lofty-rs/lofty_attr/src/lib.rs

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2022-07-24 20:08:46 +00:00
use proc_macro::TokenStream;
use proc_macro2::Span;
use quote::{format_ident, quote, quote_spanned, ToTokens};
use std::fmt::Display;
use syn::spanned::Spanned;
use syn::{
parse_macro_input, Attribute, Data, DataStruct, DeriveInput, Fields, Ident, Lit, Meta,
MetaList, NestedMeta, Type,
};
const LOFTY_FILE_TYPES: [&str; 10] = [
"AIFF", "APE", "FLAC", "MP3", "MP4", "Opus", "Vorbis", "Speex", "WAV", "WavPack",
];
#[proc_macro_derive(LoftyFile, attributes(lofty))]
pub fn tag(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let mut errors = Vec::new();
let ret = parse(input, &mut errors);
let compile_errors = errors.iter().map(syn::Error::to_compile_error);
TokenStream::from(quote! {
#(#compile_errors)*
#ret
})
}
fn parse(input: DeriveInput, errors: &mut Vec<syn::Error>) -> proc_macro2::TokenStream {
macro_rules! bail {
($errors:ident, $span:expr, $msg:literal) => {
$errors.push(err($span, $msg));
return proc_macro2::TokenStream::new();
};
}
let data = match input.data {
Data::Struct(
ref data_struct @ DataStruct {
fields: Fields::Named(_),
..
},
) => data_struct,
_ => {
bail!(
errors,
input.ident.span(),
"This macro can only be used on structs with named fields"
);
},
};
let impl_audiofile = should_impl_audiofile(&input.attrs);
let read_fn = match get_attr("read_fn", &input.attrs) {
Some(rfn) => rfn,
_ if impl_audiofile => {
bail!(
errors,
input.ident.span(),
"Expected a #[read_fn] attribute"
);
},
_ => proc_macro2::TokenStream::new(),
};
let struct_name = input.ident.clone();
let file_type = match opt_file_type(struct_name.to_string()) {
Some(ft) => ft,
_ => match get_attr("file_type", &input.attrs) {
Some(rfn) => rfn,
_ => {
bail!(
errors,
input.ident.span(),
"Expected a #[file_type] attribute"
);
},
},
};
let (tag_fields, properties_field) = match get_fields(errors, data) {
Some(fields) => fields,
None => return proc_macro2::TokenStream::new(),
};
if tag_fields.is_empty() {
errors.push(err(input.ident.span(), "Struct has no tag fields"));
}
let properties_field = if let Some(field) = properties_field {
field
} else {
bail!(errors, input.ident.span(), "Struct has no properties field");
};
let properties_field_ty = &properties_field.ty;
let assert_properties_impl = quote_spanned! {properties_field_ty.span()=>
struct _AssertIntoFileProperties where #properties_field_ty: std::convert::Into<lofty::FileProperties>;
};
let assert_tag_impl_into = tag_fields.iter().enumerate().map(|(i, f)| {
let name = format_ident!("_AssertTagExt{}", i);
let field_ty = &f.ty;
quote_spanned! {field_ty.span()=>
struct #name where #field_ty: lofty::TagExt;
}
});
let tag_exists = tag_fields.iter().map(|f| {
let name = &f.name;
if f.needs_option {
quote! { self.#name.is_some() }
} else {
quote! { true }
}
});
let tag_exists_2 = tag_exists.clone();
let tag_type = tag_fields.iter().map(|f| &f.tag_type);
let audiofile_impl = if impl_audiofile {
quote! {
impl lofty::AudioFile for #struct_name {
type Properties = #properties_field_ty;
fn read_from<R>(reader: &mut R, read_properties: bool) -> lofty::error::Result<Self>
where
R: std::io::Read + std::io::Seek,
{
