Auto merge of #16752 - jdm:css-parse-error, r=SimonSapin

Report more informative CSS errors

This requires https://github.com/servo/rust-cssparser/pull/143 for the final commit. There's no better way to split that work up, unfortunately, and it's extremely easy to bitrot. I would appreciate if we could expedite reviewing this work.

This is the work necessary to enable https://bugzilla.mozilla.org/show_bug.cgi?id=1352669. It makes sense to merge it separately because it's so much effort to keep it up to date with the ongoing Stylo work.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16752)
<!-- Reviewable:end -->

components/style/properties/longhand/text.mako.rs

@@ -104,7 +104,8 @@
             sides_are_logical: true,
         }
     }
-    pub fn parse(context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+    pub fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
+                         -> Result<SpecifiedValue, ParseError<'i>> {
         let first = try!(Side::parse(context, input));
         let second = input.try(|input| Side::parse(context, input)).ok();
         Ok(SpecifiedValue {
@@ -113,13 +114,14 @@
         })
     }
     impl Parse for Side {
-        fn parse(_context: &ParserContext, input: &mut Parser) -> Result<Side, ()> {
+        fn parse<'i, 't>(_context: &ParserContext, input: &mut Parser<'i, 't>)
+                         -> Result<Side, ParseError<'i>> {
             if let Ok(ident) = input.try(|input| input.expect_ident()) {
-                match_ignore_ascii_case! { &ident,
+                (match_ignore_ascii_case! { &ident,
                     "clip" => Ok(Side::Clip),
                     "ellipsis" => Ok(Side::Ellipsis),
                     _ => Err(())
-                }
+                }).map_err(|()| SelectorParseError::UnexpectedIdent(ident).into())
             } else {
                 Ok(Side::String(try!(input.expect_string()).into_owned().into_boxed_str()))
             }
@@ -216,34 +218,39 @@ ${helpers.single_keyword("unicode-bidi",
         SpecifiedValue::empty()
     }
     /// none | [ underline || overline || line-through || blink ]
-    pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+    pub fn parse<'i, 't>(_context: &ParserContext, input: &mut Parser<'i, 't>)
+                         -> Result<SpecifiedValue, ParseError<'i>> {
         let mut result = SpecifiedValue::empty();
         if input.try(|input| input.expect_ident_matching("none")).is_ok() {
             return Ok(result)
         }
         let mut empty = true;
 
-        while input.try(|input| {
-                if let Ok(ident) = input.expect_ident() {
-                    match_ignore_ascii_case! { &ident,
-                        "underline" => if result.contains(UNDERLINE) { return Err(()) }
-                                       else { empty = false; result.insert(UNDERLINE) },
-                        "overline" => if result.contains(OVERLINE) { return Err(()) }
-                                      else { empty = false; result.insert(OVERLINE) },
-                        "line-through" => if result.contains(LINE_THROUGH) { return Err(()) }
-                                          else { empty = false; result.insert(LINE_THROUGH) },
-                        "blink" => if result.contains(BLINK) { return Err(()) }
-                                   else { empty = false; result.insert(BLINK) },
-                        _ => return Err(())
+        loop {
+            let result: Result<_, ParseError> = input.try(|input| {
+                match input.expect_ident() {
+                    Ok(ident) => {
+                        (match_ignore_ascii_case! { &ident,
+                            "underline" => if result.contains(UNDERLINE) { Err(()) }
+                                           else { empty = false; result.insert(UNDERLINE); Ok(()) },
+                            "overline" => if result.contains(OVERLINE) { Err(()) }
+                                          else { empty = false; result.insert(OVERLINE); Ok(()) },
+                            "line-through" => if result.contains(LINE_THROUGH) { Err(()) }
+                                              else { empty = false; result.insert(LINE_THROUGH); Ok(()) },
+                            "blink" => if result.contains(BLINK) { Err(()) }
+                                       else { empty = false; result.insert(BLINK); Ok(()) },
+                            _ => Err(())
+                        }).map_err(|()| SelectorParseError::UnexpectedIdent(ident).into())
                     }
-                } else {
-                    return Err(());
+                    Err(e) => return Err(e.into())
                 }
-                Ok(())
-            }).is_ok() {
+            });
+            if result.is_err() {
+                break;
+            }
         }
 
-        if !empty { Ok(result) } else { Err(()) }
+        if !empty { Ok(result) } else { Err(StyleParseError::UnspecifiedError.into()) }
     }
 
     % if product == "servo":