Format on Save still fails silently if mode is set to `modifications`

[Scotchester]

Ruff seems to have added support for range formatting in astral-sh/ruff#9733 and/or astral-sh/ruff-lsp#373, but the VS Code extension is still silently failing to format on save if I try to use "editor.formatOnSaveMode": "modifications". Is there something else I'm missing about how to configure this correctly?

VS Code version: 1.114.0
Ruff extension version: 2026.38.0

[MichaReiser]

Can you share some example code that you would expect to be formatted? Note, that the formatter doesn't format code with syntax errors.

[Scotchester]

Sure thing. I was just starting on a script to interact with the GitHub API. I had copied the constant declarations at the top from another source that used single quotes on the strings, and saving the file does not convert them to double quotes. This project is still using all of the default Ruff settings.

import os

GH_USERNAME = os.getenv('GH_USERNAME')
GH_TOKEN = os.getenv('GH_TOKEN')


def main():
    print("Hello, world!")


if __name__ == "__main__":
    main()

[MichaReiser]

Does it format the file as expected when running "Format document" manually?

Can you enable logging between VS Code and Ruff, by adding the following to your configuration (or changing ruff.trace.server in VS Code's settings editor to messages):

{
  "ruff.trace.server": "messages"
}

And then share the output of Output (one of the bottom panels) -> ty language server (dropdown in the panel header) here? Does VS Code send a format request to Ruff?

[Scotchester]

Yes, it formats as expected if I run "Format document" manually (I assume because that always formats the whole file).

Here is the output from the trace when I hit save:

[Trace - 12:33:01 PM] Sending request 'textDocument/codeAction - (1269)'.
[Trace - 12:33:01 PM] Received response 'textDocument/codeAction - (1269)' in 2ms.
[Trace - 12:33:01 PM] Sending request 'codeAction/resolve - (1270)'.
[Trace - 12:33:01 PM] Received response 'codeAction/resolve - (1270)' in 1ms.
[Trace - 12:33:01 PM] Sending request 'textDocument/codeAction - (1271)'.
[Trace - 12:33:01 PM] Received response 'textDocument/codeAction - (1271)' in 1ms.
[Trace - 12:33:01 PM] Sending request 'codeAction/resolve - (1272)'.
[Trace - 12:33:01 PM] Received response 'codeAction/resolve - (1272)' in 0ms.

And the output if I manually run "Format document":

[Trace - 12:33:49 PM] Sending request 'textDocument/formatting - (1273)'.
[Trace - 12:33:49 PM] Received response 'textDocument/formatting - (1273)' in 1ms.
[Trace - 12:33:49 PM] Sending notification 'textDocument/didChange'.
[Trace - 12:33:49 PM] Sending request 'textDocument/diagnostic - (1274)'.
[Trace - 12:33:49 PM] Received response 'textDocument/diagnostic - (1274)' in 2ms.

[MichaReiser]

This suggests that the issue is with your VS Code configuration or that it picks some old version of Ruff.

Can you share your VS Code configuration? What's the output of the Ruff output panel (it should log the Ruff version)

[Scotchester]

It's using the version of ruff that is bundled with the extension, which is 0.15.7. Here is the Ruff output:

2026-04-06 12:35:04.179 [info] Name: Ruff
2026-04-06 12:35:04.179 [info] Module: ruff
2026-04-06 12:35:04.179 [info] Python extension loading
2026-04-06 12:35:04.179 [info] Waiting for interpreter from python extension.
2026-04-06 12:35:04.431 [info] Python extension loaded
2026-04-06 12:35:04.432 [info] Using interpreter: /usr/bin/python3
2026-04-06 12:35:04.435 [info] Workspace settings for /Users/scott/dev/gh-activity: {
    "nativeServer": "auto",
    "cwd": "/Users/scott/dev/gh-activity",
    "workspace": "file:///Users/scott/dev/gh-activity",
    "path": [],
    "ignoreStandardLibrary": true,
    "interpreter": [
        "/usr/bin/python3"
    ],
    "configuration": null,
    "importStrategy": "fromEnvironment",
    "codeAction": {
        "fixViolation": {
            "enable": true
        },
        "disableRuleComment": {
            "enable": true
        }
    },
    "lint": {
        "enable": true,
        "run": "onType",
        "args": [],
        "preview": null,
        "select": null,
        "extendSelect": null,
        "ignore": null
    },
    "format": {
        "args": [],
        "preview": null,
        "backend": "internal"
    },
    "enable": true,
    "organizeImports": true,
    "fixAll": true,
    "showNotifications": "off",
    "exclude": null,
    "lineLength": null,
    "configurationPreference": "editorFirst",
    "showSyntaxErrors": true,
    "logLevel": null,
    "logFile": null
}
2026-04-06 12:35:04.436 [info] Global settings: {
    "nativeServer": "auto",
    "cwd": "/",
    "workspace": "/",
    "path": [],
    "ignoreStandardLibrary": true,
    "interpreter": [],
    "configuration": null,
    "importStrategy": "fromEnvironment",
    "codeAction": {
        "fixViolation": {
            "enable": true
        },
        "disableRuleComment": {
            "enable": true
        }
    },
    "lint": {
        "enable": true,
        "run": "onType",
        "args": []
    },
    "format": {
        "args": [],
        "backend": "internal"
    },
    "enable": true,
    "organizeImports": true,
    "fixAll": true,
    "showNotifications": "off",
    "configurationPreference": "editorFirst",
    "showSyntaxErrors": true
}
2026-04-06 12:35:04.514 [info] Falling back to bundled executable: /Users/scott/.vscode/extensions/charliermarsh.ruff-2026.38.0-darwin-arm64/bundled/libs/bin/ruff
2026-04-06 12:35:04.727 [info] Resolved 'ruff.nativeServer: auto' to use the native server
2026-04-06 12:35:04.729 [info] Found Ruff 0.15.7 at /Users/scott/.vscode/extensions/charliermarsh.ruff-2026.38.0-darwin-arm64/bundled/libs/bin/ruff
2026-04-06 12:35:04.729 [info] Server run command: /Users/scott/.vscode/extensions/charliermarsh.ruff-2026.38.0-darwin-arm64/bundled/libs/bin/ruff server
2026-04-06 12:35:04.729 [info] Server: Start requested.

I believe these are all of the potentially relevant settings that have entries in my settings.json:

  "[python]": {
    "editor.codeActionsOnSave": {
      "source.fixAll": "explicit",
      "source.organizeImports": "explicit",
    },
    "editor.defaultFormatter": "charliermarsh.ruff",
    "editor.formatOnSave": true,
  },
  "editor.defaultFormatter": "esbenp.prettier-vscode",
  "editor.formatOnSave": true,
  "editor.formatOnSaveMode": "modifications",
  "ruff.trace.server": "messages",

Is there any other configuration it might be helpful to share?

[MichaReiser]

Is your file tracked by source control?

Note that modifications are defined by your source control provider, for example, changes as detected by Git, and that without changes in source control, no modified lines are formatted. The Quick Diff indicator on the left side of the editor is a reliable hint for what lines will be formatted.