chore(prefer-readonly-type-declaration): add upstream utils to this project

Once typescript-eslint/typescript-eslint#3658 is merged, this commit can be
reverted

Author: RebeccaStevens

.eslintrc.json

@@ -26,7 +26,7 @@
     "project": ["./tsconfig.json", "./tests/tsconfig.json", "./cz-adapter/tsconfig.json"],
     "sourceType": "module"
   },
-  "ignorePatterns": ["build/", "coverage/", "lib/", "**/*.js"],
+  "ignorePatterns": ["build/", "coverage/", "lib/", "**/*.js", "src/util/upstream/**/*"],
   "rules": {
     "@typescript-eslint/no-unnecessary-condition": "off",
     "import/no-relative-parent-imports": "error",

.nycrc

@@ -4,7 +4,8 @@
     "src/**/*"
   ],
   "exclude": [
-    "src/util/conditional-imports/**/*"
+    "src/util/conditional-imports/**/*",
+    "src/util/upstream/**/*"
   ],
   "reporter": [
     "lcov",

src/util/rule.ts

@@ -6,6 +6,8 @@ import type { Node, Type } from "typescript";
 import { shouldIgnore } from "~/common/ignore-options";
 import { version } from "~/package.json";
 
+import { isTypeReadonly } from "./upstream/eslint-typescript/isTypeReadonly";
+
 export type BaseOptions = object;
 
 // "url" will be set automatically.
@@ -150,7 +152,8 @@ export function isReadonly<Context extends RuleContext<string, BaseOptions>>(
 
   const checker = parserServices.program.getTypeChecker();
   const type = getTypeOfNode(node, context);
-  return ESLintUtils.isTypeReadonly(checker, type!);
+  // return ESLintUtils.isTypeReadonly(checker, type!);
+  return isTypeReadonly(checker, type!);
 }
 
 /**

src/util/upstream/eslint-typescript/isTypeReadonly.ts

@@ -0,0 +1,198 @@
+// @ts-nocheck
+
+import tsutils from "~/conditional-imports/tsutils";
+import ts from "~/conditional-imports/typescript";
+
+import { nullThrows, NullThrowsReasons } from "./nullThrows";
+import { getTypeOfPropertyOfType } from "./propertyTypes";
+
+const enum Readonlyness {
+  /** the type cannot be handled by the function */
+  UnknownType = 1,
+  /** the type is mutable */
+  Mutable = 2,
+  /** the type is readonly */
+  Readonly = 3,
+}
+
+function isTypeReadonlyArrayOrTuple(
+  checker: ts.TypeChecker,
+  type: ts.Type,
+  seenTypes: Set<ts.Type>
+): Readonlyness {
+  function checkTypeArguments(arrayType: ts.TypeReference): Readonlyness {
+    const typeArguments = checker.getTypeArguments
+      ? checker.getTypeArguments(arrayType)
+      : arrayType.typeArguments ?? [];
+
+    // this shouldn't happen in reality as:
+    // - tuples require at least 1 type argument
+    // - ReadonlyArray requires at least 1 type argument
+    /* istanbul ignore if */ if (typeArguments.length === 0) {
+      return Readonlyness.Readonly;
+    }
+
+    // validate the element types are also readonly
+    if (
+      typeArguments.some(
+        (typeArg) =>
+          isTypeReadonlyRecurser(checker, typeArg, seenTypes) ===
+          Readonlyness.Mutable
+      )
+    ) {
+      return Readonlyness.Mutable;
+    }
+    return Readonlyness.Readonly;
+  }
+
+  if (checker.isArrayType(type)) {
+    const symbol = nullThrows(
+      type.getSymbol(),
+      NullThrowsReasons.MissingToken("symbol", "array type")
+    );
+    const escapedName = symbol.getEscapedName();
+    if (escapedName === "Array") {
+      return Readonlyness.Mutable;
+    }
+
+    return checkTypeArguments(type);
+  }
+
+  if (checker.isTupleType(type)) {
+    if (!type.target.readonly) {
+      return Readonlyness.Mutable;
+    }
+
+    return checkTypeArguments(type);
+  }
+
+  return Readonlyness.UnknownType;
+}
+
+function isTypeReadonlyObject(
+  checker: ts.TypeChecker,
+  type: ts.Type,
+  seenTypes: Set<ts.Type>
+): Readonlyness {
+  function checkIndexSignature(kind: ts.IndexKind): Readonlyness {
+    const indexInfo = checker.getIndexInfoOfType(type, kind);
+    if (indexInfo) {
+      return indexInfo.isReadonly
+        ? Readonlyness.Readonly
+        : Readonlyness.Mutable;
+    }
+
+    return Readonlyness.UnknownType;
+  }
+
+  const properties = type.getProperties();
+  if (properties.length) {
+    // ensure the properties are marked as readonly
+    for (const property of properties) {
+      if (!tsutils.isPropertyReadonlyInType(type, property.getEscapedName(), checker)) {
+        return Readonlyness.Mutable;
+      }
+    }
+
+    // all properties were readonly
+    // now ensure that all of the values are readonly also.
+
+    // do this after checking property readonly-ness as a perf optimization,
+    // as we might be able to bail out early due to a mutable property before
+    // doing this deep, potentially expensive check.
+    for (const property of properties) {
+      const propertyType = nullThrows(
+        getTypeOfPropertyOfType(checker, type, property),
+        NullThrowsReasons.MissingToken(`property "${property.name}"`, "type")
+      );
+
+      // handle recursive types.
+      // we only need this simple check, because a mutable recursive type will break via the above prop readonly check
+      if (seenTypes.has(propertyType)) {
+        continue;
+      }
+
+      if (
+        isTypeReadonlyRecurser(checker, propertyType, seenTypes) ===
+        Readonlyness.Mutable
+      ) {
+        return Readonlyness.Mutable;
+      }
+    }
+  }
+
+  const isStringIndexSigReadonly = checkIndexSignature(ts.IndexKind.String);
+  if (isStringIndexSigReadonly === Readonlyness.Mutable) {
+    return isStringIndexSigReadonly;
+  }
+
+  const isNumberIndexSigReadonly = checkIndexSignature(ts.IndexKind.Number);
+  if (isNumberIndexSigReadonly === Readonlyness.Mutable) {
+    return isNumberIndexSigReadonly;
+  }
+
+  return Readonlyness.Readonly;
+}
+
+// a helper function to ensure the seenTypes map is always passed down, except by the external caller
+function isTypeReadonlyRecurser(
+  checker: ts.TypeChecker,
+  type: ts.Type,
+  seenTypes: Set<ts.Type>
+): Readonlyness.Readonly | Readonlyness.Mutable {
+  seenTypes.add(type);
+
+  if (tsutils.isUnionType(type)) {
+    // all types in the union must be readonly
+    const result = tsutils.unionTypeParts(type).every((t) =>
+      isTypeReadonlyRecurser(checker, t, seenTypes)
+    );
+    const readonlyness = result ? Readonlyness.Readonly : Readonlyness.Mutable;
+    return readonlyness;
+  }
+
+  // all non-object, non-intersection types are readonly.
+  // this should only be primitive types
+  if (!tsutils.isObjectType(type) && !tsutils.isUnionOrIntersectionType(type)) {
+    return Readonlyness.Readonly;
+  }
+
+  // pure function types are readonly
+  if (
+    type.getCallSignatures().length > 0 &&
+    type.getProperties().length === 0
+  ) {
+    return Readonlyness.Readonly;
+  }
+
+  const isReadonlyArray = isTypeReadonlyArrayOrTuple(checker, type, seenTypes);
+  if (isReadonlyArray !== Readonlyness.UnknownType) {
+    return isReadonlyArray;
+  }
+
+  const isReadonlyObject = isTypeReadonlyObject(checker, type, seenTypes);
+  /* istanbul ignore else */ if (
+    isReadonlyObject !== Readonlyness.UnknownType
+  ) {
+    return isReadonlyObject;
+  }
+
+  throw new Error("Unhandled type");
+}
+
+/**
+ * Checks if the given type is readonly
+ */
+function isTypeReadonly(checker: ts.TypeChecker, type: ts.Type): boolean {
+  if (ts === undefined) {
+    throw new Error("TypeScript not found.");
+  }
+  if (tsutils === undefined) {
+    throw new Error("tsutils not found.");
+  }
+  return (
+    isTypeReadonlyRecurser(checker, type, new Set()) === Readonlyness.Readonly
+  );
+}
+
+export { isTypeReadonly };

