Arbitrary inner type in named impl key #1658
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This commit refactors `write_...` functions to enable formatting a C++ representation of a `Type` into any generic `impl std::fmt::Write` instead of only supporting formatting into an `OutFile`. This is then used to provide `fn stringify_type`. The new function is not used in this commit, but will become quite handy in a follow-up commit when `inner` type of generics/templates may not necessarily be a simple `std::fmt`-friendly `Type::Ident`. Without the refactored `write_...` APIs, the follow-up would have to split *single* `writeln!` invocations (such as the ones in `fn write_shared_ptr` or `fn write_cxx_vector`) into *multiple* ones - e.g. into: `write!` + `write_type` + `write!` + `write_type` + `writeln!`. The new function is a little bit redundant wrt the already existing `trait ToTypename`, but we can't replace that trait just yet: * The trait has slightly different semantics (formatting not the whole type represented by `self`, but only formatting the inner `T`). * The trait works with `Ident` rather than `Type` (this will change in the follow-up commit mentioned above).
Before this commit `NamedImplKey` could only represent the inner type as
`rust: &'a Ident`. For example, it could represent `Vec<Foo>` but could
not represent `Vec<Box<Foo>>` where the inner type (`Box<Foo>` in our
example) is not a simple identifier.
After this commit `NamedImplKey` is refactored to support an arbitrary
inner type. Note that (to simplify and to minimize risks associated
with this commit) this new ability is not actually used at this point -
it is planned to be used in follow-up commits to incrementally relax
generic type argument restrictions in `syntax/check.rs`.
This commit is quite big, but it seems difficult to extract some changes
to smaller, separate commits, because all of the changes stem from the
refactoring of the `NamedImplKey`. At a high-level this commit contains
the following changes:
1. `syntax/instantiate.rs`: Changing `pub rust: &'a Ident` field of
`NamedImplKey` to `pub inner: &'a Type`. This is the main/root
change in this commit.
2. `gen/src/write.rs`: supporting arbitrary inner types
when writing C++ thunks exposing instantiations/monomorphizations of
templates/generics supported by `cxx`.
* This depends on `fn stringify_type` introduced in
`gen/src/write.rs` in an earlier commit.
* Handling arbitrary inner types *in general* means that we can
delete `enum UniquePtr` which provided handling of two *specific*
inner types.
3. `macro/src/expand.rs`: supporting arbitrary inner types
when writing Rust thunks exposing instantiations/monomorphizations of
templates/generics supported by `cxx`.
* Using `#inner` instead of `#ident` may now (optionally) cover
generic lifetime arguments. This is why this commit also changes
`macro/src/generics.rs`. And this is why we can no longer need
the `ty_generics` field from `struct Impl`.
* One minor functional change here is changing the error messages
so that references to type names are generated purely in the
generated bindings, without depending on `fn display_namespaced`.
4. `syntax/mangle.rs`: supporting mangling of individual types. This
helps to:
* Support the (long-term, not-yet-realized) high-level goal of
actually allowing and using arbitrary inner types
* Deduplicate mangling code details that were somewhat duplicated
in `macro/src/expand.rs` and `gen/src/write.rs`.
5. `syntax/types.rs`: Supporting arbitrary inner types in
* `fn is_maybe_trivial`
* `fn is_local` (this function supports an earlier refactoring
that changed how `cxx` decides whether to provide an *implicit*
impl of a given generic/template instantiation/monomorphization)
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PTAL?
If this PR looks okay, then the next commit/PR (anforowicz@8ab4ecc) should be able to add support for
Vec<Box<T>>(because of howBox<T>is special when evaluating the orphan rule./cc @zetafunction who has kindly provided initial feedback/review at anforowicz#4