implement flags semantics for enum

[charles-cooper]

What I did

implement operators so that enums can be used like https://docs.python.org/3/library/enum.html#enum.Flag ("Base class for creating enumerated constants that can be combined using the bitwise operations without losing their Flag membership").

This also enables bitwise and/or operators for uint256.

How I did it

Add BITAND, BITOR to the syntax. Implement codegen for &, |. Add clampers for enums - an enum must be in bound for the # of members the enum has (and also nonzero).

How to verify it

see tests, also check compilation of the following test file

# enum.vy
enum Actions:
    BUY
    SELL

@external
def foo(a: Actions) -> bool:
    return a in (Actions.BUY | Actions.SELL)

# note, bitwise ops work on ints now
@external
def bar(x: uint256, y: uint256) -> uint256:
    return x | y & x

Commit message

implement operators so that enums can be used like Python's `enum.Flag`  
("Base class for creating enumerated constants that can be combined 
 using the bitwise operations without losing their Flag membership").
    
this also enables bitwise and/or operators for uint256.             
    
this commit also adds clampers for enums - an enum must be in bound for  
the number of members the enum has (and also, any enum runtime value
must be nonzero).

Description for the changelog

add flags semantics for enums

Cute Animal Picture

[codecov-commenter]

Codecov Report

Merging #2915 (4efa50a) into master (daeae11) will increase coverage by 0.04%.
The diff coverage is 85.71%.

@@            Coverage Diff             @@
##           master    #2915      +/-   ##
==========================================
+ Coverage   88.30%   88.35%   +0.04%     
==========================================
  Files          96       97       +1     
  Lines       10611    10663      +52     
  Branches     2531     2540       +9     
==========================================
+ Hits         9370     9421      +51     
- Misses        787      791       +4     
+ Partials      454      451       -3     

Impacted Files	Coverage Δ
vyper/builtin_functions/functions.py	92.40% <25.00%> (-0.07%)	⬇️
vyper/semantics/types/user/enum.py	80.00% <75.00%> (-0.71%)	⬇️
vyper/ast/nodes.py	93.66% <100.00%> (-0.43%)	⬇️
vyper/codegen/core.py	84.79% <100.00%> (+0.20%)	⬆️
vyper/codegen/expr.py	84.53% <100.00%> (+0.80%)	⬆️
vyper/codegen/types/types.py	88.74% <100.00%> (+0.39%)	⬆️
vyper/semantics/types/user/__init__.py	100.00% <100.00%> (ø)
vyper/semantics/validation/annotation.py	89.67% <100.00%> (+0.17%)	⬆️
vyper/semantics/validation/utils.py	91.48% <100.00%> (+0.18%)	⬆️
... and 6 more

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[fubuloubu]

Would need to see some more tests about storing and manipulating stored values e.g.:

@external
def addMinter(minter: address):
    assert self.roles[msg.sender] in Roles.ADMIN
    self.roles[minter] |= Roles.MINTER

[charles-cooper]

Would need to see some more tests about storing and manipulating stored values e.g.:

@external
def addMinter(minter: address):
    assert self.roles[msg.sender] in Roles.ADMIN
    self.roles[minter] |= Roles.MINTER

nice catch, see 4efa50a

[charles-cooper]

oh shoot -- i forgot to tag @tserg in the commit message. he wrote a significant portion of the tests for this PR, wrote the docs, and helped update the grammar for the new ops.

[charles-cooper]

fixed the commit message by force pushing from 0b20014 to d675110