Do not allow elements to immediately nest inside themselves.

Plain list is omitted because they can nest.

src/parser/drawer.rs

@@ -10,6 +10,8 @@ use nom::sequence::tuple;
 
 use super::Context;
 use crate::parser::element::element;
+use crate::parser::error::CustomError;
+use crate::parser::error::MyError;
 use crate::parser::error::Res;
 use crate::parser::exiting::ExitClass;
 use crate::parser::parser_context::ContextElement;
@@ -17,6 +19,7 @@ use crate::parser::parser_context::ExitMatcherNode;
 use crate::parser::parser_with_context::parser_with_context;
 use crate::parser::util::exit_matcher_parser;
 use crate::parser::util::get_consumed;
+use crate::parser::util::immediate_in_section;
 use crate::parser::util::maybe_consume_trailing_whitespace_if_not_exiting;
 use crate::parser::util::start_of_line;
 use crate::parser::util::WORD_CONSTITUENT_CHARACTERS;
@@ -24,6 +27,11 @@ use crate::parser::Drawer;
 
 #[tracing::instrument(ret, level = "debug")]
 pub fn drawer<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str, Drawer<'s>> {
+    if immediate_in_section(context, "drawer") {
+        return Err(nom::Err::Error(CustomError::MyError(MyError(
+            "Cannot nest objects of the same element",
+        ))));
+    }
     start_of_line(context, input)?;
     let (remaining, _leading_whitespace) = space0(input)?;
     let (remaining, (_open_colon, drawer_name, _close_colon, _new_line)) = tuple((
@@ -35,6 +43,7 @@ pub fn drawer<'r, 's>(context: Context<'r, 's>, input: &'s str) -> Res<&'s str,
 
     let parser_context = context
         .with_additional_node(ContextElement::ConsumeTrailingWhitespace(true))
+        .with_additional_node(ContextElement::Context("drawer"))
         .with_additional_node(ContextElement::ExitMatcherNode(ExitMatcherNode {
             class: ExitClass::Alpha,
             exit_matcher: &drawer_end,