation(client_call_details, request)

bad_channel_with_interceptor = grpc.intercept_channel(grpc.insecure_channel("willnotwork"), PassThru())
mapdl = Mapdl(channel=bad_channel_with_interceptor)

AttributeError: 'Channel' object has no attribute 'target'

This pull request adds a check of the presence of a PID before trying to get a status from it, and improves the _channel_str method to try to find nested targets. For both example, the error is now the expected:

ansys.mapdl.core.errors.MapdlConnectionError: Unable to connect to MAPDL gRPC instance at willnotwork.
Reached either maximum amount of connection attempts (5) or timeout (15 s).

[github-actions]

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• BUG
• NEW FEATURE
• Enhancement
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[codecov]

Codecov Report

Merging #1859 (e49dd2f) into main (2d31773) will decrease coverage by 4.80%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1859      +/-   ##
==========================================
- Coverage   85.72%   80.93%   -4.80%     
==========================================
  Files          44       44              
  Lines        7840     7842       +2     
==========================================
- Hits         6721     6347     -374     
- Misses       1119     1495     +376     

[germa89]

Thank you for your contribution @plule-ansys !!

I happily approve. I just have some questions regarding implementation. Regards!

[clatapie]

I agree with @germa89's comments. Apart from that, it looks good to me. 👍
Thank you @plule-ansys!

[germa89]

Merged. Thank you @plule-ansys !! :)