[6.3] AST: Properly disallow isa/cast/dyn_cast on Type
#85561
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We currently disallow these by deleting them in the `swift` namespace. This approach has several loopholes, all of which ultimately work because we happen to define specializations of `simplify_type` for `swift::Type`: * `llvm::isa/cast/dyn_cast`. The deleted partial specializations will not be selected because they are not defined in the `llvm` namespace. * The argument is a non-const `Type`. The deleted function templates will not be selected because they all accept a `const Type &`, and there is a better `Y &Val` partial specialization in LLVM. * Other casting function templates such as `isa_and_nonull` and `cast_if_present` are not deleted. Eliminate these loopholes by instead triggering a static assertion failure with a helpful message upon instantiation of `CastInfo` for `swift::Type`. (cherry picked from commit dd5ac83)
AnthonyLatsis
changed the title
TypeType
AnthonyLatsis
changed the title
TypeType
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Explanation:
We currently disallow these by deleting them in the
swiftnamespace. This approach has several loopholes, all of which ultimately work because we happen to define specializations ofsimplify_typeforswift::Type:llvm::isa/cast/dyn_cast. The deleted partial specializations will not be selected because they are not defined in thellvmnamespace.Type. The deleted function templates will not be selected because they all accept aconst Type &, and there is a betterY &Valpartial specialization in LLVM.isa_and_nonullandcast_if_presentare not deleted.Eliminate these loopholes by instead triggering a static assertion failure with a helpful message upon instantiation of
CastInfoforswift::Type.Scope: The only behavioral change here is the replacement of several exact casts that were inadvertently using the aforementioned loopholes with desugaring casts.
Issues: —
Original PRs: AST: Properly disallow isa/cast/dyn_cast on
Type#85487Risk: Low.
Testing:
Reviewers: @hamishknight