[ty] Use python version and path from Python extension (#19012)

Cargo.lock

@@ -4307,6 +4307,7 @@ dependencies = [
  "lsp-types",
  "ruff_db",
  "ruff_notebook",
+ "ruff_python_ast",
  "ruff_source_file",
  "ruff_text_size",
  "rustc-hash",

crates/ty/src/lib.rs

@@ -121,17 +121,17 @@ fn run_check(args: CheckCommand) -> anyhow::Result<ExitStatus> {
         None => ProjectMetadata::discover(&project_path, &system)?,
     };
 
-    let options = args.into_options();
-    project_metadata.apply_options(options.clone());
     project_metadata.apply_configuration_files(&system)?;
 
+    let project_options_overrides = ProjectOptionsOverrides::new(config_file, args.into_options());
+    project_metadata.apply_overrides(&project_options_overrides);
+
     let mut db = ProjectDatabase::new(project_metadata, system)?;
 
     if !check_paths.is_empty() {
         db.project().set_included_paths(&mut db, check_paths);
     }
 
-    let project_options_overrides = ProjectOptionsOverrides::new(config_file, options);
     let (main_loop, main_loop_cancellation_token) =
         MainLoop::new(project_options_overrides, printer);
 

crates/ty_project/src/db.rs

@@ -3,6 +3,7 @@ use std::panic::{AssertUnwindSafe, RefUnwindSafe};
 use std::sync::Arc;
 use std::{cmp, fmt};
 
+pub use self::changes::ChangeResult;
 use crate::metadata::settings::file_settings;
 use crate::{DEFAULT_LINT_REGISTRY, DummyReporter};
 use crate::{ProgressReporter, Project, ProjectMetadata};

crates/ty_project/src/db/changes.rs

@@ -41,8 +41,6 @@ impl ProjectDatabase {
         let project_root = project.root(self).to_path_buf();
         let config_file_override =
             project_options_overrides.and_then(|options| options.config_file_override.clone());
-        let options =
-            project_options_overrides.map(|project_options| project_options.options.clone());
         let program = Program::get(self);
         let custom_stdlib_versions_path = program
             .custom_stdlib_search_path(self)
@@ -218,16 +216,16 @@ impl ProjectDatabase {
             };
             match new_project_metadata {
                 Ok(mut metadata) => {
-                    if let Some(cli_options) = options {
-                        metadata.apply_options(cli_options);
-                    }
-
                     if let Err(error) = metadata.apply_configuration_files(self.system()) {
                         tracing::error!(
                             "Failed to apply configuration files, continuing without applying them: {error}"
                         );
                     }
 
+                    if let Some(overrides) = project_options_overrides {
+                        metadata.apply_overrides(overrides);
+                    }
+
                     match metadata.to_program_settings(self.system(), self.vendored()) {
                         Ok(program_settings) => {
                             let program = Program::get(self);

crates/ty_project/src/lib.rs

@@ -1,7 +1,7 @@
 use crate::glob::{GlobFilterCheckMode, IncludeResult};
 use crate::metadata::options::{OptionDiagnostic, ToSettingsError};
 use crate::walk::{ProjectFilesFilter, ProjectFilesWalker};
-pub use db::{CheckMode, Db, ProjectDatabase, SalsaMemoryDump};
+pub use db::{ChangeResult, CheckMode, Db, ProjectDatabase, SalsaMemoryDump};
 use files::{Index, Indexed, IndexedFiles};
 use metadata::settings::Settings;
 pub use metadata::{ProjectMetadata, ProjectMetadataError};

crates/ty_project/src/metadata.rs

@@ -7,6 +7,7 @@ use thiserror::Error;
 use ty_python_semantic::ProgramSettings;
 
 use crate::combine::Combine;
+use crate::metadata::options::ProjectOptionsOverrides;
 use crate::metadata::pyproject::{Project, PyProject, PyProjectError, ResolveRequiresPythonError};
 use crate::metadata::value::ValueSource;
 pub use options::Options;
@@ -276,6 +277,10 @@ impl ProjectMetadata {
             .to_program_settings(self.root(), self.name(), system, vendored)
     }
 
+    pub fn apply_overrides(&mut self, overrides: &ProjectOptionsOverrides) {
+        self.options = overrides.apply_to(std::mem::take(&mut self.options));
+    }
+
     /// Combine the project options with the CLI options where the CLI options take precedence.
     pub fn apply_options(&mut self, options: Options) {
         self.options = options.combine(std::mem::take(&mut self.options));

crates/ty_project/src/metadata/options.rs

@@ -121,6 +121,9 @@ impl Options {
                         ValueSource::File(path) => PythonVersionSource::ConfigFile(
                             PythonVersionFileSource::new(path.clone(), ranged_version.range()),
                         ),
+                        ValueSource::PythonVSCodeExtension => {
+                            PythonVersionSource::PythonVSCodeExtension
+                        }
                     },
                 });
 
