using ruff to modify python source code

[ChannyClaus]

hi! i'm hoping to use ruff to programmatically edit python scripts (i.e. remove arguments from the function definition if it satisfies certain predicates, etc). i tried to tinker around with

ruff/crates/ruff_python_formatter/src/lib.rs

Lines 122 to 141 in 2a64ccc

	pub fn format_module_ast<'a>(
	parsed: &'a Parsed<Mod>,
	comment_ranges: &'a CommentRanges,
	source: &'a str,
	options: PyFormatOptions,
	) -> FormatResult<Formatted<PyFormatContext<'a>>> {
	let source_code = SourceCode::new(source);
	let comments = Comments::from_ast(parsed.syntax(), source_code, comment_ranges);
	let locator = Locator::new(source);
	let formatted = format!(
	PyFormatContext::new(options, locator.contents(), comments, parsed.tokens()),
	[parsed.syntax().format()]
	)?;
	formatted
	.context()
	.comments()
	.assert_all_formatted(source_code);
	Ok(formatted)
	}

and it's turning out to be a bit challenging due to some structs / modules being private (Comments and PyFormatContext::new in particular). is there an easy way to accomplish this or some level of forking the repo + editing inevitable for this?

[MichaReiser]

I don't think you want to use the formatter for this. The formatter is a pretty printer. It formats the code according to Black's style guide.

What I would use is:

• Transformer: To transform the AST (remove the arguments)
• Generator: To print the transformed AST back to a string

[ChannyClaus]

thanks! was able to get this work with some small edits. namely:

• ruff/crates/ruff_python_codegen/src/generator.rs

  Line 179 in e18c45c

  pub(crate) fn generate(self) -> String {

  had to make this method public.

• ruff/crates/ruff_python_codegen/src/lib.rs

  Line 2 in e18c45c

  mod stylist;

  had to make this module public since Indentation struct (necessary for instantiating Generator) was in it.

were these methods hidden from outside the module intentionally?

[MichaReiser]

I think the reason why generate isn't public is because the idea is that a consumer uses the stmt and expr methods. I would accept a PR that adds a public module method (accepts a Mod)

ruff/crates/ruff_python_codegen/src/generator.rs

Lines 107 to 117 in 8db147c

	/// Generate source code from a [`Stmt`].
	pub fn stmt(mut self, stmt: &Stmt) -> String {
	self.unparse_stmt(stmt);
	self.generate()
	}
	/// Generate source code from an [`Expr`].
	pub fn expr(mut self, expr: &Expr) -> String {
	self.unparse_expr(expr, 0);
	self.generate()
	}

Rather than making the stylist module public, consider re-exporting Indentation.

ruff/crates/ruff_python_codegen/src/lib.rs

Line 7 in bf5b62e

pub use stylist::Stylist;