3 files changed, 425 insertions, 0 deletions
diff --git a/servo/components/derive_common/Cargo.toml b/servo/components/derive_common/Cargo.toml
new file mode 100644
index 0000000000..b493988026
--- /dev/null
+++ b/servo/components/derive_common/Cargo.toml
@@ -0,0 +1,16 @@
+[package]
+name = "derive_common"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+path = "lib.rs"
+
+[dependencies]
+darling = { version = "0.20", default-features = false }
+proc-macro2 = "1"
+quote = "1"
+syn = { version = "2", default-features = false, features = ["clone-impls", "parsing"] }
+synstructure = "0.13"
diff --git a/servo/components/derive_common/cg.rs b/servo/components/derive_common/cg.rs
new file mode 100644
index 0000000000..73301af2ff
--- /dev/null
+++ b/servo/components/derive_common/cg.rs
@@ -0,0 +1,396 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use darling::{FromDeriveInput, FromField, FromVariant};
+use proc_macro2::{Span, TokenStream};
+use quote::TokenStreamExt;
+use syn::{self, AngleBracketedGenericArguments, AssocType, DeriveInput, Field};
+use syn::{GenericArgument, GenericParam, Ident, Path};
+use syn::{PathArguments, PathSegment, QSelf, Type, TypeArray, TypeGroup};
+use syn::{TypeParam, TypeParen, TypePath, TypeSlice, TypeTuple};
+use syn::{Variant, WherePredicate};
+use synstructure::{self, BindStyle, BindingInfo, VariantAst, VariantInfo};
+
+/// Given an input type which has some where clauses already, like:
+///
+/// struct InputType<T>
+/// where
+///     T: Zero,
+/// {
+///     ...
+/// }
+///
+/// Add the necessary `where` clauses so that the output type of a trait
+/// fulfils them.
+///
+/// For example:
+///
+/// ```ignore
+///     <T as ToComputedValue>::ComputedValue: Zero,
+/// ```
+///
+/// This needs to run before adding other bounds to the type parameters.
+pub fn propagate_clauses_to_output_type(
+    where_clause: &mut Option<syn::WhereClause>,
+    generics: &syn::Generics,
+    trait_path: &Path,
+    trait_output: &Ident,
+) {
+    let where_clause = match *where_clause {
+        Some(ref mut clause) => clause,
+        None => return,
+    };
+    let mut extra_bounds = vec![];
+    for pred in &where_clause.predicates {
+        let ty = match *pred {
+            syn::WherePredicate::Type(ref ty) => ty,
+            ref predicate => panic!("Unhanded complex where predicate: {:?}", predicate),
+        };
+
+        let path = match ty.bounded_ty {
+            syn::Type::Path(ref p) => &p.path,
+            ref ty => panic!("Unhanded complex where type: {:?}", ty),
+        };
+
+        assert!(
+            ty.lifetimes.is_none(),
+            "Unhanded complex lifetime bound: {:?}",
+            ty,
+        );
+
+        let ident = match path_to_ident(path) {
+            Some(i) => i,
+            None => panic!("Unhanded complex where type path: {:?}", path),
+        };
+
+        if generics.type_params().any(|param| param.ident == *ident) {
+            extra_bounds.push(ty.clone());
+        }
+    }
+
+    for bound in extra_bounds {
+        let ty = bound.bounded_ty;
+        let bounds = bound.bounds;
+        where_clause
+            .predicates
+            .push(parse_quote!(<#ty as #trait_path>::#trait_output: #bounds))
+    }
+}
+
+pub fn add_predicate(where_clause: &mut Option<syn::WhereClause>, pred: WherePredicate) {
+    where_clause
+        .get_or_insert(parse_quote!(where))
+        .predicates
+        .push(pred);
+}
+
+pub fn fmap_match<F>(input: &DeriveInput, bind_style: BindStyle, f: F) -> TokenStream
+where
+    F: FnMut(&BindingInfo) -> TokenStream,
+{
+    fmap2_match(input, bind_style, f, |_| None)
+}
+
+pub fn fmap2_match<F, G>(
+    input: &DeriveInput,
+    bind_style: BindStyle,
+    mut f: F,
+    mut g: G,
+) -> TokenStream
+where
+    F: FnMut(&BindingInfo) -> TokenStream,
+    G: FnMut(&BindingInfo) -> Option<TokenStream>,
+{
+    let mut s = synstructure::Structure::new(input);
+    s.variants_mut().iter_mut().for_each(|v| {
+        v.bind_with(|_| bind_style);
+    });
+    s.each_variant(|variant| {
+        let (mapped, mapped_fields) = value(variant, "mapped");
+        let fields_pairs = variant.bindings().iter().zip(mapped_fields.iter());
+        let mut computations = quote!();
+        computations.append_all(fields_pairs.map(|(field, mapped_field)| {
+            let expr = f(field);
+            quote! { let #mapped_field = #expr; }
+        }));
+        computations.append_all(
+            mapped_fields
+                .iter()
+                .map(|mapped_field| match g(mapped_field) {
+                    Some(expr) => quote! { let #mapped_field = #expr; },
+                    None => quote!(),
+                }),
+        );
+        computations.append_all(mapped);
+        Some(computations)
+    })
+}
+
