feat(formatter): trailing newline

.changeset/trailing-newline-option.md

@@ -0,0 +1,31 @@
+---
+"@biomejs/biome": minor
+---
+
+Added the formatter option [`trailingNewline`](https://biomejs.dev/reference/configuration/#formattertrailingnewline).
+
+When set to `false`, the formatter will remove the trailing newline at the end of formatted files. The default value is `true`, which preserves the current behavior of adding a trailing newline.
+
+This option is available globally and for each language-specific formatter configuration:
+
+```json
+{
+  "formatter": {
+    "trailingNewline": false
+  },
+  "javascript": {
+    "formatter": {
+      "trailingNewline": true
+    }
+  }
+}
+```
+
+The following CLI flags have been added. They accept `true` or `false` as value:
+- `--formatter-trailing-newline`
+- `--javascript-formatter-trailing-newline`
+- `--json-formatter-trailing-newline`
+- `--graphql-formatter-trailing-newline`
+- `--css-formatter-trailing-newline`
+- `--html-formatter-trailing-newline`
+

.claude/settings.local.json

@@ -0,0 +1,11 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(cargo clippy:*)",
+      "Bash(cargo t:*)",
+      "Bash(cargo clean:*)"
+    ],
+    "deny": [],
+    "ask": []
+  }
+}

crates/biome_cli/src/commands/mod.rs

@@ -310,16 +310,16 @@ pub enum BiomeCommand {
         #[bpaf(external(json_parser_configuration), optional, hide_usage)]
         json_parser: Option<JsonParserConfiguration>,
 
-        #[bpaf(external(css_parser_configuration), optional, hide_usage, hide)]
+        #[bpaf(external(css_parser_configuration), optional, hide_usage)]
         css_parser: Option<CssParserConfiguration>,
 
-        #[bpaf(external(graphql_formatter_configuration), optional, hide_usage, hide)]
+        #[bpaf(external(graphql_formatter_configuration), optional, hide_usage)]
         graphql_formatter: Option<GraphqlFormatterConfiguration>,
 
-        #[bpaf(external(css_formatter_configuration), optional, hide_usage, hide)]
+        #[bpaf(external(css_formatter_configuration), optional, hide_usage)]
         css_formatter: Option<CssFormatterConfiguration>,
 
-        #[bpaf(external(html_formatter_configuration), optional, hide_usage, hide)]
+        #[bpaf(external(html_formatter_configuration), optional, hide_usage)]
         html_formatter: Option<HtmlFormatterConfiguration>,
 
         #[bpaf(external(vcs_configuration), optional, hide_usage)]

crates/biome_cli/src/execute/migrate/prettier.rs

@@ -242,6 +242,7 @@ impl TryFrom<PrettierConfiguration> for biome_configuration::Configuration {
             // editorconfig support is intentionally set to true, because prettier always reads the editorconfig file
             // see: https://github.com/prettier/prettier/issues/15255
             use_editorconfig: Some(true.into()),
+            trailing_newline: None,
         };
         result.formatter = Some(formatter);
 
@@ -278,6 +279,7 @@ impl TryFrom<PrettierConfiguration> for biome_configuration::Configuration {
             jsx_quote_style: Some(jsx_quote_style),
             attribute_position: Some(AttributePosition::default()),
             operator_linebreak: None,
+            trailing_newline: None,
         };
         let js_config = biome_configuration::JsConfiguration {
             formatter: Some(js_formatter),

crates/biome_cli/src/runner/impls/process_file/format.rs

@@ -132,6 +132,7 @@ impl ProcessFile for FormatProcessFile {
             execution: _,
             skip_ignore_check,
         } = payload;
+
         let FileFeaturesResult {
             features_supported: file_features,
         } = workspace.file_features(SupportsFeatureParams {

crates/biome_cli/tests/cases/editorconfig.rs

@@ -698,3 +698,50 @@ fn indent_size_can_set_to_tab() {
         result,
     ));
 }
+
+#[test]
+fn should_support_insert_final_newline() {
+    let fs = MemoryFileSystem::default();
+    let mut console = BufferConsole::default();
+
+    let editorconfig = Utf8Path::new(".editorconfig");
+    fs.insert(
+        editorconfig.into(),
+        r#"
+[*]
+insert_final_newline = false
+"#,
+    );
+
+    let biomeconfig = Utf8Path::new("biome.json");
+    fs.insert(
+        biomeconfig.into(),
+        r#"{
+    "formatter": {
+        "useEditorconfig": true
+    }
+}
+"#,
+    );
+
+    let test_file = Utf8Path::new("test.js");
+    let contents = r#"function test() {
+    console.log("no newline")}"#;
+    fs.insert(test_file.into(), contents);
+
+    let (fs, result) = run_cli(
+        fs,
+        &mut console,
+        Args::from(["format", test_file.as_str()].as_slice()),
+    );
+
+    assert!(result.is_err(), "run_cli returned {result:?}");
+
+    assert_cli_snapshot(SnapshotPayload::new(
+        module_path!(),
+        "should_support_insert_final_newline",
+        fs,
+        console,
+        result,
+    ));
+}