fix(codegen): validate starting indent level (#25550)

## Summary

Validate `startingIndentLevel` before printing to prevent unbounded indentation-cache growth.

- Reject non-finite, fractional, negative, and unsafe integer values with a `RangeError`.
- Document the option as a non-negative integer.

packages/codegen/README.md

@@ -47,7 +47,7 @@ Returns a string containing the code for the AST `node`.
 | Option                | Type                 | Default | Description                                     |
 | :-------------------- | :------------------- | :------ | :---------------------------------------------- |
 | `indent`              | `string`             | `"\t"`  | Indentation - spaces and/or tabs only           |
-| `startingIndentLevel` | `number`             | `0`     | Indent level to start from                      |
+| `startingIndentLevel` | `number`             | `0`     | Starting indent level, from `0` to `1000`       |
 | `jsx`                 | `boolean`            | `false` | `.tsx` mode - lone type parameters print `<T,>` |
 | `ts`                  | `boolean`            | `false` | AST may contain TypeScript syntax               |
 | `sourceMap`           | `SourceMapGenerator` | -       | If present, source mappings are emitted into it |

packages/codegen/src-js/print/options.ts

@@ -49,7 +49,7 @@ export interface Options {
   indent?: string;
 
   /**
-   * Indent level to start from, defaults to `0`.
+   * Non-negative integer indent level to start from, from `0` to `1000`. Defaults to `0`.
    */
   startingIndentLevel?: number;
 

packages/codegen/src-js/state.ts

@@ -34,6 +34,9 @@ const indents = [""];
  */
 const INDENT_REGEX = /^[ \t]+$/;
 
+/** Upper bound for the process-wide indentation cache. */
+const MAX_STARTING_INDENT_LEVEL = 1_000;
+
 export class State {
   // Current output.
   // A string which is appended to as the printing process proceeds.
@@ -85,8 +88,18 @@ export class State {
   constructor(options: Options) {
     this.output = "";
 
-    let indentLevel = options.startingIndentLevel;
-    if (typeof indentLevel !== "number") indentLevel = 0;
+    let { startingIndentLevel: indentLevel } = options;
+    if (indentLevel === undefined) {
+      indentLevel = 0;
+    } else if (
+      !Number.isSafeInteger(indentLevel) ||
+      indentLevel < 0 ||
+      indentLevel > MAX_STARTING_INDENT_LEVEL
+    ) {
+      throw new RangeError(
+        "`startingIndentLevel` must be a non-negative safe integer no greater than 1000",
+      );
+    }
     this.indentLevel = indentLevel;
 
     // The `indent` option is validated here, not in the printer, and changing of it discards

packages/codegen/test/print.test.ts

@@ -107,6 +107,31 @@ function checkCases(cases: Case[]): void {
 
 // --- Tests ----------------------------------------------------------------------------------
 
+describe("starting indent level", () => {
+  const ast = e(id("x"));
+
+  test("indents from a valid level", () => {
+    expect(printSync(ast, { startingIndentLevel: 1 })).toBe("\tx;\n");
+  });
+
+  test("accepts the maximum level", () => {
+    expect(printSync(ast, { startingIndentLevel: 1000 })).toBe(`${"\t".repeat(1000)}x;\n`);
+  });
+
+  test.each([
+    ["infinity", Infinity],
+    ["negative infinity", -Infinity],
+    ["not a number", NaN],
+    ["fraction", 0.5],
+    ["negative", -1],
+    ["above the maximum", 1001],
+  ])("rejects %s", (_name, startingIndentLevel) => {
+    expect(() => printSync(ast, { startingIndentLevel })).toThrow(
+      "`startingIndentLevel` must be a non-negative safe integer no greater than 1000",
+    );
+  });
+});
+
 // A numeric literal followed by `.` needs a space when the number is plain digits, because
 // `0.toExponential()` would lex the `.` as part of the number. This is the `needSpaceBeforeDot`
 // path, and every case below is unreachable from a parsed fixture in at least one respect.