error: frontmatter close does not match the opening
  --> $DIR/mismatch-1.rs:1:1
   |
LL |   ---cargo
   |   ^--
   |   |
   |  _the opening here has 3 dashes...
   | |
LL | |
LL | | ----
   | |_---^
   |   |
   |   ...while the close has 4 dashes

error: aborting due to 1 previous error