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Limit trait bounds for derive(ToCss) to types with free variables

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This commit is contained in:
Anthony Ramine 2017-06-16 14:52:36 +02:00
parent d65a7e6f95
commit b7c83eeb64
2 changed files with 32 additions and 3 deletions
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2
components/style_derive/Cargo.toml
View file

@ -11,5 +11,5 @@ proc-macro = true
[dependencies]
quote = "0.3"
syn = "0.11"
syn = { version = "0.11", features = ["visit"] }
synstructure = "0.5.2"

29
components/style_derive/to_css.rs
View file

@ -18,12 +18,16 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
let match_body = synstructure::each_variant(&input, &style, |bindings, variant| {
let mut identifier = to_css_identifier(variant.ident.as_ref());
let mut expr = if let Some((first, rest)) = bindings.split_first() {
if has_free_params(&first.field.ty, &input.generics.ty_params) {
where_clause.predicates.push(where_predicate(first.field.ty.clone()));
}
let mut expr = quote! {
::style_traits::ToCss::to_css(#first, dest)
};
for binding in rest {
if has_free_params(&binding.field.ty, &input.generics.ty_params) {
where_clause.predicates.push(where_predicate(binding.field.ty.clone()));
}
expr = quote! {
#expr?;
::std::fmt::Write::write_str(dest, " ")?;
@ -90,6 +94,31 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
}
}
/// Returns whether `ty` is parameterized by any parameter from `params`.
fn has_free_params(ty: &syn::Ty, params: &[syn::TyParam]) -> bool {
use syn::visit::Visitor;
struct HasFreeParams<'a> {
params: &'a [syn::TyParam],
has_free: bool,
}
impl<'a> Visitor for HasFreeParams<'a> {
fn visit_path(&mut self, path: &syn::Path) {
if !path.global && path.segments.len() == 1 {
if self.params.iter().any(|param| param.ident == path.segments[0].ident) {
self.has_free = true;
}
}
syn::visit::walk_path(self, path);
}
}
let mut visitor = HasFreeParams { params: params, has_free: false };
visitor.visit_ty(ty);
visitor.has_free
}
/// `#ty: ::style_traits::ToCss`
fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {