Implement get_or_insert for configuration index

crates/ruff_server/src/session/workspace/configuration.rs

@@ -1,6 +1,11 @@
+use anyhow::anyhow;
 use lsp_types::Url;
-use ruff_workspace::resolver::ConfigurationTransformer;
-use std::{collections::BTreeMap, path::PathBuf, sync::Arc};
+use ruff_workspace::resolver::{ConfigurationTransformer, Relativity};
+use std::{
+    collections::BTreeMap,
+    path::{Path, PathBuf},
+    sync::Arc,
+};
 
 #[derive(Default)]
 pub(crate) struct RuffConfiguration {
@@ -16,13 +21,45 @@ pub(super) struct ConfigurationIndex {
 }
 
 impl ConfigurationIndex {
-    pub(super) fn get_or_insert(&mut self, path: &Url) -> Arc<RuffConfiguration> {
-        todo!("impl");
+    pub(super) fn get_or_insert(&mut self, document_url: &Url) -> Arc<RuffConfiguration> {
+        let document_path = document_url
+            .to_file_path()
+            .expect("document URL should be a valid path");
+        let folder = document_path
+            .parent()
+            .expect("document URL should be a file path and have a parent");
+        if let Some(config) = self.index.get(folder) {
+            return config.clone();
+        }
+
+        let config = Arc::new(Self::find_configuration_at_path(folder).unwrap_or_else(|err| {
+            tracing::error!("The following error occurred when trying to find a configuration file at `{}`:\n{err}", document_path.display());
+            tracing::error!("Falling back to default configuration for `{}`", document_path.display());
+            RuffConfiguration::default()
+        }));
+
+        self.index.insert(folder.to_path_buf(), config.clone());
+
+        config
     }
 
     pub(super) fn clear(&mut self) {
         self.index.clear();
     }
+
+    fn find_configuration_at_path(folder: &Path) -> crate::Result<RuffConfiguration> {
+        let pyproject = ruff_workspace::pyproject::find_settings_toml(folder)?
+            .ok_or_else(|| anyhow!("No pyproject.toml/ruff.toml/.ruff.toml file was found"))?;
+        let settings = ruff_workspace::resolver::resolve_root_settings(
+            &pyproject,
+            Relativity::Parent,
+            &LSPConfigTransformer,
+        )?;
+        Ok(RuffConfiguration {
+            linter: settings.linter,
+            formatter: settings.formatter,
+        })
+    }
 }
 
 struct LSPConfigTransformer;