Keep vertical spaces between items or statements within range

src/config.rs

@@ -651,6 +651,10 @@ create_config! {
         "Add trailing semicolon after break, continue and return";
     match_block_trailing_comma: bool, false, false,
         "Put a trailing comma after a block based match arm (non-block arms are not affected)";
+    blank_lines_upper_bound: usize, 1, false,
+        "Maximum number of blank lines which can be put between items.";
+    blank_lines_lower_bound: usize, 0, false,
+        "Minimum number of blank lines which must be put between items.";
 
     // Options that can change the source code beyond whitespace/blocks (somewhat linty things)
     merge_derives: bool, true, true, "Merge multiple `#[derive(...)]` into a single one";

src/missed_spans.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 
 use std::borrow::Cow;
+use std::iter::repeat;
 
 use syntax::codemap::{BytePos, Pos, Span};
 
@@ -74,8 +75,27 @@ impl<'a> FmtVisitor<'a> {
 
         self.last_pos = end;
         let span = mk_sp(start, end);
+        let snippet = self.snippet(span);
+        if snippet.trim().is_empty() {
+            // Keep vertical spaces within range.
+            self.push_vertical_spaces(&snippet);
+            process_last_snippet(self, "", &snippet);
+        } else {
+            self.write_snippet(span, &process_last_snippet);
+        }
+    }
 
-        self.write_snippet(span, &process_last_snippet);
+    fn push_vertical_spaces(&mut self, original: &str) {
+        let mut newline_count = original.chars().filter(|&c| c == '\n').count();
+        let newline_upper_bound = self.config.blank_lines_upper_bound() + 1;
+        let newline_lower_bound = self.config.blank_lines_lower_bound() + 1;
+        if newline_count > newline_upper_bound {
+            newline_count = newline_upper_bound;
+        } else if newline_count < newline_lower_bound {
+            newline_count = newline_lower_bound;
+        }
+        let blank_lines: String = repeat('\n').take(newline_count).collect();
+        self.buffer.push_str(&blank_lines);
     }
 
     fn write_snippet<F>(&mut self, span: Span, process_last_snippet: F)