src/util/upstream/eslint-typescript/nullThrows.ts

@@ -0,0 +1,28 @@
+/**
+ * A set of common reasons for calling nullThrows
+ */
+const NullThrowsReasons = {
+  MissingParent: 'Expected node to have a parent.',
+  MissingToken: (token: string, thing: string) =>
+    `Expected to find a ${token} for the ${thing}.`,
+} as const;
+
+/**
+ * Assert that a value must not be null or undefined.
+ * This is a nice explicit alternative to the non-null assertion operator.
+ */
+function nullThrows<T>(value: T | null | undefined, message: string): T {
+  // this function is primarily used to keep types happy in a safe way
+  // i.e. is used when we expect that a value is never nullish
+  // this means that it's pretty much impossible to test the below if...
+
+  // so ignore it in coverage metrics.
+  /* istanbul ignore if */
+  if (value === null || value === undefined) {
+    throw new Error(`Non-null Assertion Failed: ${message}`);
+  }
+
+  return value;
+}
+
+export { nullThrows, NullThrowsReasons };

src/util/upstream/eslint-typescript/propertyTypes.ts

@@ -0,0 +1,38 @@
+// @ts-nocheck
+
+import * as ts from "typescript";
+
+export function getTypeOfPropertyOfName(
+  checker: ts.TypeChecker,
+  type: ts.Type,
+  name: string,
+  escapedName?: ts.__String
+): ts.Type | undefined {
+  // Most names are directly usable in the checker and aren't different from escaped names
+  if (!escapedName || !name.startsWith("__")) {
+    return checker.getTypeOfPropertyOfType(type, name);
+  }
+
+  // Symbolic names may differ in their escaped name compared to their human-readable name
+  // https://github.com/typescript-eslint/typescript-eslint/issues/2143
+  const escapedProperty = type
+    .getProperties()
+    .find((property) => property.escapedName === escapedName);
+
+  return escapedProperty
+    ? checker.getDeclaredTypeOfSymbol(escapedProperty)
+    : undefined;
+}
+
+export function getTypeOfPropertyOfType(
+  checker: ts.TypeChecker,
+  type: ts.Type,
+  property: ts.Symbol
+): ts.Type | undefined {
+  return getTypeOfPropertyOfName(
+    checker,
+    type,
+    property.getName(),
+    property.getEscapedName()
+  );
+}