LibXML: Avoid ByteString::formatted() on static "expected" errors

This is a fairly significant (~8%) speedup when parsing references.

Userland/Libraries/LibXML/Parser/Parser.cpp

@@ -195,7 +195,7 @@ ErrorOr<void, ParseError> Parser::skip_whitespace(Required required)
     // S ::= (#x20 | #x9 | #xD | #xA)+
     auto matched = m_lexer.consume_while(is_any_of("\x20\x09\x0d\x0a"sv));
     if (required == Required::Yes && matched.is_empty())
-        return parse_error(m_lexer.current_position(), "Expected whitespace");
+        return parse_error(m_lexer.current_position(), Expectation { "whitespace"sv });
 
     rollback.disarm();
     return {};
@@ -225,7 +225,7 @@ ErrorOr<void, ParseError> Parser::parse_internal()
     }
 
     if (!m_lexer.is_eof())
-        return parse_error(m_lexer.current_position(), "Garbage after document");
+        return parse_error(m_lexer.current_position(), ByteString { "Garbage after document"sv });
 
     return {};
 }
@@ -250,7 +250,7 @@ requires(IsCallableWithArguments<Pred, bool, char>) ErrorOr<StringView, ParseErr
     auto start = m_lexer.tell();
     if (!m_lexer.next_is(predicate)) {
         if (m_options.treat_errors_as_fatal)
-            return parse_error(m_lexer.current_position(), ByteString::formatted("Expected {}", description));
+            return parse_error(m_lexer.current_position(), Expectation { description });
     }
 
     m_lexer.ignore();
@@ -271,7 +271,7 @@ requires(IsCallableWithArguments<Pred, bool, char>) ErrorOr<StringView, ParseErr
 
     if (m_lexer.tell() == start) {
         if (m_options.treat_errors_as_fatal) {
-            return parse_error(m_lexer.current_position(), ByteString::formatted("Expected {}", description));
+            return parse_error(m_lexer.current_position(), Expectation { description });
         }
     }
 
@@ -415,7 +415,7 @@ ErrorOr<void, ParseError> Parser::parse_standalone_document_decl()
 
     auto value = m_lexer.consume_quoted_string();
     if (!value.is_one_of("yes", "no"))
-        return parse_error(m_lexer.position_for(m_lexer.tell() - value.length()), "Expected one of 'yes' or 'no'");
+        return parse_error(m_lexer.position_for(m_lexer.tell() - value.length()), Expectation { "one of 'yes' or 'no'"sv });
 
     m_standalone = value == "yes";
 
@@ -445,7 +445,7 @@ ErrorOr<void, ParseError> Parser::parse_misc()
         return {};
     }
 
-    return parse_error(m_lexer.current_position(), "Expected a match for 'Misc', but found none");
+    return parse_error(m_lexer.current_position(), Expectation { "a match for 'Misc'"sv });
 }
 
 // 2.5.15 Comment, https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-Comment
@@ -522,7 +522,7 @@ ErrorOr<Name, ParseError> Parser::parse_processing_instruction_target()
     if (target.equals_ignoring_ascii_case("xml"sv) && m_options.treat_errors_as_fatal) {
         return parse_error(
             m_lexer.position_for(m_lexer.tell() - target.length()),
-            "Use of the reserved 'xml' name for processing instruction target name is disallowed");
+            ByteString { "Use of the reserved 'xml' name for processing instruction target name is disallowed"sv });
     }
 
     rollback.disarm();
@@ -634,7 +634,7 @@ ErrorOr<void, ParseError> Parser::parse_element()
 
     // Well-formedness constraint: The Name in an element's end-tag MUST match the element type in the start-tag.
     if (m_options.treat_errors_as_fatal && closing_name != tag.name)
-        return parse_error(m_lexer.position_for(tag_location), "Invalid closing tag");
+        return parse_error(m_lexer.position_for(tag_location), ByteString { "Invalid closing tag"sv });
 
     rollback.disarm();
     return {};
@@ -720,7 +720,7 @@ ErrorOr<ByteString, ParseError> Parser::parse_attribute_value_inner(StringView d
 
         if (m_lexer.next_is('<')) {
             // Not allowed, return a nice error to make it easier to debug.
-            return parse_error(m_lexer.current_position(), "Unescaped '<' not allowed in attribute values");
+            return parse_error(m_lexer.current_position(), ByteString { "Unescaped '<' not allowed in attribute values"sv });
         }
 
         if (m_lexer.next_is('&')) {
@@ -774,7 +774,7 @@ ErrorOr<Variant<Parser::EntityReference, ByteString>, ParseError> Parser::parse_
         }
 
         if (!code_point.has_value() || !s_characters.contains(*code_point))
-            return parse_error(m_lexer.position_for(reference_start), "Invalid character reference");
+            return parse_error(m_lexer.position_for(reference_start), ByteString { "Invalid character reference"sv });
 
