feat(rome_js_formatter, rome_cli): add arrowParentheses option (#4667)

CHANGELOG.md

@@ -101,6 +101,8 @@ if no error diagnostics are emitted.
 
 - Added a new option called `--jsx-quote-style` to the formatter. This option allows you to choose between single and double quotes for JSX attributes. [#4486](https://github.com/rome/tools/issues/4486)
 
+- Added a new option called `--arrow-parentheses` to the formatter. This option allows you to set the parentheses style for arrow functions. [#4666](https://github.com/rome/tools/issues/4666)
+
 ### Linter
 
 - [`noDuplicateParameters`](https://docs.rome.tools/lint/rules/noduplicateparameters/): enhanced rule to manage constructor parameters.

crates/rome_cli/tests/commands/format.rs

@@ -52,6 +52,23 @@ const APPLY_TRAILING_COMMA_AFTER: &str = r#"const a = [
 ];
 "#;
 
+const APPLY_ARROW_PARENTHESES_BEFORE: &str = r#"
+action => {}
+(action) => {}
+({ action }) => {}
+([ action ]) => {}
+(...action) => {}
+(action = 1) => {}
+"#;
+
+const APPLY_ARROW_PARENTHESES_AFTER: &str = r#"action => {};
+action => {};
+({ action }) => {};
+([action]) => {};
+(...action) => {};
+(action = 1) => {};
+"#;
+
 const DEFAULT_CONFIGURATION_BEFORE: &str = r#"function f() {
     return { a, b }
   }"#;
@@ -707,6 +724,51 @@ fn applies_custom_trailing_comma() {
     ));
 }
 
+#[test]
+fn applies_custom_arrow_parentheses() {
+    let mut fs = MemoryFileSystem::default();
+    let mut console = BufferConsole::default();
+
+    let file_path = Path::new("file.js");
+    fs.insert(file_path.into(), APPLY_ARROW_PARENTHESES_BEFORE.as_bytes());
+
+    let result = run_cli(
+        DynRef::Borrowed(&mut fs),
+        &mut console,
+        Args::from(
+            [
+                ("format"),
+                ("--arrow-parentheses"),
+                ("as-needed"),
+                ("--write"),
+                file_path.as_os_str().to_str().unwrap(),
+            ]
+            .as_slice(),
+        ),
+    );
+
+    assert!(result.is_ok(), "run_cli returned {result:?}");
+
+    let mut file = fs
+        .open(file_path)
+        .expect("formatting target file was removed by the CLI");
+
+    let mut content = String::new();
+    file.read_to_string(&mut content)
+        .expect("failed to read file from memory FS");
+
+    assert_eq!(content, APPLY_ARROW_PARENTHESES_AFTER);
+
+    drop(file);
+    assert_cli_snapshot(SnapshotPayload::new(
+        module_path!(),
+        "applies_custom_arrow_parentheses",
+        fs,
+        console,
+        result,
+    ));
+}
+
 #[test]
 fn trailing_comma_parse_errors() {
     let mut console = BufferConsole::default();

crates/rome_cli/tests/snapshots/main_commands_check/check_help.snap

@@ -33,6 +33,8 @@ The configuration that is contained inside the file `rome.json`
                               syntactic structures. Defaults to "all".
         --semicolons=<always|as-needed>  Whether the formatter prints semicolons for all statements or
                               only in for statements where it is necessary because of ASI.
+        --arrow-parentheses=<always|as-needed>  Whether to add non-necessary parentheses to arrow functions.
+                              Defaults to "always".
 
 Global options applied to all commands
         --colors=<off|force>    Set the formatting mode for markup: "off" prints everything as plain

crates/rome_cli/tests/snapshots/main_commands_ci/ci_help.snap

@@ -34,6 +34,8 @@ The configuration that is contained inside the file `rome.json`
                               syntactic structures. Defaults to "all".
         --semicolons=<always|as-needed>  Whether the formatter prints semicolons for all statements or
                               only in for statements where it is necessary because of ASI.
+        --arrow-parentheses=<always|as-needed>  Whether to add non-necessary parentheses to arrow functions.
+                              Defaults to "always".
 
