LibJS: Make Utf16String & related APIs infallible

Work towards #20449.

Userland/Libraries/LibJS/Print.cpp

@@ -847,13 +847,11 @@ ErrorOr<void> print_intl_segmenter(JS::PrintContext& print_context, JS::Intl::Se
 
 ErrorOr<void> print_intl_segments(JS::PrintContext& print_context, JS::Intl::Segments const& segments, HashTable<JS::Object*>& seen_objects)
 {
-    auto segments_string = JS::Utf16String::create(segments.vm(), segments.segments_string());
+    auto segments_string = JS::Utf16String::create(segments.segments_string());
-    if (segments_string.is_error())
-        return Error::from_errno(ENOMEM);
 
     TRY(print_type(print_context, "Segments"sv));
     out("\n  string: ");
-    TRY(print_value(print_context, JS::PrimitiveString::create(segments.vm(), segments_string.release_value()), seen_objects));
+    TRY(print_value(print_context, JS::PrimitiveString::create(segments.vm(), move(segments_string)), seen_objects));
     out("\n  segmenter: ");
     TRY(print_value(print_context, &segments.segments_segmenter(), seen_objects));
     return {};

Userland/Libraries/LibJS/Runtime/GlobalObject.cpp

@@ -388,7 +388,7 @@ JS_DEFINE_NATIVE_FUNCTION(GlobalObject::parse_int)
 // 19.2.6.5 Encode ( string, extraUnescaped ), https://tc39.es/ecma262/#sec-encode
 static ThrowCompletionOr<DeprecatedString> encode(VM& vm, DeprecatedString const& string, StringView unescaped_set)
 {
-    auto utf16_string = TRY(Utf16String::create(vm, string));
+    auto utf16_string = Utf16String::create(string);
 
     // 1. Let strLen be the length of string.
     auto string_length = utf16_string.length_in_code_units();

Userland/Libraries/LibJS/Runtime/Intl/DateTimeFormat.cpp

@@ -633,7 +633,7 @@ ThrowCompletionOr<Vector<PatternPartition>> format_date_time_pattern(VM& vm, Dat
                 // 2. If the "length" property of fv is greater than 2, let fv be the substring of fv containing the last two characters.
                 // NOTE: The first length check here isn't enough, but lets us avoid UTF-16 transcoding when the formatted value is ASCII.
                 if (formatted_value.bytes_as_string_view().length() > 2) {
-                    auto utf16_formatted_value = TRY(Utf16String::create(vm, formatted_value));
+                    auto utf16_formatted_value = Utf16String::create(formatted_value);
                     if (utf16_formatted_value.length_in_code_units() > 2)
                         formatted_value = TRY_OR_THROW_OOM(vm, utf16_formatted_value.substring_view(utf16_formatted_value.length_in_code_units() - 2).to_utf8());
                 }

Userland/Libraries/LibJS/Runtime/Intl/Segmenter.cpp

@@ -68,13 +68,13 @@ ThrowCompletionOr<NonnullGCPtr<Object>> create_segment_data_object(VM& vm, Segme
     auto segment = string.substring_view(start_index, end_index - start_index);
 
     // 7. Perform ! CreateDataPropertyOrThrow(result, "segment", segment).
-    MUST(result->create_data_property_or_throw(vm.names.segment, PrimitiveString::create(vm, TRY(Utf16String::create(vm, segment)))));
+    MUST(result->create_data_property_or_throw(vm.names.segment, PrimitiveString::create(vm, Utf16String::create(segment))));
 
     // 8. Perform ! CreateDataPropertyOrThrow(result, "index", 𝔽(startIndex)).
     MUST(result->create_data_property_or_throw(vm.names.index, Value(start_index)));
 
     // 9. Perform ! CreateDataPropertyOrThrow(result, "input", string).
-    MUST(result->create_data_property_or_throw(vm.names.input, PrimitiveString::create(vm, TRY(Utf16String::create(vm, string)))));
+    MUST(result->create_data_property_or_throw(vm.names.input, PrimitiveString::create(vm, Utf16String::create(string))));
 
