Ensure createProgram stops referencing rootNamesOrOptions to ensure oldProgram is GC'd (#61034)

Co-authored-by: cplepage <[email protected]>

Author: jakebailey

src/compiler/program.ts

@@ -1511,10 +1511,14 @@ export function createProgram(createProgramOptions: CreateProgramOptions): Progr
  * @returns A 'Program' object.
  */
 export function createProgram(rootNames: readonly string[], options: CompilerOptions, host?: CompilerHost, oldProgram?: Program, configFileParsingDiagnostics?: readonly Diagnostic[]): Program;
-export function createProgram(rootNamesOrOptions: readonly string[] | CreateProgramOptions, _options?: CompilerOptions, _host?: CompilerHost, _oldProgram?: Program, _configFileParsingDiagnostics?: readonly Diagnostic[]): Program {
-    const createProgramOptions = isArray(rootNamesOrOptions) ? createCreateProgramOptions(rootNamesOrOptions, _options!, _host, _oldProgram, _configFileParsingDiagnostics) : rootNamesOrOptions; // TODO: GH#18217
-    const { rootNames, options, configFileParsingDiagnostics, projectReferences, typeScriptVersion } = createProgramOptions;
-    let { oldProgram } = createProgramOptions;
+export function createProgram(_rootNamesOrOptions: readonly string[] | CreateProgramOptions, _options?: CompilerOptions, _host?: CompilerHost, _oldProgram?: Program, _configFileParsingDiagnostics?: readonly Diagnostic[]): Program {
+    let _createProgramOptions = isArray(_rootNamesOrOptions) ? createCreateProgramOptions(_rootNamesOrOptions, _options!, _host, _oldProgram, _configFileParsingDiagnostics) : _rootNamesOrOptions; // TODO: GH#18217
+    const { rootNames, options, configFileParsingDiagnostics, projectReferences, typeScriptVersion, host: createProgramOptionsHost } = _createProgramOptions;
+    let { oldProgram } = _createProgramOptions;
+    // Stop referencing these objects to ensure GC collects them.
+    _createProgramOptions = undefined!;
+    _rootNamesOrOptions = undefined!;
+
     for (const option of commandLineOptionOfCustomType) {
         if (hasProperty(options, option.name)) {
             if (typeof options[option.name] === "string") {
@@ -1569,7 +1573,7 @@ export function createProgram(rootNamesOrOptions: readonly string[] | CreateProg
     tracing?.push(tracing.Phase.Program, "createProgram", { configFilePath: options.configFilePath, rootDir: options.rootDir }, /*separateBeginAndEnd*/ true);
     performance.mark("beforeProgram");
 
-    const host = createProgramOptions.host || createCompilerHost(options);
+    const host = createProgramOptionsHost || createCompilerHost(options);
     const configParsingHost = parseConfigHostFromCompilerHostLike(host);
 
     let skipDefaultLib = options.noLib;