Handle the possibility of a title-less headline.

org_mode_samples/sections_and_headings/empty_heading.org

@@ -1 +1,2 @@
 * DONE
+* 

src/compare/diff.rs

@@ -546,14 +546,26 @@ fn compare_heading<'s>(
     };
 
     // Compare title
-    let title = get_property(emacs, ":title")?.ok_or("Missing :title attribute.")?;
+    let title = get_property(emacs, ":title")?;
-    let title_status = title
+    match (title, rust.title.len()) {
-        .as_list()?
+        (None, 0) => {}
-        .iter()
+        (None, _) => {
-        .zip(rust.title.iter())
+            this_status = DiffStatus::Bad;
-        .map(|(emacs_child, rust_child)| compare_object(source, emacs_child, rust_child))
+            message = Some(format!(
-        .collect::<Result<Vec<_>, _>>()?;
+                "Titles do not match (emacs != rust): {:?} != {:?}",
-    child_status.push(artificial_diff_scope("title".to_owned(), title_status)?);
+                title, rust.title
+            ))
+        }
+        (Some(title), _) => {
+            let title_status = title
+                .as_list()?
+                .iter()
+                .zip(rust.title.iter())
+                .map(|(emacs_child, rust_child)| compare_object(source, emacs_child, rust_child))
+                .collect::<Result<Vec<_>, _>>()?;
+            child_status.push(artificial_diff_scope("title".to_owned(), title_status)?);
+        }
+    };
 
     // Compare priority
     let priority = get_property(emacs, ":priority")?;

src/parser/headline.rs

@@ -8,6 +8,7 @@ use nom::combinator::eof;
 use nom::combinator::map;
 use nom::combinator::not;
 use nom::combinator::opt;
+use nom::combinator::peek;
 use nom::combinator::recognize;
 use nom::combinator::verify;
 use nom::multi::many0;
@@ -19,6 +20,11 @@ use nom::sequence::tuple;
 use super::org_source::OrgSource;
 use super::section::section;
 use super::util::get_consumed;
+use super::util::org_line_ending;
+use super::util::org_space;
+use super::util::org_space_or_line_ending;
+use super::util::org_spaces0;
+use super::util::org_spaces1;
 use super::util::start_of_line;
 use crate::context::parser_with_context;
 use crate::context::ContextElement;
@@ -81,10 +87,10 @@ fn _heading<'b, 'g, 'r, 's>(
         Heading {
             source: source.into(),
             stars: star_count,
-            todo_keyword: maybe_todo_keyword.map(|((todo_keyword_type, todo_keyword), _ws)| {
+            todo_keyword: maybe_todo_keyword.map(|(todo_keyword_type, todo_keyword)| {
                 (todo_keyword_type, Into::<&str>::into(todo_keyword))
             }),
-            priority_cookie: maybe_priority.map(|(priority, _)| priority),
+            priority_cookie: maybe_priority.map(|(_, priority)| priority),
             title,
             tags: heading_tags,
             children,
@@ -109,9 +115,9 @@ fn headline<'b, 'g, 'r, 's>(
     OrgSource<'s>,
     (
         usize,
-        Option<((TodoKeywordType, OrgSource<'s>), OrgSource<'s>)>,
+        Option<(TodoKeywordType, OrgSource<'s>)>,
-        Option<(PriorityCookie, OrgSource<'s>)>,
+        Option<(OrgSource<'s>, PriorityCookie)>,
-        Option<(OrgSource<'s>, OrgSource<'s>)>,
+        Option<OrgSource<'s>>,
         Vec<Object<'s>>,
         Vec<&'s str>,
     ),
@@ -122,45 +128,45 @@ fn headline<'b, 'g, 'r, 's>(
     });
     let parser_context = context.with_additional_node(&parser_context);
 
