Add tests for skip magic trailing comma

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## Summary

This PR adds tests that verify that the magic trailing comma is not respected if disabled in the formatter options. 

Our test setup now allows to create a `<fixture-name>.options.json` file that contains an array of configurations that should be tested. 

<!-- What's the purpose of the change? What does it do, and why? -->

## Test Plan

It's all about tests :) 

<!-- How was it tested? -->

Cargo.lock

@@ -2065,8 +2065,9 @@ dependencies = [
  "ruff_text_size",
  "rustc-hash",
  "rustpython-parser",
+ "serde",
+ "serde_json",
  "similar",
- "test-case",
 ]
 
 [[package]]

crates/ruff_formatter/src/lib.rs

@@ -59,10 +59,8 @@ use std::num::ParseIntError;
 use std::str::FromStr;
 
 #[derive(Debug, Eq, PartialEq, Clone, Copy, Hash)]
-#[cfg_attr(
-    feature = "serde",
-    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema)
-)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 #[derive(Default)]
 pub enum IndentStyle {
     /// Tab
@@ -112,10 +110,8 @@ impl std::fmt::Display for IndentStyle {
 ///
 /// The allowed range of values is 1..=320
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
-#[cfg_attr(
-    feature = "serde",
-    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema)
-)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct LineWidth(u16);
 
 impl LineWidth {
@@ -278,10 +274,8 @@ impl FormatOptions for SimpleFormatOptions {
 
 /// Lightweight sourcemap marker between source and output tokens
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
-#[cfg_attr(
-    feature = "serde",
-    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema)
-)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct SourceMarker {
     /// Position of the marker in the original source
     pub source: TextSize,
@@ -340,10 +334,8 @@ where
 pub type PrintResult<T> = Result<T, PrintError>;
 
 #[derive(Debug, Clone, Eq, PartialEq)]
-#[cfg_attr(
-    feature = "serde",
-    derive(serde::Serialize, serde::Deserialize, schemars::JsonSchema)
-)]
+#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct Printed {
     code: String,
     range: Option<TextRange>,

crates/ruff_python_formatter/Cargo.toml

@@ -25,8 +25,23 @@ itertools = { workspace = true }
 once_cell = { workspace = true }
 rustc-hash = { workspace = true }
 rustpython-parser = { workspace = true }
+serde = { workspace = true, optional = true }
 
 [dev-dependencies]
+ruff_formatter = { path = "../ruff_formatter", features = ["serde"]}
+
 insta = { workspace = true, features = ["glob"] }
-test-case = { workspace = true }
+serde = { workspace = true }
+serde_json = { workspace = true }
 similar = { workspace = true }
+
+[[test]]
+name = "ruff_python_formatter_fixtures"
+path = "tests/fixtures.rs"
+test = true
+required-features = [ "serde" ]
+
+
+[features]
+serde = ["dep:serde", "ruff_formatter/serde"]
+default = ["serde"]

crates/ruff_python_formatter/resources/test/fixtures/ruff/skip_magic_trailing_comma.options.json

@@ -0,0 +1,8 @@
+[
+  {
+    "magic_trailing_comma": "respect"
+  },
+  {
+    "magic_trailing_comma": "ignore"
+  }
+]

crates/ruff_python_formatter/resources/test/fixtures/ruff/skip_magic_trailing_comma.py

@@ -0,0 +1,22 @@
+(
+    "First entry",
+    "Second entry",
+    "last with trailing comma",
+)
+
+(
+    "First entry",
+    "Second entry",
+    "last without trailing comma"
+)
+
+(
+    "First entry",
+    "Second entry",
+    "third entry",
+    "fourth entry",
+    "fifth entry",
+    "sixt entry",
+    "seventh entry",
+    "eigth entry",
+)

crates/ruff_python_formatter/src/builders.rs

@@ -220,7 +220,7 @@ impl<'fmt, 'ast, 'buf> JoinCommaSeparatedBuilder<'fmt, 'ast, 'buf> {
         if let Some(last_end) = self.last_end.take() {
             if_group_breaks(&text(",")).fmt(self.fmt)?;
 