         TRY(expect(";"sv));
 
@@ -995,7 +995,7 @@ ErrorOr<Optional<MarkupDeclaration>, ParseError> Parser::parse_markup_declaratio
         return Optional<MarkupDeclaration> {};
     }
 
-    return parse_error(m_lexer.current_position(), "Expected one of elementdecl, attlistdecl, entitydecl, notationdecl, PI or comment");
+    return parse_error(m_lexer.current_position(), Expectation { "one of elementdecl, attlistdecl, entitydecl, notationdecl, PI or comment"sv });
 }
 
 // 2.8.28a DeclSep, https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-DeclSep
@@ -1016,7 +1016,7 @@ ErrorOr<Optional<ByteString>, ParseError> Parser::parse_declaration_separator()
         return Optional<ByteString> {};
     }
 
-    return parse_error(m_lexer.current_position(), "Expected either whitespace, or a PEReference");
+    return parse_error(m_lexer.current_position(), Expectation { "either whitespace, or a PEReference"sv });
 }
 
 // 4.1.69 PEReference, https://www.w3.org/TR/2006/REC-xml11-20060816/#NT-PEReference
@@ -1269,7 +1269,7 @@ ErrorOr<ElementDeclaration::ContentSpec, ParseError> Parser::parse_content_spec(
                     if (auto result = parse_name(); !result.is_error())
                         names.set(result.release_value());
                     else
-                        return parse_error(m_lexer.current_position(), "Expected a Name");
+                        return parse_error(m_lexer.current_position(), Expectation { "a Name"sv });
                 }
                 TRY(skip_whitespace());
                 TRY(expect(")*"sv));
@@ -1331,7 +1331,7 @@ ErrorOr<ElementDeclaration::ContentSpec, ParseError> Parser::parse_content_spec(
                 TRY(expect(")"sv));
 
                 if (choices.size() < 2)
-                    return parse_error(m_lexer.current_position(), "Expected more than one choice");
+                    return parse_error(m_lexer.current_position(), Expectation { "more than one choice"sv });
 
                 TRY(skip_whitespace());
                 auto qualifier = parse_qualifier();

Userland/Libraries/LibXML/Parser/Parser.h

@@ -21,9 +21,13 @@
 
 namespace XML {
 
+struct Expectation {
+    StringView expected;
+};
+
 struct ParseError {
     LineTrackingLexer::Position position {};
-    ByteString error;
+    Variant<ByteString, Expectation> error;
 };
 
 struct Listener {
@@ -183,9 +187,13 @@ private:
             auto rule_name = m_current_rule.rule.value_or("<?>");
             if (rule_name.starts_with("parse_"sv))
                 rule_name = rule_name.substring_view(6);
+
+            auto error_string = error.error.visit(
+                [](ByteString const& error) -> ByteString { return error; },
+                [](XML::Expectation const& expectation) -> ByteString { return ByteString::formatted("Expected {}", expectation.expected); });
             m_parse_errors.append({
                 error.position,
-                ByteString::formatted("{}: {}", rule_name, error.error),
+                ByteString::formatted("{}: {}", rule_name, error_string),
             });
         }
         return error;
@@ -218,6 +226,9 @@ template<>
 struct AK::Formatter<XML::ParseError> : public AK::Formatter<FormatString> {
     ErrorOr<void> format(FormatBuilder& builder, XML::ParseError const& error)
     {
-        return Formatter<FormatString>::format(builder, "{} at line: {}, col: {} (offset {})"sv, error.error, error.position.line, error.position.column, error.position.offset);
+        auto error_string = error.error.visit(
+            [](ByteString const& error) -> ByteString { return error; },
+            [](XML::Expectation const& expectation) -> ByteString { return ByteString::formatted("Expected {}", expectation.expected); });
+        return Formatter<FormatString>::format(builder, "{} at line: {}, col: {} (offset {})"sv, error_string, error.position.line, error.position.column, error.position.offset);
     }
 };