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extern crate proc_macro;
use proc_macro::TokenStream;
use quote::quote;
use syn::parse::ParseStream;
use syn::{
parse_macro_input,
DeriveInput,
Attribute
};
#[proc_macro_derive(ConfigFile, attributes(cfg_file))]
pub fn derive_config_file(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = &input.ident;
// Process 'cfg_file'
let path_expr = match find_cfg_file_path(&input.attrs) {
Some(path) => {
if path.starts_with("./") {
let path_str = &path[2..];
quote! {
std::env::current_dir()?.join(#path_str)
}
} else {
// Using Absolute Path
quote! {
std::path::PathBuf::from(#path)
}
}
}
None => {
let default_file = to_snake_case(&name.to_string()) + ".json";
quote! {
std::env::current_dir()?.join(#default_file)
}
}
};
let expanded = quote! {
impl cfg_file::config::ConfigFile for #name {
type DataType = #name;
fn default_path() -> Result<std::path::PathBuf, std::io::Error> {
Ok(#path_expr)
}
}
};
TokenStream::from(expanded)
}
fn find_cfg_file_path(attrs: &[Attribute]) -> Option<String> {
for attr in attrs {
if attr.path().is_ident("cfg_file") {
let parser = |meta: ParseStream| {
let path_meta: syn::MetaNameValue = meta.parse()?;
if path_meta.path.is_ident("path") {
if let syn::Expr::Lit(syn::ExprLit { lit: syn::Lit::Str(lit), .. }) = path_meta.value {
return Ok(lit.value());
}
}
Err(meta.error("expected `path = \"...\"`"))
};
if let Ok(path) = attr.parse_args_with(parser) {
return Some(path);
}
}
}
None
}
fn to_snake_case(s: &str) -> String {
let mut snake = String::new();
for (i, c) in s.chars().enumerate() {
if c.is_uppercase() {
if i != 0 {
snake.push('_');
}
snake.push(c.to_ascii_lowercase());
} else {
snake.push(c);
}
}
snake
}
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