error: expected expression, found keyword `mut`
  --> $DIR/issue-103529.rs:5:6
   |
LL | m! { mut x }
   |      ^^^ expected expression

error: expected a statement
  --> $DIR/issue-103529.rs:5:10
   |
LL |     ($s:stmt) => {}
   |      ------- while parsing argument for this `stmt` macro fragment
...
LL | m! { mut x }
   |          ^

error: invalid variable declaration
  --> $DIR/issue-103529.rs:8:6
   |
LL | m! { auto x }
   |      ^^^^
   |
help: write `let` instead of `auto` to introduce a new variable
   |
LL | m! { let x }
   |      ~~~

error: invalid variable declaration
  --> $DIR/issue-103529.rs:10:6
   |
LL | m! { var x }
   |      ^^^
   |
help: write `let` instead of `var` to introduce a new variable
   |
LL | m! { let x }
   |      ~~~

error: aborting due to 4 previous errors