[ty] Preserve valid LSP settings when configuration resolution fails (#28653)

crates/ty_server/src/session.rs

@@ -777,47 +777,48 @@ impl Session {
             ProjectMetadata::discover_with_uv(workspace_directory, &system, self.use_uv)
         };
 
-        let project = metadata
-            .context("Failed to discover project configuration")
-            .and_then(|mut metadata| {
-                if let Some(fallback_options) = workspace.settings.fallback_options() {
-                    metadata.set_fallback_options(fallback_options.clone());
+        let (mut metadata, discovery_result) =
+            match metadata.context("Failed to discover project configuration") {
+                Ok(metadata) => (metadata, Ok(())),
+                Err(err) => {
+                    let Ok(metadata) = ProjectMetadata::from_options(
+                        Options::default(),
+                        workspace_directory.to_path_buf(),
+                        None,
+                        &UseDefaultStrategy,
+                    );
+                    (metadata.with_use_uv(self.use_uv), Err(err))
                 }
+            };
 
+        if let Some(fallback_options) = workspace.settings.fallback_options() {
+            metadata.set_fallback_options(fallback_options.clone());
+        }
+
+        if let Some(override_options) = workspace.settings.override_options() {
+            metadata.set_override_options(override_options.clone());
+        }
+
+        // Load user configuration even if project discovery failed.
+        let project = discovery_result
+            .and(
                 metadata
                     .apply_configuration_files(&system)
-                    .context("Failed to apply configuration files")?;
+                    .context("Failed to apply configuration files"),
+            )
+            .and_then(|()| ProjectDatabase::fallible(metadata.clone(), system.clone()));
 
-                if let Some(override_options) = workspace.settings.override_options() {
-                    metadata.set_override_options(override_options.clone());
-                }
-
-                ProjectDatabase::fallible(metadata, system.clone())
-            });
-
-        let mut db = match project {
-            Ok(db) => db,
-            Err(err) => {
-                tracing::error!(
-                    "Failed to create project for workspace `{uri}`: {err:#}. \
-                        Falling back to default settings"
-                );
-
-                client.show_error_message(format!(
-                    "Failed to load project for workspace {uri}. {}",
-                    self.client_name.log_guidance(),
-                ));
-
-                let Ok(metadata) = ProjectMetadata::from_options(
-                    Options::default(),
-                    workspace_directory.to_path_buf(),
-                    None,
-                    &UseDefaultStrategy,
-                )
-                .map(|metadata| metadata.with_use_uv(self.use_uv));
-                ProjectDatabase::use_defaults(metadata, system)
-            }
-        };
+        let mut db = project.unwrap_or_else(|err| {
+            tracing::error!(
+                "Failed to load project for workspace `{uri}`: {err:#}. \
+                 Continuing with valid settings"
+            );
+            client.show_error_message(format!(
+                "Failed to load project for workspace {uri}. {}",
+                self.client_name.log_guidance(),
+            ));
+            ProjectDatabase::use_defaults(metadata, system)
+        });
 
         // Carry forward diagnostic state if any exists
         let previous = self.projects.remove(&root);

crates/ty_server/tests/e2e/configuration.rs

@@ -1,11 +1,13 @@
 use anyhow::Result;
 use insta::assert_json_snapshot;
 use ruff_db::system::SystemPath;
+use ruff_python_trivia::textwrap::dedent;
 use serde_json::{Map, json};
 use ty_server::{ClientOptions, WorkspaceOptions};
 
 use crate::TestServerBuilder;
 use crate::pull_diagnostics::filter_result_id;
+use crate::workspace_folders::condensed_document_diagnostic_snapshot;
 
 #[test]
 fn configuration_file() -> Result<()> {
@@ -73,6 +75,16 @@ def foo() -> str:
             Some(ClientOptions {
                 workspace: WorkspaceOptions {
                     configuration_file: Some(settings_path.to_string()),
+                    configuration: Some(
+                        Map::from_iter([
+                            ("rules".to_string(), json!({"unresolved-reference": "warn"})),
+                            (
+                                "environment".to_string(),
+                                json!({"python": "./missing-environment"}),
+                            ),
+                        ])
+                        .into(),
+                    ),
                     ..WorkspaceOptions::default()
                 },
                 ..ClientOptions::default()
@@ -104,6 +116,118 @@ unresolved-reference="warn"
     Ok(())
 }
 
