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use quote::quote;
use std::fmt;
pub struct CustomDefault {
ast: syn::DeriveInput,
fields: Vec<(String, String)>,
}
impl CustomDefault {
pub fn new(ast: syn::DeriveInput) -> Self {
let struct_data = match ast.data {
syn::Data::Struct(ref data) => data,
_ => panic!("derive(CustomDefault) is available for structs only"),
};
let mut fields = Vec::new();
for field in struct_data.fields.iter() {
let variable_name = field.ident.as_ref().expect("Named field is needed").to_string();
let mut initalizer = "Default::default()".to_owned();
for attr in field.attrs.iter() {
let meta = &attr.meta;
if meta.path().is_ident("def_exp") {
match meta {
syn::Meta::NameValue(ref value) => {
let literal = match &value.value {
syn::Expr::Lit(literal) => &literal.lit,
_ => panic!("'def_exp' expected literal value"),
};
match literal {
syn::Lit::Str(ref value) => {
initalizer = value.value();
break;
}
_ => panic!("'def_exp' should be string, correct format is #[def_exp=\"expression\"]"),
}
},
_ => panic!("'def_exp' has incorrect format, expects #[def_exp=\"expression\"]"),
}
} else if meta.path().is_ident("def_val") {
match meta {
syn::Meta::NameValue(ref value) => {
let literal = match &value.value {
syn::Expr::Lit(literal) => &literal.lit,
_ => panic!("'dev_val' expected literal value"),
};
match literal {
syn::Lit::Str(ref value) => match field.ty {
syn::Type::Path(ref path) => {
if path.path.is_ident("String") {
initalizer = format!("\"{}\".to_owned()", value.value());
} else {
initalizer = format!("\"{}\"", value.value());
}
break;
},
syn::Type::Reference(ref reference) => {
match &*reference.elem {
syn::Type::Path(ref path) if path.path.is_ident("str") => (),
_ => panic!("'def_val' with string is placed on field '{}', but it is not string", variable_name),
}
initalizer = format!("\"{}\"", value.value());
break;
},
_ => panic!("'def_val' with string is placed on field '{}', but it is not string", variable_name),
},
syn::Lit::ByteStr(ref value) => match field.ty {
syn::Type::Array(_) => {
initalizer.clear();
initalizer.push('[');
for byte in value.value() {
initalizer.push_str(&format!("{},", byte));
}
initalizer.pop();
initalizer.push(']');
break;
},
syn::Type::Reference(ref reference) => {
match &*reference.elem {
syn::Type::Slice(_) => (),
_ => panic!("'def_val' expects bytes slice, but field '{}' got some other reference", variable_name),
}
initalizer.clear();
initalizer.push('&');
initalizer.push('[');
for byte in value.value() {
initalizer.push_str(&format!("{},", byte));
}
initalizer.pop();
initalizer.push(']');
break;
},
_ => panic!("'def_val' expects bytes type for field '{}'", variable_name),
},
syn::Lit::Byte(ref value) => match field.ty {
syn::Type::Path(ref path) => {
if path.path.is_ident("u8") {
initalizer = format!("{}", value.value());
} else if path.path.is_ident("i8") {
initalizer = format!("{} as i8", value.value());
} else {
panic!("'def_val' is byte literal, but field '{}' is not u8/i8", variable_name);
}
break;
},
_ => panic!("'def_val' is byte literal, but field '{}' is not u8/i8", variable_name),
},
syn::Lit::Char(ref value) => match field.ty {
syn::Type::Path(ref path) => if path.path.is_ident("char") {
initalizer = format!("'{}'", value.value());
break;
},
_ => panic!("'def_val' is char literal, but field '{}' is not char", variable_name),
},
syn::Lit::Int(ref value) => match field.ty {
syn::Type::Path(ref path) => {
if path.path.is_ident("u8") {
initalizer = format!("{}", value.base10_parse::<u8>().unwrap());
} else if path.path.is_ident("i8") {
initalizer = format!("{}", value.base10_parse::<i8>().unwrap());
} else if path.path.is_ident("u16") {
initalizer = format!("{}", value.base10_parse::<u16>().unwrap());
} else if path.path.is_ident("i16") {
initalizer = format!("{}", value.base10_parse::<i16>().unwrap());
} else if path.path.is_ident("u32") {
initalizer = format!("{}", value.base10_parse::<u32>().unwrap());
} else if path.path.is_ident("i32") {
initalizer = format!("{}", value.base10_parse::<i32>().unwrap());
} else if path.path.is_ident("u64") {
initalizer = format!("{}", value.base10_parse::<u64>().unwrap());
} else if path.path.is_ident("i64") {
initalizer = format!("{}", value.base10_parse::<i64>().unwrap());
} else if path.path.is_ident("u128") {
initalizer = format!("{}", value.base10_parse::<u128>().unwrap());
} else if path.path.is_ident("i128") {
initalizer = format!("{}", value.base10_parse::<i128>().unwrap());
} else {
panic!("'def_val' is integer literal, but field '{}' is not integer", variable_name);
}
break;
},
_ => panic!("'def_val' is integer literal, but field '{}' is not integer", variable_name),
},
syn::Lit::Float(ref value) => match field.ty {
syn::Type::Path(ref path) => {
if path.path.is_ident("f32") {
initalizer = format!("{}", value.base10_parse::<f32>().unwrap());
} else if path.path.is_ident("f64") {
initalizer = format!("{}", value.base10_parse::<f64>().unwrap());
} else {
panic!("'def_val' is float literal, but field '{}' is not float", variable_name)
}
break;
},
_ => panic!("'def_val' is float literal, but field '{}' is not float", variable_name),
},
syn::Lit::Bool(ref value) => match field.ty {
syn::Type::Path(ref path) => if path.path.is_ident("bool") {
initalizer = format!("{}", value.value);
break;
},
_ => panic!("'def_val' is bool literal, but field '{}' is not bool", variable_name),
},
_ => panic!("'def_val' expression has unknown format"),
} //match literal
},
_ => panic!("'def_val' should has value, correct format is #[def_val=<expression>]"),
}
}
}
fields.push((variable_name, initalizer))
}
Self {
ast,
fields
}
}
pub fn generate(&self) -> proc_macro::TokenStream {
let text = self.to_string();
match text.parse() {
Ok(res) => res,
Err(error) => panic!("Error: {:?}\nGenerated code: {}", error, text)
}
}
}
impl fmt::Display for CustomDefault {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let (impl_gen, type_gen, where_clause) = self.ast.generics.split_for_impl();
writeln!(f, "{} Default for {}{} {{", quote!(impl#impl_gen), self.ast.ident, quote!(#type_gen #where_clause))?;
writeln!(f, " fn default() -> Self {{")?;
writeln!(f, " Self {{")?;
for (key, value) in self.fields.iter() {
writeln!(f, " {}: {},", key, value)?;
}
writeln!(f, " }}")?;
writeln!(f, "\n }}")?;
writeln!(f, "}}")
}
}