LibWeb/CSS: Make CSSStyleValue.to_string() return ExceptionOr

DOMMatrix.to_string() throws exceptions if any of its values are
non-finite. This ends up affecting CSSStyleValue because its subclass
CSSTransformValue (which is about to be added) serializes
CSSTransformComponents, and one of those is CSSMatrixComponent, which
calls DOMMatrix.to_string().

This is all quite unfortunate, and because at the time the spec for
DOMMatrix was written, CSS couldn't represent NaN or infinity. That's
no longer true, so I'm hoping the spec can be updated and this can be
reverted. https://github.com/w3c/fxtf-drafts/issues/611

Libraries/LibWeb/CSS/CSSImageValue.cpp

@@ -7,6 +7,7 @@
 #include "CSSImageValue.h"
 #include <LibWeb/Bindings/CSSImageValuePrototype.h>
 #include <LibWeb/Bindings/Intrinsics.h>
+#include <LibWeb/WebIDL/ExceptionOr.h>
 
 namespace Web::CSS {
 
@@ -30,7 +31,7 @@ void CSSImageValue::initialize(JS::Realm& realm)
 }
 
 // https://drafts.css-houdini.org/css-typed-om-1/#stylevalue-serialization
-String CSSImageValue::to_string() const
+WebIDL::ExceptionOr<String> CSSImageValue::to_string() const
 {
     // AD-HOC: The spec doesn't say how to serialize this, as it's intentionally a black box.
     //         We just serialize the source string that was used to construct this.

Libraries/LibWeb/CSS/CSSImageValue.h

@@ -20,7 +20,7 @@ public:
 
     virtual ~CSSImageValue() override = default;
 
-    virtual String to_string() const override;
+    virtual WebIDL::ExceptionOr<String> to_string() const override;
 
 private:
     explicit CSSImageValue(JS::Realm&, String constructed_from_string);

Libraries/LibWeb/CSS/CSSKeywordValue.cpp

@@ -55,7 +55,7 @@ WebIDL::ExceptionOr<void> CSSKeywordValue::set_value(FlyString value)
 }
 
 // https://drafts.css-houdini.org/css-typed-om-1/#keywordvalue-serialization
-String CSSKeywordValue::to_string() const
+WebIDL::ExceptionOr<String> CSSKeywordValue::to_string() const
 {
     // To serialize a CSSKeywordValue this:
     // 1. Return this’s value internal slot.

Libraries/LibWeb/CSS/CSSKeywordValue.h

@@ -28,7 +28,7 @@ public:
     FlyString const& value() const { return m_value; }
     WebIDL::ExceptionOr<void> set_value(FlyString value);
 
-    virtual String to_string() const override;
+    virtual WebIDL::ExceptionOr<String> to_string() const override;
 
 private:
     explicit CSSKeywordValue(JS::Realm&, FlyString value);

Libraries/LibWeb/CSS/CSSNumericValue.cpp

@@ -85,7 +85,7 @@ WebIDL::ExceptionOr<GC::Ref<CSSUnitValue>> CSSNumericValue::to(FlyString const&
     // 2. Let sum be the result of creating a sum value from this. If sum is failure, throw a TypeError.
     auto sum = create_a_sum_value();
     if (!sum.has_value())
-        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to create a sum from input '{}'", to_string())) };
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to create a sum from input '{}'", MUST(to_string()))) };
 
     // 3. If sum has more than one item, throw a TypeError.
     //    Otherwise, let item be the result of creating a CSSUnitValue from the sole item in sum, then converting it to
@@ -94,11 +94,11 @@ WebIDL::ExceptionOr<GC::Ref<CSSUnitValue>> CSSNumericValue::to(FlyString const&
         return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, "Sum contains more than one item"sv };
     auto item = CSSUnitValue::create_from_sum_value_item(realm(), sum->first());
     if (!item)
-        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to create CSSUnitValue from input '{}'", to_string())) };
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to create CSSUnitValue from input '{}'", MUST(to_string()))) };
 
     auto converted_item = item->converted_to_unit(unit);
     if (!converted_item)
-        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to convert input '{}' to unit '{}'", to_string(), unit)) };
+        return WebIDL::SimpleException { WebIDL::SimpleExceptionType::TypeError, MUST(String::formatted("Unable to convert input '{}' to unit '{}'", MUST(to_string()), unit)) };
 
     // 4. Return item.
     return converted_item.as_nonnull();

