feat(fmt): add JSON trailing comma config (#33383)

Fixes #27856
Fixes #28522

---------

Co-authored-by: chatgpt-codex-connector[bot] <199175422+chatgpt-codex-connector[bot]@users.noreply.github.com>
Co-authored-by: Bartek Iwańczuk <bartek@deno.com>

Author: 3 people

cli/schemas/config-file.v1.json

@@ -765,6 +765,11 @@
           "default": "onlyMultiLine",
           "enum": ["never", "always", "onlyMultiLine"]
         },
+        "json.trailingCommas": {
+          "description": "Whether to add trailing commas in JSON and JSONC. Defaults to \"never\". The \"jsonc\" option adds trailing commas in JSONC files and omits them in JSON files.",
+          "default": "never",
+          "enum": ["never", "always", "maintain", "jsonc"]
+        },
         "operatorPosition": {
           "description": "Where to place the operator for expressions that span multiple lines in JavaScript and TypeScript.",
           "default": "sameLine",

cli/tools/fmt.rs

@@ -1515,10 +1515,21 @@ fn get_resolved_markdown_config(
 fn get_resolved_json_config(
   options: &FmtOptionsConfig,
 ) -> dprint_plugin_json::configuration::Configuration {
+  use deno_config::deno_json::JsonTrailingCommaKind;
+  use dprint_plugin_json::configuration::TrailingCommaKind;
+
   let mut builder =
     dprint_plugin_json::configuration::ConfigurationBuilder::new();
 
   builder.deno();
+  if let Some(json_trailing_commas) = options.json_trailing_commas {
+    builder.trailing_commas(match json_trailing_commas {
+      JsonTrailingCommaKind::Always => TrailingCommaKind::Always,
+      JsonTrailingCommaKind::Jsonc => TrailingCommaKind::Jsonc,
+      JsonTrailingCommaKind::Maintain => TrailingCommaKind::Maintain,
+      JsonTrailingCommaKind::Never => TrailingCommaKind::Never,
+    });
+  }
 
   if let Some(use_tabs) = options.use_tabs {
     builder.use_tabs(use_tabs);
@@ -1879,6 +1890,7 @@ fn is_supported_ext_fmt(path: &Path) -> bool {
 
 #[cfg(test)]
 mod test {
+  use deno_config::deno_json::JsonTrailingCommaKind;
   use test_util::assert_starts_with;
 
   use super::*;
@@ -2061,4 +2073,102 @@ mod test {
     .unwrap();
     assert_eq!(file_text, "let a = 1;\n",);
   }
+
+  #[test]
+  fn test_jsonc_does_not_add_trailing_commas_by_default() {
+    let file_text = format_file(
+      Path::new("test.jsonc"),
+      &FileContents {
+        had_bom: false,
+        text: r#"{
+  "a": 1,
+  "b": 2
+}
+"#
+        .into(),
+      },
+      &FmtOptionsConfig::default(),
+      &UnstableFmtOptions::default(),
+      None,
+    )
+    .unwrap();
+    assert_eq!(file_text, None);
+  }
+
+  #[test]
+  fn test_json_does_not_add_trailing_commas() {
+    let file_text = format_file(
+      Path::new("test.json"),
+      &FileContents {
+        had_bom: false,
+        text: r#"{
+  "a": 1,
+  "b": 2
+}
+"#
+        .into(),
+      },
+      &FmtOptionsConfig::default(),
+      &UnstableFmtOptions::default(),
+      None,
+    )
+    .unwrap();
+    assert_eq!(file_text, None);
+  }
+
+  #[test]
+  fn test_jsonc_trailing_commas_can_be_disabled() {
+    let file_text = format_file(
+      Path::new("test.jsonc"),
+      &FileContents {
+        had_bom: false,
+        text: r#"{
+  "a": 1,
+  "b": 2
+}
+"#
+        .into(),
+      },
+      &FmtOptionsConfig {
+        json_trailing_commas: Some(JsonTrailingCommaKind::Never),
+        ..Default::default()
+      },
+      &UnstableFmtOptions::default(),
+      None,
+    )
+    .unwrap();
+    assert_eq!(file_text, None);
+  }
+
+  #[test]
+  fn test_json_trailing_commas_can_be_enabled() {
+    let file_text = format_file(
+      Path::new("test.json"),
+      &FileContents {
+        had_bom: false,
+        text: r#"{
+  "a": 1,
+  "b": 2
+}
+"#
+        .into(),
+      },
+      &FmtOptionsConfig {
+        json_trailing_commas: Some(JsonTrailingCommaKind::Always),
+        ..Default::default()
+      },
+      &UnstableFmtOptions::default(),
+      None,
+    )
+    .unwrap()
+    .unwrap();
+    assert_eq!(
+      file_text,
+      r#"{
+  "a": 1,
+  "b": 2,
+}
+"#
+    );
+  }
 }

