ruff/crates/ruff_python_formatter/tests/fixtures.rs

use std::fmt::{Formatter, Write};
use std::io::BufReader;
use std::path::Path;
use std::{fmt, fs};

use similar::TextDiff;

use crate::normalizer::Normalizer;
use ruff_formatter::FormatOptions;
use ruff_python_ast::comparable::ComparableMod;
use ruff_python_formatter::{format_module_source, PreviewMode, PyFormatOptions};
use ruff_python_parser::{parse, AsMode};

mod normalizer;

#[test]
fn black_compatibility() {
    let test_file = |input_path: &Path| {
        let content = fs::read_to_string(input_path).unwrap();

        let options_path = input_path.with_extension("options.json");

        let options: PyFormatOptions = if let Ok(options_file) = fs::File::open(&options_path) {
            let reader = BufReader::new(options_file);
            serde_json::from_reader(reader)
                .unwrap_or_else(|_| panic!("Option file {options_path:?} to be a valid Json file"))
        } else {
            PyFormatOptions::from_extension(input_path)
        };

        let printed = format_module_source(&content, options.clone()).unwrap_or_else(|err| {
            panic!(
                "Formatting of {} to succeed but encountered error {err}",
                input_path.display()
            )
        });

        let extension = input_path
            .extension()
            .expect("Test file to have py or pyi extension")
            .to_string_lossy();
        let expected_path = input_path.with_extension(format!("{extension}.expect"));
        let expected_output = fs::read_to_string(&expected_path)
            .unwrap_or_else(|_| panic!("Expected Black output file '{expected_path:?}' to exist"));

        let formatted_code = printed.as_code();

        ensure_unchanged_ast(&content, formatted_code, &options, input_path);
        ensure_stability_when_formatting_twice(formatted_code, &options, input_path);

        if formatted_code == expected_output {
            // Black and Ruff formatting matches. Delete any existing snapshot files because the Black output
            // already perfectly captures the expected output.
            // The following code mimics insta's logic generating the snapshot name for a test.
            let workspace_path = std::env::var("CARGO_MANIFEST_DIR").unwrap();

            let mut components = input_path.components().rev();
            let file_name = components.next().unwrap();
            let test_suite = components.next().unwrap();

            let snapshot_name = format!(
                "black_compatibility@{}__{}.snap",
                test_suite.as_os_str().to_string_lossy(),
                file_name.as_os_str().to_string_lossy()
            );

            let snapshot_path = Path::new(&workspace_path)
                .join("tests/snapshots")
                .join(snapshot_name);
            if snapshot_path.exists() && snapshot_path.is_file() {
                // SAFETY: This is a convenience feature. That's why we don't want to abort
                // when deleting a no longer needed snapshot fails.
                fs::remove_file(&snapshot_path).ok();
            }

            let new_snapshot_path = snapshot_path.with_extension("snap.new");
            if new_snapshot_path.exists() && new_snapshot_path.is_file() {
                // SAFETY: This is a convenience feature. That's why we don't want to abort
                // when deleting a no longer needed snapshot fails.
                fs::remove_file(&new_snapshot_path).ok();
            }
        } else {
            // Black and Ruff have different formatting. Write out a snapshot that covers the differences
            // today.
            let mut snapshot = String::new();
            write!(snapshot, "{}", Header::new("Input")).unwrap();
            write!(snapshot, "{}", CodeFrame::new("python", &content)).unwrap();

            write!(snapshot, "{}", Header::new("Black Differences")).unwrap();

            let diff = TextDiff::from_lines(expected_output.as_str(), formatted_code)
                .unified_diff()
                .header("Black", "Ruff")
                .to_string();

            write!(snapshot, "{}", CodeFrame::new("diff", &diff)).unwrap();

            write!(snapshot, "{}", Header::new("Ruff Output")).unwrap();
            write!(snapshot, "{}", CodeFrame::new("python", &formatted_code)).unwrap();

            write!(snapshot, "{}", Header::new("Black Output")).unwrap();
            write!(snapshot, "{}", CodeFrame::new("python", &expected_output)).unwrap();

            insta::with_settings!({
                omit_expression => true,
                input_file => input_path,
                prepend_module_to_snapshot => false,
            }, {
                insta::assert_snapshot!(snapshot);
            });
        }
    };

    insta::glob!(
        "../resources",
        "test/fixtures/black/**/*.{py,pyi}",
        test_file
    );
}

