Do better at preserving blank lines during pretty-printing

src/comp/syntax/print/pprust.rs

@@ -1563,7 +1563,11 @@ fn print_comment(s: &ps, cmnt: lexer::cmnt) {
       }
       lexer::blank_line. {
         // We need to do at least one, possibly two hardbreaks.
-        if is_begin(s) || is_end(s) { hardbreak(s.s) }
+        let is_semi = alt s.s.last_token() {
+          pp::STRING(s, _) { s == ";" }
+          _ { false }
+        };
+        if is_semi || is_begin(s) || is_end(s) { hardbreak(s.s) }
         hardbreak(s.s);
       }
     }

src/test/pretty/blank-lines.rs

@@ -0,0 +1,15 @@
+// pp-exact
+fn f() -> [int] {
+    let picard = 0;
+
+    let data = 1;
+
+    let worf = 2;
+
+
+    let enterprise = [picard, data, worf];
+
+
+
+    ret enterprise;
+}