Apr 07 2013

Here are some error messages that I got when updating Rust for Rubyists from Rust 0.5 to the new 0.6, and how to fix those errors.

Error:

rust.rs:1:4: 1:16 error: unresolved name
rust.rs:1 use task::spawn;
              ^~~~~~~~~~~~
rust.rs:1:4: 1:16 error: failed to resolve import: task::spawn
rust.rs:1 use task::spawn;
              ^~~~~~~~~~~~
error: failed to resolve imports
error: aborting due to 3 previous errors
make: *** [all] Error 101

or

rust.rs:1:4: 1:16 error: unresolved name
rust.rs:1 use io::println;
              ^~~~~~~~~~~~
rust.rs:1:4: 1:16 error: failed to resolve import: io::println
rust.rs:1 use io::println;
              ^~~~~~~~~~~~
error: failed to resolve imports
error: aborting due to 3 previous errors
make: *** [all] Error 101

The fix:

Imports are now more explicit, so you can’t just import things from core without specifying that you want to any more.

+ use core::task::spawn;- use task::spawn;

or

+ use core::io::println;- use io::println;

etc.

Error:

error: main function not found
error: aborting due to previous error

The fix:

When I used to write TDD’d Rust, I wouldn’t often write a main function until I had done a bunch of tests. This was okay, but now, you need one.

+ fn main() {
+ }

Error:

rustc rust.rs --test
rust.rs:5:2: 5:6 error: unresolved name: `fail`.
rust.rs:5   fail;
            ^~~~
error: aborting due to previous error
make: *** [build_test] Error 101

The fix:

fail was turned into a macro. It now needs to be passed an owned pointer to a string:

- fail;
+ fail!(~"Fail!");

Error:

rust.rs:5:18: 5:26 error: unresolved name: `int::str`.
rust.rs:5           println(int::str(num))
                            ^~~~~~~~
error: aborting due to previous error
make: *** [build] Error 101

The fix:

int::str is now int::to_str

- int::str
+ int::to_str

Error:

rust.rs:5:12: 5:18 error: cannot determine a type for this local variable: unconstrained type
rust.rs:5     let mut answer;
                      ^~~~~~
error: aborting due to previous error
make: *** [build] Error 101

The fix:

You have to tell it what kind it is. In my case, it was a string:

- let mut answer;
+ let mut answer = "";

Error:

rust.rs:3:11: 3:21 error: expected `;` or `}` after expression but found `is_fifteen`
rust.rs:3     assert is_fifteen(15)
                     ^~~~~~~~~~
make: *** [build_test] Error 101

The fix:

This happens because assert is now a macro.

- assert is_fifteen(15)
+ assert!(is_fifteen(15))

Error:

rustc rust.rs
rust.rs:11:10: 11:24 error: the type of this value must be known in this context
rust.rs:11 chan.send(10);
^~~~~~~~~~~~~~
error: aborting due to previous error
make: *** [build] Error 101

The fix:

Rust 0.6 got rid of ‘capture clauses.’ Don’t worry about it.

- do spawn |chan| {
+ do spawn {

Error:

rust.rs:10:17: 10:21 error: expected `,` but found `chan`
rust.rs:10   do spawn |move chan| {
                            ^~~~
make: *** [build] Error 101

The fix:

move is gone. Just remove it.

- do spawn |move chan| {
+ do spawn |chan| {

Note that this diff wouldn’t actually make it work, you’d still run into the issue above. But it gets rid of the move error.

Error:

rust.rs:13:6: 13:12 error: unexpected token: `static`
rust.rs:13       static fn count() {
                 ^~~~~~
make: *** [build] Error 101

The fix:

static was removed. Any method that doesn’t take self is static.

- static fn count() {
+ fn count() {

Error:

rust.rs:11:30: 11:37 error: obsolete syntax: colon-separated impl syntax

The fix:

As it says, the colon syntax is gone. Replace it with for:

- impl float: Num
+ impl Num for float

Error:

rust.rs:5:18: 5:22 error: use of undeclared type name `self`
rust.rs:5       fn new() -> self;
                            ^~~~

The fix:

This happens when you’re making a trait, and you want the implementations to return whatever type they are. The type name is now Self:

- fn new() -> self;
+ fn new() -> Self;

I hope you found that informative! Happy hacking!