fn parse_update_file_chunk()

in codex-rs/apply-patch/src/parser.rs [202:288]

• 82 lines of code
• 9 McCabe index (conditional complexity)

fn parse_update_file_chunk(
    lines: &[&str],
    line_number: usize,
    allow_missing_context: bool,
) -> Result<(UpdateFileChunk, usize), ParseError> {
    if lines.is_empty() {
        return Err(InvalidHunkError {
            message: "Update hunk does not contain any lines".to_string(),
            line_number,
        });
    }
    // If we see an explicit context marker @@ or @@ <context>, consume it; otherwise, optionally
    // allow treating the chunk as starting directly with diff lines.
    let (change_context, start_index) = if lines[0] == EMPTY_CHANGE_CONTEXT_MARKER {
        (None, 1)
    } else if let Some(context) = lines[0].strip_prefix(CHANGE_CONTEXT_MARKER) {
        (Some(context.to_string()), 1)
    } else {
        if !allow_missing_context {
            return Err(InvalidHunkError {
                message: format!(
                    "Expected update hunk to start with a @@ context marker, got: '{}'",
                    lines[0]
                ),
                line_number,
            });
        }
        (None, 0)
    };
    if start_index >= lines.len() {
        return Err(InvalidHunkError {
            message: "Update hunk does not contain any lines".to_string(),
            line_number: line_number + 1,
        });
    }
    let mut chunk = UpdateFileChunk {
        change_context,
        old_lines: Vec::new(),
        new_lines: Vec::new(),
        is_end_of_file: false,
    };
    let mut parsed_lines = 0;
    for line in &lines[start_index..] {
        match *line {
            EOF_MARKER => {
                if parsed_lines == 0 {
                    return Err(InvalidHunkError {
                        message: "Update hunk does not contain any lines".to_string(),
                        line_number: line_number + 1,
                    });
                }
                chunk.is_end_of_file = true;
                parsed_lines += 1;
                break;
            }
            line_contents => {
                match line_contents.chars().next() {
                    None => {
                        // Interpret this as an empty line.
                        chunk.old_lines.push(String::new());
                        chunk.new_lines.push(String::new());
                    }
                    Some(' ') => {
                        chunk.old_lines.push(line_contents[1..].to_string());
                        chunk.new_lines.push(line_contents[1..].to_string());
                    }
                    Some('+') => {
                        chunk.new_lines.push(line_contents[1..].to_string());
                    }
                    Some('-') => {
                        chunk.old_lines.push(line_contents[1..].to_string());
                    }
                    _ => {
                        if parsed_lines == 0 {
                            return Err(InvalidHunkError { message: format!("Unexpected line found in update hunk: '{line_contents}'. Every line should start with ' ' (context line), '+' (added line), or '-' (removed line)"), line_number: line_number + 1 });
                        }
                        // Assume this is the start of the next hunk.
                        break;
                    }
                }
                parsed_lines += 1;
            }
        }
    }

    Ok((chunk, parsed_lines + start_index))
}