fix: drop dependency on tsutils

.eslintrc.json

@@ -29,7 +29,14 @@
     ],
     "sourceType": "module"
   },
-  "ignorePatterns": ["/build/", "/coverage/", "/lib/", "/**/*.cjs", "/**/*.js"],
+  "ignorePatterns": [
+    "/build/",
+    "/coverage/",
+    "/lib/",
+    "/**/*.cjs",
+    "/**/*.js",
+    "/src/util/tsutils.ts"
+  ],
   "rules": {
     "functional/prefer-immutable-types": "off",
     "import/no-relative-parent-imports": "error"

GETTING_STARTED.md

@@ -16,10 +16,10 @@ yarn add -D eslint eslint-plugin-functional
 
 ```sh
 # Install with npm
-npm install -D eslint @typescript-eslint/parser tsutils eslint-plugin-functional
+npm install -D eslint @typescript-eslint/parser eslint-plugin-functional
 
 # Install with yarn
-yarn add -D eslint @typescript-eslint/parser tsutils eslint-plugin-functional
+yarn add -D eslint @typescript-eslint/parser eslint-plugin-functional
 ```
 
 ## Usage

package.json

@@ -134,19 +134,14 @@
     "tsc-prog": "^2.2.1",
     "tsconfig-paths": "^4.1.2",
     "tslib": "^2.4.1",
-    "tsutils": "^3.21.0",
     "typescript": "^4.9.4",
     "word-wrap": "^1.2.3"
   },
   "peerDependencies": {
     "eslint": "^8.0.0",
-    "tsutils": "^3.0.0",
     "typescript": ">=4.0.2"
   },
   "peerDependenciesMeta": {
-    "tsutils": {
-      "optional": true
-    },
     "typescript": {
       "optional": true
     }

src/rules/no-conditional-statements.ts

@@ -2,9 +2,9 @@ import type { ESLintUtils, TSESLint, TSESTree } from "@typescript-eslint/utils";
 import type { JSONSchema4 } from "json-schema";
 import type { Type } from "typescript";
 
-import tsutils from "~/conditional-imports/tsutils";
 import type { RuleResult } from "~/util/rule";
 import { createRule, getTypeOfNode } from "~/util/rule";
+import { unionTypeParts } from "~/util/tsutils";
 import {
   isBlockStatement,
   isBreakStatement,
@@ -243,16 +243,12 @@ function isExhaustiveTypeSwitchViolation(
   node: TSESTree.SwitchStatement,
   context: TSESLint.RuleContext<keyof typeof errorMessages, Options>
 ): boolean {
-  if (tsutils === undefined) {
-    return true;
-  }
-
   const discriminantType = getTypeOfNode(node.discriminant, context);
   if (discriminantType === null || !discriminantType.isUnion()) {
     return true;
   }
 
-  const unionTypes = tsutils.unionTypeParts(discriminantType);
+  const unionTypes = unionTypeParts(discriminantType);
   const caseTypes = node.cases.reduce<ReadonlySet<Type>>(
     (types, c) => new Set([...types, getTypeOfNode(c.test!, context)!]),
     new Set()

src/util/rule.ts

@@ -7,12 +7,12 @@ import { ESLintUtils } from "@typescript-eslint/utils";
 import type { Rule } from "eslint";
 import type { ImmutabilityOverrides } from "is-immutable-type";
 import { getTypeImmutability, Immutability } from "is-immutable-type";
-import { isIdentifier } from "tsutils";
 import type { Node as TSNode, Type, TypeNode } from "typescript";
 
 import ts from "~/conditional-imports/typescript";
 import { getImmutabilityOverrides } from "~/settings";
 import type { ESFunction } from "~/util/node-types";
+import { isIdentifier } from "~/util/tsutils";
 
 // eslint-disable-next-line @typescript-eslint/naming-convention, no-underscore-dangle -- This is a special var.
 const __VERSION__ = "0.0.0-development";

src/util/tsutils.ts

@@ -0,0 +1,29 @@
+/**
+ * Need functions from tsutils.
+ * Copied here so they can be patched if needed.
+ * Should in future be removed and replaced with a new lib.
+ *
+ * @see https://github.com/typescript-eslint/typescript-eslint/issues/5552
+ */
+
+import type tsType from "typescript";
+
+import ts from "~/conditional-imports/typescript";
+
+export function isUnionType(type: tsType.Type): type is tsType.UnionType {
+  if (ts === undefined) {
+    return false;
+  }
+  return (type.flags & ts.TypeFlags.Union) !== 0;
+}
+
+export function unionTypeParts(type: tsType.Type): tsType.Type[] {
+  return isUnionType(type) ? type.types : [type];
+}
+
+export function isIdentifier(node: tsType.Node): node is tsType.Identifier {
+  if (ts === undefined) {
+    return false;
+  }
+  return node.kind === ts.SyntaxKind.Identifier;
+}