fix(oxfmt/lsp): return error on config resolving error (#26003)

Instead of silently ignoring config-resolve errors, and not formatting the document,
`oxfmt --lsp` now returns an `Err` instead, allowing users to see on their LSP client a meaningful message.

Hitting Format on a file, could produce a `toast` like in this following example:
<img width="463" height="173" alt="grafik" src="https://github.com/user-attachments/assets/7d549ab1-b65b-41bc-9fa0-f5f9d10989dc" />

apps/oxfmt/src/lsp/server_formatter.rs

@@ -226,7 +226,7 @@ impl Tool for ServerFormatter {
                 &file_content
             };
 
-            let Some(result) = self.format_file(&path, source_text) else {
+            let Some(result) = self.format_file(&path, source_text)? else {
                 return Ok(vec![]); // No formatting for this file (unsupported or ignored)
             };
 
@@ -238,7 +238,7 @@ impl Tool for ServerFormatter {
                 .ok_or_else(|| "In-memory formatting requires content".to_string())?;
 
             let Some(result) =
-                self.format_in_memory(document.uri, source_text, &document.language_id)
+                self.format_in_memory(document.uri, source_text, &document.language_id)?
             else {
                 return Ok(vec![]); // currently not supported
             };
@@ -346,7 +346,7 @@ impl ServerFormatter {
         scopes: &ConfigScopes,
         path: &Path,
         source_text: &str,
-    ) -> Option<FormatResult> {
+    ) -> Result<Option<FormatResult>, String> {
         let resolver = match scopes.resolve(path) {
             Ok(r) => r,
             Err(err) => {
@@ -360,37 +360,35 @@ impl ServerFormatter {
 
         if resolver.is_path_ignored(path, false) {
             debug!("File is ignored by config ignorePatterns: {}", path.display());
-            return None;
+            return Ok(None);
         }
 
         let Some(strategy) = classify_file(path) else {
             debug!("Unsupported file type for formatting: {}", path.display());
-            return None;
+            return Ok(None);
         };
         let plan = match resolver.resolve(path, strategy) {
             Ok(ResolveOutcome::Format(plan)) => plan,
             Ok(ResolveOutcome::MissingPlugin(plugin)) => {
-                warn!(
-                    "Skipping `.{plugin}`: `{plugin}` plugin is not enabled in resolved config: {}",
+                return Err(format!(
+                    "`{plugin}` plugin is not enabled in resolved config: {}",
                     path.display()
-                );
-                return None;
+                ));
             }
             Err(err) => {
-                debug!("Config resolve error for {}: {err}", path.display());
-                return None;
+                return Err(format!("Config resolve error for {}: {err}", path.display()));
             }
         };
         debug!("plan = {plan:?}");
 
-        Some(tokio::task::block_in_place(|| self.source_formatter.format(source_text, plan)))
+        Ok(Some(tokio::task::block_in_place(|| self.source_formatter.format(source_text, plan))))
     }
 
-    fn format_file(&self, path: &Path, source_text: &str) -> Option<FormatResult> {
+    fn format_file(&self, path: &Path, source_text: &str) -> Result<Option<FormatResult>, String> {
         let state = self.snapshot();
         if is_ignored(&state.ignore_matchers, path, false, true) {
             debug!("File is ignored by .prettierignore: {}", path.display());
-            return None;
+            return Ok(None);
         }
         self.resolve_and_format(&state.scopes, path, source_text)
     }
@@ -400,11 +398,11 @@ impl ServerFormatter {
         uri: &Uri,
         source_text: &str,
         language_id: &LanguageId,
-    ) -> Option<FormatResult> {
+    ) -> Result<Option<FormatResult>, String> {
         let Some(path) = create_fake_file_path_from_language_id(language_id, &self.root_path, uri)
         else {
             debug!("Unsupported language id for in-memory formatting: {language_id:?}");
-            return None;
+            return Ok(None);
         };
         self.resolve_and_format(&self.snapshot().scopes, &path, source_text)
     }

apps/oxfmt/test/lsp/format/__snapshots__/format.test.ts.snap

@@ -21,12 +21,8 @@ const   count=1
 ---
 <button onclick={()=>count}>{count}</button>
 
---- AFTER ----------
----
-const   count=1
----
-<button onclick={()=>count}>{count}</button>
-
+--- ERROR ----------
+\`astro\` plugin is not enabled in resolved config: <cwd>/test/lsp/format/fixtures/format/test.astro
 --------------------"
 `;
 