#[test]
fn format() {
    let test_file = |input_path: &Path| {
        let content = fs::read_to_string(input_path).unwrap();

        let options = PyFormatOptions::from_extension(input_path);
        let printed =
            format_module_source(&content, options.clone()).expect("Formatting to succeed");
        let formatted_code = printed.as_code();

        ensure_unchanged_ast(&content, formatted_code, &options, input_path);
        ensure_stability_when_formatting_twice(formatted_code, &options, input_path);

        let mut snapshot = format!("## Input\n{}", CodeFrame::new("python", &content));

        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_source(&content, options.clone()).expect("Formatting to succeed");
                let formatted_code = printed.as_code();

                ensure_unchanged_ast(&content, formatted_code, &options, input_path);
                ensure_stability_when_formatting_twice(formatted_code, &options, input_path);

                writeln!(
                    snapshot,
                    "### Output {}\n{}{}",
                    i + 1,
                    CodeFrame::new("", &DisplayPyOptions(&options)),
                    CodeFrame::new("python", &formatted_code)
                )
                .unwrap();

                if options.preview().is_enabled() {
                    continue;
                }

                // We want to capture the differences in the preview style in our fixtures
                let options_preview = options.with_preview(PreviewMode::Enabled);
                let printed_preview = format_module_source(&content, options_preview.clone())
                    .expect("Formatting to succeed");
                let formatted_preview = printed_preview.as_code();

                ensure_unchanged_ast(&content, formatted_preview, &options_preview, input_path);
                ensure_stability_when_formatting_twice(
                    formatted_preview,
                    &options_preview,
                    input_path,
                );

                if formatted_code != formatted_preview {
                    // Having both snapshots makes it hard to see the difference, so we're keeping only
                    // diff.
                    writeln!(
                        snapshot,
                        "#### Preview changes\n{}",
                        CodeFrame::new(
                            "diff",
                            TextDiff::from_lines(formatted_code, formatted_preview)
                                .unified_diff()
                                .header("Stable", "Preview")
                        )
                    )
                    .unwrap();
                }
            }
        } else {
            // We want to capture the differences in the preview style in our fixtures
            let options_preview = options.with_preview(PreviewMode::Enabled);
            let printed_preview = format_module_source(&content, options_preview.clone())
                .expect("Formatting to succeed");
            let formatted_preview = printed_preview.as_code();

            ensure_unchanged_ast(&content, formatted_preview, &options_preview, input_path);
            ensure_stability_when_formatting_twice(formatted_preview, &options_preview, input_path);

            if formatted_code == formatted_preview {
                writeln!(
                    snapshot,
                    "## Output\n{}",
                    CodeFrame::new("python", &formatted_code)
                )
                .unwrap();
            } else {
                // Having both snapshots makes it hard to see the difference, so we're keeping only
                // diff.
                writeln!(
                    snapshot,
                    "## Output\n{}\n## Preview changes\n{}",
                    CodeFrame::new("python", &formatted_code),
                    CodeFrame::new(
                        "diff",
                        TextDiff::from_lines(formatted_code, formatted_preview)
                            .unified_diff()
                            .header("Stable", "Preview")
                    )
                )
                .unwrap();
            }
        }

        insta::with_settings!({
            omit_expression => true,
            input_file => input_path,
            prepend_module_to_snapshot => false,
        }, {
            insta::assert_snapshot!(snapshot);
        });
    };

    insta::glob!(
        "../resources",
        "test/fixtures/ruff/**/*.{py,pyi}",
        test_file
    );
}

/// Format another time and make sure that there are no changes anymore
fn ensure_stability_when_formatting_twice(
    formatted_code: &str,
    options: &PyFormatOptions,
    input_path: &Path,
) {
    let reformatted = match format_module_source(formatted_code, options.clone()) {
        Ok(reformatted) => reformatted,
        Err(err) => {
            panic!(
                "Expected formatted code of {} to be valid syntax: {err}:\
                    \n---\n{formatted_code}---\n",
                input_path.display()
            );
        }
    };

    if reformatted.as_code() != formatted_code {
        let diff = TextDiff::from_lines(formatted_code, reformatted.as_code())
            .unified_diff()
            .header("Formatted once", "Formatted twice")
            .to_string();
        panic!(
            r#"Reformatting the formatted code of {input_path} a second time resulted in formatting changes.