+pub fn fmap_trait_output(input: &DeriveInput, trait_path: &Path, trait_output: &Ident) -> Path {
+    let segment = PathSegment {
+        ident: input.ident.clone(),
+        arguments: PathArguments::AngleBracketed(AngleBracketedGenericArguments {
+            args: input
+                .generics
+                .params
+                .iter()
+                .map(|arg| match arg {
+                    &GenericParam::Lifetime(ref data) => {
+                        GenericArgument::Lifetime(data.lifetime.clone())
+                    },
+                    &GenericParam::Type(ref data) => {
+                        let ident = &data.ident;
+                        GenericArgument::Type(parse_quote!(<#ident as #trait_path>::#trait_output))
+                    },
+                    &GenericParam::Const(ref inner) => {
+                        let ident = &inner.ident;
+                        GenericArgument::Const(parse_quote!(#ident))
+                    },
+                })
+                .collect(),
+            colon2_token: Default::default(),
+            gt_token: Default::default(),
+            lt_token: Default::default(),
+        }),
+    };
+    segment.into()
+}
+
+pub fn map_type_params<F>(ty: &Type, params: &[&TypeParam], self_type: &Path, f: &mut F) -> Type
+where
+    F: FnMut(&Ident) -> Type,
+{
+    match *ty {
+        Type::Slice(ref inner) => Type::from(TypeSlice {
+            elem: Box::new(map_type_params(&inner.elem, params, self_type, f)),
+            ..inner.clone()
+        }),
+        Type::Array(ref inner) => {
+            //ref ty, ref expr) => {
+            Type::from(TypeArray {
+                elem: Box::new(map_type_params(&inner.elem, params, self_type, f)),
+                ..inner.clone()
+            })
+        },
+        ref ty @ Type::Never(_) => ty.clone(),
+        Type::Tuple(ref inner) => Type::from(TypeTuple {
+            elems: inner
+                .elems
+                .iter()
+                .map(|ty| map_type_params(&ty, params, self_type, f))
+                .collect(),
+            ..inner.clone()
+        }),
+        Type::Path(TypePath {
+            qself: None,
+            ref path,
+        }) => {
+            if let Some(ident) = path_to_ident(path) {
+                if params.iter().any(|ref param| &param.ident == ident) {
+                    return f(ident);
+                }
+                if ident == "Self" {
+                    return Type::from(TypePath {
+                        qself: None,
+                        path: self_type.clone(),
+                    });
+                }
+            }
+            Type::from(TypePath {
+                qself: None,
+                path: map_type_params_in_path(path, params, self_type, f),
+            })
+        },
+        Type::Path(TypePath {
+            ref qself,
+            ref path,
+        }) => Type::from(TypePath {
+            qself: qself.as_ref().map(|qself| QSelf {
+                ty: Box::new(map_type_params(&qself.ty, params, self_type, f)),
+                position: qself.position,
+                ..qself.clone()
+            }),
+            path: map_type_params_in_path(path, params, self_type, f),
+        }),
+        Type::Paren(ref inner) => Type::from(TypeParen {
+            elem: Box::new(map_type_params(&inner.elem, params, self_type, f)),
+            ..inner.clone()
+        }),
+        Type::Group(ref inner) => Type::from(TypeGroup {
+            elem: Box::new(map_type_params(&inner.elem, params, self_type, f)),
+            ..inner.clone()
+        }),
+        ref ty => panic!("type {:?} cannot be mapped yet", ty),
+    }
+}
+
+fn map_type_params_in_path<F>(
+    path: &Path,
+    params: &[&TypeParam],
+    self_type: &Path,
+    f: &mut F,
+) -> Path
+where
+    F: FnMut(&Ident) -> Type,
+{
+    Path {
+        leading_colon: path.leading_colon,
+        segments: path
+            .segments
+            .iter()
+            .map(|segment| PathSegment {
+                ident: segment.ident.clone(),
+                arguments: match segment.arguments {
+                    PathArguments::AngleBracketed(ref data) => {
+                        PathArguments::AngleBracketed(AngleBracketedGenericArguments {
+                            args: data
+                                .args
+                                .iter()
+                                .map(|arg| match arg {
+                                    ty @ &GenericArgument::Lifetime(_) => ty.clone(),
+                                    &GenericArgument::Type(ref data) => GenericArgument::Type(
+                                        map_type_params(data, params, self_type, f),
+                                    ),
+                                    &GenericArgument::AssocType(ref data) => {