     // 10. Let granularity be segmenter.[[SegmenterGranularity]].
     auto granularity = segmenter.segmenter_granularity();

Userland/Libraries/LibJS/Runtime/PrimitiveString.cpp

@@ -83,7 +83,7 @@ ThrowCompletionOr<String> PrimitiveString::utf8_string() const
         if (has_deprecated_string())
             m_utf8_string = TRY_OR_THROW_OOM(vm, String::from_deprecated_string(*m_deprecated_string));
         else if (has_utf16_string())
-            m_utf8_string = TRY(m_utf16_string->to_utf8(vm));
+            m_utf8_string = m_utf16_string->to_utf8();
         else
             VERIFY_NOT_REACHED();
     }
@@ -105,7 +105,7 @@ ThrowCompletionOr<DeprecatedString> PrimitiveString::deprecated_string() const
         if (has_utf8_string())
             m_deprecated_string = m_utf8_string->to_deprecated_string();
         else if (has_utf16_string())
-            m_deprecated_string = TRY(m_utf16_string->to_deprecated_string(vm()));
+            m_deprecated_string = m_utf16_string->to_deprecated_string();
         else
             VERIFY_NOT_REACHED();
     }
@@ -113,25 +113,25 @@ ThrowCompletionOr<DeprecatedString> PrimitiveString::deprecated_string() const
     return *m_deprecated_string;
 }
 
-ThrowCompletionOr<Utf16String> PrimitiveString::utf16_string() const
+Utf16String PrimitiveString::utf16_string() const
 {
     resolve_rope_if_needed(EncodingPreference::UTF16);
 
     if (!has_utf16_string()) {
         if (has_utf8_string()) {
-            m_utf16_string = TRY(Utf16String::create(vm(), m_utf8_string->bytes_as_string_view()));
+            m_utf16_string = Utf16String::create(m_utf8_string->bytes_as_string_view());
         } else {
             VERIFY(has_deprecated_string());
-            m_utf16_string = TRY(Utf16String::create(vm(), *m_deprecated_string));
+            m_utf16_string = Utf16String::create(*m_deprecated_string);
         }
     }
 
     return *m_utf16_string;
 }
 
-ThrowCompletionOr<Utf16View> PrimitiveString::utf16_string_view() const
+Utf16View PrimitiveString::utf16_string_view() const
 {
-    (void)TRY(utf16_string());
+    (void)utf16_string();
     return m_utf16_string->view();
 }
 
@@ -141,18 +141,18 @@ ThrowCompletionOr<Optional<Value>> PrimitiveString::get(VM& vm, PropertyKey cons
         return Optional<Value> {};
     if (property_key.is_string()) {
         if (property_key.as_string() == vm.names.length.as_string()) {
-            auto length = TRY(utf16_string()).length_in_code_units();
+            auto length = utf16_string().length_in_code_units();
             return Value(static_cast<double>(length));
         }
     }
     auto index = MUST_OR_THROW_OOM(canonical_numeric_index_string(vm, property_key, CanonicalIndexMode::IgnoreNumericRoundtrip));
     if (!index.is_index())
         return Optional<Value> {};
-    auto str = TRY(utf16_string_view());
+    auto str = utf16_string_view();
     auto length = str.length_in_code_units();
     if (length <= index.as_index())
         return Optional<Value> {};
-    return create(vm, TRY(Utf16String::create(vm, str.substring_view(index.as_index(), 1))));
+    return create(vm, Utf16String::create(str.substring_view(index.as_index(), 1)));
 }
 
 NonnullGCPtr<PrimitiveString> PrimitiveString::create(VM& vm, Utf16String string)
@@ -250,8 +250,6 @@ void PrimitiveString::resolve_rope_if_needed(EncodingPreference preference) cons
     if (!m_is_rope)
         return;
 
-    auto& vm = this->vm();
-
     // This vector will hold all the pieces of the rope that need to be assembled
     // into the resolved string.
     Vector<PrimitiveString const*> pieces;
@@ -277,9 +275,9 @@ void PrimitiveString::resolve_rope_if_needed(EncodingPreference preference) cons
 
