E095: try used where it cannot work

error IOError { NotFound(path: string) }fn open(p: string): !int { ... }fn main(): int {    immut n: int = try open("x");   // ERROR: 'main' returns 'int'    return n;}//   Hint: Handle the error here instead: `f() recover as err run { ... }`.

try e passes the error of e on: if e (a !T) failed, try returns that same error value – same variant, same payload, same message – from the function it is written in, after running that function’s pending defers exactly as a return would. On success it is just the value. So it needs:

• A function that returns !V (any V). main returns int, so nothing can fail out of it: handle the error there with recover. A function returning a plain type can be declared !T to let errors leave it.
• A place a return is allowed. A defer runs while the function is already returning, so a try anywhere inside one is an error. Handle the error inside the deferred statement: defer f() recover run { ... };.
• A fallible operand. try plain() where plain returns an int has no error to pass on; drop the try.
• A function. There is no function to return from at the top level.

try is a reserved word, and binds like a prefix operator: try a() + try b() is (try a()) + (try b()).

Run turf --explain E095 in a terminal to read this again.