@@ -140,6 +143,7 @@ impl Options {
                 ValueSource::File(path) => {
                     SysPrefixPathOrigin::ConfigFileSetting(path.clone(), python_path.range())
                 }
+                ValueSource::PythonVSCodeExtension => SysPrefixPathOrigin::PythonVSCodeExtension,
             };
 
             Some(PythonEnvironment::new(
@@ -702,6 +706,10 @@ impl Rules {
                     let lint_source = match source {
                         ValueSource::File(_) => LintSource::File,
                         ValueSource::Cli => LintSource::Cli,
+
+                        ValueSource::PythonVSCodeExtension => {
+                            unreachable!("Can't configure rules from the Python VSCode extension")
+                        }
                     };
                     if let Ok(severity) = Severity::try_from(**level) {
                         selection.enable(lint, severity, lint_source);
@@ -854,6 +862,7 @@ fn build_include_filter(
                             Severity::Info,
                             "The pattern was specified on the CLI",
                         )),
+                        ValueSource::PythonVSCodeExtension => unreachable!("Can't configure includes from the Python VSCode extension"),
                     }
                 })?;
         }
@@ -936,6 +945,9 @@ fn build_exclude_filter(
                             Severity::Info,
                             "The pattern was specified on the CLI",
                         )),
+                        ValueSource::PythonVSCodeExtension => unreachable!(
+                            "Can't configure excludes from the Python VSCode extension"
+                        )
                     }
                 })?;
         }
@@ -1497,8 +1509,11 @@ impl OptionDiagnostic {
 /// This is a wrapper for options that actually get loaded from configuration files
 /// and the CLI, which also includes a `config_file_override` option that overrides
 /// default configuration discovery with an explicitly-provided path to a configuration file
+#[derive(Debug, Default, PartialEq, Eq, Clone)]
 pub struct ProjectOptionsOverrides {
     pub config_file_override: Option<SystemPathBuf>,
+    pub fallback_python_version: Option<RangedValue<PythonVersion>>,
+    pub fallback_python: Option<RelativePathBuf>,
     pub options: Options,
 }
 
@@ -1507,8 +1522,22 @@ impl ProjectOptionsOverrides {
         Self {
             config_file_override,
             options,
+            ..Self::default()
         }
     }
+
+    pub fn apply_to(&self, options: Options) -> Options {
+        let mut combined = self.options.clone().combine(options);
+
+        // Set the fallback python version and path if set
+        combined.environment.combine_with(Some(EnvironmentOptions {
+            python_version: self.fallback_python_version.clone(),
+            python: self.fallback_python.clone(),
+            ..EnvironmentOptions::default()
+        }));
+
+        combined
+    }
 }
 
 trait OrDefault {

crates/ty_project/src/metadata/value.rs

@@ -27,6 +27,9 @@ pub enum ValueSource {
     /// The value comes from a CLI argument, while it's left open if specified using a short argument,
     /// long argument (`--extra-paths`) or `--config key=value`.
     Cli,
+
+    /// The value comes from an LSP client configuration.
+    PythonVSCodeExtension,
 }
 
 impl ValueSource {
@@ -34,6 +37,7 @@ impl ValueSource {
         match self {
             ValueSource::File(path) => Some(&**path),
             ValueSource::Cli => None,
+            ValueSource::PythonVSCodeExtension => None,
         }
     }
 
@@ -105,6 +109,14 @@ impl<T> RangedValue<T> {
         Self::with_range(value, ValueSource::Cli, TextRange::default())
     }
 
+    pub fn python_extension(value: T) -> Self {
+        Self::with_range(
+            value,
+            ValueSource::PythonVSCodeExtension,
+            TextRange::default(),
+        )
+    }
+
     pub fn with_range(value: T, source: ValueSource, range: TextRange) -> Self {
         Self {
             value,
@@ -327,6 +339,10 @@ impl RelativePathBuf {
         Self::new(path, ValueSource::Cli)
     }
 
+    pub fn python_extension(path: impl AsRef<SystemPath>) -> Self {
+        Self::new(path, ValueSource::PythonVSCodeExtension)
+    }
+
     /// Returns the relative path as specified by the user.
     pub fn path(&self) -> &SystemPath {
         &self.0
@@ -354,7 +370,7 @@ impl RelativePathBuf {
     pub fn absolute(&self, project_root: &SystemPath, system: &dyn System) -> SystemPathBuf {
         let relative_to = match &self.0.source {
             ValueSource::File(_) => project_root,
-            ValueSource::Cli => system.current_directory(),
+            ValueSource::Cli | ValueSource::PythonVSCodeExtension => system.current_directory(),
         };
 
