Build type checked bodies for more synthesized declarations #24665
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xymus
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May 10, 2019
…ng of invalid code
When applying a solution to a nil literal of Optional type, we would build a direct reference to Optional<T>.none instead of leaving the NilLiteralExpr in place, because this would generate more efficient SIL that avoided the call to the Optional(nilLiteral: ()) witness. However, a few places in the type checker build type-checked AST, and they build NilLiteralExpr directly. Moving the peephole to SILGen's lowering of NilLiteralExpr allows us to simplify generated SIL even further by eliding an unnecessary metatype value. Furthermore, it allows SILGen to accept NilLiteralExprs that do not have a ConcreteDeclRef set, which makes type-checked AST easier to build.
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.
Similarly to trivial accessors, the body of a synthesized designated initializer override is simple enough that we can build it directly without involving the constraint solver.
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This was referenced May 15, 2019
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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.