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Update MaxEncodedLen derive macro #512

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merged 12 commits into from
Sep 8, 2023
Merged

Update MaxEncodedLen derive macro #512

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e3336d1
Add failing test
pgherveou Sep 7, 2023
0af66c6
add MaxCompactEncodedLen trait
pgherveou Sep 6, 2023
49d2bab
Add max_compact_encoded_len to MaxEncodedLen trait
pgherveou Sep 7, 2023
17c4cc8
Nit only add predicate once
pgherveou Sep 7, 2023
8818af7
undo
pgherveou Sep 7, 2023
561960c
Update derive/src/trait_bounds.rs
pgherveou Sep 7, 2023
4b72be5
fix tests
pgherveou Sep 7, 2023
f14dcda
add nodoc
pgherveou Sep 7, 2023
d652607
Rework
bkchr Sep 7, 2023
04f935a
Fix
bkchr Sep 7, 2023
f96b221
fix fix
pgherveou Sep 7, 2023
e8b44f9
Revert
bkchr Sep 7, 2023
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2 changes: 1 addition & 1 deletion derive/src/max_encoded_len.rs
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Expand Up @@ -96,7 +96,7 @@ fn fields_length_expr(fields: &Fields, crate_path: &syn::Path) -> proc_macro2::T
let ty = &field.ty;
if utils::is_compact(&field) {
quote_spanned! {
ty.span() => .saturating_add(<#crate_path::Compact::<#ty> as #crate_path::MaxEncodedLen>::max_encoded_len())
ty.span() => .saturating_add(<#ty as #crate_path::MaxEncodedLen>::max_compact_encoded_len())
}
} else {
quote_spanned! {
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1 change: 1 addition & 0 deletions derive/src/trait_bounds.rs
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Expand Up @@ -161,6 +161,7 @@ pub fn add<N>(

codec_types
.into_iter()
// .take(1)
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.for_each(|ty| where_clause.predicates.push(parse_quote!(#ty : #codec_bound)));

let has_compact_bound: syn::Path = parse_quote!(#crate_path::HasCompact);
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17 changes: 15 additions & 2 deletions src/max_encoded_len.rs
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Expand Up @@ -32,6 +32,10 @@ use crate::alloc::sync::Arc;
pub trait MaxEncodedLen: Encode {
/// Upper bound, in bytes, of the maximum encoded size of this item.
fn max_encoded_len() -> usize;
/// Upper bound, in bytes, of the maximum encoded size of the compact encoding of this item.
fn max_compact_encoded_len() -> usize {
Self::max_encoded_len()
}
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Hmm... personally I'd probably prefer to keep this as a #[no_doc] and make it an internal implementation detail, instead of making it public.

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yes good point

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by internal you mean simply adding the #[doc(hidden)] attribute or is there other things you can do to truly keep it internal?

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by internal you mean simply adding the #[doc(hidden)] attribute or is there other things you can do to truly keep it internal?

Just hide it. I guess you could also prefix its name, e.g. prepend scale_internal_ to the name (which I did when I was adding scale_internal_decode_bytes on Input)

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I don't get why we need this at all.

The first thing should also be that there is a test added that fails with the old derive macro.

}

macro_rules! impl_primitives {
Expand All @@ -46,16 +50,25 @@ macro_rules! impl_primitives {
};
}

impl_primitives!(u8, u16, u32, u64, u128, i8, i16, i32, i64, i128, bool);

impl_primitives!(
i8, i16, i32, i64, i128, bool,
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You know that you skipped all unsigned types?

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For the unsigned types the impl_compact macro is used now, so they're not skipped. (:

NonZeroU8, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU128, NonZeroI8, NonZeroI16, NonZeroI32,
NonZeroI64, NonZeroI128
);

macro_rules! impl_compact {
($( $t:ty => $e:expr; )*) => {
$(
impl MaxEncodedLen for $t {
fn max_encoded_len() -> usize {
mem::size_of::<$t>()
}

fn max_compact_encoded_len() -> usize {
$e
}
}

impl MaxEncodedLen for Compact<$t> {
fn max_encoded_len() -> usize {
$e
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11 changes: 5 additions & 6 deletions tests/max_encoded_len.rs
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Expand Up @@ -65,18 +65,17 @@ fn generic_max_length() {
}

#[derive(Encode, MaxEncodedLen)]
struct CompactField {
struct CompactField<T: MaxEncodedLen> {
#[codec(compact)]
t: u64,
t: T,
v: u64,
}

#[test]
fn compact_field_max_length() {
assert_eq!(
CompactField::max_encoded_len(),
Compact::<u64>::max_encoded_len() + u64::max_encoded_len()
);
let max_len = CompactField::<u64>::max_encoded_len();
assert_eq!(max_len, Compact::<u64>::max_encoded_len() + u64::max_encoded_len());
assert_eq!(max_len, 17);
}
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I think I'd prefer to have a separate test for this, instead of modifying an existing one.

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Yes

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done, this test would fail with

  Compiling parity-scale-codec v3.6.6 (/Users/pg/github/parity-scale-codec)                                                                                                                                                                                            
error[E0277]: the trait bound `Compact<T>: MaxEncodedLen` is not satisfied                                                                                                                                                                                              
  --> tests/max_encoded_len.rs:87:5                                                                                                                                                                                                                                     
   |                                                                                                                                                                                                                                                                    
87 |     t: T,                                                                                                                                                                                                                                                          
   |        ^ the trait `MaxEncodedLen` is not implemented for `Compact<T>`                                                                                                                                                                                             
   |                                                                                                                                                                                                                                                                    
help: consider extending the `where` clause, but there might be an alternative better way to express this requirement                                                                                                                                                   
   |                                                                                                                                                                                                                                                                    
84 | #[derive(Encode, MaxEncodedLen, Compact<T>: MaxEncodedLen)]                                                                    
   |                               +++++++++++++++++++++++++++


#[derive(Encode, MaxEncodedLen)]
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