-            if self.fmt.options().magic_trailing_comma().is_preserve()
+            if self.fmt.options().magic_trailing_comma().is_respect()
                 && matches!(
                     first_non_trivia_token(last_end, self.fmt.context().contents()),
                     Some(Token {

crates/ruff_python_formatter/src/options.rs

@@ -2,6 +2,11 @@ use ruff_formatter::printer::{LineEnding, PrinterOptions};
 use ruff_formatter::{FormatOptions, IndentStyle, LineWidth};
 
 #[derive(Clone, Debug)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize),
+    serde(default)
+)]
 pub struct PyFormatOptions {
     /// Specifies the indent style:
     /// * Either a tab
@@ -9,6 +14,7 @@ pub struct PyFormatOptions {
     indent_style: IndentStyle,
 
     /// The preferred line width at which the formatter should wrap lines.
+    #[cfg_attr(feature = "serde", serde(default = "default_line_width"))]
     line_width: LineWidth,
 
     /// The preferred quote style to use (single vs double quotes).
@@ -18,6 +24,10 @@ pub struct PyFormatOptions {
     magic_trailing_comma: MagicTrailingComma,
 }
 
+fn default_line_width() -> LineWidth {
+    LineWidth::try_from(88).unwrap()
+}
+
 impl PyFormatOptions {
     pub fn magic_trailing_comma(&self) -> MagicTrailingComma {
         self.magic_trailing_comma
@@ -36,6 +46,16 @@ impl PyFormatOptions {
         self.magic_trailing_comma = trailing_comma;
         self
     }
+
+    pub fn with_indent_style(&mut self, indent_style: IndentStyle) -> &mut Self {
+        self.indent_style = indent_style;
+        self
+    }
+
+    pub fn with_line_width(&mut self, line_width: LineWidth) -> &mut Self {
+        self.line_width = line_width;
+        self
+    }
 }
 
 impl FormatOptions for PyFormatOptions {
@@ -69,6 +89,11 @@ impl Default for PyFormatOptions {
 }
 
 #[derive(Copy, Clone, Debug, Default, Eq, PartialEq)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize),
+    serde(rename_all = "kebab-case")
+)]
 pub enum QuoteStyle {
     Single,
     #[default]
@@ -105,14 +130,19 @@ impl TryFrom<char> for QuoteStyle {
 }
 
 #[derive(Copy, Clone, Debug, Default)]
+#[cfg_attr(
+    feature = "serde",
+    derive(serde::Serialize, serde::Deserialize),
+    serde(rename_all = "kebab-case")
+)]
 pub enum MagicTrailingComma {
     #[default]
-    Preserve,
-    Skip,
+    Respect,
+    Ignore,
 }
 
 impl MagicTrailingComma {
-    pub const fn is_preserve(self) -> bool {
-        matches!(self, Self::Preserve)
+    pub const fn is_respect(self) -> bool {
+        matches!(self, Self::Respect)
     }
 }

crates/ruff_python_formatter/tests/fixtures.rs

@@ -1,16 +1,18 @@
+use ruff_formatter::FormatOptions;
 use ruff_python_formatter::{format_module, PyFormatOptions};
 use similar::TextDiff;
 use std::fmt::{Formatter, Write};
-use std::fs;
+use std::io::BufReader;
 use std::path::Path;
+use std::{fmt, fs};
 
 #[test]
 fn black_compatibility() {
     let test_file = |input_path: &Path| {
         let content = fs::read_to_string(input_path).unwrap();
 
-        let printed =
-            format_module(&content, PyFormatOptions::default()).expect("Formatting to succeed");
+        let options = PyFormatOptions::default();
+        let printed = format_module(&content, options.clone()).expect("Formatting to succeed");
 
         let expected_path = input_path.with_extension("py.expect");
         let expected_output = fs::read_to_string(&expected_path)
@@ -18,7 +20,7 @@ fn black_compatibility() {
 
         let formatted_code = printed.as_code();
 