#read_fn(reader, read_properties)
}
fn properties(&self) -> &Self::Properties {
&self.properties
}
#[allow(unreachable_code)]
fn contains_tag(&self) -> bool {
#( #tag_exists )||*
}
#[allow(unreachable_code, unused_variables)]
fn contains_tag_type(&self, tag_type: TagType) -> bool {
match tag_type {
#( TagType::#tag_type => { #tag_exists_2 } ),*
_ => false
}
}
}
}
} else {
proc_macro2::TokenStream::new()
};
let conditions = tag_fields.iter().map(|f| {
let name = &f.name;
if f.needs_option {
quote! { if let Some(t) = input.#name { tags.push(t.into()); } }
} else {
quote! { tags.push(input.#name.into()); }
}
});
let getters = get_getters(&tag_fields, &struct_name);
quote! {
#assert_properties_impl
#( #assert_tag_impl_into )*
#audiofile_impl
impl std::convert::From<#struct_name> for lofty::TaggedFile {
fn from(input: #struct_name) -> Self {
lofty::TaggedFile::new(
lofty::FileType::#file_type,
lofty::FileProperties::from(input.properties),
{
let mut tags: Vec<lofty::Tag> = Vec::new();
#( #conditions )*
tags
}
)
}
}
#( #getters )*
}
}
struct FieldContents {
name: Ident,
cfg_features: Vec<Attribute>,
needs_option: bool,
getter_name: Option<proc_macro2::TokenStream>,
ty: Type,
tag_type: proc_macro2::TokenStream,
}
fn get_fields<'a>(
errors: &mut Vec<syn::Error>,
data: &'a DataStruct,
) -> Option<(Vec<FieldContents>, Option<&'a syn::Field>)> {
let mut tag_fields = Vec::new();
let mut properties_field = None;
for field in &data.fields {
let name = field.ident.clone().unwrap();
if name.to_string().ends_with("_tag") {
let tag_type = match get_attr("tag_type", &field.attrs) {
Some(tt) => tt,
_ => {
errors.push(err(field.span(), "Field has no `tag_type` attribute"));
return None;
},
};
let cfg = field
.attrs
.iter()
.cloned()
.filter_map(|a| get_attr_list("cfg", &a).map(|_| a))
.collect::<Vec<_>>();
let contents = FieldContents {
name,
getter_name: get_attr("getter", &field.attrs),
ty: extract_type_from_option(&field.ty)
.map_or_else(|| field.ty.clone(), |t| t.clone()),
tag_type,
needs_option: needs_option(&field.attrs),
cfg_features: cfg,
};
tag_fields.push(contents);
continue;
}
if name == "properties" {
properties_field = Some(field);
}
}
Some((tag_fields, properties_field))
}
fn opt_file_type(struct_name: String) -> Option<proc_macro2::TokenStream> {
let stripped = struct_name.strip_suffix("File");
if let Some(prefix) = stripped {
if let Some(pos) = LOFTY_FILE_TYPES
.iter()
.position(|p| p.eq_ignore_ascii_case(prefix))
{
return Some(
LOFTY_FILE_TYPES[pos]
.parse::<proc_macro2::TokenStream>()
.unwrap(),
);
}
}
None
}
fn get_attr(name: &str, attrs: &[Attribute]) -> Option<proc_macro2::TokenStream> {
for attr in attrs {
if let Some(list) = get_attr_list("lofty", attr) {
if let Some(NestedMeta::Meta(Meta::NameValue(mnv))) = list.nested.first() {
if mnv
.path
.segments
.first()
.expect("path shouldn't be empty")
.ident == name
{
if let Lit::Str(lit_str) = &mnv.lit {
return Some(lit_str.parse::<proc_macro2::TokenStream>().unwrap());
}
}
}
}
}
None
}
fn needs_option(attrs: &[Attribute]) -> bool {
for attr in attrs {
if has_path_attr(attr, "always_present") {
return false;
}
}
true
}
fn should_impl_audiofile(attrs: &[Attribute]) -> bool {
for attr in attrs {
if has_path_attr(attr, "no_audiofile_impl") {