         Utf16Data code_units;
         for (auto const* current : pieces)
-            code_units.extend(MUST(current->utf16_string()).string());
+            code_units.extend(current->utf16_string().string());
 
-        m_utf16_string = MUST(Utf16String::create(vm, move(code_units)));
+        m_utf16_string = Utf16String::create(move(code_units));
         m_is_rope = false;
         m_lhs = nullptr;
         m_rhs = nullptr;

Userland/Libraries/LibJS/Runtime/PrimitiveString.h

@@ -45,8 +45,8 @@ public:
     ThrowCompletionOr<DeprecatedString> deprecated_string() const;
     bool has_deprecated_string() const { return m_deprecated_string.has_value(); }
 
-    ThrowCompletionOr<Utf16String> utf16_string() const;
+    [[nodiscard]] Utf16String utf16_string() const;
-    ThrowCompletionOr<Utf16View> utf16_string_view() const;
+    [[nodiscard]] Utf16View utf16_string_view() const;
     bool has_utf16_string() const { return m_utf16_string.has_value(); }
 
     ThrowCompletionOr<Optional<Value>> get(VM&, PropertyKey const&) const;

Userland/Libraries/LibJS/Runtime/RegExpLegacyStaticProperties.cpp

@@ -68,7 +68,7 @@ ThrowCompletionOr<void> set_legacy_regexp_static_property(VM& vm, RegExpConstruc
 }
 
 // UpdateLegacyRegExpStaticProperties ( C, S, startIndex, endIndex, capturedValues ), https://github.com/tc39/proposal-regexp-legacy-features#updatelegacyregexpstaticproperties--c-s-startindex-endindex-capturedvalues-
-ThrowCompletionOr<void> update_legacy_regexp_static_properties(VM& vm, RegExpConstructor& constructor, Utf16String const& string, size_t start_index, size_t end_index, Vector<Utf16String> const& captured_values)
+void update_legacy_regexp_static_properties(RegExpConstructor& constructor, Utf16String const& string, size_t start_index, size_t end_index, Vector<Utf16String> const& captured_values)
 {
     auto& legacy_static_properties = constructor.legacy_static_properties();
 
@@ -92,7 +92,7 @@ ThrowCompletionOr<void> update_legacy_regexp_static_properties(VM& vm, RegExpCon
 
     // 8. Set the value of C’s [[RegExpLastMatch]] internal slot to a String whose length is endIndex - startIndex and containing the code units from S with indices startIndex through endIndex - 1, in ascending order.
     auto last_match = string.view().substring_view(start_index, end_index - start_index);
-    legacy_static_properties.set_last_match(TRY(Utf16String::create(vm, last_match)));
+    legacy_static_properties.set_last_match(Utf16String::create(last_match));
 
     // 9. If n > 0, set the value of C’s [[RegExpLastParen]] internal slot to the last element of capturedValues.
     if (group_count > 0) {
@@ -101,22 +101,22 @@ ThrowCompletionOr<void> update_legacy_regexp_static_properties(VM& vm, RegExpCon
     }
     // 10. Else, set the value of C’s [[RegExpLastParen]] internal slot to the empty String.
     else {
-        legacy_static_properties.set_last_paren(TRY(Utf16String::create(vm)));
+        legacy_static_properties.set_last_paren(Utf16String::create());
     }
 
     // 11. Set the value of C’s [[RegExpLeftContext]] internal slot to a String whose length is startIndex and containing the code units from S with indices 0 through startIndex - 1, in ascending order.
     auto left_context = string.view().substring_view(0, start_index);
-    legacy_static_properties.set_left_context(TRY(Utf16String::create(vm, left_context)));
+    legacy_static_properties.set_left_context(Utf16String::create(left_context));
 
     // 12. Set the value of C’s [[RegExpRightContext]] internal slot to a String whose length is len - endIndex and containing the code units from S with indices endIndex through len - 1, in ascending order.
     auto right_context = string.view().substring_view(end_index, len - end_index);
-    legacy_static_properties.set_right_context(TRY(Utf16String::create(vm, right_context)));
+    legacy_static_properties.set_right_context(Utf16String::create(right_context));
 
