Expression: Expression cloning and mapper tests

[mlange05]

Note: Only for testing so far ...

The primary intention behind this PR is to increase test coverage of the expression mappers and rigorously duplicate symbols when expression mappers (LokiIdentityMapper and SubstituteExpressionMapper). It also fixes a bunch of other issues along the way that this threw up and now fixes #379 .

In a little more detail:

• Add dedicated tests for expression walker (via ExpressionRetriever) and the mappers LokitIdentityMapper and SubstituteExrpressionMapper
• Lint-clean the expression tests directory
• Remove the now redundant invalidate_source argument from Loki mappers (we do not store source on expressions anymore)
  • Fix the resulting issue in recursive_expression_map_update by checking for ancestry of SubstituteExpressionMapper before handing the map to constructors
• Duplicate symbols in LokiIdentityMapper and SubstotuteExpressionMapper
  • Add a local _rebuild() method the base class that check for scope-carrying and scope-free symbols
  • Add a dedicated symbols test for correct re-instatiation of all our symbols types and fix the ones that do not behave
  • Always update the symbol after enrichment, to ensure that DeferredTypeSymbols are replaced with ProcedureTypeSymbols in CallStatement.name after the type updates.

[github-actions]

Documentation for this branch can be viewed at https://sites.ecmwf.int/docs/loki/419/index.html

[codecov]

Codecov Report

Attention: Patch coverage is 98.62069% with 2 lines in your changes missing coverage. Please review.

Project coverage is 93.11%. Comparing base (899f5ac) to head (193742c).
Report is 41 commits behind head on main.

Files with missing lines	Patch %	Lines
loki/expression/mappers.py	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #419      +/-   ##
==========================================
+ Coverage   93.04%   93.11%   +0.06%     
==========================================
  Files         198      200       +2     
  Lines       39320    39550     +230     
==========================================
+ Hits        36587    36827     +240     
+ Misses       2733     2723      -10     

Flag	Coverage Δ
lint_rules	96.39% <ø> (ø)
loki	93.06% <98.62%> (+0.06%)	⬆️

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[mlange05]

FYI: Checking with ec-physics regression locall, there is no noticeable performance impact on loki processing speed from this.

[reuterbal]

This is fantastic, many thanks. I also appreciate the number of clean-ups along the way, like the stray source handling for expression nodes.

Only comment is a suggestion for a stricter test, but otherwise nothing to add.

@Andrew-Beggs-ECMWF would you mind confirming if this resolves your issue?

[Andrew-Beggs-ECMWF]

This is fantastic, many thanks. I also appreciate the number of clean-ups along the way, like the stray source handling for expression nodes.

Only comment is a suggestion for a stricter test, but otherwise nothing to add.

@Andrew-Beggs-ECMWF would you mind confirming if this resolves your issue?

I'd like to reiterate Balthasar's comments, I'm really please to see this patch. Thank you for doing it! 😁

I can confirm all my tests now pass!