servo: Merge #18376 - Support None and NotSet for the fallback type of SVGPaint (from kuoe0:set-fallbacktype-to-none-when-the-fallback-color-of-context-property-is-none); r=xidorn

<!-- Please describe your changes on the following line: -->

We didn't set None and NotSet for the fallback type of SVGPaint, and it caused the fallback color is wrong when fallback color is empty or keyword `none`. So, we add the None and NotSet support for it.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1380590](https://bugzilla.mozilla.org/show_bug.cgi?id=1380590)

<!-- Either: -->
- [ ] There are tests for these changes OR
- [X] These changes do not require tests because of the test cases already in Gecko.

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

Source-Repo: https://github.com/servo/servo
Source-Revision: 1cf87a243a60cefd35bfea694ad442a6a9ab9d14

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 664b4c31496a280ab537bd1de4c5a3a765e3ff21

servo/components/style/properties/gecko.mako.rs

@@ -60,7 +60,7 @@ use selector_parser::PseudoElement;
 use servo_arc::{Arc, RawOffsetArc};
 use std::mem::{forget, uninitialized, transmute, zeroed};
 use std::{cmp, ops, ptr};
-use values::{self, Auto, CustomIdent, Either, KeyframesName};
+use values::{self, Auto, CustomIdent, Either, KeyframesName, None_};
 use values::computed::{NonNegativeAu, ToComputedValue, Percentage};
 use values::computed::effects::{BoxShadow, Filter, SimpleShadow};
 use computed_values::border_style;
@@ -743,10 +743,16 @@ def set_gecko_property(ffi_name, expr):
             }
         }
 
-        if let Some(fallback) = fallback {
-            paint.mFallbackType = nsStyleSVGFallbackType::eStyleSVGFallbackType_Color;
-            paint.mFallbackColor = convert_rgba_to_nscolor(&fallback);
-        }
+        paint.mFallbackType = match fallback {
+            Some(Either::First(color)) => {
+                paint.mFallbackColor = convert_rgba_to_nscolor(&color);
+                nsStyleSVGFallbackType::eStyleSVGFallbackType_Color
+            },
+            Some(Either::Second(_)) => {
+                nsStyleSVGFallbackType::eStyleSVGFallbackType_None
+            },
+            None => nsStyleSVGFallbackType::eStyleSVGFallbackType_NotSet
+        };
     }
 
     #[allow(non_snake_case)]
@@ -771,11 +777,17 @@ def set_gecko_property(ffi_name, expr):
         use self::structs::nsStyleSVGPaintType;
         use self::structs::nsStyleSVGFallbackType;
         let ref paint = ${get_gecko_property(gecko_ffi_name)};
-        let fallback = if let nsStyleSVGFallbackType::eStyleSVGFallbackType_Color = paint.mFallbackType {
-            Some(convert_nscolor_to_rgba(paint.mFallbackColor))
-        } else {
-            None
+
+        let fallback = match paint.mFallbackType {
+            nsStyleSVGFallbackType::eStyleSVGFallbackType_Color => {
+                Some(Either::First(convert_nscolor_to_rgba(paint.mFallbackColor)))
+            },
+            nsStyleSVGFallbackType::eStyleSVGFallbackType_None => {
+                Some(Either::Second(None_))
+            },
+            nsStyleSVGFallbackType::eStyleSVGFallbackType_NotSet => None,
         };
+
         let kind = match paint.mType {
             nsStyleSVGPaintType::eStyleSVGPaintType_None => SVGPaintKind::None,
             nsStyleSVGPaintType::eStyleSVGPaintType_ContextFill => SVGPaintKind::ContextFill,

servo/components/style/values/generics/svg.rs

@@ -8,6 +8,7 @@ use cssparser::Parser;
 use parser::{Parse, ParserContext};
 use std::fmt;
 use style_traits::{ParseError, StyleParseError, ToCss};
+use values::{Either, None_};
 use values::computed::NumberOrPercentage;
 use values::computed::length::LengthOrPercentage;
 use values::distance::{ComputeSquaredDistance, SquaredDistance};
@@ -21,8 +22,8 @@ use values::distance::{ComputeSquaredDistance, SquaredDistance};
 pub struct SVGPaint<ColorType, UrlPaintServer> {
     /// The paint source
     pub kind: SVGPaintKind<ColorType, UrlPaintServer>,
-    /// The fallback color
-    pub fallback: Option<ColorType>,
+    /// The fallback color. It would be empty, the `none` keyword or <color>.
+    pub fallback: Option<Either<ColorType, None_>>,
 }
 
 /// An SVG paint value without the fallback
@@ -60,15 +61,19 @@ impl<ColorType, UrlPaintServer> SVGPaintKind<ColorType, UrlPaintServer> {
 }
 
 /// Parse SVGPaint's fallback.
-/// fallback is keyword(none) or Color.
+/// fallback is keyword(none), Color or empty.
 /// https://svgwg.org/svg2-draft/painting.html#SpecifyingPaint
 fn parse_fallback<'i, 't, ColorType: Parse>(context: &ParserContext,
                                             input: &mut Parser<'i, 't>)
-                                            -> Option<ColorType> {
+                                            -> Option<Either<ColorType, None_>> {
     if input.try(|i| i.expect_ident_matching("none")).is_ok() {
-        None
+        Some(Either::Second(None_))
     } else {
-        input.try(|i| ColorType::parse(context, i)).ok()
+        if let Ok(color) = input.try(|i| ColorType::parse(context, i)) {
+            Some(Either::First(color))
+        } else {
+            None
+        }
     }
 }