feat(oxfmt): Add insertFinalNewline option

apps/oxfmt/src-js/index.ts

@@ -86,6 +86,8 @@ export type FormatOptions = {
   singleAttributePerLine?: boolean;
   /** Control whether formats quoted code embedded in the file. (Default: `"auto"`) */
   embeddedLanguageFormatting?: "auto" | "off";
+  /** Whether to insert a final newline at the end of the file. (Default: `true`) */
+  insertFinalNewline?: boolean;
   /** Experimental: Sort import statements. Disabled by default. */
   experimentalSortImports?: SortImportsOptions;
   /** Experimental: Sort `package.json` keys. (Default: `true`) */

apps/oxfmt/src/core/config.rs

@@ -53,15 +53,20 @@ pub enum ResolvedOptions {
         format_options: FormatOptions,
         /// For embedded language formatting (e.g., CSS in template literals)
         external_options: Value,
+        insert_final_newline: bool,
     },
     /// For TOML files.
-    OxfmtToml { toml_options: TomlFormatterOptions },
+    OxfmtToml { toml_options: TomlFormatterOptions, insert_final_newline: bool },
     /// For non-JS files formatted by external formatter (Prettier).
     #[cfg(feature = "napi")]
-    ExternalFormatter { external_options: Value },
+    ExternalFormatter { external_options: Value, insert_final_newline: bool },
     /// For `package.json` files: optionally sorted then formatted.
     #[cfg(feature = "napi")]
-    ExternalFormatterPackageJson { external_options: Value, sort_package_json: bool },
+    ExternalFormatterPackageJson {
+        external_options: Value,
+        sort_package_json: bool,
+        insert_final_newline: bool,
+    },
 }
 
 /// Configuration resolver that derives all config values from a single `serde_json::Value`.
@@ -174,7 +179,6 @@ impl ConfigResolver {
 
     /// Resolve format options for a specific file.
     pub fn resolve(&self, strategy: &FormatFileStrategy) -> ResolvedOptions {
-        #[cfg_attr(not(feature = "napi"), expect(unused_variables))]
         let (format_options, oxfmt_options, external_options) = if let Some(editorconfig) =
             &self.editorconfig
             && let Some(props) = get_editorconfig_overrides(editorconfig, strategy.path())
@@ -190,22 +194,28 @@ impl ConfigResolver {
                 .expect("`build_and_validate()` must be called before `resolve()`")
         };
 
+        let insert_final_newline = oxfmt_options.insert_final_newline;
+
         match strategy {
-            FormatFileStrategy::OxcFormatter { .. } => {
-                ResolvedOptions::OxcFormatter { format_options, external_options }
-            }
-            FormatFileStrategy::OxfmtToml { .. } => {
-                ResolvedOptions::OxfmtToml { toml_options: build_toml_options(&format_options) }
-            }
+            FormatFileStrategy::OxcFormatter { .. } => ResolvedOptions::OxcFormatter {
+                format_options,
+                external_options,
+                insert_final_newline,
+            },
+            FormatFileStrategy::OxfmtToml { .. } => ResolvedOptions::OxfmtToml {
+                toml_options: build_toml_options(&format_options),
+                insert_final_newline,
+            },
             #[cfg(feature = "napi")]
             FormatFileStrategy::ExternalFormatter { .. } => {
-                ResolvedOptions::ExternalFormatter { external_options }
+                ResolvedOptions::ExternalFormatter { external_options, insert_final_newline }
             }
             #[cfg(feature = "napi")]
             FormatFileStrategy::ExternalFormatterPackageJson { .. } => {
                 ResolvedOptions::ExternalFormatterPackageJson {
                     external_options,
                     sort_package_json: oxfmt_options.sort_package_json,
+                    insert_final_newline,
                 }
             }
             #[cfg(not(feature = "napi"))]
@@ -251,6 +261,7 @@ impl ConfigResolver {
 /// - end_of_line
 /// - indent_style
 /// - indent_size
+/// - insert_final_newline
 fn get_editorconfig_overrides(
     editorconfig: &EditorConfig,
     path: &Path,
@@ -274,13 +285,15 @@ fn get_editorconfig_overrides(
                 || resolved.end_of_line != root.end_of_line
                 || resolved.indent_style != root.indent_style
                 || resolved.indent_size != root.indent_size
+                || resolved.insert_final_newline != root.insert_final_newline
         }
         // No `[*]` section means any resolved property is an override
         None => {
             resolved.max_line_length != EditorConfigProperty::Unset
                 || resolved.end_of_line != EditorConfigProperty::Unset
                 || resolved.indent_style != EditorConfigProperty::Unset
                 || resolved.indent_size != EditorConfigProperty::Unset
+                || resolved.insert_final_newline != EditorConfigProperty::Unset
         }
     };
 
@@ -326,6 +339,12 @@ fn apply_editorconfig(oxfmtrc: &mut Oxfmtrc, props: &EditorConfigProperties) {
     {
         oxfmtrc.tab_width = Some(size as u8);
     }
+
+    if oxfmtrc.insert_final_newline.is_none()
+        && let EditorConfigProperty::Value(v) = props.insert_final_newline
+    {
+        oxfmtrc.insert_final_newline = Some(v);
+    }
 }
 
