Summary

This PR fixes a bug in the Ruff language server where the editor-specified configuration was resolved relative to the configuration directory and not the current working directory.

The existing behavior is confusing given that this config file is specified by the user and is not discovered by Ruff itself. The behavior of resolving this configuration file should be similar to that of the --config flag on the command-line which uses the current working directory:

This creates problems where certain configuration options doesn't work because the paths resolved in that case are relative to the configuration directory and not the current working directory in which the editor is expected to be in. For example, the lint.per-file-ignores doesn't work as mentioned in the linked issue along with exclude, extend-exclude, etc.

fixes: #14282

Test Plan

Using the following directory tree structure:

.
├── .config
│   └── ruff.toml
└── src
    └── migrations
        └── versions
            └── a.py

where, the ruff.toml is:

# 1. Comment this out to test `per-file-ignores`
extend-exclude = ["**/versions/*.py"]

[lint]
select = ["D"]

# 2. Comment this out to test `extend-exclude`
[lint.per-file-ignores]
"**/versions/*.py" = ["D"]

# 3. Comment both `per-file-ignores` and `extend-exclude` to test selection works

And, the content of a.py:

"""Test"""

And, the VS Code settings:

{
  "ruff.nativeServer": "on",
  "ruff.path": ["/Users/dhruv/work/astral/ruff/target/debug/ruff"],
  // For single-file mode where current working directory is `/`
  // "ruff.configuration": "/tmp/ruff-repro/.config/ruff.toml",
  // When a workspace is opened containing this path
  "ruff.configuration": "./.config/ruff.toml",
  "ruff.trace.server": "messages",
  "ruff.logLevel": "trace"
}

I also tested out just opening the file in single-file mode where the current working directory is / in VS Code. Here, the ruff.configuration needs to be updated to use absolute path as shown in the above VS Code settings.