This commit switches all of `wasm-bindgen` from the `failure` crate to
`anyhow`. The `anyhow` crate should serve all the purposes that we
previously used `failure` for but has a few advantages:
* It's based on the standard `Error` trait rather than a custom `Fail`
trait, improving ecosystem compatibility.
* We don't need a `#[derive(Fail)]`, which means that's less code to
compile for `wasm-bindgen`. This notably helps the compile time of
`web-sys` itself.
* Using `Result<()>` in `fn main` with `anyhow::Error` produces
human-readable output, so we can use that natively.
This commit is the second, and hopefully last massive, refactor for
using WebIDL bindings internally in `wasm-bindgen`. This commit actually
fully executes on the task at hand, moving `wasm-bindgen` to internally
using WebIDL bindings throughout its code generation, anyref passes,
etc. This actually fixes a number of issues that have existed in the
anyref pass for some time now!
The main changes here are to basically remove the usage of `Descriptor`
from generating JS bindings. Instead two new types are introduced:
`NonstandardIncoming` and `NonstandardOutgoing` which are bindings lists
used for incoming/outgoing bindings. These mirror the standard
terminology and literally have variants which are the standard values.
All `Descriptor` types are now mapped into lists of incoming/outgoing
bindings and used for process in wasm-bindgen. All JS generation has
been refactored and updated to now process these lists of bindings
instead of the previous `Descriptor`.
In other words this commit takes `js2rust.rs` and `rust2js.rs` and first
splits them in two. Interpretation of `Descriptor` and what to do for
conversions is in the binding selection modules. The actual generation
of JS from the binding selection is now performed by `incoming.rs` and
`outgoing.rs`. To boot this also deduplicates all the code between the
argument handling of `js2rust.rs` and return value handling of
`rust2js.rs`. This means that to implement a new binding you only need
to implement it one place and it's implemented for free in the other!
This commit is not the end of the story though. I would like to add a
mdoe to `wasm-bindgen` that literally emits a WebIDL bindings section.
That's left for a third (and hopefully final) refactoring which is also
intended to optimize generated JS for bindings.
This commit currently loses the optimization where an imported is hooked
up by value directly whenever a shim isn't needed. It's planned that
the next refactoring to emit a webidl binding section that can be added
back in. It shouldn't be too too hard hopefully since all the
scaffolding is in place now.
cc #1524
