I cant believe its not eval

src/compiler/core.ts

@@ -6,6 +6,7 @@ import {
     EqualityComparer,
     MapLike,
     Queue,
+    RawTSConfig,
     SortedArray,
     SortedReadonlyArray,
     TextSpan,
@@ -2716,3 +2717,8 @@ export function isNodeLikeSystem(): boolean {
         && !(process as any).browser
         && typeof require !== "undefined";
 }
+
+export function config<const T extends RawTSConfig>(config: T): T {
+    Debug.fail("This function does nothing at runtime.");
+    return config;
+}

src/compiler/program.ts

@@ -1147,7 +1147,7 @@ export function getLibraryNameFromLibFileName(libFileName: string) {
 
 function getLibFileNameFromLibReference(libReference: FileReference) {
     const libName = toFileNameLowerCase(libReference.fileName);
-    const libFileName = libMap.get(libName);
+    const libFileName = libMap.get(libName as Parameters<(typeof libMap)["get"]>[0]);
     return { libName, libFileName };
 }
 

src/compiler/tsbuildPublic.ts

@@ -11,6 +11,7 @@ import {
     closeFileWatcher,
     closeFileWatcherOf,
     combinePaths,
+    CommandLineOption,
     commonOptionsWithBuild,
     CompilerHost,
     CompilerOptions,
@@ -324,7 +325,7 @@ export function createSolutionBuilderWithWatchHost<T extends BuilderProgram = Em
 
 function getCompilerOptionsOfBuildOptions(buildOptions: BuildOptions): CompilerOptions {
     const result = {} as CompilerOptions;
-    commonOptionsWithBuild.forEach(option => {
+    commonOptionsWithBuild.forEach((option: CommandLineOption) => {
         if (hasProperty(buildOptions, option.name)) result[option.name] = buildOptions[option.name];
     });
     return result;

src/compiler/types.ts

@@ -9,6 +9,7 @@ import {
     ModuleResolutionCache,
     MultiMap,
     NodeFactoryFlags,
+    optionDeclarations,
     OptionsNameMap,
     PackageJsonInfo,
     PackageJsonInfoCache,
@@ -9912,6 +9913,48 @@ export interface PragmaMap extends Map<string, PragmaPseudoMap[keyof PragmaPseud
     forEach(action: <TKey extends keyof PragmaPseudoMap>(value: PragmaPseudoMap[TKey] | PragmaPseudoMap[TKey][], key: TKey, map: PragmaMap) => void): void;
 }
 
+type IntoCompilerOptionsValue<T extends CommandLineOption> =
+    T["type"] extends "string"
+        ? string
+    : T["type"] extends "number"
+        ? number
+    : T["type"] extends "boolean"
+        ? boolean
+    : T["type"] extends "object"
+       ? Record<string, any>
+    : T["type"] extends "list"
+        ? IntoCompilerOptionsValue<Extract<T, CommandLineOptionOfListType>["element"]>[]
+    : T["type"] extends "listOrElement"
+        ? IntoCompilerOptionsValue<Extract<T, CommandLineOptionOfListType>["element"]>[] | IntoCompilerOptionsValue<Extract<T, CommandLineOptionOfListType>["element"]>
+    : T["type"] extends Map<infer InputKeyTypes, infer _EnumType>
+        ? InputKeyTypes
+    : never;
+
+type IntoCompilerOptionsNameValuePair<T extends CommandLineOption> = {
+    [K in T["name"]]?: IntoCompilerOptionsValue<T>;
+};
+
+type IntoCompilerOptionsNameValuePairs<T extends CommandLineOption> = T extends T ? IntoCompilerOptionsNameValuePair<T> : never;
+
+type IntoCompilerOptionsDefinitionWorker<T extends CommandLineOption[]> = UnionToIntersection<IntoCompilerOptionsNameValuePairs<T[number]>>;
+
+type IntoCompilerOptionsDefinition<T extends CommandLineOption[]> = IntoCompilerOptionsDefinitionWorker<T> extends infer U ? {[K in keyof U]: U[K]} : never;
+
+export const _optionsType = [undefined! as IntoCompilerOptionsDefinition<typeof optionDeclarations> | undefined][0];
+
+/**
+ * An unprocessed TSConfig object, suitable to read as JSON and transform into command line options
+ */
+export interface RawTSConfig {
+    extends?: string | string[];
+    compilerOptions?: NonNullable<typeof _optionsType>;
+    references?: { path: string }[];
+    files?: string[];
+    include?: string[];
+    exclude?: string[];
+    compileOnSave?: boolean;
+}
+
 /** @internal */
 export interface CommentDirectivesMap {
     getUnusedExpectations(): CommentDirective[];

