1 files changed, 323 insertions, 0 deletions
diff --git a/servo/components/style_derive/parse.rs b/servo/components/style_derive/parse.rs
new file mode 100644
index 0000000000..b1a1213435
--- /dev/null
+++ b/servo/components/style_derive/parse.rs
@@ -0,0 +1,323 @@
+/* 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 crate::to_css::{CssBitflagAttrs, CssVariantAttrs};
+use derive_common::cg;
+use proc_macro2::{Span, TokenStream};
+use quote::TokenStreamExt;
+use syn::{self, DeriveInput, Ident, Path};
+use synstructure::{Structure, VariantInfo};
+
+#[derive(Default, FromVariant)]
+#[darling(attributes(parse), default)]
+pub struct ParseVariantAttrs {
+    pub aliases: Option<String>,
+    pub condition: Option<Path>,
+}
+
+#[derive(Default, FromField)]
+#[darling(attributes(parse), default)]
+pub struct ParseFieldAttrs {
+    field_bound: bool,
+}
+
+fn parse_bitflags(bitflags: &CssBitflagAttrs) -> TokenStream {
+    let mut match_arms = TokenStream::new();
+    for (rust_name, css_name) in bitflags.single_flags() {
+        let rust_ident = Ident::new(&rust_name, Span::call_site());
+        match_arms.append_all(quote! {
+            #css_name if result.is_empty() => {
+                single_flag = true;
+                Self::#rust_ident
+            },
+        });
+    }
+
+    for (rust_name, css_name) in bitflags.mixed_flags() {
+        let rust_ident = Ident::new(&rust_name, Span::call_site());
+        match_arms.append_all(quote! {
+            #css_name => Self::#rust_ident,
+        });
+    }
+
+    let mut validate_condition = quote! { !result.is_empty() };
+    if let Some(ref function) = bitflags.validate_mixed {
+        validate_condition.append_all(quote! {
+            && #function(&mut result)
+        });
+    }
+
+    // NOTE(emilio): this loop has this weird structure because we run this code
+    // to parse stuff like text-decoration-line in the text-decoration
+    // shorthand, so we need to be a bit careful that we don't error if we don't
+    // consume the whole thing because we find an invalid identifier or other
+    // kind of token. Instead, we should leave it unconsumed.
+    quote! {
+        let mut result = Self::empty();
+        loop {
+            let mut single_flag = false;
+            let flag: Result<_, style_traits::ParseError<'i>> = input.try_parse(|input| {
+                Ok(try_match_ident_ignore_ascii_case! { input,
+                    #match_arms
+                })
+            });
+
+            let flag = match flag {
+                Ok(flag) => flag,
+                Err(..) => break,
+            };
+
+            if single_flag {
+                return Ok(flag);
+            }
+
+            if result.intersects(flag) {
+                return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+            }
+
+            result.insert(flag);
+        }
+        if #validate_condition {
+            Ok(result)
+        } else {
+            Err(input.new_custom_error(style_traits::StyleParseErrorKind::UnspecifiedError))
+        }
+    }
+}
+
+fn parse_non_keyword_variant(
+    where_clause: &mut Option<syn::WhereClause>,
+    name: &syn::Ident,
+    variant: &VariantInfo,
+    variant_attrs: &CssVariantAttrs,
+    parse_attrs: &ParseVariantAttrs,
+    skip_try: bool,
+) -> TokenStream {
+    let bindings = variant.bindings();
+    assert!(parse_attrs.aliases.is_none());
+    assert!(variant_attrs.function.is_none());
+    assert!(variant_attrs.keyword.is_none());
+    assert_eq!(
+        bindings.len(),
+        1,
+        "We only support deriving parse for simple variants"
+    );
+    let variant_name = &variant.ast().ident;
+    let binding_ast = &bindings[0].ast();
+    let ty = &binding_ast.ty;
+
+    if let Some(ref bitflags) = variant_attrs.bitflags {
+        assert!(skip_try, "Should be the only variant");
+        assert!(
+            parse_attrs.condition.is_none(),
+            "Should be the only variant"
+        );
+        assert!(where_clause.is_none(), "Generic bitflags?");
+        return parse_bitflags(bitflags);
+    }
+
+    let field_attrs = cg::parse_field_attrs::<ParseFieldAttrs>(binding_ast);
+    if field_attrs.field_bound {
+        cg::add_predicate(where_clause, parse_quote!(#ty: crate::parser::Parse));
+    }
+
+    let mut parse = if skip_try {
+        quote! {
+            let v = <#ty as crate::parser::Parse>::parse(context, input)?;
+            return Ok(#name::#variant_name(v));
+        }
+    } else {
+        quote! {
+            if let Ok(v) = input.try(|i| <#ty as crate::parser::Parse>::parse(context, i)) {
+                return Ok(#name::#variant_name(v));
+            }
+        }
+    };
+
+    if let Some(ref condition) = parse_attrs.condition {
+        parse = quote! {
+            if #condition(context) {
+                #parse
+            }
+        };
+
+        if skip_try {
+            // We're the last variant and we can fail to parse due to the
+            // condition clause. If that happens, we need to return an error.