     // 13. For each integer i such that 1 ≤ i ≤ 9
     for (size_t i = 1; i <= 9; i++) {
         // i. If i ≤ n, set the value of C’s [[RegExpPareni]] internal slot to the ith element of capturedValues.
         // ii. Else, set the value of C’s [[RegExpPareni]] internal slot to the empty String.
-        auto value = (i <= group_count) ? captured_values[i - 1] : TRY(Utf16String::create(vm));
+        auto value = (i <= group_count) ? captured_values[i - 1] : Utf16String::create();
 
         if (i == 1) {
             legacy_static_properties.set_$1(move(value));
@@ -138,8 +138,6 @@ ThrowCompletionOr<void> update_legacy_regexp_static_properties(VM& vm, RegExpCon
             legacy_static_properties.set_$9(move(value));
         }
     }
-
-    return {};
 }
 
 // InvalidateLegacyRegExpStaticProperties ( C ), https://github.com/tc39/proposal-regexp-legacy-features#invalidatelegacyregexpstaticproperties--c

Userland/Libraries/LibJS/Runtime/RegExpLegacyStaticProperties.h

@@ -72,7 +72,7 @@ private:
 
 ThrowCompletionOr<void> set_legacy_regexp_static_property(VM& vm, RegExpConstructor& constructor, Value this_value, void (RegExpLegacyStaticProperties::*property_setter)(Utf16String), Value value);
 ThrowCompletionOr<Value> get_legacy_regexp_static_property(VM& vm, RegExpConstructor& constructor, Value this_value, Optional<Utf16String> const& (RegExpLegacyStaticProperties::*property_getter)() const);
-ThrowCompletionOr<void> update_legacy_regexp_static_properties(VM& vm, RegExpConstructor& constructor, Utf16String const& string, size_t start_index, size_t end_index, Vector<Utf16String> const& captured_values);
+void update_legacy_regexp_static_properties(RegExpConstructor& constructor, Utf16String const& string, size_t start_index, size_t end_index, Vector<Utf16String> const& captured_values);
 void invalidate_legacy_regexp_static_properties(RegExpConstructor& constructor);
 
 }

Userland/Libraries/LibJS/Runtime/RegExpPrototype.cpp

@@ -277,7 +277,7 @@ static ThrowCompletionOr<Value> regexp_builtin_exec(VM& vm, RegExpObject& regexp
 
     // 28. Let matchedValue be ! GetMatchString(S, match).
     // 29. Perform ! CreateDataPropertyOrThrow(A, "0", matchedValue).
-    MUST(array->create_data_property_or_throw(0, PrimitiveString::create(vm, TRY(Utf16String::create(vm, match.view.u16_view())))));
+    MUST(array->create_data_property_or_throw(0, PrimitiveString::create(vm, Utf16String::create(match.view.u16_view()))));
 
     // 30. If R contains any GroupName, then
     //     a. Let groups be OrdinaryObjectCreate(null).
@@ -302,7 +302,7 @@ static ThrowCompletionOr<Value> regexp_builtin_exec(VM& vm, RegExpObject& regexp
             // ii. Append undefined to indices.
             indices.append({});
             // iii. Append capture to indices.
-            captured_values.append(TRY(Utf16String::create(vm)));
+            captured_values.append(Utf16String::create());
         }
         // c. Else,
         else {
@@ -313,7 +313,7 @@ static ThrowCompletionOr<Value> regexp_builtin_exec(VM& vm, RegExpObject& regexp
             //     2. Set captureEnd to ! GetStringIndex(S, Input, captureEnd).
             // iv. Let capture be the Match { [[StartIndex]]: captureStart, [[EndIndex]: captureEnd }.
             // v. Let capturedValue be ! GetMatchString(S, capture).
-            auto capture_as_utf16_string = TRY(Utf16String::create(vm, capture.view.u16_view()));
+            auto capture_as_utf16_string = Utf16String::create(capture.view.u16_view());
             captured_value = PrimitiveString::create(vm, capture_as_utf16_string);
             // vi. Append capture to indices.
             indices.append(Match::create(capture));
@@ -352,7 +352,7 @@ static ThrowCompletionOr<Value> regexp_builtin_exec(VM& vm, RegExpObject& regexp
         // i. If the value of R’s [[LegacyFeaturesEnabled]] internal slot is true, then
         if (regexp_object.legacy_features_enabled()) {
             // a. Perform UpdateLegacyRegExpStaticProperties(%RegExp%, S, lastIndex, e, capturedValues).
-            TRY(update_legacy_regexp_static_properties(vm, realm.intrinsics().regexp_constructor(), string, match_indices.start_index, match_indices.end_index, captured_values));
+            update_legacy_regexp_static_properties(realm.intrinsics().regexp_constructor(), string, match_indices.start_index, match_indices.end_index, captured_values);
         }
         // ii. Else,
         else {
@@ -985,7 +985,7 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::symbol_split)
         auto substring = string.substring_view(last_match_end, next_search_from - last_match_end);
 
