box try!(MyStruct::new()) as Box<MyTrait> no longer works without being put on separate lines

[daboross]

This code worked on the nightly from the 18th, and is broken by the nightly on the 21st.

Last nightly working version: rustc 0.13.0-nightly (2a231594c 2014-12-18 12:21:57 +0000)
First nightly broken version: rustc 0.13.0-nightly (cc19e3380 2014-12-20 20:00:36 +0000)

Here's the full error:

<std macros>:4:24: 4:27 error: mismatched types: expected `MyTrait + 'static`, found `MyStruct` (expected trait MyTrait, found struct MyStruct)
<std macros>:4             Ok(val) => val,
                                      ^~~
<std macros>:1:1: 8:2 note: in expansion of try!
src/main.rs:16:21: 16:45 note: expansion site
src/main.rs:16:17: 16:68 error: the trait `core::kinds::Sized` is not implemented for the type `MyTrait + 'static`
src/main.rs:16     let boxed = box try!(MyStruct::new()) as Box<MyTrait + 'static>;
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/main.rs:16:17: 16:68 note: only sized types can be made into objects
src/main.rs:16     let boxed = box try!(MyStruct::new()) as Box<MyTrait + 'static>;
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/main.rs:16:17: 16:68 error: the trait `MyTrait` is not implemented for the type `MyTrait + 'static`
src/main.rs:16     let boxed = box try!(MyStruct::new()) as Box<MyTrait + 'static>;
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/main.rs:16:17: 16:68 note: required for the cast to the object type `MyTrait + 'static`
src/main.rs:16     let boxed = box try!(MyStruct::new()) as Box<MyTrait + 'static>;
                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to 3 previous errors

Here's the code producing the above error:

trait MyTrait {}

struct MyStruct;

impl MyStruct {
    fn new() -> Result<MyStruct, String> {
        return Ok(MyStruct);
    }
}

impl MyTrait for MyStruct {}

/// This used to work, and doesn't work anymore
fn get1() -> Result<Box<MyTrait + 'static>, String> {
    let boxed = box try!(MyStruct::new()) as Box<MyTrait + 'static>;

    return Ok(boxed);
}

/// This works fine
fn get2() -> Result<Box<MyTrait + 'static>, String> {
    let thing = box try!(MyStruct::new());
    let boxed = thing as Box<MyTrait + 'static>;

    return Ok(boxed);
}

fn main() {}

Rust playpen: http://is.gd/JNqrmN

[oli-obk]

related to #20093 and might be fixed by #20099

[ftxqxd]

I don’t think this is related to #20093. It’s not a parsing issue: it gets past the parsing stage without issues, and adding delimiters ({}) doesn’t affect it. Also, #20093 only affects macro invocations that begin statements.

[daboross]

I don't think it's related to #20099, as it fails even when using a match statement instead of try!().

trait MyTrait {}

struct MyStruct;

impl MyStruct {
    fn new() -> Result<MyStruct, String> {
        return Ok(MyStruct);
    }
}

impl MyTrait for MyStruct {}

fn get() -> Result<(), String> {

    box match MyStruct::new() {
        Ok(v) => v,
        Err(e) => return Err(e),
    } as Box<MyTrait>;

    return Ok(());
}

fn main() {
}

[daboross]

Closing as this seems to work in the latest nightly! (rustc 0.13.0-nightly (96a3c7c6a 2014-12-23 22:21:10 +0000))