error[E0381]: used binding `x` isn't initialized in all conditions
  --> $DIR/borrowck-if-no-else.rs:5:9
   |
LL |     let x: isize; if 1 > 2 { x = 10; }
   |         -            ----- this `if` expression might be missing an `else` arm that initializes `x`
   |         |
   |         binding declared here but left uninitialized
LL |     foo(x);
   |         ^ `x` used here but it isn't initialized in all conditions

error: aborting due to previous error

For more information about this error, try `rustc --explain E0381`.