+            parse = quote! {
+                #parse
+                Err(input.new_custom_error(style_traits::StyleParseErrorKind::UnspecifiedError))
+            };
+        }
+    }
+
+    parse
+}
+
+pub fn derive(mut input: DeriveInput) -> TokenStream {
+    let mut where_clause = input.generics.where_clause.take();
+    for param in input.generics.type_params() {
+        cg::add_predicate(
+            &mut where_clause,
+            parse_quote!(#param: crate::parser::Parse),
+        );
+    }
+
+    let name = &input.ident;
+    let s = Structure::new(&input);
+
+    let mut saw_condition = false;
+    let mut match_keywords = quote! {};
+    let mut non_keywords = vec![];
+
+    let mut effective_variants = 0;
+    for variant in s.variants().iter() {
+        let css_variant_attrs = cg::parse_variant_attrs_from_ast::<CssVariantAttrs>(&variant.ast());
+        if css_variant_attrs.skip {
+            continue;
+        }
+        effective_variants += 1;
+
+        let parse_attrs = cg::parse_variant_attrs_from_ast::<ParseVariantAttrs>(&variant.ast());
+
+        saw_condition |= parse_attrs.condition.is_some();
+
+        if !variant.bindings().is_empty() {
+            non_keywords.push((variant, css_variant_attrs, parse_attrs));
+            continue;
+        }
+
+        let identifier = cg::to_css_identifier(
+            &css_variant_attrs
+                .keyword
+                .unwrap_or_else(|| variant.ast().ident.to_string()),
+        );
+        let ident = &variant.ast().ident;
+
+        let condition = match parse_attrs.condition {
+            Some(ref p) => quote! { if #p(context) },
+            None => quote! {},
+        };
+
+        match_keywords.extend(quote! {
+            #identifier #condition => Ok(#name::#ident),
+        });
+
+        let aliases = match parse_attrs.aliases {
+            Some(aliases) => aliases,
+            None => continue,
+        };
+
+        for alias in aliases.split(',') {
+            match_keywords.extend(quote! {
+                #alias #condition => Ok(#name::#ident),
+            });
+        }
+    }
+
+    let needs_context = saw_condition || !non_keywords.is_empty();
+
+    let context_ident = if needs_context {
+        quote! { context }
+    } else {
+        quote! { _ }
+    };
+
+    let has_keywords = non_keywords.len() != effective_variants;
+
+    let mut parse_non_keywords = quote! {};
+    for (i, (variant, css_attrs, parse_attrs)) in non_keywords.iter().enumerate() {
+        let skip_try = !has_keywords && i == non_keywords.len() - 1;
+        let parse_variant = parse_non_keyword_variant(
+            &mut where_clause,
+            name,
+            variant,
+            css_attrs,
+            parse_attrs,
+            skip_try,
+        );
+        parse_non_keywords.extend(parse_variant);
+    }
+
+    let parse_body = if needs_context {
+        let parse_keywords = if has_keywords {
+            quote! {
+                let location = input.current_source_location();
+                let ident = input.expect_ident()?;
+                match_ignore_ascii_case! { &ident,
+                    #match_keywords
+                    _ => Err(location.new_unexpected_token_error(
+                        cssparser::Token::Ident(ident.clone())
+                    ))
+                }
+            }
+        } else {
+            quote! {}
+        };
+
+        quote! {
+            #parse_non_keywords
+            #parse_keywords
+        }
+    } else {
+        quote! { Self::parse(input) }
+    };
+
+    let has_non_keywords = !non_keywords.is_empty();
+
+    input.generics.where_clause = where_clause;
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
+    let parse_trait_impl = quote! {
+        impl #impl_generics crate::parser::Parse for #name #ty_generics #where_clause {
+            #[inline]
+            fn parse<'i, 't>(
+                #context_ident: &crate::parser::ParserContext,
+                input: &mut cssparser::Parser<'i, 't>,
+            ) -> Result<Self, style_traits::ParseError<'i>> {
+                #parse_body
+            }
+        }
+    };
+
+    if needs_context {
+        return parse_trait_impl;
+    }
+
+    assert!(!has_non_keywords);
+
+    // TODO(emilio): It'd be nice to get rid of these, but that makes the
+    // conversion harder...
+    let methods_impl = quote! {
+        impl #name {
+            /// Parse this keyword.
+            #[inline]
+            pub fn parse<'i, 't>(
+                input: &mut cssparser::Parser<'i, 't>,
+            ) -> Result<Self, style_traits::ParseError<'i>> {
+                let location = input.current_source_location();
+                let ident = input.expect_ident()?;
+                Self::from_ident(ident.as_ref()).map_err(|()| {
+                    location.new_unexpected_token_error(
+                        cssparser::Token::Ident(ident.clone())
+                    )
+                })
+            }
+
+            /// Parse this keyword from a string slice.
+            #[inline]
+            pub fn from_ident(ident: &str) -> Result<Self, ()> {
+                match_ignore_ascii_case! { ident,
+                    #match_keywords
+                    _ => Err(()),
+                }
+            }
+        }
+    };
+
+    quote! {
+        #parse_trait_impl
+        #methods_impl
+    }
+}