Same trick for symbol.id, and always set it to 0.

src/compiler/checker.ts

@@ -287,12 +287,13 @@ namespace ts {
     }
 
     export function getSymbolId(symbol: Symbol): SymbolId {
-        if (!symbol.id) {
-            symbol.id = nextSymbolId;
+        let id = symbol.id;
+        if (!id) {
+            symbol.id = id = nextSymbolId;
             nextSymbolId++;
         }
 
-        return symbol.id;
+        return id;
     }
 
     export function isInstantiatedModule(node: ModuleDeclaration, preserveConstEnums: boolean) {

src/compiler/types.ts

@@ -4900,7 +4900,7 @@ namespace ts {
         members?: SymbolTable;                  // Class, interface or object literal instance members
         exports?: SymbolTable;                  // Module exports
         globalExports?: SymbolTable;            // Conditional global UMD exports
-        /* @internal */ id?: SymbolId;          // Unique id (used to look up SymbolLinks)
+        /* @internal */ id: SymbolId;          // Unique id (used to look up SymbolLinks)
         /* @internal */ mergeId?: number;       // Merge id (used to look up merged symbol)
         /* @internal */ parent?: Symbol;        // Parent symbol
         /* @internal */ exportSymbol?: Symbol;  // Exported symbol associated with this symbol

src/compiler/utilities.ts

@@ -5798,7 +5798,7 @@ namespace ts {
         this.escapedName = name;
         this.declarations = undefined;
         this.valueDeclaration = undefined;
-        this.id = undefined;
+        this.id = 0;
         this.mergeId = undefined;
         this.parent = undefined;
     }