generated ASDL code should support garbage collection

[andychu]

• Related to classes and ASDL types need correct GC field masks #1164

Parts

• code generated by build/dev.sh oil-asdl-to-cpp-gc should compile
• asdl/runtime.gc.{h,cc} # this needs to be correct
  • hnode stuff
• asdl/gc_test.cc -- this should be able to pretty print

[andychu]

Progress: a1120f2

[andychu]

Issue with generated code. There are 2 allocations in initializer lists. Doesn't that break a GC invariant?

class lvalue__Named : public lvalue_t {                                                                                                                                                                            
 public:                                                                                                                                                                                                           
  lvalue__Named() : type_tag_(static_cast<uint16_t>(lvalue_e::Named)),                                                                                                                                             
                name(NewStr("")), spids(new List<int>()) {                                                                                                                                                         
  }  

[andychu]

I think we need a plain old function wrapper for every type. Just like NewStr / NewList / NewDict functions, we need new_lvalue__Named() ?

[andychu]

https://oilshell.zulipchat.com/#narrow/stream/121539-oil-dev/topic/Targeting.20ASDL.20to.20New.20GC.20Runtime

At least two parts to this task:

• field masks which I noted on classes and ASDL types need correct GC field masks #1164
• The f(g()) "missing stack root" problem. The ASDL pretty printer does this all over the place.
  • Variant: the constructor(g()) missing stack root problem. I think we need to generate separate methods
  • related: mycpp tool improvements #568

[andychu]

mycpp related issue:

• mycpp should generate field masks for classes (e.g. DirStack in examples/scoped_resource) #1322

[andychu]

Released: https://www.oilshell.org/release/0.12.7/