nigig-org/REVIEWS/MATRIX_CLIENT_FEATURE_GATE.md

# `matrix_client`: the `native` feature does not do what it says

- **Date:** 2026-08-18
- **Status:** raised, not fixed. This is not my crate and nothing currently
  depends on the broken combination; fixing it blind risks changing
  behaviour someone is relying on.
- **Found while:** measuring what `makepad-table` would cost if it depended
  on `nigig-uikit` for camera and location.

## The defect

`crates/matrix_client/Cargo.toml` declares a feature that gates three heavy
dependencies:

```toml
[features]
default = ["native"]
native = ["dep:tokio", "dep:reqwest", "dep:rusqlite"]
```

The source does **not** gate on that feature. It gates on the target:

```rust
// crates/matrix_client/src/lib.rs
#[cfg(not(target_arch = "wasm32"))]
pub mod auth;
#[cfg(not(target_arch = "wasm32"))]
pub mod client;
// ... and so on for http, persistence, sync_service, worker
```

Two different switches for the same set of modules. On a native target with
the feature turned off, the modules still compile but their dependencies are
absent:

```
cargo check -p matrix_client --no-default-features
  -> 19 errors: unresolved import `reqwest`, cannot find `tokio`,
     unresolved import `rusqlite`
```

26 ungated uses across 7 files:

| File | Uses |
|---|---|
| `worker.rs` | 9 |
| `error.rs` | 4 |
| `persistence.rs` | 4 |
| `sync_service.rs` | 4 |
| `client.rs` | 2 |
| `http.rs` | 2 |
| `types.rs` | 1 |

## What is *not* broken

The wasm path is coherent:

```
cargo check -p matrix_client --no-default-features --target wasm32-unknown-unknown
  -> 0 errors
```

`target_arch = "wasm32"` and the absent dependencies agree there, because on
wasm the `[target.'cfg(not(target_arch = "wasm32"))'.dependencies]` section
is skipped anyway. The only broken combination is **native target with the
feature off**, which nothing in this repo builds and no CI job covers —
which is why it rotted without anyone noticing.

## Correcting an overstatement

I previously said fixing this would "unblock wasm". That was wrong, and I
should have checked before saying it. `nigig-core` has 8 wasm errors of its
own that have nothing to do with `matrix_client`:

```
cargo check -p nigig-core --no-default-features --target wasm32-unknown-unknown
  -> 8 errors: cannot find function `spawn` in module `crate::platform`
```

Fixing `matrix_client` moves nobody closer to a wasm build on its own.

## Why it was not fixed here

It buys the thing that surfaced it precisely nothing. `makepad-table` wanted
`nigig-uikit` for its camera and location widgets, and `camera_widget`
imports exactly two items from `nigig-core`:

```rust
use nigig_core::syncing::{send_geocode_request, request_map_tile, ...};
```

Both call `spawn_async`, which *is* the shared Tokio runtime, and
`send_geocode_request` makes an HTTPS call to Nominatim. So the camera widget
requires `nigig-core/native` by its own nature. `matrix_client` sits on the
same flag: making it honour the feature would let *it* build without tokio,
but `nigig-uikit` turns tokio straight back on through `nigig-core`. Net
saving for that use case: zero.

Measured, so the numbers are not guesses:

| Configuration | Crates in the tree |
|---|---|
| `makepad-widgets` alone | 88 |
| `+ nigig-uikit` | 274 |
| `matrix_client` with `native` | 199 |
| `matrix_client` without `native` (if it compiled) | 140 |

## Two ways to fix it

**A. Make the source honour the feature.** Change 26 sites from
`#[cfg(not(target_arch = "wasm32"))]` to `#[cfg(feature = "native")]`, and
move the dependencies out of the target section into the plain one, where
`optional = true` is what decides. This is the honest reading of what the
feature claims. It is also the version that could change behaviour for a
native build that somehow relied on the modules existing without the
dependencies — none exists today, but the check is a compile, not a test.

**B. Delete the feature.** If `matrix_client` is native-only in practice —
and the 26 sites say it is — then `native` is a claim the crate does not
honour, and removing it is more truthful than a flag nobody can use. The
dependencies stay non-optional in the target section, where the wasm split
already works.

B is smaller and matches observed reality. A is right if a wasm or
dependency-light build is actually wanted, in which case `nigig-core`'s 8
errors need fixing too, and that is the larger piece.

## Whichever is chosen, it needs a gate

There is no CI job for `matrix_client`. A feature that nothing builds is a
feature that breaks silently, which is exactly what happened. One line in a
workflow:

```yaml
- name: The native feature means what it says
  run: cargo check -p matrix_client --no-default-features
```

That step fails today. It should be added with the fix, not before it.