Only allocate memory if removing text for lesser blocks.

src/parser/lesser_block.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use nom::branch::alt;
 use nom::bytes::complete::is_not;
 use nom::bytes::complete::tag;
@@ -651,6 +653,11 @@ fn switch_word<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
     ))(input)
 }
 
+enum ContentState {
+    Normal,
+    Modified(String),
+}
+
 #[cfg_attr(
     feature = "tracing",
     tracing::instrument(ret, level = "debug", skip(context))
@@ -658,8 +665,8 @@ fn switch_word<'s>(input: OrgSource<'s>) -> Res<OrgSource<'s>, OrgSource<'s>> {
 pub(crate) fn content<'b, 'g, 'r, 's>(
     context: RefContext<'b, 'g, 'r, 's>,
     input: OrgSource<'s>,
-) -> Res<OrgSource<'s>, String> {
-    let mut ret = String::new();
+) -> Res<OrgSource<'s>, Cow<'s, str>> {
+    let mut state = ContentState::Normal;
     let mut remaining = input;
     let exit_matcher_parser = parser_with_context!(exit_matcher_parser)(context);
     loop {
@@ -669,13 +676,28 @@ pub(crate) fn content<'b, 'g, 'r, 's>(
 
         let (remain, (pre_escape_whitespace, line)) = content_line(remaining)?;
         if let Some(val) = pre_escape_whitespace {
-            ret.push_str(Into::<&str>::into(val));
+            if let ContentState::Modified(ref mut ret) = state {
+                ret.push_str(Into::<&str>::into(val));
+            } else {
+                let mut ret = String::new();
+                ret.push_str(Into::<&str>::into(input.get_until(remaining)));
+                ret.push_str(Into::<&str>::into(val));
+                state = ContentState::Modified(ret);
+            }
+        }
+        if let ContentState::Modified(ref mut ret) = state {
+            ret.push_str(line.into());
         }
-        ret.push_str(line.into());
         remaining = remain;
     }
 
-    Ok((remaining, ret))
+    match state {
+        ContentState::Normal => Ok((
+            remaining,
+            Cow::Borrowed(Into::<&str>::into(input.get_until(remaining))),
+        )),
+        ContentState::Modified(ret) => Ok((remaining, Cow::Owned(ret))),
+    }
 }
 
 #[cfg_attr(feature = "tracing", tracing::instrument(ret, level = "debug"))]