serde_codegen does not generate code for derive in cfg_attr

[codyps]

For example, this doesn't work:

#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
struct Foo {
 a: u32,
};

It appears that the codegen simply doesn't know what to do about cfg_attr.

I suppose it's possible that not enough info is available when codegen occurs to actually resolve this. If so, feel free to close.

[dtolnay]

@jmesmon I just tried this and it seems to work. Can you try again and report back? Here is the code I used:

#![feature(plugin, custom_derive)]
#![plugin(serde_macros)]

#[cfg(feature = "serde")]
extern crate serde;

#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
struct Foo {
    a: u32,
}

#[cfg(feature = "serde")]
fn main() {
    println!("with serde");

    fn assert<T: serde::Serialize + serde::Deserialize>(_: T) {}
    assert(Foo { a: 0 });
}

#[cfg(not(feature = "serde"))]
fn main() {
    println!("without serde");
}

[codyps]

@dtolnay you're using serde_macros (plugin). This bug is talking about serde_codegen (generates code with a build script that you then include!).

I'm still able to reproduce this with serde_codegen.

Here's a project that reproduces: https://github.com/jmesmon/serde-readme

[dtolnay]

I suppose it's possible that not enough info is available when codegen occurs to actually resolve this. If so, feel free to close.

I suspect this is the case, but we can fix it anyway, at least for the common cases. We need to transform this:

#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
struct Foo { ... }

... into this:

#[cfg(feature = "serde")]
impl Serialize for Foo { ... }
#[cfg(feature = "serde")]
impl Deserialize for Foo { ... }
struct Foo { ... }

[dtolnay]

For those not watching the Syntex repo - check out the PR at serde-deprecated/syntex#71.

[erickt]

bad homu, this isn't implemented in serde yet.

[dtolnay]

Actually it is. 😄 That's all it took.

[nox]

I have a similar problem with:

#[cfg(target_os = "macos")]
pub type NativeFontHandle = CGFont;

/// Native fonts are not used on Linux; all fonts are raw.
#[cfg(not(target_os = "macos"))]
#[derive(Clone, Serialize, Deserialize)]
pub struct NativeFontHandle;

Is it the same bug? Should I file another one?

[dtolnay]

Different bug unfortunately. I filed it as serde-deprecated/syntex#81.