future_to_promise: accept JsError instead of anyhow::Error

`future_to_promise` is responsible for taking the `Future`s that result from
running rust code, and wrapping them into javascript Promises. Currently, it
takes a `Result<T, anyhow::Error>`, meaning that all our errors get
wrapped into `anyhow::Error`; `future_to_promise` then converts that
`anyhow::Error` into a `JsError`.

However:

 1. This doesn't work terribly well under matrix-rust-sdk 0.12.0, because some
    of our error types no longer implement `Send + Sync`, which means that
    `anyhow::Error::from()` will no longer accept them.

 2. It's redundant anyway. It turns out that almost all of the async blocks we
    pass to `future_to_promise` are just as happy to directly return a
    `JsError`, thus cutting out the middleman. And
    `JsError::from(std::error::Error)` doesn't require that the error be `Send
    + Sync`.

The only remaining exception is in `verification.rs`, which is soon fixed up.

Author: richvdh

src/future.rs

@@ -1,18 +1,29 @@
 use std::future::Future;
 
-use futures_util::TryFutureExt;
 use js_sys::Promise;
 use wasm_bindgen::{JsError, JsValue, UnwrapThrowExt};
 use wasm_bindgen_futures::spawn_local;
 
+/**
+ * Convert a Rust [`Future`] which returns [`Result<T, JsError>`] into a
+ * Javascript [`Promise`] which either resolves with an object of type `T`,
+ * or rejects with an error of type [`Error`].
+ *
+ * [`Error`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error
+ */
 pub(crate) fn future_to_promise<F, T>(future: F) -> Promise
 where
-    F: Future<Output = Result<T, anyhow::Error>> + 'static,
+    F: Future<Output = Result<T, JsError>> + 'static,
     T: Into<JsValue>,
 {
-    future_to_promise_with_custom_error(future.map_err(|error| JsError::new(&error.to_string())))
+    future_to_promise_with_custom_error(future)
 }
 
+/**
+ * Convert a Rust [`Future`] which returns [`Result<T, E>`] into a
+ * Javascript [`Promise`] which either resolves with an object of type `T`,
+ * or rejects with an error of type `E`.
+ */
 pub(crate) fn future_to_promise_with_custom_error<F, T, E>(future: F) -> Promise
 where
     F: Future<Output = Result<T, E>> + 'static,

src/verification.rs

@@ -1034,9 +1034,7 @@ impl VerificationRequest {
                 .transpose()
             {
                 Ok(a) => Ok(a),
-                Err(_) => {
-                    Err(anyhow::Error::msg("Failed to build the outgoing verification request"))
-                }
+                Err(_) => Err(JsError::new("Failed to build the outgoing verification request")),
             }
         })
     }