+#[test]
+fn invalid_python_environment_preserves_valid_configuration() -> Result<()> {
+    let main = SystemPath::new("src/main.py");
+    let content = dedent(
+        "
+        import sys
+        sys.platform
+        ",
+    );
+
+    let mut server = TestServerBuilder::new()?
+        .with_workspace(SystemPath::new("src"), None)?
+        .with_file(
+            "src/ty.toml",
+            dedent(
+                r#"
+                [environment]
+                python = "./missing-environment"
+                python-platform = "win32"
+                "#,
+            ),
+        )?
+        .with_file(main, &content)?
+        .build()
+        .wait_until_workspaces_are_initialized();
+
+    let message = server.await_notification::<lsp_types::ShowMessageNotification>();
+    assert_eq!(message.kind, lsp_types::MessageType::Error);
+
+    server.open_text_document(main, &content, 1);
+    let platform = server.hover_request(main, lsp_types::Position::new(2, 5));
+    assert_json_snapshot!(platform, @r#"
+    {
+      "contents": {
+        "kind": "plaintext",
+        "value": "Literal[\"win32\"]"
+      },
+      "range": {
+        "start": {
+          "line": 2,
+          "character": 4
+        },
+        "end": {
+          "line": 2,
+          "character": 12
+        }
+      }
+    }
+    "#);
+
+    Ok(())
+}
+
+#[test]
+fn invalid_include_pattern_preserves_rules_and_diagnostics() -> Result<()> {
+    let main = SystemPath::new("src/main.py");
+    let content = "undefined";
+    let mut server = TestServerBuilder::new()?
+        .with_workspace(SystemPath::new("src"), None)?
+        .with_file(
+            "src/ty.toml",
+            dedent(
+                r#"
+                [src]
+                include = ["["]
+
+                [rules]
+                unresolved-reference = "warn"
+                unknown-rule = "warn"
+                "#,
+            ),
+        )?
+        .with_file(main, content)?
+        .build()
+        .wait_until_workspaces_are_initialized();
+
+    let message = server.await_notification::<lsp_types::ShowMessageNotification>();
+    assert_eq!(message.kind, lsp_types::MessageType::Error);
+
+    let settings_diagnostics =
+        server.await_notification::<lsp_types::PublishDiagnosticsNotification>();
+    assert_json_snapshot!(settings_diagnostics, @r#"
+    {
+      "uri": "file://<temp_dir>/src/ty.toml",
+      "diagnostics": [
+        {
+          "range": {
+            "start": {
+              "line": 6,
+              "character": 0
+            },
+            "end": {
+              "line": 6,
+              "character": 12
+            }
+          },
+          "severity": 2,
+          "code": "unknown-rule",
+          "source": "ty",
+          "message": "Unknown rule `unknown-rule`. Did you mean `unknown-argument`?"
+        }
+      ]
+    }
+    "#);
+
+    server.open_text_document(main, content, 1);
+    let diagnostics = server.document_diagnostic_request(main, None);
+    insta::assert_snapshot!(condensed_document_diagnostic_snapshot(diagnostics), @"0:0..0:9[WARNING]: Name `undefined` used when not defined");
+
+    Ok(())
+}
+
 #[test]
 fn configuration_overrides() -> Result<()> {
     let _filter = filter_result_id();

crates/ty_server/tests/e2e/snapshots/e2e__configuration__invalid_configuration_file-2.snap

@@ -16,7 +16,7 @@ expression: diagnostics
           "character": 12
         }
       },
-      "severity": 1,
+      "severity": 2,
       "code": "unresolved-reference",
       "codeDescription": {
         "href": "https://ty.dev/rules#unresolved-reference"