         // 2. Perform ! CreateDataPropertyOrThrow(A, ! ToString(𝔽(lengthA)), T).
-        MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, TRY(Utf16String::create(vm, substring)))));
+        MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, Utf16String::create(substring))));
 
         // 3. Set lengthA to lengthA + 1.
         ++array_length;
@@ -1031,7 +1031,7 @@ JS_DEFINE_NATIVE_FUNCTION(RegExpPrototype::symbol_split)
     auto substring = string.substring_view(last_match_end);
 
     // 21. Perform ! CreateDataPropertyOrThrow(A, ! ToString(𝔽(lengthA)), T).
-    MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, TRY(Utf16String::create(vm, substring)))));
+    MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, Utf16String::create(substring))));
 
     // 22. Return A.
     return array;

Userland/Libraries/LibJS/Runtime/StringConstructor.cpp

@@ -99,7 +99,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringConstructor::from_char_code)
     }
 
     // 3. Return result.
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, move(string))));
+    return PrimitiveString::create(vm, Utf16String::create(move(string)));
 }
 
 // 22.1.2.2 String.fromCodePoint ( ...codePoints ), https://tc39.es/ecma262/#sec-string.fromcodepoint
@@ -134,7 +134,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringConstructor::from_code_point)
         VERIFY(string.is_empty());
 
     // 4. Return result.
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, move(string))));
+    return PrimitiveString::create(vm, Utf16String::create(move(string)));
 }
 
 // 22.1.2.4 String.raw ( template, ...substitutions ), https://tc39.es/ecma262/#sec-string.raw

Userland/Libraries/LibJS/Runtime/StringObject.cpp

@@ -40,7 +40,7 @@ void StringObject::initialize(Realm& realm)
     auto& vm = this->vm();
     Base::initialize(realm);
 
-    define_direct_property(vm.names.length, Value(MUST(m_string->utf16_string_view()).length_in_code_units()), 0);
+    define_direct_property(vm.names.length, Value(m_string->utf16_string_view().length_in_code_units()), 0);
 }
 
 void StringObject::visit_edges(Cell::Visitor& visitor)
@@ -73,7 +73,7 @@ static ThrowCompletionOr<Optional<PropertyDescriptor>> string_get_own_property(S
 
     // 6. Let str be S.[[StringData]].
     // 7. Assert: Type(str) is String.
-    auto str = TRY(string.primitive_string().utf16_string_view());
+    auto str = string.primitive_string().utf16_string_view();
 
     // 8. Let len be the length of str.
     auto length = str.length_in_code_units();
@@ -83,7 +83,7 @@ static ThrowCompletionOr<Optional<PropertyDescriptor>> string_get_own_property(S
         return Optional<PropertyDescriptor> {};
 
     // 10. Let resultStr be the String value of length 1, containing one code unit from str, specifically the code unit at index ℝ(index).
-    auto result_str = PrimitiveString::create(vm, TRY(Utf16String::create(vm, str.substring_view(index.as_index(), 1))));
+    auto result_str = PrimitiveString::create(vm, Utf16String::create(str.substring_view(index.as_index(), 1)));
 
     // 11. Return the PropertyDescriptor { [[Value]]: resultStr, [[Writable]]: false, [[Enumerable]]: true, [[Configurable]]: false }.
     return PropertyDescriptor {
@@ -140,7 +140,7 @@ ThrowCompletionOr<MarkedVector<Value>> StringObject::internal_own_property_keys(
     auto keys = MarkedVector<Value> { heap() };
 
     // 2. Let str be O.[[StringData]].
-    auto str = TRY(m_string->utf16_string_view());
+    auto str = m_string->utf16_string_view();
 
     // 3. Assert: Type(str) is String.
 