src/executeCommandLine/executeCommandLine.ts

@@ -169,7 +169,7 @@ function getOptionsForHelp(commandLine: ParsedCommandLine) {
     // Sort our options by their names, (e.g. "--noImplicitAny" comes before "--watch")
     return !!commandLine.options.all ?
         sort(optionDeclarations, (a, b) => compareStringsCaseInsensitive(a.name, b.name)) :
-        filter(optionDeclarations.slice(), v => !!v.showInSimplifiedHelpView);
+        filter(optionDeclarations.slice(), (v: CommandLineOption) => !!v.showInSimplifiedHelpView);
 }
 
 function printVersion(sys: System) {

src/services/transpile.ts

@@ -1,6 +1,7 @@
 import {
     addRange,
     cloneCompilerOptions,
+    CommandLineOption,
     CommandLineOptionOfCustomType,
     CompilerHost,
     CompilerOptions,
@@ -169,7 +170,7 @@ let commandLineOptionsStringToEnum: CommandLineOptionOfCustomType[];
 export function fixupCompilerOptions(options: CompilerOptions, diagnostics: Diagnostic[]): CompilerOptions {
     // Lazily create this value to fix module loading errors.
     commandLineOptionsStringToEnum = commandLineOptionsStringToEnum ||
-        filter(optionDeclarations, o => typeof o.type === "object" && !forEachEntry(o.type, v => typeof v !== "number")) as CommandLineOptionOfCustomType[];
+        filter(optionDeclarations, (o: CommandLineOption) => typeof o.type === "object" && !forEachEntry(o.type, v => typeof v !== "number")) as CommandLineOptionOfCustomType[];
 
     options = cloneCompilerOptions(options);
 

src/testRunner/projectsRunner.ts

@@ -472,13 +472,13 @@ function createCompilerOptions(testCase: ProjectRunnerTestCase & ts.CompilerOpti
     const optionNameMap = ts.arrayToMap(ts.optionDeclarations, option => option.name);
     for (const name in testCase) {
         if (name !== "mapRoot" && name !== "sourceRoot") {
-            const option = optionNameMap.get(name);
+            const option = optionNameMap.get(name as Parameters<(typeof optionNameMap)["get"]>[0]);
             if (option) {
                 const optType = option.type;
                 let value = testCase[name] as any;
                 if (!ts.isString(optType)) {
                     const key = value.toLowerCase();
-                    const optTypeValue = optType.get(key);
+                    const optTypeValue = optType.get(key as never);
                     if (optTypeValue) {
                         value = optTypeValue;
                     }

src/testRunner/unittests/config/commandLineParsing.ts

@@ -253,9 +253,9 @@ describe("unittests:: config:: commandLineParsing:: parseBuildOptions", () => {
 describe("unittests:: config:: commandLineParsing:: optionDeclarations", () => {
     it("should have affectsBuildInfo true for every option with affectsSemanticDiagnostics", () => {
         for (const option of ts.optionDeclarations) {
-            if (option.affectsSemanticDiagnostics) {
+            if ((option as ts.CommandLineOption).affectsSemanticDiagnostics) {
                 // semantic diagnostics affect the build info, so ensure they're included
-                assert(option.affectsBuildInfo ?? false, option.name);
+                assert((option as ts.CommandLineOption).affectsBuildInfo ?? false, option.name);
             }
         }
     });