 // ---

apps/oxfmt/src/core/format.rs

@@ -48,46 +48,70 @@ impl SourceFormatter {
         source_text: &str,
         resolved_options: ResolvedOptions,
     ) -> FormatResult {
-        let result = match (entry, resolved_options) {
+        let (result, insert_final_newline) = match (entry, resolved_options) {
             (
                 FormatFileStrategy::OxcFormatter { path, source_type },
-                ResolvedOptions::OxcFormatter { format_options, external_options },
-            ) => self.format_by_oxc_formatter(
-                source_text,
-                path,
-                *source_type,
-                format_options,
-                external_options,
+                ResolvedOptions::OxcFormatter {
+                    format_options,
+                    external_options,
+                    insert_final_newline,
+                },
+            ) => (
+                self.format_by_oxc_formatter(
+                    source_text,
+                    path,
+                    *source_type,
+                    format_options,
+                    external_options,
+                ),
+                insert_final_newline,
             ),
-            (FormatFileStrategy::OxfmtToml { .. }, ResolvedOptions::OxfmtToml { toml_options }) => {
-                Ok(Self::format_by_toml(source_text, toml_options))
-            }
+            (
+                FormatFileStrategy::OxfmtToml { .. },
+                ResolvedOptions::OxfmtToml { toml_options, insert_final_newline },
+            ) => (Ok(Self::format_by_toml(source_text, toml_options)), insert_final_newline),
             #[cfg(feature = "napi")]
             (
                 FormatFileStrategy::ExternalFormatter { path, parser_name },
-                ResolvedOptions::ExternalFormatter { external_options },
-            ) => {
-                self.format_by_external_formatter(source_text, path, parser_name, external_options)
-            }
+                ResolvedOptions::ExternalFormatter { external_options, insert_final_newline },
+            ) => (
+                self.format_by_external_formatter(source_text, path, parser_name, external_options),
+                insert_final_newline,
+            ),
             #[cfg(feature = "napi")]
             (
                 FormatFileStrategy::ExternalFormatterPackageJson { path, parser_name },
                 ResolvedOptions::ExternalFormatterPackageJson {
                     external_options,
                     sort_package_json,
+                    insert_final_newline,
                 },
-            ) => self.format_by_external_formatter_package_json(
-                source_text,
-                path,
-                parser_name,
-                external_options,
-                sort_package_json,
+            ) => (
+                self.format_by_external_formatter_package_json(
+                    source_text,
+                    path,
+                    parser_name,
+                    external_options,
+                    sort_package_json,
+                ),
+                insert_final_newline,
             ),
             _ => unreachable!("FormatFileStrategy and ResolvedOptions variant mismatch"),
         };
 
         match result {
-            Ok(code) => FormatResult::Success { is_changed: source_text != code, code },
+            Ok(mut code) => {
+                // NOTE: `insert_final_newline` relies on the fact that:
+                // - each formatter already ensures there is traliling newline
+                // - each formatter does not have an option to disable trailing newline
+                // So we can trim it here without allocating new string.
+                if !insert_final_newline {
+                    let trimmed_len = code.trim_end().len();
+                    code.truncate(trimmed_len);
+                }
+
+                FormatResult::Success { is_changed: source_text != code, code }
+            }
             Err(err) => FormatResult::Error(vec![err]),
         }
     }

apps/oxfmt/test/__snapshots__/insert_final_newline.test.ts.snap

@@ -0,0 +1,67 @@
+// Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
+
+exports[`insertFinalNewline > editorconfig setting removes final newline 1`] = `
+"--- FILE -----------
+test.ts
+--- BEFORE ---------
+const foo = 1
+
+--- AFTER ----------
+const foo = 1;
+--------------------
+
+--- FILE -----------
+test.css
+--- BEFORE ---------
+.foo { color: red }
+
+--- AFTER ----------
+.foo {
+  color: red;
+}
+--------------------
+
+--- FILE -----------
+test.toml
+--- BEFORE ---------
+[foo]
+bar = 1
+
+--- AFTER ----------
+[foo]
+bar = 1
+--------------------"
+`;
+
+exports[`insertFinalNewline > oxfmtrc setting removes final newline 1`] = `
+"--- FILE -----------
+test.ts
+--- BEFORE ---------
+const foo = 1
+
+--- AFTER ----------
+const foo = 1;
+--------------------
+
+--- FILE -----------
+test.css
+--- BEFORE ---------
+.foo { color: red }
+
+--- AFTER ----------
+.foo {
+  color: red;
+}
+--------------------
+
+--- FILE -----------
+test.toml
+--- BEFORE ---------
+[foo]
+bar = 1
+
+--- AFTER ----------
+[foo]
+bar = 1
+--------------------"
+`;