 Global options applied to all commands
         --colors=<off|force>    Set the formatting mode for markup: "off" prints everything as plain

crates/rome_cli/tests/snapshots/main_commands_format/applies_custom_arrow_parentheses.snap

@@ -0,0 +1,23 @@
+---
+source: crates/rome_cli/tests/snap_test.rs
+expression: content
+---
+## `file.js`
+
+```js
+action => {};
+action => {};
+({ action }) => {};
+([action]) => {};
+(...action) => {};
+(action = 1) => {};
+
+```
+
+# Emitted Messages
+
+```block
+Formatted 1 file(s) in <TIME>
+```
+
+

crates/rome_cli/tests/snapshots/main_commands_format/format_help.snap

@@ -59,6 +59,8 @@ Available options:
                               syntactic structures. Defaults to "all".
         --semicolons=<always|as-needed>  Whether the formatter prints semicolons for all statements or
                               only in for statements where it is necessary because of ASI.
+        --arrow-parentheses=<always|as-needed>  Whether to add non-necessary parentheses to arrow functions.
+                              Defaults to "always".
         --stdin-file-path=PATH  A file name with its extension to pass when reading from standard in,
                               e.g. echo 'let a;' | rome format --stdin-file-path=file.js".
         --write                 Writes formatted files to file system.

crates/rome_cli/tests/snapshots/main_commands_lint/check_help.snap

@@ -33,6 +33,8 @@ The configuration that is contained inside the file `rome.json`
                               syntactic structures. Defaults to "all".
         --semicolons=<always|as-needed>  Whether the formatter prints semicolons for all statements or
                               only in for statements where it is necessary because of ASI.
+        --arrow-parentheses=<always|as-needed>  Whether to add non-necessary parentheses to arrow functions.
+                              Defaults to "always".
 
 Global options applied to all commands
         --colors=<off|force>    Set the formatting mode for markup: "off" prints everything as plain

crates/rome_js_formatter/src/context.rs

@@ -156,6 +156,9 @@ pub struct JsFormatOptions {
     /// Whether the formatter prints semicolons for all statements, class members, and type members or only when necessary because of [ASI](https://tc39.es/ecma262/multipage/ecmascript-language-lexical-grammar.html#sec-automatic-semicolon-insertion).
     semicolons: Semicolons,
 
+    /// Whether to add non-necessary parentheses to arrow functions. Defaults to "always".
+    arrow_parentheses: ArrowParentheses,
+
     /// Information related to the current file
     source_type: JsFileSource,
 }
@@ -171,9 +174,15 @@ impl JsFormatOptions {
             quote_properties: QuoteProperties::default(),
             trailing_comma: TrailingComma::default(),
             semicolons: Semicolons::default(),
+            arrow_parentheses: ArrowParentheses::default(),
         }
     }
 
+    pub fn with_arrow_parentheses(mut self, arrow_parentheses: ArrowParentheses) -> Self {
+        self.arrow_parentheses = arrow_parentheses;
+        self
+    }
+
     pub fn with_indent_style(mut self, indent_style: IndentStyle) -> Self {
         self.indent_style = indent_style;
         self
@@ -209,6 +218,10 @@ impl JsFormatOptions {
         self
     }
 
+    pub fn arrow_parentheses(&self) -> ArrowParentheses {
+        self.arrow_parentheses
+    }
+
     pub fn quote_style(&self) -> QuoteStyle {
         self.quote_style
     }
@@ -263,7 +276,8 @@ impl fmt::Display for JsFormatOptions {
         writeln!(f, "JSX quote style: {}", self.jsx_quote_style)?;
         writeln!(f, "Quote properties: {}", self.quote_properties)?;
         writeln!(f, "Trailing comma: {}", self.trailing_comma)?;
-        writeln!(f, "Semicolons: {}", self.semicolons)
+        writeln!(f, "Semicolons: {}", self.semicolons)?;
+        writeln!(f, "Arrow parentheses: {}", self.arrow_parentheses)
     }
 }
 
@@ -487,3 +501,64 @@ impl VisitNode<JsonLanguage> for Semicolons {
         Some(())
     }
 }
+
+#[derive(Debug, Eq, PartialEq, Clone, Copy, Default)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema),
+    serde(rename_all = "camelCase")
+)]
+pub enum ArrowParentheses {
+    #[default]
+    Always,
+    AsNeeded,
+}
+
+impl ArrowParentheses {
+    pub(crate) const KNOWN_VALUES: &'static [&'static str] = &["always", "asNeeded"];
+
+    pub const fn is_as_needed(&self) -> bool {
+        matches!(self, Self::AsNeeded)
+    }
+
+    pub const fn is_always(&self) -> bool {
+        matches!(self, Self::Always)
+    }
+}
+
+impl FromStr for ArrowParentheses {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "as-needed" | "AsNeeded" => Ok(Self::AsNeeded),
+            "always" | "Always" => Ok(Self::Always),
+            _ => Err("Value not supported for Arrow parentheses. Supported values are 'as-needed' and 'always'."),
+        }
+    }
+}
+
+impl fmt::Display for ArrowParentheses {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ArrowParentheses::AsNeeded => write!(f, "As needed"),
+            ArrowParentheses::Always => write!(f, "Always"),
+        }
+    }
+}
+
+impl VisitNode<JsonLanguage> for ArrowParentheses {
+    fn visit_member_value(
+        &mut self,
+        node: &SyntaxNode<JsonLanguage>,
+        diagnostics: &mut Vec<DeserializationDiagnostic>,
+    ) -> Option<()> {
+        let node = with_only_known_variants(node, ArrowParentheses::KNOWN_VALUES, diagnostics)?;
+        if node.inner_string_text().ok()?.text() == "asNeeded" {
+            *self = ArrowParentheses::AsNeeded;
+        } else {
+            *self = ArrowParentheses::Always;
+        }
+        Some(())
+    }
+}

