Method pop_class

regex/regex-syntax/src/ast/parse.rs:862–904

Parse the end of a character class set and pop the character class parser stack. The union given corresponds to the last union built before seeing the closing `]`. The union returned corresponds to the parent character class set with the nested class added to it. This assumes that the parser is positioned at a `]` and will advance the parser to the byte immediately following the `]`. If the stac

(
        &self,
        nested_union: ast::ClassSetUnion,
    )

    /// If there is no corresponding opening bracket on the parser's stack,
    /// then an error is returned.
    fn pop_class(
        &self,
        nested_union: ast::ClassSetUnion,
    ) -> Result<Either<ast::ClassSetUnion, ast::Class>> {
        assert_eq!(self.char(), ']');

        let item = ast::ClassSet::Item(nested_union.into_item());
        let prevset = self.pop_class_op(item);
        let mut stack = self.parser().stack_class.borrow_mut();
        match stack.pop() {
            None => {
                // We can never observe an empty stack:
                //
                // 1) We are guaranteed to start with a non-empty stack since
                //    the character class parser is only initiated when it sees
                //    a `[`.
                // 2) If we ever observe an empty stack while popping after
                //    seeing a `]`, then we signal the character class parser
                //    to terminate.
                panic!("unexpected empty character class stack")
            },
            Some(ClassState::Op { .. }) => {
                // This panic is unfortunate, but this case is impossible
                // since we already popped the Op state if one exists above.
                // Namely, every push to the class parser stack is guarded by
                // whether an existing Op is already on the top of the stack.
                // If it is, the existing Op is modified. That is, the stack
                // can never have consecutive Op states.
                panic!("unexpected ClassState::Op")
            }
            Some(ClassState::Open { mut union, mut set }) => {
                self.bump();
                set.span.end = self.pos();
                set.kind = prevset;
                if stack.is_empty() {
                    Ok(Either::Right(ast::Class::Bracketed(set)))
                } else {
                    union.push(ast::ClassSetItem::Bracketed(Box::new(set)));
                    Ok(Either::Left(union))
                }
            }
        }
    }

    /// Return an "unclosed class" error whose span points to the most
    /// recently opened class.