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style: Make rust generate better code for derive(Animate) and derive(…
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…ComputeSquaredDistance).

See rust-lang/rust#68867.

This technically changes the semantics of #[animate(fallback)] and such when
combined with #[animate(error)]. But no such combination exists and the new
semantics are perfectly reasonable as well, IMHO.

Differential Revision: https://phabricator.services.mozilla.com/D61761
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@emilio
emilio authored and Istvan Miklos committed Feb 12, 2020
1 parent aeb5776 commit 1cf3f40
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Showing 4 changed files with 105 additions and 89 deletions.
2 changes: 1 addition & 1 deletion components/style/values/animated/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -107,7 +107,7 @@ pub fn animate_multiplicative_factor(
/// be equal or an error is returned.
///
/// If a variant is annotated with `#[animation(error)]`, the corresponding
/// `match` arm is not generated.
/// `match` arm returns an error.
///
/// If the two values are not similar, an error is returned unless a fallback
/// function has been specified through `#[animate(fallback)]`.
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2 changes: 1 addition & 1 deletion components/style/values/distance.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ use std::ops::Add;
/// on each fields of the values.
///
/// If a variant is annotated with `#[animation(error)]`, the corresponding
/// `match` arm is not generated.
/// `match` arm returns an error.
///
/// If the two values are not similar, an error is returned unless a fallback
/// function has been specified through `#[distance(fallback)]`.
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55 changes: 29 additions & 26 deletions components/style_derive/animate.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,8 @@ use synstructure::{Structure, VariantInfo};

pub fn derive(mut input: DeriveInput) -> TokenStream {
let animation_input_attrs = cg::parse_input_attrs::<AnimationInputAttrs>(&input);
let input_attrs = cg::parse_input_attrs::<AnimateInputAttrs>(&input);

let no_bound = animation_input_attrs.no_bound.unwrap_or_default();
let mut where_clause = input.generics.where_clause.take();
for param in input.generics.type_params() {
Expand All @@ -21,39 +23,32 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
);
}
}
let (mut match_body, append_error_clause) = {
let (mut match_body, needs_catchall_branch) = {
let s = Structure::new(&input);
let mut append_error_clause = s.variants().len() > 1;

let needs_catchall_branch = s.variants().len() > 1;
let match_body = s.variants().iter().fold(quote!(), |body, variant| {
let arm = match derive_variant_arm(variant, &mut where_clause) {
Ok(arm) => arm,
Err(()) => {
append_error_clause = true;
return body;
},
};
let arm = derive_variant_arm(variant, &mut where_clause);
quote! { #body #arm }
});
(match_body, append_error_clause)
(match_body, needs_catchall_branch)
};

input.generics.where_clause = where_clause;

if append_error_clause {
let input_attrs = cg::parse_input_attrs::<AnimateInputAttrs>(&input);
if let Some(fallback) = input_attrs.fallback {
match_body.append_all(quote! {
(this, other) => #fallback(this, other, procedure)
});
} else {
match_body.append_all(quote! { _ => Err(()) });
}
if needs_catchall_branch {
// This ideally shouldn't be needed, but see
// https://github.com/rust-lang/rust/issues/68867
match_body.append_all(quote! { _ => unsafe { debug_unreachable!() } });
}

let name = &input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

let fallback = match input_attrs.fallback {
Some(fallback) => quote! { #fallback(self, other, procedure) },
None => quote! { Err(()) },
};

quote! {
impl #impl_generics crate::values::animated::Animate for #name #ty_generics #where_clause {
#[allow(unused_variables, unused_imports)]
Expand All @@ -63,6 +58,9 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
other: &Self,
procedure: crate::values::animated::Procedure,
) -> Result<Self, ()> {
if std::mem::discriminant(self) != std::mem::discriminant(other) {
return #fallback;
}
match (self, other) {
#match_body
}
Expand All @@ -74,13 +72,17 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
fn derive_variant_arm(
variant: &VariantInfo,
where_clause: &mut Option<WhereClause>,
) -> Result<TokenStream, ()> {
) -> TokenStream {
let variant_attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
if variant_attrs.error {
return Err(());
}
let (this_pattern, this_info) = cg::ref_pattern(&variant, "this");
let (other_pattern, other_info) = cg::ref_pattern(&variant, "other");

if variant_attrs.error {
return quote! {
(&#this_pattern, &#other_pattern) => Err(()),
};
}

let (result_value, result_info) = cg::value(&variant, "result");
let mut computations = quote!();
let iter = result_info.iter().zip(this_info.iter().zip(&other_info));
Expand All @@ -107,12 +109,13 @@ fn derive_variant_arm(
}
}
}));
Ok(quote! {

quote! {
(&#this_pattern, &#other_pattern) => {
#computations
Ok(#result_value)
}
})
}
}