         SystemPath::absolute(&self.0, relative_to)
@@ -409,7 +425,7 @@ impl RelativeGlobPattern {
     ) -> Result<AbsolutePortableGlobPattern, PortableGlobError> {
         let relative_to = match &self.0.source {
             ValueSource::File(_) => project_root,
-            ValueSource::Cli => system.current_directory(),
+            ValueSource::Cli | ValueSource::PythonVSCodeExtension => system.current_directory(),
         };
 
         let pattern = PortableGlobPattern::parse(&self.0, kind)?;

crates/ty_python_semantic/src/program.rs

@@ -113,6 +113,9 @@ pub enum PythonVersionSource {
     /// long argument (`--extra-paths`) or `--config key=value`.
     Cli,
 
+    /// The value comes from the Python VS Code extension (the selected interpreter).
+    PythonVSCodeExtension,
+
     /// We fell back to a default value because the value was not specified via the CLI or a config file.
     #[default]
     Default,

crates/ty_python_semantic/src/site_packages.rs

@@ -1065,6 +1065,8 @@ pub enum SysPrefixPathOrigin {
     ConfigFileSetting(Arc<SystemPathBuf>, Option<TextRange>),
     /// The `sys.prefix` path came from a `--python` CLI flag
     PythonCliFlag,
+    /// The selected interpreter in the VS Code's Python extension.
+    PythonVSCodeExtension,
     /// The `sys.prefix` path came from the `VIRTUAL_ENV` environment variable
     VirtualEnvVar,
     /// The `sys.prefix` path came from the `CONDA_PREFIX` environment variable
@@ -1086,6 +1088,7 @@ impl SysPrefixPathOrigin {
             Self::LocalVenv | Self::VirtualEnvVar => true,
             Self::ConfigFileSetting(..)
             | Self::PythonCliFlag
+            | Self::PythonVSCodeExtension
             | Self::DerivedFromPyvenvCfg
             | Self::CondaPrefixVar => false,
         }
@@ -1097,7 +1100,9 @@ impl SysPrefixPathOrigin {
     /// the `sys.prefix` directory, e.g. the `--python` CLI flag.
     pub(crate) const fn must_point_directly_to_sys_prefix(&self) -> bool {
         match self {
-            Self::PythonCliFlag | Self::ConfigFileSetting(..) => false,
+            Self::PythonCliFlag | Self::ConfigFileSetting(..) | Self::PythonVSCodeExtension => {
+                false
+            }
             Self::VirtualEnvVar
             | Self::CondaPrefixVar
             | Self::DerivedFromPyvenvCfg
@@ -1115,6 +1120,9 @@ impl std::fmt::Display for SysPrefixPathOrigin {
             Self::CondaPrefixVar => f.write_str("`CONDA_PREFIX` environment variable"),
             Self::DerivedFromPyvenvCfg => f.write_str("derived `sys.prefix` path"),
             Self::LocalVenv => f.write_str("local virtual environment"),
+            Self::PythonVSCodeExtension => {
+                f.write_str("selected interpreter in the VS Code Python extension")
+            }
         }
     }
 }

crates/ty_python_semantic/src/util/diagnostics.rs

@@ -62,6 +62,12 @@ pub fn add_inferred_python_version_hint_to_diagnostic(
                 or in a configuration file",
             );
         }
+        crate::PythonVersionSource::PythonVSCodeExtension => {
+            diagnostic.info(format_args!(
+                "Python {version} was assumed when {action} \
+                because it's the version of the selected Python interpreter in the VS Code Python extension",
+            ));
+        }
         crate::PythonVersionSource::InstallationDirectoryLayout {
             site_packages_parent_dir,
         } => {

crates/ty_server/Cargo.toml

@@ -13,6 +13,7 @@ license = { workspace = true }
 [dependencies]
 ruff_db = { workspace = true, features = ["os"] }
 ruff_notebook = { workspace = true }
+ruff_python_ast = { workspace = true }
 ruff_source_file = { workspace = true }
 ruff_text_size = { workspace = true }
 

crates/ty_server/src/server/api/notifications/did_change.rs

@@ -40,22 +40,16 @@ impl SyncNotificationHandler for DidChangeTextDocumentHandler {
             .update_text_document(&key, content_changes, version)
             .with_failure_code(ErrorCode::InternalError)?;
 