Libraries/LibWeb/CSS/CSSNumericValue.h

@@ -10,6 +10,7 @@
 #include <LibWeb/Bindings/CSSNumericValuePrototype.h>
 #include <LibWeb/CSS/CSSStyleValue.h>
 #include <LibWeb/CSS/NumericType.h>
+#include <LibWeb/WebIDL/ExceptionOr.h>
 #include <LibWeb/WebIDL/Types.h>
 
 namespace Web::CSS {
@@ -59,7 +60,7 @@ public:
     CSSNumericType type_for_bindings() const;
     NumericType const& type() const { return m_type; }
 
-    virtual String to_string() const final override { return to_string({}); }
+    virtual WebIDL::ExceptionOr<String> to_string() const final override { return to_string({}); }
     String to_string(SerializationParams const&) const;
 
     static WebIDL::ExceptionOr<GC::Ref<CSSNumericValue>> parse(JS::VM&, String const& css_text);

Libraries/LibWeb/CSS/CSSPerspective.cpp

@@ -89,13 +89,13 @@ WebIDL::ExceptionOr<Utf16String> CSSPerspective::to_string() const
     builder.append("perspective("sv);
 
     // 2. Serialize this’s length internal slot, with a minimum of 0px, and append it to s.
-    auto serialized_length = m_length.visit(
+    auto serialized_length = TRY(m_length.visit(
-        [](GC::Ref<CSSNumericValue> const& numeric_value) {
+        [](GC::Ref<CSSNumericValue> const& numeric_value) -> WebIDL::ExceptionOr<String> {
             return numeric_value->to_string({ .minimum = 0 });
         },
-        [](GC::Ref<CSSKeywordValue> const& keyword_value) {
+        [](GC::Ref<CSSKeywordValue> const& keyword_value) -> WebIDL::ExceptionOr<String> {
             return keyword_value->to_string();
-        });
+        }));
     builder.append(serialized_length);
 
     // 3. Append ")" to s, and return s.

Libraries/LibWeb/CSS/CSSRotate.cpp

@@ -104,25 +104,25 @@ WebIDL::ExceptionOr<Utf16String> CSSRotate::to_string() const
         builder.append("rotate3d("sv);
 
         // 2. Serialize this’s x internal slot, and append it to s.
-        builder.append(m_x->to_string());
+        builder.append(TRY(m_x->to_string()));
 
         // 3. Append ", " to s.
         builder.append(", "sv);
 
         // 4. Serialize this’s y internal slot, and append it to s.
-        builder.append(m_y->to_string());
+        builder.append(TRY(m_y->to_string()));
 
         // 5. Append ", " to s.
         builder.append(", "sv);
 
         // 6. Serialize this’s z internal slot, and append it to s.
-        builder.append(m_z->to_string());
+        builder.append(TRY(m_z->to_string()));
 
         // 7. Append "," to s.
         builder.append(", "sv);
 
         // 8. Serialize this’s angle internal slot, and append it to s.
-        builder.append(m_angle->to_string());
+        builder.append(TRY(m_angle->to_string()));
 
         // 9. Append ")" to s, and return s.
         builder.append(")"sv);
@@ -134,7 +134,7 @@ WebIDL::ExceptionOr<Utf16String> CSSRotate::to_string() const
         builder.append("rotate("sv);
 
         // 2. Serialize this’s angle internal slot, and append it to s.
-        builder.append(m_angle->to_string());
+        builder.append(TRY(m_angle->to_string()));
 
         // 3. Append ")" to s, and return s.
         builder.append(")"sv);

Libraries/LibWeb/CSS/CSSScale.cpp

@@ -89,19 +89,19 @@ WebIDL::ExceptionOr<Utf16String> CSSScale::to_string() const
         builder.append("scale3d("sv);
 
         // 2. Serialize this’s x internal slot, and append it to s.
-        builder.append(m_x->to_string());
+        builder.append(TRY(m_x->to_string()));
 
         // 3. Append ", " to s.
         builder.append(", "sv);
 
         // 4. Serialize this’s y internal slot, and append it to s.
-        builder.append(m_y->to_string());
+        builder.append(TRY(m_y->to_string()));
 
         // 5. Append ", " to s.
         builder.append(", "sv);
 
         // 6. Serialize this’s z internal slot, and append it to s.
-        builder.append(m_z->to_string());
+        builder.append(TRY(m_z->to_string()));
 
         // 7. Append ")" to s, and return s.
         builder.append(")"sv);
@@ -114,7 +114,7 @@ WebIDL::ExceptionOr<Utf16String> CSSScale::to_string() const
         builder.append("scale("sv);
 
         // 2. Serialize this’s x internal slot, and append it to s.
-        builder.append(m_x->to_string());
+        builder.append(TRY(m_x->to_string()));
 
