Method push_class_open

regex/regex-syntax/src/ast/parse.rs:834–846

Parse the opening of a character class and push the current class parsing context onto the parser's stack. This assumes that the parser is positioned at an opening `[`. The given union should correspond to the union of set items built up before seeing the `[`. If there was a problem parsing the opening of the class, then an error is returned. Otherwise, a new union of set items for the class is r

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

    /// is returned. Otherwise, a new union of set items for the class is
    /// returned (which may be populated with either a `]` or a `-`).
    fn push_class_open(
        &self,
        parent_union: ast::ClassSetUnion,
    ) -> Result<ast::ClassSetUnion> {
        assert_eq!(self.char(), '[');

        let (nested_set, nested_union) = self.parse_set_class_open()?;
        self.parser().stack_class.borrow_mut().push(ClassState::Open {
            union: parent_union,
            set: nested_set,
        });
        Ok(nested_union)
    }

    /// Parse the end of a character class set and pop the character class
    /// parser stack. The union given corresponds to the last union built