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965d6ce4e4
This is a no-op in terms of function, but provides a nicer way to derive the
ContentHash trait for structs using the `#[derive(ContentHash)]` syntax used
for other traits such as `Debug`.
This commit only adds the macro. A subsequent commit will replace uses of
`content_hash!{}` with `#[derive(ContentHash)]`.
The new macro generates nice error messages, just like the old macro:
```
error[E0277]: the trait bound `NotImplemented: content_hash::ContentHash` is not satisfied
--> lib/src/content_hash.rs:265:16
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265 | z: NotImplemented,
| ^^^^^^^^^^^^^^ the trait `content_hash::ContentHash` is not implemented for `NotImplemented`
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= help: the following other types implement trait `content_hash::ContentHash`:
bool
i32
i64
u8
u32
u64
std::collections::HashMap<K, V>
BTreeMap<K, V>
and 38 others
```
This commit does two things to make proc macros re-exported by jj_lib useable
by deps:
1. jj_lib needs to be able refer to itself as `jj_lib` which it does
by adding an `extern crate self as jj_lib` declaration.
2. jj_lib::content_hash needs to re-export the `digest::Update` type so that
users of jj_lib can use the `#[derive(ContentHash)]` proc macro without
directly depending on the digest crate. This is done by re-exporting it
as `DigestUpdate`.
#3054
40 lines
1.4 KiB
Rust
40 lines
1.4 KiB
Rust
use proc_macro2::TokenStream;
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use quote::{quote, quote_spanned};
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use syn::spanned::Spanned;
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use syn::{Data, Fields, Index};
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pub fn generate_hash_impl(data: &Data) -> TokenStream {
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match *data {
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Data::Struct(ref data) => match data.fields {
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Fields::Named(ref fields) => {
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let hash_statements = fields.named.iter().map(|f| {
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let field_name = &f.ident;
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let ty = &f.ty;
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quote_spanned! {ty.span()=>
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<#ty as ::jj_lib::content_hash::ContentHash>::hash(
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&self.#field_name, state);
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}
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});
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quote! {
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#(#hash_statements)*
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}
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}
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Fields::Unnamed(ref fields) => {
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let hash_statements = fields.unnamed.iter().enumerate().map(|(i, f)| {
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let index = Index::from(i);
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let ty = &f.ty;
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quote_spanned! {ty.span() =>
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<#ty as ::jj_lib::content_hash::ContentHash>::hash(&self.#index, state);
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}
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});
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quote! {
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#(#hash_statements)*
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}
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}
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Fields::Unit => {
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quote! {}
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}
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},
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_ => unimplemented!("ContentHash can only be derived for structs."),
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}
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}
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