@@ -49,10 +45,8 @@ file://<fixture>/format/test.svelte
 <script>let   count=$state(0);</script>
 <button onclick={()=>count++}>{count}</button>
 
---- AFTER ----------
-<script>let   count=$state(0);</script>
-<button onclick={()=>count++}>{count}</button>
-
+--- ERROR ----------
+\`svelte\` plugin is not enabled in resolved config: <cwd>/test/lsp/format/fixtures/format/test.svelte
 --------------------"
 `;
 
@@ -381,6 +375,18 @@ const x = "1"
 --------------------"
 `;
 
+exports[`LSP formatting > error handling on format > should handle config-invalid-override/test.ts 1`] = `
+"--- URI -----------
+file://<fixture>/config-invalid-override/test.ts
+--- BEFORE ---------
+const   value   =   1;
+
+--- ERROR ----------
+Config resolve error for <cwd>/test/lsp/format/fixtures/config-invalid-override/test.ts: Invalid tabWidth: The indent width should be between 0 and 24
+
+--------------------"
+`;
+
 exports[`LSP formatting > ignore patterns > should handle ignore-config/file.generated.ts 1`] = `
 "--- URI -----------
 file://<fixture>/ignore-config/file.generated.ts

apps/oxfmt/test/lsp/format/fixtures/config-invalid-override/.oxfmtrc.json

@@ -0,0 +1,10 @@
+{
+  "overrides": [
+    {
+      "files": ["*.ts"],
+      "options": {
+        "tabWidth": 250
+      }
+    }
+  ]
+}

apps/oxfmt/test/lsp/format/fixtures/config-invalid-override/test.ts

@@ -0,0 +1 @@
+const   value   =   1;

apps/oxfmt/test/lsp/format/format.test.ts

@@ -166,6 +166,15 @@ describe("LSP formatting", () => {
     });
   });
 
+  describe("error handling on format", () => {
+    it.each([["config-invalid-override/test.ts", "typescript"]])(
+      "should handle %s",
+      async (path, languageId) => {
+        expect(await formatFixture(FIXTURES_DIR, path, languageId)).toMatchSnapshot();
+      },
+    );
+  });
+
   describe("initializationOptions", () => {
     it("should use custom config path from fmt.configPath", async () => {
       expect(

apps/oxfmt/test/lsp/utils.ts

@@ -173,19 +173,36 @@ export async function formatFixtureContent(
   }
   await clientOrConfig.didOpen(fileUri, languageId, content);
 
-  const edits = await clientOrConfig.format(fileUri);
+  try {
+    const edits = await clientOrConfig.format(fileUri);
 
-  if (innerClient) {
-    await innerClient[Symbol.asyncDispose]();
-  }
+    if (innerClient) {
+      await innerClient[Symbol.asyncDispose]();
+    }
 
-  return `${uriSnapshotHeader(fileUri, fixturesDir)}
+    return `${uriSnapshotHeader(fileUri, fixturesDir)}
 --- BEFORE ---------
 ${content}
 --- AFTER ----------
 ${applyEdits(content, edits, languageId)}
 --------------------
 `.trim();
+  } catch (error) {
+    const msg =
+      error instanceof Error ? sanitizeMessage(error.message) : sanitizeMessage(error as string);
+
+    if (innerClient) {
+      await innerClient[Symbol.asyncDispose]();
+    }
+
+    return `${uriSnapshotHeader(fileUri, fixturesDir)}
+--- BEFORE ---------
+${content}
+--- ERROR ----------
+${msg}
+--------------------
+`.trim();
+  }
 }
 
 export async function formatMultipleFixtures(
@@ -302,3 +319,7 @@ function uriSnapshotHeader(fileUri: string, fixtureDir: string): string {
   --- URI -----------
 ${safeUri}`;
 }
+
+function sanitizeMessage(message: string): string {
+  return message.replaceAll(process.cwd(), "<cwd>");
+}

crates/oxc_language_server/src/backend.rs

@@ -961,6 +961,7 @@ impl LanguageServer for Backend {
                 Ok(Some(edits))
             }
             Err(err) => {
+                error!(err);
                 Err(Error { code: ErrorCode::ServerError(1), message: Cow::Owned(err), data: None })
             }
         }