Handle the possibility of a title-less headline.

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)
+}