-        match key.path() {
+        let changes = match key.path() {
             AnySystemPath::System(path) => {
-                let db = match session.project_db_for_path_mut(path) {
+                vec![ChangeEvent::file_content_changed(path.clone())]
-                    Some(db) => db,
-                    None => session.default_project_db_mut(),
-                };
-                db.apply_changes(vec![ChangeEvent::file_content_changed(path.clone())], None);
             }
             AnySystemPath::SystemVirtual(virtual_path) => {
-                let db = session.default_project_db_mut();
+                vec![ChangeEvent::ChangedVirtual(virtual_path.clone())]
-                db.apply_changes(
-                    vec![ChangeEvent::ChangedVirtual(virtual_path.clone())],
-                    None,
-                );
-            }
             }
+        };
+
+        session.apply_changes(key.path(), changes);
 
         publish_diagnostics(session, &key, client);
 

crates/ty_server/src/server/api/notifications/did_change_watched_files.rs

@@ -88,12 +88,7 @@ impl SyncNotificationHandler for DidChangeWatchedFiles {
         for (root, changes) in events_by_db {
             tracing::debug!("Applying changes to `{root}`");
 
-            // SAFETY: Only paths that are part of the workspace are registered for file watching.
+            let result = session.apply_changes(&AnySystemPath::System(root), changes);
-            // So, virtual paths and paths that are outside of a workspace does not trigger this
-            // notification.
-            let db = session.project_db_for_path_mut(&*root).unwrap();
-
-            let result = db.apply_changes(changes, None);
 
             project_changed |= result.project_changed();
         }

crates/ty_server/src/server/api/notifications/did_close.rs

@@ -39,10 +39,9 @@ impl SyncNotificationHandler for DidCloseTextDocumentHandler {
             .with_failure_code(ErrorCode::InternalError)?;
 
         if let AnySystemPath::SystemVirtual(virtual_path) = key.path() {
-            let db = session.default_project_db_mut();
+            session.apply_changes(
-            db.apply_changes(
+                key.path(),
                 vec![ChangeEvent::DeletedVirtual(virtual_path.clone())],
-                None,
             );
         }
 

crates/ty_server/src/server/api/notifications/did_close_notebook.rs

@@ -39,10 +39,9 @@ impl SyncNotificationHandler for DidCloseNotebookHandler {
             .with_failure_code(lsp_server::ErrorCode::InternalError)?;
 
         if let AnySystemPath::SystemVirtual(virtual_path) = key.path() {
-            let db = session.default_project_db_mut();
+            session.apply_changes(
-            db.apply_changes(
+                key.path(),
                 vec![ChangeEvent::DeletedVirtual(virtual_path.clone())],
-                None,
             );
         }
 

crates/ty_server/src/server/api/notifications/did_open.rs

@@ -46,11 +46,7 @@ impl SyncNotificationHandler for DidOpenTextDocumentHandler {
 
         match key.path() {
             AnySystemPath::System(system_path) => {
-                let db = match session.project_db_for_path_mut(system_path) {
+                session.apply_changes(key.path(), vec![ChangeEvent::Opened(system_path.clone())]);
-                    Some(db) => db,
-                    None => session.default_project_db_mut(),
-                };
-                db.apply_changes(vec![ChangeEvent::Opened(system_path.clone())], None);
             }
             AnySystemPath::SystemVirtual(virtual_path) => {
                 let db = session.default_project_db_mut();

crates/ty_server/src/server/api/notifications/did_open_notebook.rs

@@ -40,11 +40,7 @@ impl SyncNotificationHandler for DidOpenNotebookHandler {
 
         match &path {
             AnySystemPath::System(system_path) => {
-                let db = match session.project_db_for_path_mut(system_path) {
+                session.apply_changes(&path, vec![ChangeEvent::Opened(system_path.clone())]);
-                    Some(db) => db,
-                    None => session.default_project_db_mut(),
-                };
-                db.apply_changes(vec![ChangeEvent::Opened(system_path.clone())], None);
             }
             AnySystemPath::SystemVirtual(virtual_path) => {
                 let db = session.default_project_db_mut();

crates/ty_server/src/server/api/requests/workspace_diagnostic.rs

@@ -33,7 +33,7 @@ impl BackgroundRequestHandler for WorkspaceDiagnosticRequestHandler {
         let index = snapshot.index();
 
         if !index.global_settings().diagnostic_mode().is_workspace() {
-            tracing::debug!("Workspace diagnostics is disabled; returning empty report");
+            tracing::trace!("Workspace diagnostics is disabled; returning empty report");
             return Ok(WorkspaceDiagnosticReportResult::Report(
                 WorkspaceDiagnosticReport { items: vec![] },
             ));

