Remove parser dependency from ruff-python-ast (#6096)

crates/ruff_python_codegen/src/lib.rs

@@ -0,0 +1,19 @@
+mod generator;
+mod stylist;
+
+pub use generator::Generator;
+use ruff_source_file::Locator;
+use rustpython_ast::Suite;
+use rustpython_parser::{lexer, Mode, Parse, ParseError};
+pub use stylist::{Quote, Stylist};
+
+/// Run round-trip source code generation on a given Python code.
+pub fn round_trip(code: &str, source_path: &str) -> Result<String, ParseError> {
+    let locator = Locator::new(code);
+    let python_ast = Suite::parse(code, source_path)?;
+    let tokens: Vec<_> = lexer::lex(code, Mode::Module).collect();
+    let stylist = Stylist::from_tokens(&tokens, &locator);
+    let mut generator: Generator = (&stylist).into();
+    generator.unparse_suite(&python_ast);
+    Ok(generator.generate())
+}