Userland/Libraries/LibJS/Runtime/StringPrototype.cpp

@@ -274,7 +274,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::at)
         return js_undefined();
 
     // 7. Return ? Get(O, ! ToString(𝔽(k))).
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, string.substring_view(index.value(), 1))));
+    return PrimitiveString::create(vm, Utf16String::create(string.substring_view(index.value(), 1)));
 }
 
 // 22.1.3.2 String.prototype.charAt ( pos ), https://tc39.es/ecma262/#sec-string.prototype.charat
@@ -293,7 +293,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::char_at)
         return PrimitiveString::create(vm, String {});
 
     // 6. Return the substring of S from position to position + 1.
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, string.substring_view(position, 1))));
+    return PrimitiveString::create(vm, Utf16String::create(string.substring_view(position, 1)));
 }
 
 // 22.1.3.3 String.prototype.charCodeAt ( pos ), https://tc39.es/ecma262/#sec-string.prototype.charcodeat
@@ -693,7 +693,7 @@ static ThrowCompletionOr<Value> pad_string(VM& vm, Utf16String string, Value max
         return PrimitiveString::create(vm, move(string));
 
     // 5. If fillString is undefined, let filler be the String value consisting solely of the code unit 0x0020 (SPACE).
-    auto filler = TRY(Utf16String::create(vm, Utf16Data { 0x20 }));
+    auto filler = Utf16String::create(Utf16Data { 0x20 });
     if (!fill_string.is_undefined()) {
         // 6. Else, let filler be ? ToString(fillString).
         filler = TRY(fill_string.to_utf16_string(vm));
@@ -1052,7 +1052,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::slice)
         return PrimitiveString::create(vm, String {});
 
     // 13. Return the substring of S from from to to.
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, string.substring_view(int_start, int_end - int_start))));
+    return PrimitiveString::create(vm, Utf16String::create(string.substring_view(int_start, int_end - int_start)));
 }
 
 // 22.1.3.23 String.prototype.split ( separator, limit ), https://tc39.es/ecma262/#sec-string.prototype.split
@@ -1133,7 +1133,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::split)
         auto segment = string.substring_view(start, position - start);
 
         // b. Append T to substrings.
-        MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, TRY(Utf16String::create(vm, segment)))));
+        MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, Utf16String::create(segment))));
         ++array_length;
 
         // c. If the number of elements in substrings is lim, return CreateArrayFromList(substrings).
@@ -1151,7 +1151,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::split)
     auto rest = string.substring_view(start);
 
     // 16. Append T to substrings.
-    MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, TRY(Utf16String::create(vm, rest)))));
+    MUST(array->create_data_property_or_throw(array_length, PrimitiveString::create(vm, Utf16String::create(rest))));
 
     // 17. Return CreateArrayFromList(substrings).
     return array;
@@ -1243,7 +1243,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::substring)
     size_t to = max(final_start, final_end);
 
     // 10. Return the substring of S from from to to.
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, string.substring_view(from, to - from))));
+    return PrimitiveString::create(vm, Utf16String::create(string.substring_view(from, to - from)));
 }
 
 enum class TargetCase {
@@ -1512,7 +1512,7 @@ JS_DEFINE_NATIVE_FUNCTION(StringPrototype::substr)
         return PrimitiveString::create(vm, String {});
 
     // 11. Return the substring of S from intStart to intEnd.
-    return PrimitiveString::create(vm, TRY(Utf16String::create(vm, string.substring_view(int_start, int_end - int_start))));
+    return PrimitiveString::create(vm, Utf16String::create(string.substring_view(int_start, int_end - int_start)));
 }
 
