Cannot configure/disable the rust formatter

[marc2332]

Description

Tweaking or disabling the rust formatter config in opencode.json does not make opencode behave differently in any way, it keeps formatting with the built-in default command.

So for example, even with this config:

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": {
    "rustfmt": {
      "disabled": true,
    }
  }
}

Or:

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": {
    "rustfmt": {
      "command": [
        "rustfmt",
        "+nightly-2025-09-25",
        "--error-on-unformatted",
        "--unstable-features",
        "$FILE"
      ],
      "extensions": [".rs"]
    }
  }
}

It keeps formatting with the default command.

Plugins

None I think? just a baremetal opencode config

OpenCode version

1.1.6 (latest as of now)

Steps to reproduce

1. Clone https://github.com/marc2332/opencode-broken-rustfmt
2. Launch opencode
3. Ask: Change the 'nice' text in main.rs to 'Hello, World'
4. See that now opencode has not only changed said text but also formatted both main.rs and other_file.rs even though opencode.json is clearly configured to disable rustfmt

Screenshot and/or share link

https://opncd.ai/share/KO2n2DWl

Operating System

Ubuntu 24.04

Terminal

Wezterm

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Automatic stylistic changes due to linting errors are not ideal #6876: Automatic stylistic changes due to linting errors - reports unwanted formatting changes being applied
• Formatters not running after changes #4051: Formatters not running after changes - reports formatters not being applied/respected in configurations (closed, appears to be regression)

Feel free to ignore if none of these address your specific case.

[cravenceiling]

I think it's because of cargo fmt, try this config

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": {
    "rustfmt": {
      "disabled": true,
    },
    "cargo fmt": {
      "disabled": true
    }
  }
}

it worked for me with your repo.

[marc2332]

I think it's because of cargo fmt, try this config

{
"$schema": "https://opencode.ai/config.json",
"formatter": {
"rustfmt": {
"disabled": true,
},
"cargo fmt": {
"disabled": true
}
}
}

it worked for me with your repo.

Yep! That fixed the issue for me in the repo and in my project, are the docs in https://opencode.ai/docs/formatters/#built-in then wrong/outdated? I am happy to make a PR then.

This was my intended config btw, just with cargo fmt works.

{
  "$schema": "https://opencode.ai/config.json",
  "formatter": {
    "cargo fmt": {
      "command": [
        "rustfmt",
        "+nightly-2025-09-25",
        "--error-on-unformatted",
        "--unstable-features",
        "$FILE"
      ],
      "extensions": [".rs"]
    }
  }
}

[cravenceiling]

I think that's the case, this commit added the cargo fmt support but, as you mention, the docs for this formatter is missing. And of course, I'd say a PR for this is necessary.

[marc2332]

I think that's the case, this commit added the cargo fmt support but, as you mention, the docs for this formatter is missing. And of course, I'd say a PR for this is necessary.

Done! #7383

[rekram1-node]

To those seeing this, note that when this is released the key will be "cargofmt" not "cargo fmt", this is inline with our other configs and I should've caught it in original pr.

Ik this could "break" some configs but given docs were wrong I think it is okay