#[darling(attributes(animate), default)]
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135 changes: 74 additions & 61 deletions components/style_derive/compute_squared_distance.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,11 +6,12 @@ use crate::animate::{AnimationFieldAttrs, AnimationInputAttrs, AnimationVariantA
use derive_common::cg;
use proc_macro2::TokenStream;
use quote::TokenStreamExt;
use syn::{DeriveInput, Path};
use syn::{DeriveInput, Path, WhereClause};
use synstructure;

pub fn derive(mut input: DeriveInput) -> TokenStream {
let animation_input_attrs = cg::parse_input_attrs::<AnimationInputAttrs>(&input);
let input_attrs = cg::parse_input_attrs::<DistanceInputAttrs>(&input);
let no_bound = animation_input_attrs.no_bound.unwrap_or_default();
let mut where_clause = input.generics.where_clause.take();
for param in input.generics.type_params() {
Expand All @@ -22,76 +23,31 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
}
}

let (mut match_body, append_error_clause) = {
let (mut match_body, needs_catchall_branch) = {
let s = synstructure::Structure::new(&input);
let mut append_error_clause = s.variants().len() > 1;
let needs_catchall_branch = s.variants().len() > 1;

let match_body = s.variants().iter().fold(quote!(), |body, variant| {
let attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
if attrs.error {
append_error_clause = true;
return body;
}

let (this_pattern, this_info) = cg::ref_pattern(&variant, "this");
let (other_pattern, other_info) = cg::ref_pattern(&variant, "other");
let sum = if this_info.is_empty() {
quote! { crate::values::distance::SquaredDistance::from_sqrt(0.) }
} else {
let mut sum = quote!();
sum.append_separated(this_info.iter().zip(&other_info).map(|(this, other)| {
let field_attrs = cg::parse_field_attrs::<DistanceFieldAttrs>(&this.ast());
if field_attrs.field_bound {
let ty = &this.ast().ty;
cg::add_predicate(
&mut where_clause,
parse_quote!(#ty: crate::values::distance::ComputeSquaredDistance),
);
}

let animation_field_attrs =
cg::parse_field_attrs::<AnimationFieldAttrs>(&this.ast());

if animation_field_attrs.constant {
quote! {
{
if #this != #other {
return Err(());
}
crate::values::distance::SquaredDistance::from_sqrt(0.)
}
}
} else {
quote! {
crate::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
}
}
}), quote!(+));
sum
};
quote! {
#body
(&#this_pattern, &#other_pattern) => {
Ok(#sum)
}
}
let arm = derive_variant_arm(variant, &mut where_clause);
quote! { #body #arm }
});

(match_body, append_error_clause)
(match_body, needs_catchall_branch)
};

input.generics.where_clause = where_clause;

if append_error_clause {
let input_attrs = cg::parse_input_attrs::<DistanceInputAttrs>(&input);
if let Some(fallback) = input_attrs.fallback {
match_body.append_all(quote! {
(this, other) => #fallback(this, other)
});
} else {
match_body.append_all(quote! { _ => Err(()) });
}
if needs_catchall_branch {
// This ideally shouldn't be needed, but see:
// https://github.com/rust-lang/rust/issues/68867
match_body.append_all(quote! { _ => unsafe { debug_unreachable!() } });
}

let fallback = match input_attrs.fallback {
Some(fallback) => quote! { #fallback(self, other) },
None => quote! { Err(()) },
};

let name = &input.ident;
let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();

Expand All @@ -103,6 +59,9 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
&self,
other: &Self,
) -> Result<crate::values::distance::SquaredDistance, ()> {
if std::mem::discriminant(self) != std::mem::discriminant(other) {
return #fallback;
}
match (self, other) {
#match_body
}
Expand All @@ -111,6 +70,60 @@ pub fn derive(mut input: DeriveInput) -> TokenStream {
}
}

fn derive_variant_arm(
variant: &synstructure::VariantInfo,
mut where_clause: &mut Option<WhereClause>,
) -> TokenStream {
let variant_attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
let (this_pattern, this_info) = cg::ref_pattern(&variant, "this");
let (other_pattern, other_info) = cg::ref_pattern(&variant, "other");

if variant_attrs.error {
return quote! {
(&#this_pattern, &#other_pattern) => Err(()),
};
}

let sum = if this_info.is_empty() {
quote! { crate::values::distance::SquaredDistance::from_sqrt(0.) }
} else {
let mut sum = quote!();
sum.append_separated(this_info.iter().zip(&other_info).map(|(this, other)| {
let field_attrs = cg::parse_field_attrs::<DistanceFieldAttrs>(&this.ast());
if field_attrs.field_bound {
let ty = &this.ast().ty;
cg::add_predicate(
&mut where_clause,
parse_quote!(#ty: crate::values::distance::ComputeSquaredDistance),
);
}

let animation_field_attrs =
cg::parse_field_attrs::<AnimationFieldAttrs>(&this.ast());

if animation_field_attrs.constant {
quote! {
{
if #this != #other {
return Err(());
}
crate::values::distance::SquaredDistance::from_sqrt(0.)
}
}
} else {
quote! {
crate::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
}
}
}), quote!(+));
sum
};

return quote! {
(&#this_pattern, &#other_pattern) => Ok(#sum),
};
}

#[darling(attributes(distance), default)]
#[derive(Default, FromDeriveInput)]
struct DistanceInputAttrs {
Expand Down

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