inter-struct-codegen 0.2.1

Proc macro codegen crate for merge-struct.
Documentation 
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use std::path::PathBuf;

use proc_macro2::TokenStream;
use syn::ItemStruct;

use crate::error::*;

/// Get the root path of the crate that's currently using this proc macro.
/// This is done via the `CARGO_MANIFEST_DIR` variable, that's always supplied by cargo and
/// represents the directory containing the `Cargo.toml` for the current crate.
pub fn get_root_src_path(span: &ItemStruct) -> Result<PathBuf, TokenStream> {
    match std::env::var("CARGO_MANIFEST_DIR") {
        Err(error) => Err(err!(
            span,
            "Couldn't read CARGO_MANIFEST_DIR environment variable in InterStruct: {}",
            error
        )),
        Ok(path) => {
            let mut path = PathBuf::from(path);
            if !path.exists() {
                return Err(err!(
                    span,
                    "CARGO_MANIFEST_DIR path doesn't exist in InterStruct: {:?}",
                    path
                ));
            }

            // TODO: We expect the source tree to start in `$CARGO_MANIFEST_DIR/src`.
            // For everything else, we would have to manually parse the Cargo manifest.
            path.push("src");
            if !path.exists() {
                return Err(
                    err!(
                        span,
                        "InterStruct currently expects the source to be located in $CARGO_MANIFEST_DIR/src: {:?}", path
                    )
                );
            }

            Ok(path)
        }
    }
}