-        ensure_stability_when_formatting_twice(formatted_code);
+        ensure_stability_when_formatting_twice(formatted_code, options);
 
         if formatted_code == expected_output {
             // Black and Ruff formatting matches. Delete any existing snapshot files because the Black output
@@ -66,7 +68,7 @@ fn black_compatibility() {
             write!(snapshot, "{}", CodeFrame::new("diff", &diff)).unwrap();
 
             write!(snapshot, "{}", Header::new("Ruff Output")).unwrap();
-            write!(snapshot, "{}", CodeFrame::new("py", formatted_code)).unwrap();
+            write!(snapshot, "{}", CodeFrame::new("py", &formatted_code)).unwrap();
 
             write!(snapshot, "{}", Header::new("Black Output")).unwrap();
             write!(snapshot, "{}", CodeFrame::new("py", &expected_output)).unwrap();
@@ -89,21 +91,52 @@ fn format() {
     let test_file = |input_path: &Path| {
         let content = fs::read_to_string(input_path).unwrap();
 
-        let printed =
-            format_module(&content, PyFormatOptions::default()).expect("Formatting to succeed");
+        let options = PyFormatOptions::default();
+        let printed = format_module(&content, options.clone()).expect("Formatting to succeed");
         let formatted_code = printed.as_code();
 
-        ensure_stability_when_formatting_twice(formatted_code);
+        ensure_stability_when_formatting_twice(formatted_code, options);
 
-        let snapshot = format!(
-            r#"## Input
-{}
+        let mut snapshot = format!("## Input\n{}", CodeFrame::new("py", &content));
 
-## Output
-{}"#,
-            CodeFrame::new("py", &content),
-            CodeFrame::new("py", formatted_code)
-        );
+        let options_path = input_path.with_extension("options.json");
+        if let Ok(options_file) = fs::File::open(options_path) {
+            let reader = BufReader::new(options_file);
+            let options: Vec<PyFormatOptions> =
+                serde_json::from_reader(reader).expect("Options to be a valid Json file");
+
+            writeln!(snapshot, "## Outputs").unwrap();
+
+            for (i, options) in options.into_iter().enumerate() {
+                let printed =
+                    format_module(&content, options.clone()).expect("Formatting to succeed");
+                let formatted_code = printed.as_code();
+
+                ensure_stability_when_formatting_twice(formatted_code, options.clone());
+
+                writeln!(
+                    snapshot,
+                    "### Output {}\n{}{}",
+                    i + 1,
+                    CodeFrame::new("", &DisplayPyOptions(&options)),
+                    CodeFrame::new("py", &formatted_code)
+                )
+                .unwrap();
+            }
+        } else {
+            let options = PyFormatOptions::default();
+            let printed = format_module(&content, options.clone()).expect("Formatting to succeed");
+            let formatted_code = printed.as_code();
+
+            ensure_stability_when_formatting_twice(formatted_code, options);
+
+            writeln!(
+                snapshot,
+                "## Output\n{}",
+                CodeFrame::new("py", &formatted_code)
+            )
+            .unwrap();
+        }
 
         insta::with_settings!({
             omit_expression => true,
@@ -118,8 +151,8 @@ fn format() {
 }
 
 /// Format another time and make sure that there are no changes anymore
-fn ensure_stability_when_formatting_twice(formatted_code: &str) {
-    let reformatted = match format_module(formatted_code, PyFormatOptions::default()) {
+fn ensure_stability_when_formatting_twice(formatted_code: &str, options: PyFormatOptions) {
+    let reformatted = match format_module(formatted_code, options) {
         Ok(reformatted) => reformatted,
         Err(err) => {
             panic!(
@@ -170,11 +203,11 @@ impl std::fmt::Display for Header<'_> {
 
 struct CodeFrame<'a> {
     language: &'a str,
-    code: &'a str,
+    code: &'a dyn std::fmt::Display,
 }
 
