error: frontmatter close does not match the opening
  --> $DIR/mismatch-2.rs:1:1
   |
LL |   ----cargo
   |   ^---
   |   |
   |  _the opening here has 4 dashes...
   | |
LL | |
LL | | ---cargo
   | |_---____^
   |   |
   |   ...while the close has 3 dashes

error: extra characters after frontmatter close are not allowed
  --> $DIR/mismatch-2.rs:3:1
   |
LL | ---cargo
   | ^^^^^^^^

error: aborting due to 2 previous errors