error[E0515]: cannot return value referencing temporary value

[joshstoik1]

Hi there!

I'm getting the following error when adding the latest release (1.0.0-alpha.15) as a project dependency, but not when running cargo check directly against the contents of the parcel-css repo (the latter works just fine):

# cargo check
    Checking parcel_css v1.0.0-alpha.15
error[E0515]: cannot return value referencing temporary value
  --> /usr/local/cargo/registry/src/github.com-1ecc6299db9ec823/parcel_css-1.0.0-alpha.15/src/bundler.rs:49:5
   |
45 |       let res = self.inputs.entry(file.to_owned())
   |  _______________-
46 | |       .or_insert(source)
47 | |       .downgrade()
   | |__________________- temporary value created here
48 |         .value();
49 |       Ok(res)
   |       ^^^^^^^ returns a value referencing data owned by the current function

It doesn't seem to matter whether or not the project actually uses parcel; simply adding the dependency line is all it takes for me to get the error. The following cargo init boilerplate, for example, triggers it:

[package]
name = "just_a_boilerplate"
version = "0.1.0"
edition = "2021"

[dependencies.parcel_css]
version = "1.0.0-alpha.15"

I tried linking directly to git/master, toggling the "cli" feature on and off, and tested both stable 1.58.1 and nightly compilers, but none of that made any difference.

My build machine is a Debian Bullseye Docker environment (x86_64-unknown-linux-gnu).

I didn't have any issues with prior releases, but since the error is in bundler.rs, I suppose that doesn't mean much. Haha.

[devongovett]

I haven't tested yet (on mobile), but looks like perhaps the new version of dashmap might have changed some lifetimes: xacrimon/dashmap#167. It's set to 5.0.0 in the Cargo.lock in the repo so might be why it works there. I'll take a look in the morning.

[joshstoik1]

Ah yep, that's it exactly. Running cargo update against master and then cargo check is enough to bring about the error. 😉

[ije]

i also got the same error after upgraded to 1.0.0-alpha.15.

[ije]

@devongovett thanks

[devongovett]

So I implemented a different approach, but ended up relying on some unsafe rust unfortunately. If anyone knows a better way to accomplish this, let me know.

It's late here, so I'll get this released in the morning.

[ije]

@devongovett thanks no worries, good night

[ije]

i am not expert of rust, fyi https://github.com/denoland/deno_graph/blob/main/src/source.rs seems has the same file handling op

[joshstoik1]

Yeah, there isn't really a safe way to return non-Copy content that lives behind a Mutex. You could try replacing String with something like ustr, but they use pointer magic too.