         // 3. If this’s x and y internal slots are equal numeric values, append ")" to s and return s.
         if (m_x->is_equal_numeric_value(m_y)) {
@@ -126,7 +126,7 @@ WebIDL::ExceptionOr<Utf16String> CSSScale::to_string() const
         builder.append(", "sv);
 
         // 5. Serialize this’s y internal slot, and append it to s.
-        builder.append(m_y->to_string());
+        builder.append(TRY(m_y->to_string()));
 
         // 6. Append ")" to s, and return s.
         builder.append(")"sv);

Libraries/LibWeb/CSS/CSSSkew.cpp

@@ -67,7 +67,7 @@ WebIDL::ExceptionOr<Utf16String> CSSSkew::to_string() const
     builder.append("skew("sv);
 
     // 2. Serialize this’s ax internal slot, and append it to s.
-    builder.append(m_ax->to_string());
+    builder.append(TRY(m_ax->to_string()));
 
     // 3. If this’s ay internal slot is a CSSUnitValue with a value of 0, then append ")" to s and return s.
     if (auto* ay_unit_value = as_if<CSSUnitValue>(*m_ay); ay_unit_value && ay_unit_value->value() == 0) {
@@ -79,7 +79,7 @@ WebIDL::ExceptionOr<Utf16String> CSSSkew::to_string() const
     builder.append(", "sv);
 
     // 5. Serialize this’s ay internal slot, and append it to s.
-    builder.append(m_ay->to_string());
+    builder.append(TRY(m_ay->to_string()));
 
     // 6. Append ")" to s, and return s.
     builder.append(")"sv);

Libraries/LibWeb/CSS/CSSSkewX.cpp

@@ -62,7 +62,7 @@ WebIDL::ExceptionOr<Utf16String> CSSSkewX::to_string() const
     builder.append("skewX("sv);
 
     // 2. Serialize this’s ax internal slot, and append it to s.
-    builder.append(m_ax->to_string());
+    builder.append(TRY(m_ax->to_string()));
 
     // 3. Append ")" to s, and return s.
     builder.append(")"sv);

Libraries/LibWeb/CSS/CSSSkewY.cpp

@@ -62,7 +62,7 @@ WebIDL::ExceptionOr<Utf16String> CSSSkewY::to_string() const
     builder.append("skewY("sv);
 
     // 2. Serialize this’s ay internal slot, and append it to s.
-    builder.append(m_ay->to_string());
+    builder.append(TRY(m_ay->to_string()));
 
     // 3. Append ")" to s, and return s.
     builder.append(")"sv);

Libraries/LibWeb/CSS/CSSStyleValue.cpp

@@ -92,7 +92,7 @@ WebIDL::ExceptionOr<Variant<GC::Ref<CSSStyleValue>, GC::RootVector<GC::Ref<CSSSt
 }
 
 // https://drafts.css-houdini.org/css-typed-om-1/#stylevalue-serialization
-String CSSStyleValue::to_string() const
+WebIDL::ExceptionOr<String> CSSStyleValue::to_string() const
 {
     // if the value was constructed from a USVString
     if (m_constructed_from_string.has_value()) {
@@ -108,7 +108,7 @@ String CSSStyleValue::to_string() const
     {
         // the serialization is specified in §6.7 Serialization from CSSOM Values below.
     }
-    return {};
+    return String {};
 }
 
 }

Libraries/LibWeb/CSS/CSSStyleValue.h

@@ -25,7 +25,7 @@ public:
     static WebIDL::ExceptionOr<GC::Ref<CSSStyleValue>> parse(JS::VM&, String property, String css_text);
     static WebIDL::ExceptionOr<GC::RootVector<GC::Ref<CSSStyleValue>>> parse_all(JS::VM&, String property, String css_text);
 
-    virtual String to_string() const;
+    virtual WebIDL::ExceptionOr<String> to_string() const;
 
 protected:
     explicit CSSStyleValue(JS::Realm&);

Libraries/LibWeb/CSS/CSSTranslate.cpp

@@ -87,19 +87,19 @@ WebIDL::ExceptionOr<Utf16String> CSSTranslate::to_string() const
         builder.append("translate3d("sv);
 
         // 2. Serialize this’s x internal slot, and append it to s.
-        builder.append(m_x->to_string());
+        builder.append(TRY(m_x->to_string()));
 
         // 3. Append ", " to s.
         builder.append(", "sv);
 
         // 4. Serialize this’s y internal slot, and append it to s.
-        builder.append(m_y->to_string());
+        builder.append(TRY(m_y->to_string()));
 
         // 5. Append ", " to s.
         builder.append(", "sv);
 
