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Use FfiConverter for metadata generation/storage #1469

Merged
merged 6 commits into from
Mar 31, 2023
Merged

Use FfiConverter for metadata generation/storage #1469

merged 6 commits into from
Mar 31, 2023

Commits on Mar 31, 2023

  1. New system for interface metadata 

    - Added the `uniffi_core::metadata` module, which provides a system for
  building metadata buffers using const code.
- Added the `FfiConverter::TYPE_ID_META` const, which holds metadata
  to identify the type.
- Made the proc-macros generate use the new system to generate metadata
  consts, then export them using static variables.
- Removed the current code to generate/store metadata based on the syn
  parsing.
- Removed the type assertions and the requirement for a `uniffi_types`
  module.  We don't need them now that we`re getting the type ids from
  the type itself.
- Made the `FnMetadata.throws` field a Type rather than a String.
- Calculate module paths with the `module_path!()` macro.  This means we
  get accurate module paths without nightly.  Changed mod_path to be a
  String, rather than a Vec since this is what `module_path!()` outputs.
- Added code to strip the `r#` part out of raw idents before serializing
  it into the metadata.
- Replaced the `collect_params()` function with the `ScaffoldingBits`
  struct.  There was too much complexity for a single function -- for
  example unzip() only works with pairs, not 3-tuples.

In general, the new metadata system is more reliable doing everything in
the proc-macros.  Proc-macros can only see the type identifiers, but
they don't anything about the underlying type, since users can rename
types with type aliases.  It's also simpler since you don't have to walk
the AST so much.

One TODO is getting checksum working again.  One limitation of the const
code is that we can't use it to generate function identifiers.
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  2. Added return handling to FfiConverter 

    Added the `FfiConverter::lower_return` method.  This is like `lower()`
but specialized for scaffolding returns.  This allows us to always use a
single function to handle scaffolding calls, rather than
`call_with_output` or `call_with_result` depending on if the return type
is a `Result<>` or not.

Having a single code-path for return handling simplifies the code
generation, especially the macros.  We no longer need to try to parse
`Result<>` type names.  This is especially useful for crates that
type-alias their `Result<>` types.

Updated the async code to work with the new system.  Now `RustFuture`
only needs 1 generic argument.

Updated `object_references.md` and removed example code that's no longer
valid.  Replaced it with higher-level descriptions of what's going on,
hopefully this will stay not get out of date as quickly.
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  3. Fixes from review.

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  4. Refactoring the rustcall/rustfuture code 

    Define a lower-level version of `rust_call()` that
`uniffi_rustfuture_poll` can use without going through so many hoops.
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  5. New checksum handling 

    Updated the checksum handling to work with the new proc-macro metadata
system.  Now that the metadata is calcualted using const functions
rather than inside the macro code, we don't have a way to include the
checksum in the exported symbol name.

Instead, calculate the metadata and store it as its own symbol.  Then
the bindings code checks the checksums on startup as well as the
contract ABI version.  One nice aspect of this is that we can output a
nicer error message than just "linker error".

- Added scripts to test this.
- Added flag to allow FFIFunctions to not always have the `&mut
  RustCallStatus` arg.
- Changed the contract version to be a u32 rather than a &str.  This
  simplifies the bindings code.
- Added the `uniffi_meta::ffi_names` module.  This contains the
  canonical code to generate ffi symbol names.
- Use the module path that we calculate in the proc-macro when
  generating the metadata rather than calling `module_path!()`.
  `module_path!()` returns the full module path, but it's more important
  that our metadata agrees with the module path we used whene generating
  the scaffolding.
- Reworked the `metadata::reader` code
- Make `uniffi_meta` depend on `uniffi_core`.  I was trying to avoid
  this, but uniffi_core is where the metadata buffer code lives and I
  don't want to duplicate it.  Maybe we could make this a separate
  crate, but it doesn't seem worth it yet since `uniffi_core`
  is fairly small.
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  6. Fixes from review

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