 impl<'a> CodeFrame<'a> {
-    fn new(language: &'a str, code: &'a str) -> Self {
+    fn new(language: &'a str, code: &'a dyn std::fmt::Display) -> Self {
         Self { language, code }
     }
 }
@@ -187,3 +220,21 @@ impl std::fmt::Display for CodeFrame<'_> {
         writeln!(f)
     }
 }
+
+struct DisplayPyOptions<'a>(&'a PyFormatOptions);
+
+impl fmt::Display for DisplayPyOptions<'_> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        writeln!(
+            f,
+            r#"indent-style            = {indent_style}
+line-width              = {line_width}
+quote-style             = {quote_style:?}
+magic-trailing-comma    = {magic_trailing_comma:?}"#,
+            indent_style = self.0.indent_style(),
+            line_width = self.0.line_width().value(),
+            quote_style = self.0.quote_style(),
+            magic_trailing_comma = self.0.magic_trailing_comma()
+        )
+    }
+}

crates/ruff_python_formatter/tests/snapshots/format@expression__attribute.py.snap

@@ -109,8 +109,6 @@ x53 = (
 
 ```
 
-
-
 ## Output
 ```py
 NOT_YET_IMPLEMENTED_StmtImportFrom
@@ -196,3 +194,4 @@ x53 = a.askjdfahdlskjflsajfadhsaf.akjdsf.aksjdlfadhaljsashdfljaf.askjdflhasfdlas
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__binary.py.snap

@@ -200,8 +200,6 @@ for user_id in set(target_user_ids) - {u.user_id for u in updates}:
     updates.append(UserPresenceState.default(user_id))
 ```
 
-
-
 ## Output
 ```py
 (
@@ -447,3 +445,4 @@ for (
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__boolean_operation.py.snap

@@ -70,8 +70,6 @@ if (
     pass
 ```
 
-
-
 ## Output
 ```py
 if (
@@ -141,3 +139,4 @@ if (
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__compare.py.snap

@@ -67,8 +67,6 @@ return 1 == 2 and (
 ]
 ```
 
-
-
 ## Output
 ```py
 a == b
@@ -187,3 +185,4 @@ return (
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__dict.py.snap

@@ -64,8 +64,6 @@ a = {
 }
 ```
 
-
-
 ## Output
 ```py
 # before
@@ -131,3 +129,4 @@ a = {
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__list.py.snap

@@ -16,8 +16,6 @@ a3 = [
 ]
 ```
 
-
-
 ## Output
 ```py
 # Dangling comment placement in empty lists
@@ -33,3 +31,4 @@ a3 = [
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__slice.py.snap

@@ -88,8 +88,6 @@ e202 = "e"[a() :: a()]
 e210 = "e"[a() : 1 :]
 ```
 
-
-
 ## Output
 ```py
 # Handle comments both when lower and upper exist and when they don't
@@ -175,3 +173,4 @@ e210 = "e"[NOT_IMPLEMENTED_call() : 1 :]
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__string.py.snap

@@ -58,8 +58,6 @@ String \"\"\"
 '''
 ```
 
-
-
 ## Output
 ```py
 "' test"
@@ -117,3 +115,4 @@ String \"\"\"
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__tuple.py.snap

@@ -65,8 +65,6 @@ h2 = ((((1, "qweiurpoiqwurepqiurpqirpuqoiwrupqoirupqoirupqoiurpqiorupwqiourpqurp
 h3 = 1, "qweiurpoiqwurepqiurpqirpuqoiwrupqoirupqoirupqoiurpqiorupwqiourpqurpqurpqurpqurpqurpqurüqurqpuriq"
 ```
 
-
-
 ## Output
 ```py
 # Non-wrapping parentheses checks
@@ -264,3 +262,4 @@ h3 = (
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@expression__unary.py.snap

@@ -144,8 +144,6 @@ if not \
     pass
 ```
 
-
-
 ## Output
 ```py
 if (
@@ -300,3 +298,4 @@ if not a:
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@skip_magic_trailing_comma.py.snap