 // B.2.2.2.1 CreateHTML ( string, tag, attribute, value ), https://tc39.es/ecma262/#sec-createhtml

Userland/Libraries/LibJS/Runtime/Utf16String.cpp

@@ -11,9 +11,9 @@
 namespace JS {
 namespace Detail {
 
-static ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> the_empty_utf16_string(VM& vm)
+static NonnullRefPtr<Utf16StringImpl> the_empty_utf16_string()
 {
-    static NonnullRefPtr<Utf16StringImpl> empty_string = TRY(Utf16StringImpl::create(vm));
+    static NonnullRefPtr<Utf16StringImpl> empty_string = Utf16StringImpl::create();
     return empty_string;
 }
 
@@ -22,27 +22,27 @@ Utf16StringImpl::Utf16StringImpl(Utf16Data string)
 {
 }
 
-ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> Utf16StringImpl::create(VM& vm)
+NonnullRefPtr<Utf16StringImpl> Utf16StringImpl::create()
 {
-    return TRY_OR_THROW_OOM(vm, adopt_nonnull_ref_or_enomem(new (nothrow) Utf16StringImpl()));
+    return adopt_ref(*new Utf16StringImpl);
 }
 
-ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> Utf16StringImpl::create(VM& vm, Utf16Data string)
+NonnullRefPtr<Utf16StringImpl> Utf16StringImpl::create(Utf16Data string)
 {
-    return TRY_OR_THROW_OOM(vm, adopt_nonnull_ref_or_enomem(new (nothrow) Utf16StringImpl(move(string))));
+    return adopt_ref(*new Utf16StringImpl(move(string)));
 }
 
-ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> Utf16StringImpl::create(VM& vm, StringView string)
+NonnullRefPtr<Utf16StringImpl> Utf16StringImpl::create(StringView string)
 {
-    return create(vm, TRY_OR_THROW_OOM(vm, utf8_to_utf16(string)));
+    return create(MUST(utf8_to_utf16(string)));
 }
 
-ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> Utf16StringImpl::create(VM& vm, Utf16View const& view)
+NonnullRefPtr<Utf16StringImpl> Utf16StringImpl::create(Utf16View const& view)
 {
     Utf16Data string;
-    TRY_OR_THROW_OOM(vm, string.try_ensure_capacity(view.length_in_code_units()));
+    string.ensure_capacity(view.length_in_code_units());
     string.unchecked_append(view.data(), view.length_in_code_units());
-    return create(vm, move(string));
+    return create(move(string));
 }
 
 Utf16Data const& Utf16StringImpl::string() const
@@ -57,24 +57,24 @@ Utf16View Utf16StringImpl::view() const
 
 }
 
-ThrowCompletionOr<Utf16String> Utf16String::create(VM& vm)
+Utf16String Utf16String::create()
 {
-    return Utf16String { TRY(Detail::the_empty_utf16_string(vm)) };
+    return Utf16String { Detail::the_empty_utf16_string() };
 }
 
-ThrowCompletionOr<Utf16String> Utf16String::create(VM& vm, Utf16Data string)
+Utf16String Utf16String::create(Utf16Data string)
 {
-    return Utf16String { TRY(Detail::Utf16StringImpl::create(vm, move(string))) };
+    return Utf16String { Detail::Utf16StringImpl::create(move(string)) };
 }
 
-ThrowCompletionOr<Utf16String> Utf16String::create(VM& vm, StringView string)
+Utf16String Utf16String::create(StringView string)
 {
-    return Utf16String { TRY(Detail::Utf16StringImpl::create(vm, string)) };
+    return Utf16String { Detail::Utf16StringImpl::create(string) };
 }
 
-ThrowCompletionOr<Utf16String> Utf16String::create(VM& vm, Utf16View const& string)
+Utf16String Utf16String::create(Utf16View const& string)
 {
-    return Utf16String { TRY(Detail::Utf16StringImpl::create(vm, string)) };
+    return Utf16String { Detail::Utf16StringImpl::create(string) };
 }
 
