feat: replace AnnAssign with VariableDef

[tserg]

What I did

Improve conversion of Python AST to Vyper AST.

How I did it

Replace Python's AnnAssign nodes for contract variable declarations with a newly introduced VariableDef Vyper AST node.

The VariableDef has four three additional attributes, which are set during semantics validation.

• is_state_variable
• is_constant
• is_public
• is_immutable

How to verify it

See updated tests.

Commit message

feat: add VariableDef Vyper AST node

Adds a VariableDef Vyper AST node for variable declarations.

Description for the changelog

Add VariableDef Vyper AST node

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[codecov-commenter]

Codecov Report

Merging #2881 (958fba6) into master (aac0be8) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2881      +/-   ##
==========================================
+ Coverage   88.13%   88.16%   +0.02%     
==========================================
  Files          97       97              
  Lines       10802    10820      +18     
  Branches     2562     2569       +7     
==========================================
+ Hits         9520     9539      +19     
+ Misses        824      823       -1     
  Partials      458      458              

Impacted Files	Coverage Δ
vyper/semantics/types/bases.py	84.50% <ø> (ø)
vyper/semantics/types/utils.py	89.76% <ø> (ø)
vyper/ast/expansion.py	94.11% <100.00%> (ø)
vyper/ast/folding.py	91.73% <100.00%> (ø)
vyper/ast/nodes.py	92.84% <100.00%> (+0.22%)	⬆️
vyper/ast/utils.py	69.69% <100.00%> (+5.41%)	⬆️
vyper/builtin_functions/utils.py	100.00% <100.00%> (ø)
vyper/codegen/global_context.py	74.78% <100.00%> (ø)
vyper/semantics/types/function.py	87.12% <100.00%> (ø)
vyper/semantics/types/user/interface.py	83.19% <100.00%> (ø)
... and 4 more

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[charles-cooper]

from_VariableDef could probably be renamed to something like getter_from_VariableDef

[charles-cooper]

looks quite nice. my only question is whether local variables should also be defined with VariableDef (breaking from python) or stay as AnnAssign. the extra fields on VariableDef (is_constant etc) make a lot of sense on contract variables; not as much on local variables.

[tserg]

looks quite nice. my only question is whether local variables should also be defined with VariableDef (breaking from python) or stay as AnnAssign. the extra fields on VariableDef (is_constant etc) make a lot of sense on contract variables; not as much on local variables.

I think another approach, taking from solc-typed-ast, is to consolidate is_constant and is_immutable into a mutability attribute that takes a VariableMutability enum of either (1) MUTABLE; (2) IMMUTABLE; or (3) CONSTANT. This would make it more relevant for local variables.

I think it would be clearer and more consistent to have both contract and local variable declarations be of VariableDef, than for local variable declarations to be of AnnAssign node type alongside e.g. struct/event members.