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

crates/ruff_python_trivia/src/whitespace.rs

@@ -1,3 +1,41 @@
+use ruff_source_file::Locator;
+use ruff_text_size::{TextRange, TextSize};
+
+/// Extract the leading indentation from a line.
+pub fn indentation_at_offset<'a>(locator: &'a Locator, offset: TextSize) -> Option<&'a str> {
+    let line_start = locator.line_start(offset);
+    let indentation = &locator.contents()[TextRange::new(line_start, offset)];
+
+    if indentation.chars().all(is_python_whitespace) {
+        Some(indentation)
+    } else {
+        None
+    }
+}
+
+/// Return `true` if the node starting the given [`TextSize`] has leading content.
+pub fn has_leading_content(offset: TextSize, locator: &Locator) -> bool {
+    let line_start = locator.line_start(offset);
+    let leading = &locator.contents()[TextRange::new(line_start, offset)];
+    leading.chars().any(|char| !is_python_whitespace(char))
+}
+
+/// Return `true` if the node ending at the given [`TextSize`] has trailing content.
+pub fn has_trailing_content(offset: TextSize, locator: &Locator) -> bool {
+    let line_end = locator.line_end(offset);
+    let trailing = &locator.contents()[TextRange::new(offset, line_end)];
+
+    for char in trailing.chars() {
+        if char == '#' {
+            return false;
+        }
+        if !is_python_whitespace(char) {
+            return true;
+        }
+    }
+    false
+}
+
 /// Returns `true` for [whitespace](https://docs.python.org/3/reference/lexical_analysis.html#whitespace-between-tokens)
 /// characters.
 pub const fn is_python_whitespace(c: char) -> bool {
@@ -41,3 +79,50 @@ impl PythonWhitespace for str {
         self.trim_end_matches(is_python_whitespace)
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::has_trailing_content;
+    use ruff_source_file::Locator;
+    use rustpython_ast::{Ranged, Suite};
+    use rustpython_parser::{Parse, ParseError};
+
+    #[test]
+    fn trailing_content() -> Result<(), ParseError> {
+        let contents = "x = 1";
+        let program = Suite::parse(contents, "<filename>")?;
+        let stmt = program.first().unwrap();
+        let locator = Locator::new(contents);
+        assert!(!has_trailing_content(stmt.end(), &locator));
+
+        let contents = "x = 1; y = 2";
+        let program = Suite::parse(contents, "<filename>")?;
+        let stmt = program.first().unwrap();
+        let locator = Locator::new(contents);
+        assert!(has_trailing_content(stmt.end(), &locator));
+
+        let contents = "x = 1  ";
+        let program = Suite::parse(contents, "<filename>")?;
+        let stmt = program.first().unwrap();
+        let locator = Locator::new(contents);
+        assert!(!has_trailing_content(stmt.end(), &locator));
+
+        let contents = "x = 1  # Comment";
+        let program = Suite::parse(contents, "<filename>")?;
+        let stmt = program.first().unwrap();
+        let locator = Locator::new(contents);
+        assert!(!has_trailing_content(stmt.end(), &locator));
+
+        let contents = r#"
+x = 1
+y = 2
+"#
+        .trim();
+        let program = Suite::parse(contents, "<filename>")?;
+        let stmt = program.first().unwrap();
+        let locator = Locator::new(contents);
+        assert!(!has_trailing_content(stmt.end(), &locator));
+
+        Ok(())
+    }
+}