Accessors logically belong to their storage and can be synthesized
on the fly, so removing them from the members list eliminates one
source of mutability (but doesn't eliminate it; there are also
witnesses for derived conformances, and implicit constructors).
Since a few ASTWalker implementations break in non-trivial ways when
the traversal is changed to visit accessors as children of the storage
rather than peers, I hacked up the ASTWalker to optionally preserve
the old traversal order for now. This is ugly and needs to be cleaned up,
but I want to avoid breaking _too_ much with this commit.
This includes all synthesized accessors except for lazy getters
and observer setters.
Building checked AST has certain advantages:
- It is faster, avoiding the need to create and solve ConstraintSystems
or performing various diagnostic and semantic walks over the AST.
- It allows us to postpone delayed body synthesis until needed in SILGen,
instead of having to walk a list of "external declarations" in Sema.
It also unblocks lazier conformance checking. Now that SILGen can
trigger conformance checking on its own, we need to be able to
synthesize bodies of accessors that witness protocol requirements.
This will allow us to eventually remove Sema's "used conformances"
list.
Note that for now, various utility functions in CodeSynthesis.cpp are
used for both checked and unchecked function bodies, so they take a
'typeChecked' boolean parameter that complicates some logic more than
necessary. Once the remaining body synthesizers are refactored to
build type-checked AST, the 'typeChecked' flag will go away.