Options:
{options}
---
{diff}---

Formatted once:
---
{formatted_code}---

Formatted twice:
---
{reformatted}---"#,
            input_path = input_path.display(),
            options = &DisplayPyOptions(options),
            reformatted = reformatted.as_code(),
        );
    }
}

/// Ensure that formatting doesn't change the AST.
///
/// Like Black, there are a few exceptions to this "invariant" which are encoded in
/// [`NormalizedMod`] and related structs. Namely, formatting can change indentation within strings,
/// and can also flatten tuples within `del` statements.
fn ensure_unchanged_ast(
    unformatted_code: &str,
    formatted_code: &str,
    options: &PyFormatOptions,
    input_path: &Path,
) {
    let source_type = options.source_type();

    // Parse the unformatted code.
    let mut unformatted_ast = parse(
        unformatted_code,
        source_type.as_mode(),
        &input_path.to_string_lossy(),
    )
    .expect("Unformatted code to be valid syntax");
    Normalizer.visit_module(&mut unformatted_ast);
    let unformatted_ast = ComparableMod::from(&unformatted_ast);

    // Parse the formatted code.
    let mut formatted_ast = parse(
        formatted_code,
        source_type.as_mode(),
        &input_path.to_string_lossy(),
    )
    .expect("Formatted code to be valid syntax");
    Normalizer.visit_module(&mut formatted_ast);
    let formatted_ast = ComparableMod::from(&formatted_ast);

    if formatted_ast != unformatted_ast {
        let diff = TextDiff::from_lines(
            &format!("{unformatted_ast:#?}"),
            &format!("{formatted_ast:#?}"),
        )
        .unified_diff()
        .header("Unformatted", "Formatted")
        .to_string();
        panic!(
            r#"Reformatting the unformatted code of {} resulted in AST changes.
---
{diff}
"#,
            input_path.display(),
        );
    }
}

struct Header<'a> {
    title: &'a str,
}

impl<'a> Header<'a> {
    fn new(title: &'a str) -> Self {
        Self { title }
    }
}

impl std::fmt::Display for Header<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        writeln!(f, "## {}", self.title)?;
        writeln!(f)
    }
}

struct CodeFrame<'a> {
    language: &'a str,
    code: &'a dyn std::fmt::Display,
}

impl<'a> CodeFrame<'a> {
    fn new(language: &'a str, code: &'a dyn std::fmt::Display) -> Self {
        Self { language, code }
    }
}

impl std::fmt::Display for CodeFrame<'_> {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        writeln!(f, "```{}", self.language)?;
        write!(f, "{}", self.code)?;
        writeln!(f, "```")?;
        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}
indent-width               = {indent_width}
quote-style                = {quote_style:?}
line-ending                = {line_ending:?}
magic-trailing-comma       = {magic_trailing_comma:?}
docstring-code             = {docstring_code:?}
docstring-code-line-width  = {docstring_code_line_width:?}
preview                    = {preview:?}
target_version             = {target_version:?}"#,
            indent_style = self.0.indent_style(),
            indent_width = self.0.indent_width().value(),
            line_width = self.0.line_width().value(),
            quote_style = self.0.quote_style(),
            line_ending = self.0.line_ending(),
            magic_trailing_comma = self.0.magic_trailing_comma(),
            docstring_code = self.0.docstring_code(),
            docstring_code_line_width = self.0.docstring_code_line_width(),
            preview = self.0.preview(),
            target_version = self.0.target_version()
        )
    }
}