crates/ty_server/src/session.rs

@@ -13,7 +13,8 @@ use ruff_db::Db;
 use ruff_db::files::File;
 use ruff_db::system::{System, SystemPath, SystemPathBuf};
 use ty_project::metadata::Options;
-use ty_project::{ProjectDatabase, ProjectMetadata};
+use ty_project::watch::ChangeEvent;
+use ty_project::{ChangeResult, ProjectDatabase, ProjectMetadata};
 
 pub(crate) use self::capabilities::ResolvedClientCapabilities;
 pub(crate) use self::index::DocumentQuery;
@@ -49,7 +50,12 @@ pub(crate) struct Session {
     /// The projects across all workspaces.
     projects: BTreeMap<SystemPathBuf, ProjectDatabase>,
 
-    default_project: ProjectDatabase,
+    /// The project to use for files outside any workspace. For example, if the user
+    /// opens the project `<home>/my_project` in VS code but they then opens a Python file from their Desktop.
+    /// This file isn't part of the active workspace, nor is it part of any project. But we still want
+    /// to provide some basic functionality like navigation, completions, syntax highlighting, etc.
+    /// That's what we use the default project for.
+    default_project: DefaultProject,
 
     /// The global position encoding, negotiated during LSP initialization.
     position_encoding: PositionEncoding,
@@ -77,26 +83,15 @@ impl Session {
 
         let mut workspaces = Workspaces::default();
         for (url, options) in workspace_folders {
-            workspaces.register(url, options)?;
+            workspaces.register(url, options.into_settings())?;
         }
 
-        let default_project = {
-            let system = LSPSystem::new(index.clone());
-            let metadata = ProjectMetadata::from_options(
-                Options::default(),
-                system.current_directory().to_path_buf(),
-                None,
-            )
-            .unwrap();
-            ProjectDatabase::new(metadata, system).unwrap()
-        };
-
         Ok(Self {
             position_encoding,
             workspaces,
             deferred_messages: VecDeque::new(),
             index: Some(index),
-            default_project,
+            default_project: DefaultProject::new(),
             projects: BTreeMap::new(),
             resolved_client_capabilities: Arc::new(ResolvedClientCapabilities::new(
                 client_capabilities,
@@ -109,7 +104,6 @@ impl Session {
     pub(crate) fn request_queue(&self) -> &RequestQueue {
         &self.request_queue
     }
-
     pub(crate) fn request_queue_mut(&mut self) -> &mut RequestQueue {
         &mut self.request_queue
     }
@@ -204,21 +198,46 @@ impl Session {
             .map(|(_, db)| db)
     }
 
-    /// Returns a reference to the default project [`ProjectDatabase`]. The default project is the
+    pub(crate) fn apply_changes(
-    /// minimum root path in the project map.
+        &mut self,
+        path: &AnySystemPath,
+        changes: Vec<ChangeEvent>,
+    ) -> ChangeResult {
+        let overrides = path.as_system().and_then(|root| {
+            self.workspaces()
+                .for_path(root)?
+                .settings()
+                .project_options_overrides()
+                .cloned()
+        });
+
+        let db = match path {
+            AnySystemPath::System(path) => match self.project_db_for_path_mut(path) {
+                Some(db) => db,
+                None => self.default_project_db_mut(),
+            },
+            AnySystemPath::SystemVirtual(_) => self.default_project_db_mut(),
+        };
+
+        db.apply_changes(changes, overrides.as_ref())
+    }
+
+    /// Returns a reference to the default project [`ProjectDatabase`].
     pub(crate) fn default_project_db(&self) -> &ProjectDatabase {
-        &self.default_project
+        self.default_project.get(self.index.as_ref())
     }
 
     /// Returns a mutable reference to the default project [`ProjectDatabase`].
     pub(crate) fn default_project_db_mut(&mut self) -> &mut ProjectDatabase {
-        &mut self.default_project
+        self.default_project.get_mut(self.index.as_ref())
     }
 
+    /// Returns a mutable iterator over all project databases that have been initialized to this point.
+    ///
+    /// This iterator will only yield the default project database if it has been used.
     fn projects_mut(&mut self) -> impl Iterator<Item = &'_ mut ProjectDatabase> + '_ {
-        self.projects
+        let default_project = self.default_project.try_get_mut();
-            .values_mut()
+        self.projects.values_mut().chain(default_project)
-            .chain(std::iter::once(&mut self.default_project))
     }
 
