error: incorrect function inside `extern` block
  --> $DIR/issue-97193.rs:2:8
   |
LL |   extern "C" {
   |   ---------- `extern` blocks define existing foreign functions and functions inside of them cannot have a body
LL |       fn a(&mut self) {
   |  ________^____________-
   | |        |
   | |        cannot have a body
LL | |
LL | |
LL | |         fn b(buf: &Self) {}
LL | |     }
   | |_____- help: remove the invalid body: `;`
   |
   = help: you might have meant to write a function accessible through FFI, which can be done by writing `extern fn` outside of the `extern` block
   = note: for more information, visit https://doc.rust-lang.org/std/keyword.extern.html

error: `self` parameter is only allowed in associated functions
  --> $DIR/issue-97193.rs:2:10
   |
LL |     fn a(&mut self) {
   |          ^^^^^^^^^ not semantically valid as function parameter
   |
   = note: associated functions are those in `impl` or `trait` definitions

error: aborting due to 2 previous errors