Support for disabling functions with feature flags

[eitsupi]

We may want to disable a function that does not work on a particular platform by using a feature flag.
For example, the following functions in Python Polars do not work on WASM and will be disabled in the build for WASM.

#[pymethods]
impl PyExpr {
    #[cfg(feature = "extract_jsonpath")]
    fn str_json_path_match(&self, pat: Self) -> Self {
        self.inner.clone().str().json_path_match(pat.inner).into()
    }
}

https://github.com/pola-rs/polars/blob/f5f4cb55e98c60f723036b932796d972104b5f93/crates/polars-python/src/expr/string.rs#L243-L246

Compiling the following code, which does the same thing using savvy, yields an error.

#[savvy]
impl PlRExpr {
    #[cfg(not(target_arch = "wasm32"))]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Ok(self
            .inner
            .clone()
            .str()
            .json_path_match(pat.inner.clone())
            .into())
    }
}

https://github.com/eitsupi/neo-r-polars/blob/14b234c300779ef4e7d0612bbfe9aaac03d8502e/src/rust/src/expr/string.rs#L114-L123

error[E0425]: cannot find function `savvy_PlRExpr_str_json_path_match_inner` in this scope
 --> src/expr/string.rs:5:6
  |
4 | #[savvy]
  | -------- similarly named function `savvy_PlRExpr_str_json_path_match__ffi` defined here
5 | impl PlRExpr {
  |      ^^^^^^^ help: a function with a similar name exists: `savvy_PlRExpr_str_json_path_match__ffi`

https://github.com/eitsupi/neo-r-polars/actions/runs/12536892771/job/34960399544

Using the following approach, Rust compiles successfully, but the R package build fails because multiple functions with the same name are generated on the C file generated by the savvy-cli update command.

#[cfg(not(target_arch = "wasm32"))]
#[savvy]
impl PlRExpr {
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Ok(self
            .inner
            .clone()
            .str()
            .json_path_match(pat.inner.clone())
            .into())
    }
}

#[cfg(target_arch = "wasm32")]
#[savvy]
impl PlRExpr {
    #[allow(unused_variables)]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Err(RPolarsErr::Other(format!("Not supported in WASM")).into())
    }
}

[yutannihilation]

Unfortunately, I don't think this will be possible. Handling feature flags properly is a too heavy job for static analysis.

On the other hand, I think this should be improved. Maybe just ignore duplicated one if the signatures match, and raise an error if the signatures don't match?

but the R package build fails because multiple functions with the same name are generated on the C file

[eitsupi]

Thanks for your reply!

On the other hand, I think this should be improved. Maybe just ignore duplicated one if the signatures match, and raise an error if the signatures don't match?

I think that makes sense.

[yutannihilation]

@eitsupi
The binary of the fixed version is available here. Could you test when you have time? No hurry at all!

https://github.com/yutannihilation/savvy/releases/tag/v0.8.3-rc.1

[eitsupi]

Thanks for the update!
I have confirmed that the following pattern works:

#[cfg(not(target_arch = "wasm32"))]
#[savvy]
impl PlRExpr {
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Ok(self
            .inner
            .clone()
            .str()
            .json_path_match(pat.inner.clone())
            .into())
    }
}

#[cfg(target_arch = "wasm32")]
#[savvy]
impl PlRExpr {
    #[allow(unused_variables)]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Err(RPolarsErr::Other(format!("Not supported in WASM")).into())
    }
}

I am wondering if the following pattern are also supported (I will have time to try within the next few days)

#[savvy]
impl PlRExpr {
    #[cfg(not(target_arch = "wasm32"))]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Ok(self
            .inner
            .clone()
            .str()
            .json_path_match(pat.inner.clone())
            .into())
    }

    #[cfg(target_arch = "wasm32")]
    #[allow(unused_variables)]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Err(RPolarsErr::Other(format!("Not supported in WASM")).into())
    }
}

[eitsupi]

I am wondering if the following pattern are also supported (I will have time to try within the next few days)

#[savvy]
impl PlRExpr {
    #[cfg(not(target_arch = "wasm32"))]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Ok(self
            .inner
            .clone()
            .str()
            .json_path_match(pat.inner.clone())
            .into())
    }

    #[cfg(target_arch = "wasm32")]
    #[allow(unused_variables)]
    fn str_json_path_match(&self, pat: &PlRExpr) -> Result<Self> {
        Err(RPolarsErr::Other(format!("Not supported in WASM")).into())
    }
}

This pattern does not seems supported.

[yutannihilation]

Thanks for testing. Let me check.

[yutannihilation]

I can't reproduce the problem. What error do you see when you run savvy-cli update?

[yutannihilation]

Ah, sorry, I hit the problem. Please forget my comment above.

error[E0428]: the name `savvy_StructWithConfig_new__ffi` is defined multiple times
  --> /Users/runner/work/savvy/savvy/R-package/src/rust/src/multiple_defs.rs:20:1
   |
20 | #[savvy]
   | ^^^^^^^^ `savvy_StructWithConfig_new__ffi` redefined here
   |
   = note: `savvy_StructWithConfig_new__ffi` must be defined only once in the value namespace of this module
   = note: this error originates in the attribute macro `savvy` (in Nightly builds, run with -Z macro-backtrace for more info)

[yutannihilation]

It turned out that the problem is on #[savvy] macro. Should be fixed now, but you need to specify the RC version in your Cargo.toml to try this.

https://crates.io/crates/savvy/0.8.3-rc.2

[eitsupi]

Thanks for the update!
But perhaps associated functions still seem to fail?

   error[E0428]: the name `savvy_PlRLazyFrame_new_from_parquet__ffi` is defined multiple times
     --> src/lazyframe/general.rs:12:1
      |
   12 | #[savvy]
      | ^^^^^^^^ `savvy_PlRLazyFrame_new_from_parquet__ffi` redefined here
      |
      = note: `savvy_PlRLazyFrame_new_from_parquet__ffi` must be defined only once in the value namespace of this module
      = note: this error originates in the attribute macro `savvy` (in Nightly builds, run with -Z macro-backtrace for more info)
   
   error[E0428]: the name `savvy_PlRLazyFrame_new_from_ndjson__ffi` is defined multiple times
     --> src/lazyframe/general.rs:12:1
      |
   12 | #[savvy]
      | ^^^^^^^^ `savvy_PlRLazyFrame_new_from_ndjson__ffi` redefined here
      |
      = note: `savvy_PlRLazyFrame_new_from_ndjson__ffi` must be defined only once in the value namespace of this module
      = note: this error originates in the attribute macro `savvy` (in Nightly builds, run with -Z macro-backtrace for more info)
   
✔ Setting active project to "/workspaces/neo-r-polars".
   For more information about this error, try `rustc --explain E0428`.
   error: could not compile `r-polars` (lib) due to 2 previous errors

from eitsupi/neo-r-polars@00fdcad

[yutannihilation]

This version should work!

https://crates.io/crates/savvy/0.8.3-rc.4

[eitsupi]

Confirmed in eitsupi/neo-r-polars#50, thanks!

[yutannihilation]

Great. Let's merge and release then!