style: Cleanup generic font-family handling.

To be more similar between Rust and C++. This introduces GenericFontFamily and
exposes that plus FontFamilyNameSyntax to C++, using that where appropriate
instead of plain uint8_t as we were doing.

As a follow-up, as discussed on IRC with Jonathan, we can remove the -moz-fixed
family, and turn it just into an alias of Monospace.

The only non-trivial change is the MatchType changes, but they're ok I think.
The code already assumed at most one CSS generic, and the struct still takes 8
bits. I've verified that the relevant tests are passing (though try is closed).

Differential Revision: https://phabricator.services.mozilla.com/D24272

components/style/properties/cascade.rs

@@ -683,6 +683,7 @@ impl<'a, 'b: 'a> Cascade<'a, 'b> {
     #[cfg(feature = "gecko")]
     fn recompute_default_font_family_type_if_needed(&mut self) {
         use crate::gecko_bindings::{bindings, structs};
+        use crate::values::computed::font::GenericFontFamily;
 
         if !self.seen.contains(LonghandId::XLang) &&
            !self.seen.contains(LonghandId::FontFamily) {
@@ -697,7 +698,7 @@ impl<'a, 'b: 'a> Cascade<'a, 'b> {
             // System fonts are all right, and should have the default font type
             // set to none already, so bail out early.
             if font.mFont.systemFont {
-                debug_assert_eq!(font.mFont.fontlist.mDefaultFontType, structs::FontFamilyType::eFamily_none);
+                debug_assert_eq!(font.mFont.fontlist.mDefaultFontType, GenericFontFamily::None);
                 return;
             }
 
@@ -717,11 +718,11 @@ impl<'a, 'b: 'a> Cascade<'a, 'b> {
                 !use_document_fonts &&
                 matches!(
                     font.mGenericID,
-                    structs::kGenericFont_NONE |
-                    structs::kGenericFont_fantasy |
-                    structs::kGenericFont_cursive
+                    GenericFontFamily::None |
+                    GenericFontFamily::Fantasy |
+                    GenericFontFamily::Cursive
                 ) &&
-                default_font_type != structs::FontFamilyType::eFamily_none;
+                default_font_type != GenericFontFamily::None;
 
             if !prioritize_user_fonts && default_font_type == font.mFont.fontlist.mDefaultFontType {
                 // Nothing to do.

components/style/properties/gecko.mako.rs

@@ -1984,20 +1984,20 @@ fn static_assert() {
     <% impl_font_settings("font_variation_settings", "gfxFontVariation", "VariationValue", "f32", "f32") %>
 
     pub fn set_font_family(&mut self, v: longhands::font_family::computed_value::T) {
-        use crate::gecko_bindings::structs::FontFamilyType;
+        use crate::values::computed::font::GenericFontFamily;
 
         let is_system_font = v.is_system_font;
         self.gecko.mFont.systemFont = is_system_font;
         self.gecko.mGenericID = if is_system_font {
-            structs::kGenericFont_NONE
+            GenericFontFamily::None
         } else {
-            v.families.single_generic().unwrap_or(structs::kGenericFont_NONE)
+            v.families.single_generic().unwrap_or(GenericFontFamily::None)
         };
         self.gecko.mFont.fontlist.mFontlist.mBasePtr.set_move(
             v.families.shared_font_list().clone()
         );
         // Fixed-up if needed in Cascade::fixup_font_stuff.
-        self.gecko.mFont.fontlist.mDefaultFontType = FontFamilyType::eFamily_none;
+        self.gecko.mFont.fontlist.mDefaultFontType = GenericFontFamily::None;
     }
 
     pub fn copy_font_family_from(&mut self, other: &Self) {
@@ -2011,33 +2011,13 @@ fn static_assert() {
     }
 
     pub fn clone_font_family(&self) -> longhands::font_family::computed_value::T {
-        use crate::gecko_bindings::structs::FontFamilyType;
         use crate::values::computed::font::{FontFamily, SingleFontFamily, FontFamilyList};
 
         let fontlist = &self.gecko.mFont.fontlist;
         let shared_fontlist = unsafe { fontlist.mFontlist.mBasePtr.to_safe() };
 
         let families = if shared_fontlist.mNames.is_empty() {
-            let default = fontlist.mDefaultFontType;
-            let default = match default {
-                FontFamilyType::eFamily_serif => {
-                    SingleFontFamily::Generic(atom!("serif"))
-                }
-                _ => {
-                    // This can break with some combinations of user prefs, see
-                    // bug 1442195 for example. It doesn't really matter in this
-                    // case...
-                    //
-                    // FIXME(emilio): Probably should be storing the whole
-                    // default font name instead though.
-                    debug_assert_eq!(
-                        default,
-                        FontFamilyType::eFamily_sans_serif,
-                        "Default generic should be serif or sans-serif"
-                    );
-                    SingleFontFamily::Generic(atom!("sans-serif"))
-                }
-            };
+            let default = SingleFontFamily::Generic(fontlist.mDefaultFontType);
             FontFamilyList::new(Box::new([default]))
         } else {
             FontFamilyList::SharedFontList(shared_fontlist)

components/style/properties/longhands/font.mako.rs

@@ -326,7 +326,7 @@ ${helpers.predefined_type(
 
         use app_units::Au;
         use cssparser::{Parser, ToCss};
-        use crate::gecko_bindings::structs::FontFamilyType;
+        use crate::values::computed::font::GenericFontFamily;
         use crate::properties::longhands;
         use std::fmt;
         use std::hash::{Hash, Hasher};
@@ -466,7 +466,7 @@ ${helpers.predefined_type(
                 pub ${name}: longhands::${name}::computed_value::T,
             % endfor
             pub system_font: SystemFont,
-            pub default_font_type: FontFamilyType,
+            pub default_font_type: GenericFontFamily,
         }
 
         impl SystemFont {