LibJS: Make invalid RegExp flags a SyntaxError at parse time

This patch changes the validation of RegExp flags (checking for
invalid and duplicate values) from a SyntaxError at runtime to a
SyntaxError at parse time - it's not something that's supposed to be
catchable.
As a nice side effect, this simplifies the RegExpObject constructor a
bit, as it can no longer throw an exception and doesn't have to validate
the flags itself.

Userland/Libraries/LibJS/Parser.cpp

@@ -6,6 +6,7 @@
  */
 
 #include "Parser.h"
+#include <AK/HashTable.h>
 #include <AK/ScopeGuard.h>
 #include <AK/StdLibExtras.h>
 #include <AK/TemporaryChange.h>
@@ -686,7 +687,20 @@ NonnullRefPtr<RegExpLiteral> Parser::parse_regexp_literal()
     auto pattern = consume().value();
     // Remove leading and trailing slash.
     pattern = pattern.substring_view(1, pattern.length() - 2);
-    auto flags = match(TokenType::RegexFlags) ? consume().value() : "";
+    auto flags = String::empty();
+    if (match(TokenType::RegexFlags)) {
+        auto flags_start = position();
+        flags = consume().value();
+        HashTable<char> seen_flags;
+        for (size_t i = 0; i < flags.length(); ++i) {
+            auto flag = flags.substring_view(i, 1);
+            if (!flag.is_one_of("g", "i", "m", "s", "u", "y"))
+                syntax_error(String::formatted("Invalid RegExp flag '{}'", flag), Position { flags_start.line, flags_start.column + i });
+            if (seen_flags.contains(*flag.characters_without_null_termination()))
+                syntax_error(String::formatted("Repeated RegExp flag '{}'", flag), Position { flags_start.line, flags_start.column + i });
+            seen_flags.set(*flag.characters_without_null_termination());
+        }
+    }
     return create_ast_node<RegExpLiteral>({ m_parser_state.m_current_token.filename(), rule_start.position(), position() }, pattern, flags);
 }
 

Userland/Libraries/LibJS/Runtime/ErrorTypes.h

@@ -138,8 +138,6 @@
     M(ReflectBadNewTarget, "Optional third argument of Reflect.construct() must be a constructor")                                      \
     M(ReflectBadDescriptorArgument, "Descriptor argument is not an object")                                                             \
     M(RegExpCompileError, "RegExp compile error: {}")                                                                                   \
-    M(RegExpObjectBadFlag, "Invalid RegExp flag '{}'")                                                                                  \
-    M(RegExpObjectRepeatedFlag, "Repeated RegExp flag '{}'")                                                                            \
     M(StringRawCannotConvert, "Cannot convert property 'raw' to object from {}")                                                        \
     M(StringRepeatCountMustBe, "repeat count must be a {} number")                                                                      \
     M(ThisHasNotBeenInitialized, "|this| has not been initialized")                                                                     \

Userland/Libraries/LibJS/Runtime/RegExpObject.cpp

@@ -13,9 +13,8 @@
 
 namespace JS {
 
-static Flags options_from(const String& flags, VM& vm, GlobalObject& global_object)
+static Flags options_from(const String& flags)
 {
-    bool g = false, i = false, m = false, s = false, u = false, y = false;
     Flags options {
         // JS regexps are all 'global' by default as per our definition, but the "global" flag enables "stateful".
         // FIXME: Enable 'BrowserExtended' only if in a browser context.
@@ -26,44 +25,26 @@ static Flags options_from(const String& flags, VM& vm, GlobalObject& global_obje
     for (auto ch : flags) {
         switch (ch) {
         case 'g':
-            if (g)
-                vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectRepeatedFlag, ch);
-            g = true;
             options.effective_flags |= regex::ECMAScriptFlags::Global;
             options.declared_flags |= regex::ECMAScriptFlags::Global;
             break;
         case 'i':
-            if (i)
-                vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectRepeatedFlag, ch);
-            i = true;
             options.effective_flags |= regex::ECMAScriptFlags::Insensitive;
             options.declared_flags |= regex::ECMAScriptFlags::Insensitive;
             break;
         case 'm':
-            if (m)
-                vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectRepeatedFlag, ch);
-            m = true;
             options.effective_flags |= regex::ECMAScriptFlags::Multiline;
             options.declared_flags |= regex::ECMAScriptFlags::Multiline;
             break;
         case 's':
-            if (s)
-                vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectRepeatedFlag, ch);
-            s = true;
             options.effective_flags |= regex::ECMAScriptFlags::SingleLine;
             options.declared_flags |= regex::ECMAScriptFlags::SingleLine;
             break;
         case 'u':
-            if (u)
-                vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectRepeatedFlag, ch);
-            u = true;
             options.effective_flags |= regex::ECMAScriptFlags::Unicode;
             options.declared_flags |= regex::ECMAScriptFlags::Unicode;
             break;
         case 'y':
-            if (y)
-                vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectRepeatedFlag, ch);
-            y = true;
             // Now for the more interesting flag, 'sticky' actually unsets 'global', part of which is the default.
             options.effective_flags.reset_flag(regex::ECMAScriptFlags::Global);
             // "What's the difference between sticky and global, then", that's simple.
@@ -74,8 +55,8 @@ static Flags options_from(const String& flags, VM& vm, GlobalObject& global_obje
             options.declared_flags |= regex::ECMAScriptFlags::Sticky;
             break;
         default:
-            vm.throw_exception<SyntaxError>(global_object, ErrorType::RegExpObjectBadFlag, ch);
-            return options;
+            // RegExp flags must be validated by the parser.
+            VERIFY_NOT_REACHED();
         }
     }
 
@@ -91,7 +72,7 @@ RegExpObject::RegExpObject(String pattern, String flags, Object& prototype)
     : Object(prototype)
     , m_pattern(pattern)
     , m_flags(flags)
-    , m_active_flags(options_from(m_flags, this->vm(), this->global_object()))
+    , m_active_flags(options_from(m_flags))
     , m_regex(pattern, m_active_flags.effective_flags)
 {
     if (m_regex.parser_result.error != regex::Error::NoError) {
@@ -167,11 +148,7 @@ RegExpObject* regexp_create(GlobalObject& global_object, Value pattern, Value fl
         if (f.is_null())
             return nullptr;
     }
-    // FIXME: This is awkward: the RegExpObject C++ constructor may throw a VM exception.
-    auto* obj = RegExpObject::create(global_object, move(p), move(f));
-    if (global_object.vm().exception())
-        return nullptr;
-    return obj;
+    return RegExpObject::create(global_object, move(p), move(f));
 }
 
 }

Userland/Libraries/LibJS/Tests/builtins/RegExp/RegExp.prototype.test.js

@@ -49,10 +49,10 @@ test("flag and options", () => {
     expect(re.unicode).toBe(false);
 
     expect(() => {
-        /foo/gg;
+        Function("/foo/gg");
     }).toThrowWithMessage(SyntaxError, "Repeated RegExp flag 'g'");
 
     expect(() => {
-        /foo/x;
+        Function("/foo/x");
     }).toThrowWithMessage(SyntaxError, "Invalid RegExp flag 'x'");
 });