[experimental-feature] Missing features (help wanted!)

[Henry-Hiles]

Hello! This looks really interesting, and I wanted to use it to use the matrix-sdk crate. So, I ran flutter_rust_bridge_codegen integrate, then changed flutter_rust_bridge.yaml to have rust_input: crate:matrix-sdk, but it just says this when I generate:

[2026-01-16T19:15:16.428Z INFO frb_codegen/src/library/commands/fvm.rs:15] Has .fvmrc but no fvm binary installation, thus skip using fvm.
[2026-01-16T19:15:17.021Z WARN frb_codegen/src/library/commands/command_runner.rs:161] command=cd "/home/quadradical/Documents/Code/nexus/rust" && RUSTFLAGS="--cfg frb_expand" "cargo" "expand" "--lib" "--theme=none" "--ugly" "-p" "crate:matrix-sdk" stdout= stderr=error: unexpected prerelease field, expected a version like "1.32"

[0.5s] Parse  
  └── [0.5s] Cargo expand & syn parse                                                                                                                                                                      Error: cargo expand returned empty output

It's quite possible I'm doing something wrong, maybe I need some rust code? I just wanted to translate the library directly and use it, but maybe that's not possible?
What am I doing wrong? Thanks!

[Henry-Hiles]

Interestingly, cargo expand -p matrix-sdk does give an output.

[Henry-Hiles]

Oh, maybe I don't need to put crate:?

[Henry-Hiles]

Yep, that worked!

However, I now have:

The type 'Future' is declared with 0 type parameters, but 1 type arguments were given.
Try adjusting the number of type arguments to match the number of type parameters.

In a lot of the generated stuff.

[Henry-Hiles]

Future here appears to be abstract class Future implements RustOpaqueInterface {}

[Henry-Hiles]

Theres also a few:

'new' can't be used as an identifier because it's a keyword.
Try renaming this to be an identifier that isn't a keyword.

[Henry-Hiles]

So, the issue appears to be shadowing? Maybe the SDK should rename things that has the same name as inbuilt types like Future or new to something else.

[Henry-Hiles]

There is also this:

Error: parse_function halt since stop_on_error=true and see error (function={"namespace":"matrix_sdk::account","owner":{"StructOrEnum":{"impl_ty":"Account","trait_def_name":null}},"sources":["Normal"],"item_fn":"GeneralizedItemFn(name=observe_media_preview_config, vis=Some(Visibility::Public(Pub)), attrs=[# [doc = \" Observes the media preview configuration.\"], # [doc = \"\"], # [doc = \" This value is linked to the [MSC 4278](https://github.com/matrix-org/matrix-spec-proposals/pull/4278) which is still in an unstable state.\"], # [doc = \"\"], # [doc = \" This will return the initial value of the configuration and a stream\"], # [doc = \" that will yield new values as they are received.\"], # [doc = \"\"], # [doc = \" The initial value is the one that was stored in the account data\"], # [doc = \" when the client was started.\"], # [doc = \" and the following code is using a temporary solution until we know which\"], # [doc = \" Matrix version will support the stable type.\"], # [doc = \"\"], # [doc = \" # Examples\"], # [doc = \"\"], # [doc = \" ```no_run\"], # [doc = \" # use futures_util::{pin_mut, StreamExt};\"], # [doc = \" # use matrix_sdk::Client;\"], # [doc = \" # use matrix_sdk::ruma::events::media_preview_config::MediaPreviews;\"], # [doc = \" # use url::Url;\"], # [doc = \" # async {\"], # [doc = \" # let homeserver = Url::parse(\\\"http://localhost:8080\\\")?;\"], # [doc = \" # let client = Client::new(homeserver).await?;\"], # [doc = \" let account = client.account();\"], # [doc = \"\"], # [doc = \" let (initial_config, config_stream) =\"], # [doc = \"     account.observe_media_preview_config().await?;\"], # [doc = \"\"], # [doc = \" println!(\\\"Initial media preview config: {:?}\\\", initial_config);\"], # [doc = \"\"], # [doc = \" pin_mut!(config_stream);\"], # [doc = \" while let Some(new_config) = config_stream.next().await {\"], # [doc = \"     println!(\\\"Updated media preview config: {:?}\\\", new_config);\"], # [doc = \" }\"], # [doc = \" # anyhow::Ok(()) };\"], # [doc = \" ```\"]])"})

Caused by:
    0: when trying to parse DartFn
    1: Unknown ident: Stream

[Henry-Hiles]

This bridge seems to almost get it to work, though, its very close! It's mainly:

• Shadowing
  One option for fixing this could be importing event_handler under a different name, e.g. as eh and using that in the generated code. This won't fix the new ones, but it will fix the Future ones.
• Unknown ident: Stream
  I don't know about this one / what it means.
• Generics:

These functions are ignored because they have generic arguments: `add_event_handler_context`, `add_event_handler`, `add_room_event_handler`, `observe_events`, `observe_room_events`, `register_notification_handler`, `send`, `sync_with_callback`, `sync_with_result_callback`

Any idea how I can fix this? I think some needs to be done in this bridge tool, and maybe some others I will need to override by myself?

[fzyzcjy]

Hi, yes I expect the experimental feature to have some issues parsing corner cases for arbitrary Rust crates. For generics, it is a feature not yet implemented in frb (and is somehow nontrivial). For stream, I guess maybe it somehow conflicts w/ the built-in stream thing. One way may be firstly try to add ignores to the things that frb does not understand and see whether it works.

[Henry-Hiles]

I wonder if something like this would work:

import "package:analyzer/dart/analysis/utilities.dart";
import "package:analyzer/dart/analysis/session.dart";
import "package:analyzer/dart/sdk/sdk.dart";
import "package:analyzer/dart/element/element.dart";

void main() async {
  final reservedKeywords = <String>{
    "abstract","else","import","show","as","enum","in","static","assert","export","interface","super",
    "async","extends","is","switch","await","external","late","sync","break","factory","library","this",
    "case","false","mixin","throw","catch","final","new","true","try","const",
    "for","on","typedef","continue","operator","var","covariant","get","part","void","default",
    "hide","rethrow","while","deferred","if","return","with","do","implements","set"
  };

  final builtins = <String>{};
  builtins.addAll(reservedKeywords);

  final sdk = await FolderBasedDartSdk.defaultSdk;

  void addLibrary(String uri) {
    final lib = sdk.mapDartUri(uri);
    if (lib == null) return;
    final analysisSession = lib.context.analysisSession;
    final libraryElement = analysisSession.getLibraryByUri(uri).element;
    builtins.addAll(libraryElement.exportNamespace.definedNames.keys);
  }

  addLibrary("dart:core");
  addLibrary("dart:async");

  // We now check each new name against this builtins list, and rename it if it conflicts
}

Or something similar in Rust, since I think the generator is fully in Rust?

[Henry-Hiles]

Should I move this to a dedicated Feature Request issue or smth?

[fzyzcjy]

Feel free to have a try, there are many tests to protect the system, thus just ensure all existing tests + new tests pass :)

[Henry-Hiles]

I found another SDK I was able to use where I didn't have to worry about complex bindings like here, so I will close this :)

[fzyzcjy]

Looks great!