Changes (by Roland Haas):

For grid variables declared PRIVATE in interface.ccl the fully qualified variable name is ThornName::VariableName while for PUBLIC or PROTECTED variables the fully qualified variable name is ImplementationName::VariableName and those forms are what needs to be passed to eg CCTK_VarIndex or CCTK_VarDataPtr.

rdwr.pl seems always use the thorn name, which fails if thorn name and implementation name differ and non-PRIVATE variables are used.

An example is https://bitbucket.org/cactuscode/cactustest/src/master/TestReadWrite/interface.ccl where var1 is of that time since the implementation is TestReadWriteImp. The auto-generated DECLARE_CCTK_ARGUMENTS_TestReadWrite_TestC_A macro contains:

cctki_vi_Var1 = CCTK_VarIndex("testreadwrite::var1");

which uses the thorn name, leading to NULL pointer for var1 even though TestReadWrite_TestC_A declares the variable as WRITES.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2359/declare_cctk_arguments_functionname-does