-    let (
+    let (remaining, (_, star_count, _)) = tuple((
-        remaining,
-        (
-            _,
-            star_count,
-            _,
-            maybe_todo_keyword,
-            maybe_priority,
-            maybe_comment,
-            title,
-            maybe_tags,
-            _,
-            _,
-        ),
-    ) = tuple((
         start_of_line,
         verify(many1_count(tag("*")), |star_count| {
             *star_count > parent_stars
         }),
-        space1,
+        peek(org_space),
-        opt(tuple((
-            parser_with_context!(heading_keyword)(&parser_context),
-            space1,
-        ))),
-        opt(tuple((priority_cookie, space1))),
-        opt(tuple((tag("COMMENT"), space1))),
-        many1(parser_with_context!(standard_set_object)(&parser_context)),
-        opt(tuple((space0, tags))),
-        space0,
-        alt((line_ending, eof)),
     ))(input)?;
+
+    let (remaining, maybe_todo_keyword) = opt(tuple((
+        org_spaces1,
+        parser_with_context!(heading_keyword)(&parser_context),
+        peek(org_space_or_line_ending),
+    )))(remaining)?;
+
+    let (remaining, maybe_priority) = opt(tuple((org_spaces1, priority_cookie)))(remaining)?;
+
+    let (remaining, maybe_comment) = opt(tuple((
+        org_spaces1,
+        tag("COMMENT"),
+        peek(org_space_or_line_ending),
+    )))(remaining)?;
+
+    let (remaining, maybe_title) = opt(tuple((
+        org_spaces1,
+        many1(parser_with_context!(standard_set_object)(&parser_context)),
+    )))(remaining)?;
+
+    let (remaining, maybe_tags) = opt(tuple((org_spaces0, tags)))(remaining)?;
+
+    let (remaining, _) = tuple((org_spaces0, org_line_ending))(remaining)?;
+
     Ok((
         remaining,
         (
             star_count,
-            maybe_todo_keyword,
+            maybe_todo_keyword.map(|(_, todo, _)| todo),
             maybe_priority,
-            maybe_comment,
+            maybe_comment.map(|(_, comment, _)| comment),
-            title,
+            maybe_title.map(|(_, title)| title).unwrap_or(Vec::new()),
             maybe_tags
                 .map(|(_ws, tags)| {
                     tags.into_iter()

src/parser/util.rs

@@ -1,4 +1,5 @@
 use nom::branch::alt;
+use nom::bytes::complete::is_a;
 use nom::character::complete::anychar;
 use nom::character::complete::line_ending;
 use nom::character::complete::none_of;
@@ -9,9 +10,11 @@ use nom::combinator::not;
 use nom::combinator::opt;
 use nom::combinator::peek;
 use nom::combinator::recognize;
+use nom::combinator::verify;
 use nom::multi::many0;
 use nom::multi::many_till;
 use nom::sequence::tuple;
+use nom::Slice;
 
 use super::org_source::OrgSource;
 use crate::context::parser_with_context;
@@ -212,6 +215,9 @@ fn text_until_eol<'r, 's>(
     Ok(line.trim())
 }
 
+/// Return a tuple of (input, output) from a nom parser.
+///
+/// This is similar to recognize except it returns the input instead of the portion of the input that was consumed.
 pub(crate) fn include_input<'s, F, O>(
     mut inner: F,
 ) -> impl FnMut(OrgSource<'s>) -> Res<OrgSource<'s>, (OrgSource<'s>, O)>
@@ -223,3 +229,44 @@ where
         Ok((remaining, (input, output)))
     }
 }
+
+/// Match single space or tab.
+///
+/// In org-mode syntax, spaces and tabs are interchangeable.
+pub(crate) fn org_space<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, char> {
+    one_of(" \t")(input)
+}
+
+/// Matches a single space, tab, line ending, or end of file.
+///
+/// In org-mode syntax there are often delimiters that could be any whitespace at all or the end of file.
+pub(crate) fn org_space_or_line_ending<'s>(
+    input: OrgSource<'s>,
+) -> Res<OrgSource<'s>, OrgSource<'s>> {
+    alt((recognize(one_of(" \t")), org_line_ending))(input)
+}
+
+/// Match as many spaces and tabs as possible. No minimum match.
+///
+/// In org-mode syntax, spaces and tabs are interchangeable.
+pub(crate) fn org_spaces0<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
+    let found = is_a(" \t")(input);
+    if found.is_ok() {
+        return found;
+    }
+    Ok((input, input.slice(..0)))
+}
+
+/// Match as many spaces and tabs as possible. Minimum 1 character.
+///
+/// In org-mode syntax, spaces and tabs are interchangeable.
+pub(crate) fn org_spaces1<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
+    verify(is_a(" \t"), |res: &OrgSource<'_>| res.len() > 0)(input)
+}
+
+/// Match a line break or the end of the file.
+///
+/// In org-mode syntax, the end of the file can serve the same purpose as a line break syntactically.
+pub(crate) fn org_line_ending<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
+    alt((line_ending, eof))(input)
+}