libs/config/deno_json/mod.rs

@@ -337,6 +337,15 @@ pub enum TrailingCommas {
   OnlyMultiLine,
 }
 
+#[derive(Clone, Copy, Debug, Serialize, Deserialize, Hash, PartialEq)]
+#[serde(deny_unknown_fields, rename_all = "camelCase")]
+pub enum JsonTrailingCommaKind {
+  Always,
+  Jsonc,
+  Maintain,
+  Never,
+}
+
 #[derive(Clone, Copy, Debug, Serialize, Deserialize, Hash, PartialEq)]
 #[serde(deny_unknown_fields, rename_all = "camelCase")]
 pub enum OperatorPosition {
@@ -394,6 +403,7 @@ pub struct FmtOptionsConfig {
   pub single_body_position: Option<SingleBodyPosition>,
   pub next_control_flow_position: Option<NextControlFlowPosition>,
   pub trailing_commas: Option<TrailingCommas>,
+  pub json_trailing_commas: Option<JsonTrailingCommaKind>,
   pub operator_position: Option<OperatorPosition>,
   pub jsx_bracket_position: Option<BracketPosition>,
   pub jsx_force_new_lines_surrounding_content: Option<bool>,
@@ -420,6 +430,7 @@ impl FmtOptionsConfig {
       && self.single_body_position.is_none()
       && self.next_control_flow_position.is_none()
       && self.trailing_commas.is_none()
+      && self.json_trailing_commas.is_none()
       && self.operator_position.is_none()
       && self.jsx_bracket_position.is_none()
       && self.jsx_force_new_lines_surrounding_content.is_none()
@@ -491,6 +502,8 @@ struct SerializedFmtConfig {
   pub single_body_position: Option<SingleBodyPosition>,
   pub next_control_flow_position: Option<NextControlFlowPosition>,
   pub trailing_commas: Option<TrailingCommas>,
+  #[serde(rename = "json.trailingCommas")]
+  pub json_trailing_commas: Option<JsonTrailingCommaKind>,
   pub operator_position: Option<OperatorPosition>,
   #[serde(rename = "jsx.bracketPosition")]
   pub jsx_bracket_position: Option<BracketPosition>,
@@ -533,6 +546,7 @@ impl SerializedFmtConfig {
       single_body_position: self.single_body_position,
       next_control_flow_position: self.next_control_flow_position,
       trailing_commas: self.trailing_commas,
+      json_trailing_commas: self.json_trailing_commas,
       operator_position: self.operator_position,
       jsx_bracket_position: self.jsx_bracket_position,
       jsx_force_new_lines_surrounding_content: self
@@ -2529,6 +2543,7 @@ mod tests {
         "singleBodyPosition": "nextLine",
         "nextControlFlowPosition": "sameLine",
         "trailingCommas": "never",
+        "json.trailingCommas": "maintain",
         "operatorPosition": "maintain",
         "jsx.bracketPosition": "maintain",
         "jsx.forceNewLinesSurroundingContent": true,
@@ -2604,6 +2619,7 @@ mod tests {
           single_body_position: Some(SingleBodyPosition::NextLine),
           next_control_flow_position: Some(NextControlFlowPosition::SameLine),
           trailing_commas: Some(TrailingCommas::Never),
+          json_trailing_commas: Some(JsonTrailingCommaKind::Maintain),
           operator_position: Some(OperatorPosition::Maintain),
           jsx_bracket_position: Some(BracketPosition::Maintain),
           jsx_force_new_lines_surrounding_content: Some(true),