return false;
}
}
true
}
fn has_path_attr(attr: &Attribute, name: &str) -> bool {
if let Some(list) = get_attr_list("lofty", attr) {
if let Some(NestedMeta::Meta(Meta::Path(p))) = list.nested.first() {
if p.is_ident(name) {
return true;
}
}
}
false
}
fn get_attr_list(path: &str, attr: &Attribute) -> Option<MetaList> {
if attr.path.is_ident(path) {
if let Ok(Meta::List(list)) = attr.parse_meta() {
return Some(list);
}
}
None
}
fn get_getters<'a>(
tag_fields: &'a [FieldContents],
struct_name: &'a Ident,
) -> impl Iterator<Item = proc_macro2::TokenStream> + 'a {
tag_fields.iter().map(move |f| {
let name = f.getter_name.clone().unwrap_or_else(|| {
let name = f.name.to_string().strip_suffix("_tag").unwrap().to_string();
Ident::new(&name, f.name.span()).into_token_stream()
});
let (ty_prefix, ty_suffix) = if f.needs_option {
(quote! {Option<}, quote! {>})
} else {
(quote! {}, quote! {})
};
let field_name = &f.name;
let field_ty = &f.ty;
let assert_field_ty_default = quote_spanned! {f.name.span()=>
struct _AssertDefault where #field_ty: core::default::Default;
};
let ref_access = if f.needs_option {
quote! {self.#field_name.as_ref()}
} else {
quote! {&self.#field_name}
};
let mut_ident = Ident::new(&format!("{}_mut", name), Span::call_site());
let mut_access = if f.needs_option {
quote! {self.#field_name.as_mut()}
} else {
quote! {&mut self.#field_name}
};
let remove_ident = Ident::new(&format!("remove_{}", name), Span::call_site());
let remover = if f.needs_option {
quote! {self.#field_name = None;}
} else {
quote! {
#assert_field_ty_default
self.#field_name = <#field_ty>::default();
}
};
let cfg = &f.cfg_features;
quote! {
#( #cfg )*
impl #struct_name {
/// Returns a reference to the tag
pub fn #name(&self) -> #ty_prefix &#field_ty #ty_suffix {
#ref_access
}
/// Returns a mutable reference to the tag
pub fn #mut_ident(&mut self) -> #ty_prefix &mut #field_ty #ty_suffix {
#mut_access
}
/// Removes the tag
pub fn #remove_ident(&mut self) {
#remover
}
}
}
})
}
// https://stackoverflow.com/questions/55271857/how-can-i-get-the-t-from-an-optiont-when-using-syn
fn extract_type_from_option(ty: &Type) -> Option<&Type> {
use syn::{GenericArgument, Path, PathArguments, PathSegment};
fn extract_type_path(ty: &Type) -> Option<&Path> {
match *ty {
Type::Path(ref typepath) if typepath.qself.is_none() => Some(&typepath.path),
_ => None,
}
}
fn extract_option_segment(path: &Path) -> Option<&PathSegment> {
let idents_of_path = path
.segments
.iter()
.into_iter()
.fold(String::new(), |mut acc, v| {
acc.push_str(&v.ident.to_string());
acc.push('|');
acc
});
vec!["Option|", "std|option|Option|", "core|option|Option|"]
.into_iter()
.find(|s| idents_of_path == *s)
.and_then(|_| path.segments.last())
}
extract_type_path(ty)
.and_then(extract_option_segment)
.and_then(|path_seg| {
let type_params = &path_seg.arguments;
// It should have only on angle-bracketed param ("<String>"):
match *type_params {
PathArguments::AngleBracketed(ref params) => params.args.first(),
_ => None,
}
})
.and_then(|generic_arg| match *generic_arg {
GenericArgument::Type(ref ty) => Some(ty),
_ => None,
})
}
fn err<T: Display>(span: Span, error: T) -> syn::Error {
syn::Error::new(span, error)
}