Create Symbol for unknown symbols (closes #876)

[arporter]

No description provided.

[codecov-commenter]

Codecov Report

Merging #887 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #887   +/-   ##
=======================================
  Coverage   98.54%   98.54%           
=======================================
  Files         143      143           
  Lines       29367    29394   +27     
=======================================
+ Hits        28939    28966   +27     
  Misses        428      428           

Impacted Files	Coverage Δ
src/psyclone/psyir/frontend/fparser2.py	99.04% <100.00%> (-0.01%)	⬇️
src/psyclone/psyir/nodes/node.py	95.74% <100.00%> (-0.03%)	⬇️
src/psyclone/psyir/symbols/datasymbol.py	100.00% <100.00%> (ø)
src/psyclone/psyir/symbols/symbol.py	100.00% <100.00%> (ø)
src/psyclone/psyir/symbols/symboltable.py	100.00% <100.00%> (ø)
...one/tests/psyir/frontend/fparser2_literals_test.py	100.00% <100.00%> (ø)
src/psyclone/tests/psyir/frontend/fparser2_test.py	100.00% <100.00%> (ø)
src/psyclone/transformations.py	99.22% <100.00%> (+<0.01%)	⬆️

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[arporter]

Missed coverage showed that we had duplicated the functionality of generating a Symbol for a kind parameter. I've now removed this duplication. We also had fparser2._get_symbol_table() which has been superseded by Rupert's new node.scope.symbol_table functionality so I've removed that too.

[arporter]

Functionality wise, this is a small change to use Symbol rather than DataSymbol when we encounter a symbol of unknown type. However, this then required generalisation of some functionality (esp. the copy method) and I've removed some code duplication.
Ready for first review from either @sergisiso or @rupertford.

[sergisiso]

@arporter I made a first review of the high-level implementation aspects, I made some suggestions about the interface, but in general I like the simplifications of code that this PR brings (although I need more context regarding the changes of the symbol copy method).

[arporter]

Assuming Travis is happy, this is ready for next review.

[sergisiso]

@arporter I see that the issue mentioned in the title (issue 876) is still not solved with this PR, and in fact there are 2 TODOs still mentioning this issue int he code. So this is just some work needed to do towards solving the issue. Is that right?

[arporter]

No, this should close #876. Let me take a look at the TODOs I've missed...

[arporter]

Well, that was really weird - I appear to have simply not altered the routine that was supposed to be at the heart of this PR! I thought maybe I could blame a merge with master but I've not found any evidence for that. In fact 'fixing' find_or_create_symbol() actually required me to update one of the tests too so it seems unlikely that I ever did it.
Many thanks for spotting this!
Once Travis has reported this should be ready for review.

[sergisiso]

@arporter I removed myself one last unused symbol. This PR is now ready to be merged.