Remove MarkMap::merge_into since it is no longer used in this series

Author: ratmice

cfgrammar/src/lib/markmap.rs

@@ -428,57 +428,6 @@ impl<K: Ord + Clone, V> MarkMap<K, V> {
         Ok(())
     }
 
-    /// Similar to `merge_from` except the `MergeBehavior` of self is used when merging into `*other*`.
-    pub fn merge_into<U>(
-        mut self,
-        other: &'_ mut MarkMap<K, U>,
-    ) -> Result<(), MergeError<K, Box<V>>>
-    where
-        V: Into<U>,
-    {
-        for (src_key, src_mark, src_val) in self.contents.drain(..) {
-            let pos = other.contents.binary_search_by(|x| x.0.cmp(&src_key));
-            match pos {
-                Ok(pos) => {
-                    let (_, dest_mark, dest_val) = &mut other.contents[pos];
-                    let theirs_mark = Mark::MergeBehavior(MergeBehavior::Theirs).repr();
-                    let ours_mark = Mark::MergeBehavior(MergeBehavior::Ours).repr();
-                    let exclusive_mark =
-                        Mark::MergeBehavior(MergeBehavior::MutuallyExclusive).repr();
-                    let mut merge_behavior = (src_mark & exclusive_mark)
-                        | (src_mark & ours_mark)
-                        | (src_mark & theirs_mark);
-                    if merge_behavior == 0 {
-                        merge_behavior = Mark::MergeBehavior(self.default_merge_behavior).repr();
-                    }
-                    if merge_behavior == exclusive_mark {
-                        // If only clippy could convince me and the borrow checker this is actually unnecessary.
-                        #[allow(clippy::unnecessary_unwrap)]
-                        if src_val.is_some() && dest_val.is_some() {
-                            return Err(MergeError::Exclusivity(
-                                src_key,
-                                Box::new(src_val.unwrap()),
-                            ));
-                        } else if dest_val.is_none() {
-                            *dest_val = src_val.map(|x| x.into());
-                        }
-                    } else if merge_behavior == ours_mark && src_val.is_some()
-                        || merge_behavior == theirs_mark && dest_val.is_none()
-                    {
-                        *dest_mark = src_mark;
-                        *dest_val = src_val.map(|x| x.into());
-                    }
-                }
-                Err(pos) => {
-                    other
-                        .contents
-                        .insert(pos, (src_key, src_mark, src_val.map(|x| x.into())));
-                }
-            }
-        }
-        Ok(())
-    }
-
     /// Returns whether `key` has been marked as used.
     pub fn is_used<Q>(&self, key: &Q) -> bool
     where