apps/oxfmt/test/fixtures/insert_final_newline/editorconfig_only/.editorconfig

@@ -0,0 +1,4 @@
+root = true
+
+[*]
+insert_final_newline = false

apps/oxfmt/test/fixtures/insert_final_newline/editorconfig_only/test.css

@@ -0,0 +1 @@
+.foo { color: red }

apps/oxfmt/test/fixtures/insert_final_newline/editorconfig_only/test.toml

@@ -0,0 +1,2 @@
+[foo]
+bar = 1

apps/oxfmt/test/fixtures/insert_final_newline/editorconfig_only/test.ts

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

apps/oxfmt/test/fixtures/insert_final_newline/oxfmtrc_only/.oxfmtrc.json

@@ -0,0 +1,3 @@
+{
+  "insertFinalNewline": false
+}

apps/oxfmt/test/fixtures/insert_final_newline/oxfmtrc_only/test.css

@@ -0,0 +1 @@
+.foo { color: red }

apps/oxfmt/test/fixtures/insert_final_newline/oxfmtrc_only/test.toml

@@ -0,0 +1,2 @@
+[foo]
+bar = 1

apps/oxfmt/test/fixtures/insert_final_newline/oxfmtrc_only/test.ts

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

apps/oxfmt/test/insert_final_newline.test.ts

@@ -0,0 +1,33 @@
+import { describe, expect, it } from "vitest";
+import { join } from "node:path";
+import { runWriteModeAndSnapshot } from "./utils";
+
+const fixturesDir = join(__dirname, "fixtures", "insert_final_newline");
+
+describe("insertFinalNewline", () => {
+  // .oxfmtrc.json:
+  //   insertFinalNewline=false
+  //
+  // Expected: No trailing newline in formatted output
+  // - test.ts: TypeScript file (oxc_formatter)
+  // - test.css: CSS file (external formatter)
+  // - test.toml: TOML file (toml formatter)
+  it("oxfmtrc setting removes final newline", async () => {
+    const cwd = join(fixturesDir, "oxfmtrc_only");
+    const snapshot = await runWriteModeAndSnapshot(cwd, ["test.ts", "test.css", "test.toml"]);
+    expect(snapshot).toMatchSnapshot();
+  });
+
+  // .editorconfig:
+  //   [*] insert_final_newline=false
+  //
+  // Expected: No trailing newline in formatted output
+  // - test.ts: TypeScript file (oxc_formatter)
+  // - test.css: CSS file (external formatter)
+  // - test.toml: TOML file (toml formatter)
+  it("editorconfig setting removes final newline", async () => {
+    const cwd = join(fixturesDir, "editorconfig_only");
+    const snapshot = await runWriteModeAndSnapshot(cwd, ["test.ts", "test.css", "test.toml"]);
+    expect(snapshot).toMatchSnapshot();
+  });
+});

crates/oxc_formatter/src/oxfmtrc.rs

@@ -84,6 +84,10 @@ pub struct Oxfmtrc {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub embedded_language_formatting: Option<EmbeddedLanguageFormattingConfig>,
 
+    /// Whether to insert a final newline at the end of the file. (Default: `true`)
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub insert_final_newline: Option<bool>,
+
     /// Experimental: Sort import statements. Disabled by default.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub experimental_sort_imports: Option<SortImportsConfig>,
@@ -239,11 +243,12 @@ pub enum SortOrderConfig {
 pub struct OxfmtOptions {
     pub ignore_patterns: Vec<String>,
     pub sort_package_json: bool,
+    pub insert_final_newline: bool,
 }
 
 impl Default for OxfmtOptions {
     fn default() -> Self {
-        Self { ignore_patterns: vec![], sort_package_json: true }
+        Self { ignore_patterns: vec![], sort_package_json: true, insert_final_newline: true }
     }
 }
 
@@ -426,6 +431,9 @@ impl Oxfmtrc {
         if let Some(sort_package_json) = self.experimental_sort_package_json {
             oxfmt_options.sort_package_json = sort_package_json;
         }
+        if let Some(insert_final_newline) = self.insert_final_newline {
+            oxfmt_options.insert_final_newline = insert_final_newline;
+        }
 
         Ok((format_options, oxfmt_options))
     }
@@ -556,6 +564,7 @@ impl Oxfmtrc {
 
         // Below are our own extensions, just remove them
         obj.remove("ignorePatterns");
+        obj.remove("insertFinalNewline");
         obj.remove("experimentalSortImports");
         obj.remove("experimentalSortPackageJson");
 

crates/oxc_formatter/tests/snapshots/schema_json.snap

@@ -229,6 +229,14 @@ expression: json
         "null"
       ]
     },
+    "insertFinalNewline": {
+      "description": "Whether to insert a final newline at the end of the file. (Default: `true`)",
+      "markdownDescription": "Whether to insert a final newline at the end of the file. (Default: `true`)",
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
     "jsxSingleQuote": {
       "description": "Use single quotes instead of double quotes in JSX. (Default: `false`)",
       "markdownDescription": "Use single quotes instead of double quotes in JSX. (Default: `false`)",