[ec1dev]

Fixes #3951.

A PlotShape without a display (ShapePlotData) had no variable until variable() was called, while one with a display (ShapePlot) starts with v, which is also what the PlotShape docs say. So nrn_get_plotshape_varname gave "", and ps.plot(pyplot) or ps.plot(plotly) without a display didn't color the shape by v. ShapePlotData now starts with v, looked up the same way as in ShapePlotImpl (hoc_table_lookup("v", hoc_built_in_symlist)).

So a no-display ps.plot(...) without variable() is now colored by v, as with a display. For a default PlotShape(False), get_plotshape_data gives ('', None, -80.0, 40.0) on 9.1.0.dev46 and ('v', None, -80.0, 40.0) with this, the same as after ps.variable("v").

test/api/plotshape_interface.cpp now checks the default name too. It fails without the change ("FAIL: default varname") and passes with it.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 68.68%. Comparing base (783998a) to head (a29c498).

Files with missing lines	Patch %	Lines
src/nrniv/shapeplt.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3954   +/-   ##
=======================================
  Coverage   68.68%   68.68%           
=======================================
  Files         716      716           
  Lines      115559   115560    +1     
=======================================
+ Hits        79369    79372    +3     
+ Misses      36190    36188    -2     

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