     /// Returns the [`DocumentKey`] for the given URL.
@@ -232,16 +251,18 @@ impl Session {
         assert!(!self.workspaces.all_initialized());
 
         for (url, options) in workspace_settings {
-            let Some(workspace) = self.workspaces.initialize(&url, options) else {
+            tracing::debug!("Initializing workspace `{url}`");
+
+            let settings = options.into_settings();
+            let Some((root, workspace)) = self.workspaces.initialize(&url, settings) else {
                 continue;
             };
+
             // For now, create one project database per workspace.
             // In the future, index the workspace directories to find all projects
             // and create a project database for each.
             let system = LSPSystem::new(self.index.as_ref().unwrap().clone());
-            let system_path = workspace.root();
 
-            let root = system_path.to_path_buf();
             let project = ProjectMetadata::discover(&root, &system)
                 .context("Failed to find project configuration")
                 .and_then(|mut metadata| {
@@ -249,6 +270,11 @@ impl Session {
                     metadata
                         .apply_configuration_files(&system)
                         .context("Failed to apply configuration files")?;
+
+                    if let Some(overrides) = workspace.settings.project_options_overrides() {
+                        metadata.apply_overrides(overrides);
+                    }
+
                     ProjectDatabase::new(metadata, system)
                         .context("Failed to create project database")
                 });
@@ -516,12 +542,19 @@ impl SessionSnapshot {
 
 #[derive(Debug, Default)]
 pub(crate) struct Workspaces {
-    workspaces: BTreeMap<Url, Workspace>,
+    workspaces: BTreeMap<SystemPathBuf, Workspace>,
     uninitialized: usize,
 }
 
 impl Workspaces {
-    pub(crate) fn register(&mut self, url: Url, options: ClientOptions) -> anyhow::Result<()> {
+    /// Registers a new workspace with the given URL and default settings for the workspace.
+    ///
+    /// It's the caller's responsibility to later call [`initialize`] with the resolved settings
+    /// for this workspace. Registering and initializing a workspace is a two-step process because
+    /// the workspace are announced to the server during the `initialize` request, but the
+    /// resolved settings are only available after the client has responded to the `workspace/configuration`
+    /// request.
+    pub(crate) fn register(&mut self, url: Url, settings: ClientSettings) -> anyhow::Result<()> {
         let path = url
             .to_file_path()
             .map_err(|()| anyhow!("Workspace URL is not a file or directory: {url:?}"))?;
@@ -530,35 +563,47 @@ impl Workspaces {
         let system_path = SystemPathBuf::from_path_buf(path)
             .map_err(|_| anyhow!("Workspace URL is not valid UTF8"))?;
 
-        self.workspaces.insert(
+        self.workspaces
-            url,
+            .insert(system_path, Workspace { url, settings });
-            Workspace {
-                options,
-                root: system_path,
-            },
-        );
 
         self.uninitialized += 1;
 
         Ok(())
     }
 
+    /// Initializes the workspace with the resolved client settings for the workspace.
+    ///
+    /// ## Returns
+    ///
+    /// `None` if URL doesn't map to a valid path or if the workspace is not registered.
     pub(crate) fn initialize(
         &mut self,
         url: &Url,
-        options: ClientOptions,
+        settings: ClientSettings,
-    ) -> Option<&mut Workspace> {
+    ) -> Option<(SystemPathBuf, &mut Workspace)> {
-        if let Some(workspace) = self.workspaces.get_mut(url) {
+        let path = url.to_file_path().ok()?;
-            workspace.options = options;
+
+        // Realistically I don't think this can fail because we got the path from a Url
+        let system_path = SystemPathBuf::from_path_buf(path).ok()?;
+
+        if let Some(workspace) = self.workspaces.get_mut(&system_path) {
+            workspace.settings = settings;
             self.uninitialized -= 1;
-            Some(workspace)
+            Some((system_path, workspace))
         } else {
             None
         }
     }
 
+    pub(crate) fn for_path(&self, path: impl AsRef<SystemPath>) -> Option<&Workspace> {
+        self.workspaces
+            .range(..=path.as_ref().to_path_buf())
+            .next_back()
+            .map(|(_, db)| db)
+    }
+
     pub(crate) fn urls(&self) -> impl Iterator<Item = &Url> + '_ {
-        self.workspaces.keys()
+        self.workspaces.values().map(Workspace::url)
     }
 
     pub(crate) fn all_initialized(&self) -> bool {
@@ -567,8 +612,8 @@ impl Workspaces {
 }
 
 impl<'a> IntoIterator for &'a Workspaces {
-    type Item = (&'a Url, &'a Workspace);
+    type Item = (&'a SystemPathBuf, &'a Workspace);
-    type IntoIter = std::collections::btree_map::Iter<'a, Url, Workspace>;
+    type IntoIter = std::collections::btree_map::Iter<'a, SystemPathBuf, Workspace>;
 
     fn into_iter(self) -> Self::IntoIter {
         self.workspaces.iter()
@@ -577,12 +622,61 @@ impl<'a> IntoIterator for &'a Workspaces {
 
