feat(rome_json_parser): support allowTrailingCommas option (#326)

CHANGELOG.md

@@ -62,6 +62,19 @@ Read our [guidelines for writing a good changelog entry](https://github.com/biom
 ### Parser
 
 - Enhance diagnostic for infer type handling in the parser. The 'infer' keyword can only be utilized within the 'extends' clause of a conditional type. Using it outside of this context will result in an error. Ensure that any type declarations using 'infer' are correctly placed within the conditional type structure to avoid parsing issues. Contributed by @denbezrukov
+- Add support for parsing trailing commas inside JSON files:
+
+  ```json
+  {
+    "json": {
+      "parser": {
+        "allowTrailingCommas": true
+      }
+    }
+  }
+  ```
+
+  Contributed by @nissy-dev
 
 ### VSCode
 

crates/biome_cli/tests/commands/format.rs

@@ -1856,13 +1856,13 @@ fn ignore_comments_error_when_allow_comments() {
 }
 
 	"#;
-    let rome_config = "biome.json";
+    let biome_config = "biome.json";
     let code = r#"
 /*test*/ [1, 2, 3]
 	"#;
     let file_path = Path::new("tsconfig.json");
     fs.insert(file_path.into(), code.as_bytes());
-    fs.insert(rome_config.into(), config_json);
+    fs.insert(biome_config.into(), config_json);
 
     let result = run_cli(
         DynRef::Borrowed(&mut fs),
@@ -1911,6 +1911,43 @@ fn format_jsonc_files() {
     ));
 }
 
+#[test]
+fn format_json_when_allow_trailing_commas() {
+    let mut fs = MemoryFileSystem::default();
+    let mut console = BufferConsole::default();
+
+    let config_json = r#"{
+    "json": {
+        "parser": { "allowTrailingCommas": true }
+    }
+}"#;
+    let biome_config = "biome.json";
+    let code = r#"{
+    "array": [
+        1,
+    ],
+}"#;
+    let file_path = Path::new("file.json");
+    fs.insert(file_path.into(), code.as_bytes());
+    fs.insert(biome_config.into(), config_json);
+
+    let result = run_cli(
+        DynRef::Borrowed(&mut fs),
+        &mut console,
+        Args::from([("format"), file_path.as_os_str().to_str().unwrap()].as_slice()),
+    );
+
+    assert!(result.is_ok(), "run_cli returned {result:?}");
+
+    assert_cli_snapshot(SnapshotPayload::new(
+        module_path!(),
+        "format_json_when_allow_trailing_commas",
+        fs,
+        console,
+        result,
+    ));
+}
+
 #[test]
 fn treat_known_json_files_as_jsonc_files() {
     let mut fs = MemoryFileSystem::default();

crates/biome_cli/tests/snapshots/main_commands_format/format_json_when_allow_trailing_commas.snap

@@ -0,0 +1,45 @@
+---
+source: crates/biome_cli/tests/snap_test.rs
+expression: content
+---
+## `biome.json`
+
+```json
+{
+  "json": {
+    "parser": { "allowTrailingCommas": true }
+  }
+}
+```
+
+## `file.json`
+
+```json
+{
+    "array": [
+        1,
+    ],
+}
+```
+
+# Emitted Messages
+
+```block
+file.json format ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  i Formatter would have printed the following content:
+  
+    3 3 │           1,
+    4 4 │       ],
+    5   │ - }
+      5 │ + }
+      6 │ + 
+  
+
+```
+
+```block
+Compared 1 file(s) in <TIME>
+```
+
+

crates/biome_json_parser/src/lexer/mod.rs

@@ -36,7 +36,7 @@ pub(crate) struct Lexer<'src> {
     position: usize,
 
     diagnostics: Vec<ParseDiagnostic>,
-    config: JsonParserOptions,
+    options: JsonParserOptions,
 }
 
 impl<'src> Lexer<'src> {
@@ -46,7 +46,7 @@ impl<'src> Lexer<'src> {
             source: string,
             position: 0,
             diagnostics: vec![],
-            config: JsonParserOptions::default(),
+            options: JsonParserOptions::default(),
         }
     }
 
@@ -699,7 +699,7 @@ impl<'src> Lexer<'src> {
                         b'*' if self.peek_byte() == Some(b'/') => {
                             self.advance(2);
 
-                            if !self.config.allow_comments {
+                            if !self.options.allow_comments {
                                 self.diagnostics.push(ParseDiagnostic::new(
                                     "JSON standard does not allow comments.",
                                     start..self.text_position(),
@@ -745,7 +745,7 @@ impl<'src> Lexer<'src> {
                     }
                 }
 
-                if !self.config.allow_comments {
+                if !self.options.allow_comments {
                     self.diagnostics.push(ParseDiagnostic::new(
                         "JSON standard does not allow comments.",
                         start..self.text_position(),
@@ -758,8 +758,8 @@ impl<'src> Lexer<'src> {
         }
     }
 
-    pub(crate) fn with_config(mut self, config: JsonParserOptions) -> Self {
-        self.config = config;
+    pub(crate) fn with_options(mut self, options: JsonParserOptions) -> Self {
+        self.options = options;
         self
     }
 }

crates/biome_json_parser/src/parser.rs

@@ -9,25 +9,33 @@ use biome_parser::ParserContext;
 pub(crate) struct JsonParser<'source> {
     context: ParserContext<JsonSyntaxKind>,
     source: JsonTokenSource<'source>,
+    options: JsonParserOptions,
 }
 