libs/config/workspace/mod.rs

@@ -2301,6 +2301,10 @@ impl WorkspaceDirectory {
           .options
           .trailing_commas
           .or(root_config.options.trailing_commas),
+        json_trailing_commas: member_config
+          .options
+          .json_trailing_commas
+          .or(root_config.options.json_trailing_commas),
         operator_position: member_config
           .options
           .operator_position
@@ -3064,6 +3068,7 @@ pub mod test {
   use crate::deno_json::BracePosition;
   use crate::deno_json::BracketPosition;
   use crate::deno_json::DenoJsonCache;
+  use crate::deno_json::JsonTrailingCommaKind;
   use crate::deno_json::MultiLineParens;
   use crate::deno_json::NewLineKind;
   use crate::deno_json::NextControlFlowPosition;
@@ -4067,6 +4072,7 @@ pub mod test {
           "singleBodyPosition": "sameLine",
           "nextControlFlowPosition": "nextLine",
           "trailingCommas": "always",
+          "json.trailingCommas": "never",
           "operatorPosition": "sameLine",
           "jsx.bracketPosition": "sameLine",
           "jsx.forceNewLinesSurroundingContent": false,
@@ -4092,6 +4098,7 @@ pub mod test {
           "singleBodyPosition": "maintain",
           "nextControlFlowPosition": "maintain",
           "trailingCommas": "onlyMultiLine",
+          "json.trailingCommas": "maintain",
           "operatorPosition": "nextLine",
           "jsx.bracketPosition": "nextLine",
           "jsx.forceNewLinesSurroundingContent": true,
@@ -4123,6 +4130,7 @@ pub mod test {
           single_body_position: Some(SingleBodyPosition::Maintain),
           next_control_flow_position: Some(NextControlFlowPosition::Maintain),
           trailing_commas: Some(TrailingCommas::OnlyMultiLine),
+          json_trailing_commas: Some(JsonTrailingCommaKind::Maintain),
           operator_position: Some(OperatorPosition::NextLine),
           jsx_bracket_position: Some(BracketPosition::NextLine),
           jsx_force_new_lines_surrounding_content: Some(true),
@@ -4167,6 +4175,7 @@ pub mod test {
           single_body_position: Some(SingleBodyPosition::SameLine),
           next_control_flow_position: Some(NextControlFlowPosition::NextLine),
           trailing_commas: Some(TrailingCommas::Always),
+          json_trailing_commas: Some(JsonTrailingCommaKind::Never),
           operator_position: Some(OperatorPosition::SameLine),
           jsx_bracket_position: Some(BracketPosition::SameLine),
           jsx_force_new_lines_surrounding_content: Some(false),

tests/specs/fmt/jsonc_trailing_commas/__test__.jsonc

@@ -0,0 +1,19 @@
+{
+  "tests": {
+    "fmt_jsonc_default_trailing_commas": {
+      "args": "fmt --ext=jsonc -",
+      "input": "{\n  \"a\": 1,\n  \"b\": 2\n}\n",
+      "output": "{\n  \"a\": 1,\n  \"b\": 2\n}\n"
+    },
+    "fmt_jsonc_trailing_commas_never": {
+      "args": "fmt --config deno.never.jsonc --ext=jsonc -",
+      "input": "{\n  \"a\": 1,\n  \"b\": 2\n}\n",
+      "output": "{\n  \"a\": 1,\n  \"b\": 2\n}\n"
+    },
+    "fmt_json_trailing_commas_always": {
+      "args": "fmt --config deno.always.jsonc --ext=json -",
+      "input": "{\n  \"a\": 1,\n  \"b\": 2\n}\n",
+      "output": "{\n  \"a\": 1,\n  \"b\": 2,\n}\n"
+    }
+  }
+}

tests/specs/fmt/jsonc_trailing_commas/deno.always.jsonc

@@ -0,0 +1,5 @@
+{
+  "fmt": {
+    "json.trailingCommas": "always"
+  }
+}

tests/specs/fmt/jsonc_trailing_commas/deno.never.jsonc

@@ -0,0 +1,5 @@
+{
+  "fmt": {
+    "json.trailingCommas": "never"
+  }
+}

tests/specs/fmt/malformed_config/error.out

@@ -1,4 +1,4 @@
 error: Failed to parse "fmt" configuration
 
 Caused by:
-    unknown field `dont_know_this_field`, expected one of `useTabs`, `lineWidth`, `indentWidth`, `singleQuote`, `proseWrap`, `semiColons`, `quoteProps`, `newLineKind`, `useBraces`, `bracePosition`, `singleBodyPosition`, `nextControlFlowPosition`, `trailingCommas`, `operatorPosition`, `jsx.bracketPosition`, `jsx.forceNewLinesSurroundingContent`, `jsx.multiLineParens`, `typeLiteral.separatorKind`, `spaceAround`, `spaceSurroundingProperties`, `vueComponentCase`, `angularNextControlFlowSameLine`, `options`, `include`, `exclude`, `files`
+    unknown field `dont_know_this_field`, expected one of `useTabs`, `lineWidth`, `indentWidth`, `singleQuote`, `proseWrap`, `semiColons`, `quoteProps`, `newLineKind`, `useBraces`, `bracePosition`, `singleBodyPosition`, `nextControlFlowPosition`, `trailingCommas`, `json.trailingCommas`, `operatorPosition`, `jsx.bracketPosition`, `jsx.forceNewLinesSurroundingContent`, `jsx.multiLineParens`, `typeLiteral.separatorKind`, `spaceAround`, `spaceSurroundingProperties`, `vueComponentCase`, `angularNextControlFlowSameLine`, `options`, `include`, `exclude`, `files`