@@ -0,0 +1,88 @@
+---
+source: crates/ruff_python_formatter/tests/fixtures.rs
+input_file: crates/ruff_python_formatter/resources/test/fixtures/ruff/skip_magic_trailing_comma.py
+---
+## Input
+```py
+(
+    "First entry",
+    "Second entry",
+    "last with trailing comma",
+)
+
+(
+    "First entry",
+    "Second entry",
+    "last without trailing comma"
+)
+
+(
+    "First entry",
+    "Second entry",
+    "third entry",
+    "fourth entry",
+    "fifth entry",
+    "sixt entry",
+    "seventh entry",
+    "eigth entry",
+)
+```
+
+## Outputs
+### Output 1
+```
+indent-style            = Spaces, size: 4
+line-width              = 88
+quote-style             = Double
+magic-trailing-comma    = Respect
+```
+
+```py
+(
+    "First entry",
+    "Second entry",
+    "last with trailing comma",
+)
+
+("First entry", "Second entry", "last without trailing comma")
+
+(
+    "First entry",
+    "Second entry",
+    "third entry",
+    "fourth entry",
+    "fifth entry",
+    "sixt entry",
+    "seventh entry",
+    "eigth entry",
+)
+```
+
+
+### Output 2
+```
+indent-style            = Spaces, size: 4
+line-width              = 88
+quote-style             = Double
+magic-trailing-comma    = Ignore
+```
+
+```py
+("First entry", "Second entry", "last with trailing comma")
+
+("First entry", "Second entry", "last without trailing comma")
+
+(
+    "First entry",
+    "Second entry",
+    "third entry",
+    "fourth entry",
+    "fifth entry",
+    "sixt entry",
+    "seventh entry",
+    "eigth entry",
+)
+```
+
+
+

crates/ruff_python_formatter/tests/snapshots/format@statement__assign.py.snap

@@ -16,8 +16,6 @@ a2 = (
 a = asdf = fjhalsdljfalflaflapamsakjsdhflakjdslfjhalsdljfalflaflapamsakjsdhflakjdslfjhalsdljfal = 1
 ```
 
-
-
 ## Output
 ```py
 # break left hand side
@@ -31,3 +29,4 @@ a = asdf = fjhalsdljfalflaflapamsakjsdhflakjdslfjhalsdljfalflaflapamsakjsdhflakj
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@statement__break.py.snap

@@ -11,8 +11,6 @@ while True:  # block comment
     # post comment
 ```
 
-
-
 ## Output
 ```py
 # leading comment
@@ -23,3 +21,4 @@ while True:  # block comment
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@statement__class_definition.py.snap

@@ -42,8 +42,6 @@ class Test(Aaaa): # trailing comment
     pass
 ```
 
-
-
 ## Output
 ```py
 class Test(
@@ -95,3 +93,4 @@ class Test(Aaaa):  # trailing comment
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@statement__for.py.snap

@@ -40,8 +40,6 @@ for x in (): # type: int
     ...
 ```
 
-
-
 ## Output
 ```py
 for x in y:  # trailing test comment
@@ -85,3 +83,4 @@ for x in ():  # type: int
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@statement__function.py.snap

@@ -239,8 +239,6 @@ def f42(
     pass
 ```
 
-
-
 ## Output
 ```py
 # Dangling comments
@@ -516,3 +514,4 @@ def f42(
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@statement__if.py.snap

@@ -79,8 +79,6 @@ else:  # Comment
     pass
 ```
 
-
-
 ## Output
 ```py
 if x == y:  # trailing if condition
@@ -158,3 +156,4 @@ else:  # Comment
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@statement__while.py.snap

@@ -36,8 +36,6 @@ while (
     print("Do something")
 ```
 
-
-
 ## Output
 ```py
 while 34:  # trailing test comment
@@ -74,3 +72,4 @@ while (
 ```
 
 
+

crates/ruff_python_formatter/tests/snapshots/format@trivia.py.snap

@@ -38,8 +38,6 @@ while b == 20:
 e = 50  # one empty line before
 ```
 
-
-
 ## Output
 ```py
 # Removes the line above
@@ -79,3 +77,4 @@ e = 50  # one empty line before
 ```
 
 
+