+                                        GenericArgument::AssocType(AssocType {
+                                            ty: map_type_params(&data.ty, params, self_type, f),
+                                            ..data.clone()
+                                        })
+                                    },
+                                    ref arg => panic!("arguments {:?} cannot be mapped yet", arg),
+                                })
+                                .collect(),
+                            ..data.clone()
+                        })
+                    },
+                    ref arg @ PathArguments::None => arg.clone(),
+                    ref parameters => panic!("parameters {:?} cannot be mapped yet", parameters),
+                },
+            })
+            .collect(),
+    }
+}
+
+fn path_to_ident(path: &Path) -> Option<&Ident> {
+    match *path {
+        Path {
+            leading_colon: None,
+            ref segments,
+        } if segments.len() == 1 => {
+            if segments[0].arguments.is_empty() {
+                Some(&segments[0].ident)
+            } else {
+                None
+            }
+        },
+        _ => None,
+    }
+}
+
+pub fn parse_field_attrs<A>(field: &Field) -> A
+where
+    A: FromField,
+{
+    match A::from_field(field) {
+        Ok(attrs) => attrs,
+        Err(e) => panic!("failed to parse field attributes: {}", e),
+    }
+}
+
+pub fn parse_input_attrs<A>(input: &DeriveInput) -> A
+where
+    A: FromDeriveInput,
+{
+    match A::from_derive_input(input) {
+        Ok(attrs) => attrs,
+        Err(e) => panic!("failed to parse input attributes: {}", e),
+    }
+}
+
+pub fn parse_variant_attrs_from_ast<A>(variant: &VariantAst) -> A
+where
+    A: FromVariant,
+{
+    let v = Variant {
+        ident: variant.ident.clone(),
+        attrs: variant.attrs.to_vec(),
+        fields: variant.fields.clone(),
+        discriminant: variant.discriminant.clone(),
+    };
+    parse_variant_attrs(&v)
+}
+
+pub fn parse_variant_attrs<A>(variant: &Variant) -> A
+where
+    A: FromVariant,
+{
+    match A::from_variant(variant) {
+        Ok(attrs) => attrs,
+        Err(e) => panic!("failed to parse variant attributes: {}", e),
+    }
+}
+
+pub fn ref_pattern<'a>(
+    variant: &'a VariantInfo,
+    prefix: &str,
+) -> (TokenStream, Vec<BindingInfo<'a>>) {
+    let mut v = variant.clone();
+    v.bind_with(|_| BindStyle::Ref);
+    v.bindings_mut().iter_mut().for_each(|b| {
+        b.binding = Ident::new(&format!("{}_{}", b.binding, prefix), Span::call_site())
+    });
+    (v.pat(), v.bindings().to_vec())
+}
+
+pub fn value<'a>(variant: &'a VariantInfo, prefix: &str) -> (TokenStream, Vec<BindingInfo<'a>>) {
+    let mut v = variant.clone();
+    v.bindings_mut().iter_mut().for_each(|b| {
+        b.binding = Ident::new(&format!("{}_{}", b.binding, prefix), Span::call_site())
+    });
+    v.bind_with(|_| BindStyle::Move);
+    (v.pat(), v.bindings().to_vec())
+}
+
+/// Transforms "FooBar" to "foo-bar".
+///
+/// If the first Camel segment is "Moz", "Webkit", or "Servo", the result string
+/// is prepended with "-".
+pub fn to_css_identifier(mut camel_case: &str) -> String {
+    camel_case = camel_case.trim_end_matches('_');
+    let mut first = true;
+    let mut result = String::with_capacity(camel_case.len());
+    while let Some(segment) = split_camel_segment(&mut camel_case) {
+        if first {
+            match segment {
+                "Moz" | "Webkit" | "Servo" => first = false,
+                _ => {},
+            }
+        }
+        if !first {
+            result.push('-');
+        }
+        first = false;
+        result.push_str(&segment.to_lowercase());
+    }
+    result
+}
+
+/// Transforms foo-bar to FOO_BAR.
+pub fn to_scream_case(css_case: &str) -> String {
+    css_case.to_uppercase().replace('-', "_")
+}
+
+/// Given "FooBar", returns "Foo" and sets `camel_case` to "Bar".
+fn split_camel_segment<'input>(camel_case: &mut &'input str) -> Option<&'input str> {
+    let index = match camel_case.chars().next() {
+        None => return None,
+        Some(ch) => ch.len_utf8(),
+    };
+    let end_position = camel_case[index..]
+        .find(char::is_uppercase)
+        .map_or(camel_case.len(), |pos| index + pos);
+    let result = &camel_case[..end_position];
+    *camel_case = &camel_case[end_position..];
+    Some(result)
+}
diff --git a/servo/components/derive_common/lib.rs b/servo/components/derive_common/lib.rs
new file mode 100644
index 0000000000..1441535144
--- /dev/null
+++ b/servo/components/derive_common/lib.rs
@@ -0,0 +1,13 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+extern crate darling;
+extern crate proc_macro2;
+#[macro_use]
+extern crate quote;
+#[macro_use]
+extern crate syn;
+extern crate synstructure;
+
+pub mod cg;