[vm] Remove gap from symbol list.

TEST=ci
Change-Id: Ib4aa1a48fdcf47f6e27c21428628d06d4de9fd9e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/490348
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/vm/app_snapshot.cc

@@ -7002,7 +7002,7 @@ class VMSerializationRoots : public SerializationRoots {
   }
 
   void WriteRoots(Serializer* s) {
-    for (intptr_t i = 1; i < Symbols::kMaxPredefinedId; i++) {
+    for (intptr_t i = 0; i < Symbols::kMaxPredefinedId; i++) {
       s->WriteRootRef(Symbols::Symbol(i).ptr(), "<symbol>");
     }
     s->WriteRootRef(
@@ -7099,7 +7099,7 @@ class VMDeserializationRoots : public DeserializationRoots {
   }
 
   void ReadRoots(Deserializer* d) override {
-    for (intptr_t i = 1; i < Symbols::kMaxPredefinedId; i++) {
+    for (intptr_t i = 0; i < Symbols::kMaxPredefinedId; i++) {
       String* symbol = String::ReadOnlyHandle();
       *symbol ^= d->ReadRef();
       Symbols::InitSymbol(i, symbol);

runtime/vm/compiler/method_recognizer.cc

@@ -314,7 +314,7 @@ static const struct {
   const uint32_t finger_print;
   const char* const name;
 } factory_recognizer_list[] = {RECOGNIZED_LIST_FACTORY_LIST(RECOGNIZE_FACTORY){
-    Symbols::kIllegal, -1, 0, nullptr}};
+    Symbols::kEmptyId, kIllegalCid, 0, nullptr}};
 
 #undef RECOGNIZE_FACTORY
 
@@ -326,7 +326,7 @@ intptr_t FactoryRecognizer::ResultCid(const Function& factory) {
          (lib.ptr() == Library::TypedDataLibrary()));
   const String& factory_name = String::Handle(factory.name());
   for (intptr_t i = 0;
-       factory_recognizer_list[i].symbol_id != Symbols::kIllegal; i++) {
+       factory_recognizer_list[i].symbol_id != Symbols::kEmptyId; i++) {
     if (String::EqualsIgnoringPrivateKey(
             factory_name,
             Symbols::Symbol(factory_recognizer_list[i].symbol_id))) {

runtime/vm/symbols.cc

@@ -22,14 +22,13 @@ StringPtr Symbols::predefined_[Symbols::kNumberOfOneCharCodeSymbols];
 String* Symbols::symbol_handles_[Symbols::kMaxPredefinedId];
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
+// clang-format off
 static const char* const names[] = {
-    // clang-format off
-  nullptr,
 #define DEFINE_SYMBOL_LITERAL(symbol, literal) literal,
   PREDEFINED_SYMBOLS_LIST(DEFINE_SYMBOL_LITERAL)
 #undef DEFINE_SYMBOL_LITERAL
-    // clang-format on
 };
+// clang-format on
 #endif
 
 StringPtr StringFrom(const uint8_t* data, intptr_t len, Heap::Space space) {
@@ -83,7 +82,7 @@ void Symbols::Init(IsolateGroup* vm_isolate_group) {
   // Create symbols for language keywords. Some keywords are equal to
   // symbols we already created, so use New() instead of Add() to ensure
   // that the symbols are canonicalized.
-  for (intptr_t i = 1; i < Symbols::kNullCharId; i++) {
+  for (intptr_t i = 0; i < Symbols::kNullCharId; i++) {
     String* str = String::ReadOnlyHandle();
     *str = OneByteString::New(names[i], Heap::kOld);
     str->Hash();

runtime/vm/symbols.h

@@ -577,18 +577,15 @@ class Symbols : public AllStatic {
   enum { kMaxOneCharCodeSymbol = 0xFF };
 
   // List of strings that are pre created in the vm isolate.
+  // clang-format off
   enum SymbolId {
-    // clang-format off
-    kIllegal = 0,
-
 #define DEFINE_SYMBOL_INDEX(symbol, literal) k##symbol##Id,
-    PREDEFINED_SYMBOLS_LIST(DEFINE_SYMBOL_INDEX)
+PREDEFINED_SYMBOLS_LIST(DEFINE_SYMBOL_INDEX)
 #undef DEFINE_SYMBOL_INDEX
-
     kNullCharId,  // One char code symbol starts here and takes up 256 entries.
     kMaxPredefinedId = kNullCharId + kMaxOneCharCodeSymbol + 1,
-    // clang-format on
   };
+  // clang-format on
 
   // Number of one character symbols being predefined in the predefined_ array.
   static constexpr int kNumberOfOneCharCodeSymbols =
@@ -598,11 +595,11 @@ class Symbols : public AllStatic {
   static constexpr int kNullCharCodeSymbolOffset = 0;
 
   static const String& Symbol(intptr_t index) {
-    ASSERT((index > kIllegal) && (index < kMaxPredefinedId));
+    ASSERT((index >= 0) && (index < kMaxPredefinedId));
     return *(symbol_handles_[index]);
   }
   static void InitSymbol(intptr_t index, String* symbol) {
-    ASSERT((index > kIllegal) && (index < kMaxPredefinedId));
+    ASSERT((index >= 0) && (index < kMaxPredefinedId));
     symbol_handles_[index] = symbol;
   }