 #[derive(Debug)]
 pub(crate) struct Workspace {
-    root: SystemPathBuf,
+    /// The workspace root URL as sent by the client during initialization.
-    options: ClientOptions,
+    url: Url,
+    settings: ClientSettings,
 }
 
 impl Workspace {
-    pub(crate) fn root(&self) -> &SystemPath {
+    pub(crate) fn url(&self) -> &Url {
-        &self.root
+        &self.url
+    }
+
+    pub(crate) fn settings(&self) -> &ClientSettings {
+        &self.settings
+    }
+}
+
+/// Thin wrapper around the default project database that ensures it only gets initialized
+/// when it's first accessed.
+///
+/// There are a few advantages to this:
+///
+/// 1. Salsa has a fast-path for query lookups for the first created database.
+///    We really want that to be the actual project database and not our fallback database.
+/// 2. The logs when the server starts can be confusing if it once shows it uses Python X (for the default db)
+///    but then has another log that it uses Python Y (for the actual project db).
+struct DefaultProject(std::sync::OnceLock<ProjectDatabase>);
+
+impl DefaultProject {
+    pub(crate) fn new() -> Self {
+        DefaultProject(std::sync::OnceLock::new())
+    }
+
+    pub(crate) fn get(&self, index: Option<&Arc<Index>>) -> &ProjectDatabase {
+        self.0.get_or_init(|| {
+            tracing::info!("Initialize default project");
+
+            let system = LSPSystem::new(index.unwrap().clone());
+            let metadata = ProjectMetadata::from_options(
+                Options::default(),
+                system.current_directory().to_path_buf(),
+                None,
+            )
+            .unwrap();
+            ProjectDatabase::new(metadata, system).unwrap()
+        })
+    }
+
+    pub(crate) fn get_mut(&mut self, index: Option<&Arc<Index>>) -> &mut ProjectDatabase {
+        let _ = self.get(index);
+
+        // SAFETY: The `OnceLock` is guaranteed to be initialized at this point because
+        // we called `get` above, which initializes it if it wasn't already.
+        self.0.get_mut().unwrap()
+    }
+
+    pub(crate) fn try_get_mut(&mut self) -> Option<&mut ProjectDatabase> {
+        self.0.get_mut()
     }
 }

crates/ty_server/src/session/options.rs

@@ -1,10 +1,14 @@
 use lsp_types::Url;
 use ruff_db::system::SystemPathBuf;
+use ruff_python_ast::PythonVersion;
 use rustc_hash::FxHashMap;
 use serde::Deserialize;
+use ty_project::metadata::Options;
+use ty_project::metadata::options::ProjectOptionsOverrides;
+use ty_project::metadata::value::{RangedValue, RelativePathBuf};
 
 use crate::logging::LogLevel;
-use crate::session::settings::ClientSettings;
+use crate::session::ClientSettings;
 
 pub(crate) type WorkspaceOptionsMap = FxHashMap<Url, ClientOptions>;
 
@@ -43,7 +47,7 @@ struct WorkspaceOptions {
 }
 
 /// This is a direct representation of the settings schema sent by the client.
-#[derive(Debug, Deserialize, Default)]
+#[derive(Clone, Debug, Deserialize, Default)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[serde(rename_all = "camelCase")]
 pub(crate) struct ClientOptions {
@@ -52,6 +56,8 @@ pub(crate) struct ClientOptions {
     python: Option<Python>,
     /// Diagnostic mode for the language server.
     diagnostic_mode: Option<DiagnosticMode>,
+
+    python_extension: Option<PythonExtension>,
 }
 