 Utf16String::Utf16String(NonnullRefPtr<Detail::Utf16StringImpl> string)
@@ -102,14 +102,14 @@ Utf16View Utf16String::substring_view(size_t code_unit_offset) const
     return view().substring_view(code_unit_offset);
 }
 
-ThrowCompletionOr<String> Utf16String::to_utf8(VM& vm) const
+String Utf16String::to_utf8() const
 {
-    return TRY_OR_THROW_OOM(vm, view().to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
+    return MUST(view().to_utf8(Utf16View::AllowInvalidCodeUnits::Yes));
 }
 
-ThrowCompletionOr<DeprecatedString> Utf16String::to_deprecated_string(VM& vm) const
+DeprecatedString Utf16String::to_deprecated_string() const
 {
-    return TRY_OR_THROW_OOM(vm, view().to_deprecated_string(Utf16View::AllowInvalidCodeUnits::Yes));
+    return MUST(view().to_deprecated_string(Utf16View::AllowInvalidCodeUnits::Yes));
 }
 
 u16 Utf16String::code_unit_at(size_t index) const

Userland/Libraries/LibJS/Runtime/Utf16String.h

@@ -21,10 +21,10 @@ class Utf16StringImpl : public RefCounted<Utf16StringImpl> {
 public:
     ~Utf16StringImpl() = default;
 
-    static ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> create(VM&);
+    [[nodiscard]] static NonnullRefPtr<Utf16StringImpl> create();
-    static ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> create(VM&, Utf16Data);
+    [[nodiscard]] static NonnullRefPtr<Utf16StringImpl> create(Utf16Data);
-    static ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> create(VM&, StringView);
+    [[nodiscard]] static NonnullRefPtr<Utf16StringImpl> create(StringView);
-    static ThrowCompletionOr<NonnullRefPtr<Utf16StringImpl>> create(VM&, Utf16View const&);
+    [[nodiscard]] static NonnullRefPtr<Utf16StringImpl> create(Utf16View const&);
 
     Utf16Data const& string() const;
     Utf16View view() const;
@@ -40,18 +40,18 @@ private:
 
 class Utf16String {
 public:
-    static ThrowCompletionOr<Utf16String> create(VM&);
+    [[nodiscard]] static Utf16String create();
-    static ThrowCompletionOr<Utf16String> create(VM&, Utf16Data);
+    [[nodiscard]] static Utf16String create(Utf16Data);
-    static ThrowCompletionOr<Utf16String> create(VM&, StringView);
+    [[nodiscard]] static Utf16String create(StringView);
-    static ThrowCompletionOr<Utf16String> create(VM&, Utf16View const&);
+    [[nodiscard]] static Utf16String create(Utf16View const&);
 
     Utf16Data const& string() const;
     Utf16View view() const;
     Utf16View substring_view(size_t code_unit_offset, size_t code_unit_length) const;
     Utf16View substring_view(size_t code_unit_offset) const;
 
-    ThrowCompletionOr<String> to_utf8(VM&) const;
+    [[nodiscard]] String to_utf8() const;
-    ThrowCompletionOr<DeprecatedString> to_deprecated_string(VM&) const;
+    [[nodiscard]] DeprecatedString to_deprecated_string() const;
     u16 code_unit_at(size_t index) const;
 
     size_t length_in_code_units() const;

Userland/Libraries/LibJS/Runtime/Value.cpp

@@ -459,10 +459,10 @@ ThrowCompletionOr<DeprecatedString> Value::to_deprecated_string(VM& vm) const
 ThrowCompletionOr<Utf16String> Value::to_utf16_string(VM& vm) const
 {
     if (is_string())
-        return TRY(as_string().utf16_string());
+        return as_string().utf16_string();
 
     auto utf8_string = TRY(to_string(vm));
-    return Utf16String::create(vm, utf8_string.bytes_as_string_view());
+    return Utf16String::create(utf8_string.bytes_as_string_view());
 }
 
 // 7.1.2 ToBoolean ( argument ), https://tc39.es/ecma262/#sec-toboolean