crates/rome_js_formatter/src/js/bindings/parameters.rs

@@ -1,12 +1,13 @@
 use crate::prelude::*;
 use rome_formatter::{write, CstFormatContext};
 
+use crate::js::expressions::arrow_function_expression::can_avoid_parentheses;
 use crate::js::lists::parameter_list::FormatJsAnyParameterList;
 use crate::utils::test_call::is_test_call_argument;
 use rome_js_syntax::parameter_ext::{AnyJsParameterList, AnyParameter};
 use rome_js_syntax::{
-    AnyJsConstructorParameter, AnyJsFormalParameter, AnyTsType, JsConstructorParameters,
-    JsParameters, JsSyntaxToken,
+    AnyJsConstructorParameter, AnyJsFormalParameter, AnyTsType, JsArrowFunctionExpression,
+    JsConstructorParameters, JsParameters, JsSyntaxToken,
 };
 use rome_rowan::{declare_node_union, SyntaxResult};
 
@@ -48,6 +49,10 @@ impl Format<JsFormatContext> for FormatAnyJsParameters {
         let l_paren_token = self.l_paren_token()?;
         let r_paren_token = self.r_paren_token()?;
 
+        let parentheses_not_needed = self
+            .as_arrow_function_expression()
+            .map_or(false, |expression| can_avoid_parentheses(&expression, f));
+
         match layout {
             ParameterLayout::NoParameters => {
                 write!(
@@ -60,27 +65,50 @@ impl Format<JsFormatContext> for FormatAnyJsParameters {
                 )
             }
             ParameterLayout::Hug => {
+                if !parentheses_not_needed {
+                    write!(f, [l_paren_token.format()])?;
+                } else {
+                    write!(f, [format_removed(&l_paren_token)])?;
+                }
+
                 write!(
                     f,
-                    [
-                        l_paren_token.format(),
-                        FormatJsAnyParameterList::with_layout(&list, ParameterLayout::Hug),
-                        &r_paren_token.format()
-                    ]
-                )
+                    [FormatJsAnyParameterList::with_layout(
+                        &list,
+                        ParameterLayout::Hug
+                    )]
+                )?;
+
+                if !parentheses_not_needed {
+                    write!(f, [&r_paren_token.format()])?;
+                } else {
+                    write!(f, [format_removed(&r_paren_token)])?;
+                }
+
+                Ok(())
             }
             ParameterLayout::Default => {
+                if !parentheses_not_needed {
+                    write!(f, [l_paren_token.format()])?;
+                } else {
+                    write!(f, [format_removed(&l_paren_token)])?;
+                }
+
                 write!(
                     f,
-                    [
-                        l_paren_token.format(),
-                        soft_block_indent(&FormatJsAnyParameterList::with_layout(
-                            &list,
-                            ParameterLayout::Default
-                        )),
-                        r_paren_token.format()
-                    ]
-                )
+                    [soft_block_indent(&FormatJsAnyParameterList::with_layout(
+                        &list,
+                        ParameterLayout::Default
+                    ))]
+                )?;
+
+                if !parentheses_not_needed {
+                    write!(f, [r_paren_token.format()])?;
+                } else {
+                    write!(f, [format_removed(&r_paren_token)])?;
+                }
+
+                Ok(())
             }
         }
     }
@@ -128,6 +156,16 @@ impl FormatAnyJsParameters {
 
         Ok(result)
     }
+
+    fn as_arrow_function_expression(&self) -> Option<JsArrowFunctionExpression> {
+        match self {
+            FormatAnyJsParameters::JsParameters(parameters) => parameters
+                .syntax()
+                .parent()
+                .and_then(JsArrowFunctionExpression::cast),
+            FormatAnyJsParameters::JsConstructorParameters(_) => None,
+        }
+    }
 }
 
 #[derive(Copy, Debug, Clone, Eq, PartialEq)]