 /// Diagnostic mode for the language server.
@@ -75,6 +81,47 @@ impl DiagnosticMode {
 impl ClientOptions {
     /// Returns the client settings that are relevant to the language server.
     pub(crate) fn into_settings(self) -> ClientSettings {
+        let overrides = self.python_extension.and_then(|extension| {
+            let active_environment = extension.active_environment?;
+
+            let mut overrides = ProjectOptionsOverrides::new(None, Options::default());
+
+            overrides.fallback_python = if let Some(environment) = &active_environment.environment {
+                environment.folder_uri.to_file_path().ok().and_then(|path| {
+                    Some(RelativePathBuf::python_extension(
+                        SystemPathBuf::from_path_buf(path).ok()?,
+                    ))
+                })
+            } else {
+                Some(RelativePathBuf::python_extension(
+                    active_environment.executable.sys_prefix.clone(),
+                ))
+            };
+
+            overrides.fallback_python_version =
+                active_environment.version.as_ref().and_then(|version| {
+                    Some(RangedValue::python_extension(PythonVersion::from((
+                        u8::try_from(version.major).ok()?,
+                        u8::try_from(version.minor).ok()?,
+                    ))))
+                });
+
+            if let Some(python) = &overrides.fallback_python {
+                tracing::debug!(
+                    "Using the Python environment selected in the VS Code Python extension in case the configuration doesn't specify a Python environment: {python}",
+                    python = python.path()
+                );
+            }
+
+            if let Some(version) = &overrides.fallback_python_version {
+                tracing::debug!(
+                    "Using the Python version selected in the VS Code Python extension: {version} in case the configuration doesn't specify a Python version",
+                );
+            }
+
+            Some(overrides)
+        });
+
         ClientSettings {
             disable_language_services: self
                 .python
@@ -82,6 +129,7 @@ impl ClientOptions {
                 .and_then(|ty| ty.disable_language_services)
                 .unwrap_or_default(),
             diagnostic_mode: self.diagnostic_mode.unwrap_or_default(),
+            overrides,
         }
     }
 }
@@ -90,14 +138,63 @@ impl ClientOptions {
 // would be useful to instead use `workspace/configuration` instead. This would be then used to get
 // all settings and not just the ones in "python.*".
 
-#[derive(Debug, Deserialize, Default)]
+#[derive(Clone, Debug, Deserialize, Default)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[serde(rename_all = "camelCase")]
 struct Python {
     ty: Option<Ty>,
 }
 
-#[derive(Debug, Deserialize, Default)]
+#[derive(Clone, Debug, Deserialize, Default)]
+#[cfg_attr(test, derive(PartialEq, Eq))]
+#[serde(rename_all = "camelCase")]
+struct PythonExtension {
+    active_environment: Option<ActiveEnvironment>,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+#[cfg_attr(test, derive(PartialEq, Eq))]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct ActiveEnvironment {
+    pub(crate) executable: PythonExecutable,
+    pub(crate) environment: Option<PythonEnvironment>,
+    pub(crate) version: Option<EnvironmentVersion>,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+#[cfg_attr(test, derive(PartialEq, Eq))]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct EnvironmentVersion {
+    pub(crate) major: i64,
+    pub(crate) minor: i64,
+    #[allow(dead_code)]
+    pub(crate) patch: i64,
+    #[allow(dead_code)]
+    pub(crate) sys_version: String,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+#[cfg_attr(test, derive(PartialEq, Eq))]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct PythonEnvironment {
+    pub(crate) folder_uri: Url,
+    #[allow(dead_code)]
+    #[serde(rename = "type")]
+    pub(crate) kind: String,
+    #[allow(dead_code)]
+    pub(crate) name: Option<String>,
+}
+
+#[derive(Clone, Debug, Deserialize)]
+#[cfg_attr(test, derive(PartialEq, Eq))]
+#[serde(rename_all = "camelCase")]
+pub(crate) struct PythonExecutable {
+    #[allow(dead_code)]
+    pub(crate) uri: Url,
+    pub(crate) sys_prefix: SystemPathBuf,
+}
+
+#[derive(Clone, Debug, Deserialize, Default)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[serde(rename_all = "camelCase")]
 struct Ty {

crates/ty_server/src/session/settings.rs

@@ -1,5 +1,7 @@
 use super::options::DiagnosticMode;
 
+use ty_project::metadata::options::ProjectOptionsOverrides;
+
 /// Resolved client settings for a specific document. These settings are meant to be
 /// used directly by the server, and are *not* a 1:1 representation with how the client
 /// sends them.
@@ -8,6 +10,7 @@ use super::options::DiagnosticMode;
 pub(crate) struct ClientSettings {
     pub(super) disable_language_services: bool,
     pub(super) diagnostic_mode: DiagnosticMode,
+    pub(super) overrides: Option<ProjectOptionsOverrides>,
 }
 
 impl ClientSettings {
@@ -18,4 +21,8 @@ impl ClientSettings {
     pub(crate) fn diagnostic_mode(&self) -> DiagnosticMode {
         self.diagnostic_mode
     }
+
+    pub(crate) fn project_options_overrides(&self) -> Option<&ProjectOptionsOverrides> {
+        self.overrides.as_ref()
+    }
 }