         // 6. Serialize this’s z internal slot, and append it to s.
-        builder.append(m_z->to_string());
+        builder.append(TRY(m_z->to_string()));
 
         // 7. Append ")" to s, and return s.
         builder.append(")"sv);
@@ -111,13 +111,13 @@ WebIDL::ExceptionOr<Utf16String> CSSTranslate::to_string() const
         builder.append("translate("sv);
 
         // 2. Serialize this’s x internal slot, and append it to s.
-        builder.append(m_x->to_string());
+        builder.append(TRY(m_x->to_string()));
 
         // 3. Append ", " to s.
         builder.append(", "sv);
 
         // 4. Serialize this’s y internal slot, and append it to s.
-        builder.append(m_y->to_string());
+        builder.append(TRY(m_y->to_string()));
 
         // 5. Append ")" to s, and return s.
         builder.append(")"sv);

Libraries/LibWeb/CSS/CSSUnparsedValue.cpp

@@ -116,7 +116,7 @@ WebIDL::ExceptionOr<void> CSSUnparsedValue::set_value_of_new_indexed_property(u3
 }
 
 // https://drafts.css-houdini.org/css-typed-om-1/#serialize-a-cssunparsedvalue
-String CSSUnparsedValue::to_string() const
+WebIDL::ExceptionOr<String> CSSUnparsedValue::to_string() const
 {
     // To serialize a CSSUnparsedValue this:
     // 1. Let s initially be the empty string.
@@ -126,15 +126,17 @@ String CSSUnparsedValue::to_string() const
     for (auto const& item : m_tokens) {
         // FIXME: In order to match the expected test behaviour, this should insert comments, with the same rules as
         //        serialize_a_series_of_component_values(). See https://github.com/w3c/css-houdini-drafts/issues/1148
-        item.visit(
+        TRY(item.visit(
             // 1. If item is a USVString, append it to s.
-            [&](String const& string) {
+            [&](String const& string) -> WebIDL::ExceptionOr<void> {
                 s.append(string);
+                return {};
             },
             // 2. Otherwise, item is a CSSVariableReferenceValue. Serialize it, then append the result to s.
-            [&](GC::Ref<CSSVariableReferenceValue> const& variable) {
+            [&](GC::Ref<CSSVariableReferenceValue> const& variable) -> WebIDL::ExceptionOr<void> {
-                s.append(variable->to_string());
+                s.append(TRY(variable->to_string()));
-            });
+                return {};
+            }));
     }
 
     // 3. Return s.

Libraries/LibWeb/CSS/CSSUnparsedValue.h

@@ -30,7 +30,7 @@ public:
     virtual WebIDL::ExceptionOr<void> set_value_of_existing_indexed_property(u32, JS::Value) override;
     virtual WebIDL::ExceptionOr<void> set_value_of_new_indexed_property(u32, JS::Value) override;
 
-    virtual String to_string() const override;
+    virtual WebIDL::ExceptionOr<String> to_string() const override;
 
 private:
     explicit CSSUnparsedValue(JS::Realm&, Vector<CSSUnparsedSegment>);

Libraries/LibWeb/CSS/CSSVariableReferenceValue.cpp

@@ -89,7 +89,7 @@ WebIDL::ExceptionOr<void> CSSVariableReferenceValue::set_fallback(GC::Ptr<CSSUnp
 }
 
 // https://drafts.css-houdini.org/css-typed-om-1/#serialize-a-cssvariablereferencevalue
-String CSSVariableReferenceValue::to_string() const
+WebIDL::ExceptionOr<String> CSSVariableReferenceValue::to_string() const
 {
     // To serialize a CSSVariableReferenceValue this:
     // 1. Let s initially be "var(".
@@ -103,7 +103,7 @@ String CSSVariableReferenceValue::to_string() const
     if (m_fallback) {
         // AD-HOC: Tested behaviour requires we append "," without the space. https://github.com/w3c/css-houdini-drafts/issues/1148
         s.append(","sv);
-        s.append(m_fallback->to_string());
+        s.append(TRY(m_fallback->to_string()));
     }
 
     // 4. Append ")" to s and return s.

Libraries/LibWeb/CSS/CSSVariableReferenceValue.h

@@ -27,7 +27,7 @@ public:
     GC::Ptr<CSSUnparsedValue> fallback() const;
     WebIDL::ExceptionOr<void> set_fallback(GC::Ptr<CSSUnparsedValue>);
 
-    String to_string() const;
+    WebIDL::ExceptionOr<String> to_string() const;
 
 private:
     CSSVariableReferenceValue(JS::Realm&, FlyString variable, GC::Ptr<CSSUnparsedValue> fallback);