fix(oxfmt/lsp): prefer language_id over file extension when formatting

apps/oxfmt/src/lsp/mod.rs

@@ -11,7 +11,9 @@ mod server_formatter;
 mod tester;
 const FORMAT_CONFIG_FILES: &[&str; 2] = &[".oxfmtrc.json", ".oxfmtrc.jsonc"];
 
-fn get_file_extension_from_language_id(language_id: &LanguageId) -> Option<&'static str> {
+pub(super) fn get_file_extension_from_language_id(
+    language_id: &LanguageId,
+) -> Option<&'static str> {
     match language_id.as_str() {
         "javascript" => Some("js"),
         "typescript" => Some("ts"),
@@ -36,14 +38,25 @@ fn get_file_extension_from_language_id(language_id: &LanguageId) -> Option<&'sta
     }
 }
 
+/// Returns a copy of `path` with the extension replaced by the one corresponding to `language_id`.
+/// Returns `None` if `language_id` is not recognized.
+pub(super) fn apply_language_id_extension(
+    language_id: &LanguageId,
+    path: &Path,
+) -> Option<PathBuf> {
+    let ext = get_file_extension_from_language_id(language_id)?;
+    let mut p = path.to_path_buf();
+    p.set_extension(ext);
+    Some(p)
+}
+
 pub fn create_fake_file_path_from_language_id(
     language_id: &LanguageId,
     root: &Path,
     uri: &Uri,
 ) -> Option<PathBuf> {
-    let file_extension = get_file_extension_from_language_id(language_id)?;
-    let file_name = format!("{}.{}", uri.authority()?, file_extension);
-    Some(root.join(file_name))
+    let base = root.join(uri.authority()?.as_str());
+    apply_language_id_extension(language_id, &base)
 }
 
 /// Run the language server

apps/oxfmt/src/lsp/server_formatter.rs

@@ -268,7 +268,7 @@ 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, language_id) else {
                 return Ok(vec![]); // No formatting for this file (unsupported or ignored)
             };
 
@@ -334,18 +334,27 @@ impl ServerFormatter {
         }
     }
 
-    fn format_file(&self, path: &Path, source_text: &str) -> Option<FormatResult> {
+    fn format_file(
+        &self,
+        path: &Path,
+        source_text: &str,
+        language_id: &LanguageId,
+    ) -> Option<FormatResult> {
         if self.is_ignored(path) {
             debug!("File is ignored: {}", path.display());
             return None;
         }
 
-        // Determine format strategy from file path (supports JS/TS, JSON, YAML, CSS, etc.)
-        let Ok(strategy) = FormatFileStrategy::try_from(path.to_path_buf()) else {
+        // Prefer language_id over file extension to determine the format strategy.
+        // This allows e.g. a `.txt` file opened as `typescript` to be formatted.
+        let strategy_opt = super::apply_language_id_extension(language_id, path)
+            .and_then(|p| FormatFileStrategy::try_from(p).ok())
+            .or_else(|| FormatFileStrategy::try_from(path.to_path_buf()).ok());
+
+        let Some(strategy) = strategy_opt else {
             debug!("Unsupported file type for formatting: {}", path.display());
             return None;
         };
-
         // Resolve options for this file
         let resolved_options = self.config_resolver.resolve(&strategy);
         debug!("resolved_options = {resolved_options:?}");

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

@@ -40,6 +40,18 @@ version = "1.0.0"
 --------------------"
 `;
 
+exports[`LSP formatting > basic formatting > should handle format/test.ts.txt 1`] = `
+"--- URI -----------
+file://<fixture>/format/test.ts.txt
+--- BEFORE ---------
+const   x   =   1
+
+--- AFTER ----------
+const x = 1;
+
+--------------------"
+`;
+
 exports[`LSP formatting > basic formatting > should handle format/test.tsx 1`] = `
 "--- URI -----------
 file://<fixture>/format/test.tsx

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

@@ -0,0 +1 @@
+const   x   =   1

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

@@ -14,6 +14,7 @@ describe("LSP formatting", () => {
       ["format/test.toml", "toml"],
       ["format/formatted.ts", "typescript"],
       ["format/test.txt", "plaintext"],
+      ["format/test.ts.txt", "typescript"],
     ])("should handle %s", async (path, languageId) => {
       expect(await formatFixture(FIXTURES_DIR, path, languageId)).toMatchSnapshot();
     });