 #[derive(Default, Debug, Clone, Copy)]
 pub struct JsonParserOptions {
     pub allow_comments: bool,
+    pub allow_trailing_commas: bool,
 }
 
 impl JsonParserOptions {
     pub fn with_allow_comments(mut self) -> Self {
         self.allow_comments = true;
         self
     }
+
+    pub fn with_allow_trailing_commas(mut self) -> Self {
+        self.allow_trailing_commas = true;
+        self
+    }
 }
 
 impl<'source> JsonParser<'source> {
-    pub fn new(source: &'source str, config: JsonParserOptions) -> Self {
+    pub fn new(source: &'source str, options: JsonParserOptions) -> Self {
         Self {
             context: ParserContext::default(),
-            source: JsonTokenSource::from_str(source, config),
+            source: JsonTokenSource::from_str(source, options),
+            options,
         }
     }
 
@@ -45,6 +53,10 @@ impl<'source> JsonParser<'source> {
 
         (events, diagnostics, trivia)
     }
+
+    pub fn options(&self) -> &JsonParserOptions {
+        &self.options
+    }
 }
 
 impl<'source> Parser for JsonParser<'source> {

crates/biome_json_parser/src/syntax.rs

@@ -36,7 +36,7 @@ pub(crate) fn parse_root(p: &mut JsonParser) {
     };
 
     // Process the file to the end, e.g. in cases where there have been multiple values
-    if !p.at(EOF) {
+    if !(p.at(EOF)) {
         parse_rest(p, value);
     }
 
@@ -181,6 +181,10 @@ fn parse_sequence(p: &mut JsonParser, root_kind: SequenceKind) -> ParsedSyntax {
 
             match current.parse_item(p) {
                 SequenceItem::Parsed(Absent) => {
+                    if p.options().allow_trailing_commas && p.last() == Some(T![,]) {
+                        break;
+                    }
+
                     let range = if p.at(T![,]) {
                         p.cur_range()
                     } else {
@@ -249,7 +253,9 @@ fn parse_object_member(p: &mut JsonParser) -> SequenceItem {
     let m = p.start();
 
     if parse_member_name(p).is_absent() {
-        p.error(expected_property(p, p.cur_range()));
+        if !(p.options().allow_trailing_commas && p.last() == Some(T![,])) {
+            p.error(expected_property(p, p.cur_range()));
+        }
 
         if !p.at(T![:]) && !p.at_ts(VALUE_START) {
             m.abandon(p);

crates/biome_json_parser/src/token_source.rs

@@ -13,20 +13,20 @@ pub(crate) struct JsonTokenSource<'source> {
     current: JsonSyntaxKind,
     current_range: TextRange,
     preceding_line_break: bool,
-    config: JsonParserOptions,
+    options: JsonParserOptions,
 }
 
 impl<'source> JsonTokenSource<'source> {
-    pub fn from_str(source: &'source str, config: JsonParserOptions) -> Self {
-        let lexer = Lexer::from_str(source).with_config(config);
+    pub fn from_str(source: &'source str, options: JsonParserOptions) -> Self {
+        let lexer = Lexer::from_str(source).with_options(options);
 
         let mut source = Self {
             lexer,
             trivia: Vec::new(),
             current: TOMBSTONE,
             current_range: TextRange::default(),
             preceding_line_break: false,
-            config,
+            options,
         };
 
         source.next_non_trivia_token(true);
@@ -46,7 +46,7 @@ impl<'source> JsonTokenSource<'source> {
                     // Not trivia
                     break;
                 }
-                Ok(trivia_kind) if trivia_kind.is_comment() && !self.config.allow_comments => {
+                Ok(trivia_kind) if trivia_kind.is_comment() && !self.options.allow_comments => {
                     self.set_current_token(token);
 
                     // Not trivia

crates/biome_json_parser/tests/json_test_suite/allow_trailing_commas/err/null.json

@@ -0,0 +1 @@
+null,

crates/biome_json_parser/tests/json_test_suite/allow_trailing_commas/err/null.json.snap

@@ -0,0 +1,69 @@
+---
+source: crates/biome_json_parser/tests/spec_test.rs
+expression: snapshot
+---
+
+## Input
+
+```json
+null,
+
+```
+
+
+## AST
+
+```
+JsonRoot {
+    value: JsonArrayValue {
+        l_brack_token: missing (required),
+        elements: JsonArrayElementList [
+            JsonNullValue {
+                value_token: NULL_KW@0..4 "null" [] [],
+            },
+            missing separator,
+            JsonBogusValue {
+                items: [
+                    COMMA@4..5 "," [] [],
+                ],
+            },
+        ],
+        r_brack_token: missing (required),
+    },
+    eof_token: EOF@5..6 "" [Newline("\n")] [],
+}
+```
+
+## CST
+
+```
+0: [email protected]
+  0: [email protected]
+    0: (empty)
+    1: [email protected]
+      0: [email protected]
+        0: [email protected] "null" [] []
+      1: (empty)
+      2: [email protected]
+        0: [email protected] "," [] []
+    2: (empty)
+  1: [email protected] "" [Newline("\n")] []
+
+```
+
+## Diagnostics
+
+```
+null.json:1:5 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  × End of file expected
+  
+  > 1 │ null,
+      │     ^
+    2 │ 
+  
+  i Use an array for a sequence of values: `[1, 2]`
+  
+```
+
+

crates/biome_json_parser/tests/json_test_suite/allow_trailing_commas/err/object.json

@@ -0,0 +1 @@
+{},