From d7fefba3741a526ff2b58dd713995c3ee5603962 Mon Sep 17 00:00:00 2001
From: Brad Zacher <brad.zacher@gmail.com>
Date: Tue, 21 Jul 2020 11:20:28 -0700
Subject: [PATCH] fix(typescript-estree): correct AST regression introduced by
 TS4.0 upgrade (#2316)

---
 packages/typescript-estree/src/convert.ts     | 18 ++++++++++--
 packages/typescript-estree/src/node-utils.ts  | 11 ++------
 .../typescript-estree/src/version-check.ts    | 28 +++++++++++++++++++
 3 files changed, 45 insertions(+), 12 deletions(-)
 create mode 100644 packages/typescript-estree/src/version-check.ts

diff --git a/packages/typescript-estree/src/convert.ts b/packages/typescript-estree/src/convert.ts
index 470a9108aef..7a137c3335f 100644
--- a/packages/typescript-estree/src/convert.ts
+++ b/packages/typescript-estree/src/convert.ts
@@ -29,6 +29,7 @@ import {
   TSNode,
   TSESTreeToTSNode,
 } from './ts-estree';
+import { typescriptVersionIsAtLeast } from './version-check';
 
 const SyntaxKind = ts.SyntaxKind;
 
@@ -1998,12 +1999,20 @@ export class Converter {
           raw: 'false',
         });
 
-      case SyntaxKind.NullKeyword:
+      case SyntaxKind.NullKeyword: {
+        if (!typescriptVersionIsAtLeast['4.0'] && this.inTypeMode) {
+          // 4.0 started nesting null types inside a LiteralType node, but we still need to support pre-4.0
+          return this.createNode<TSESTree.TSNullKeyword>(node, {
+            type: AST_NODE_TYPES.TSNullKeyword,
+          });
+        }
+
         return this.createNode<TSESTree.Literal>(node, {
           type: AST_NODE_TYPES.Literal,
           value: null,
           raw: 'null',
         });
+      }
 
       case SyntaxKind.EmptyStatement:
         return this.createNode<TSESTree.EmptyStatement>(node, {
@@ -2672,8 +2681,11 @@ export class Converter {
         });
       }
       case SyntaxKind.LiteralType: {
-        if (node.literal.kind === SyntaxKind.NullKeyword) {
-          // 4.0.0 started nesting null types inside a LiteralType node
+        if (
+          typescriptVersionIsAtLeast['4.0'] &&
+          node.literal.kind === SyntaxKind.NullKeyword
+        ) {
+          // 4.0 started nesting null types inside a LiteralType node
           // but our AST is designed around the old way of null being a keyword
           return this.createNode<TSESTree.TSNullKeyword>(
             node.literal as ts.NullLiteral,
diff --git a/packages/typescript-estree/src/node-utils.ts b/packages/typescript-estree/src/node-utils.ts
index b97f78b8dbd..82b98b29301 100644
--- a/packages/typescript-estree/src/node-utils.ts
+++ b/packages/typescript-estree/src/node-utils.ts
@@ -1,7 +1,7 @@
 import unescape from 'lodash/unescape';
-import * as semver from 'semver';
 import * as ts from 'typescript';
 import { AST_NODE_TYPES, AST_TOKEN_TYPES, TSESTree } from './ts-estree';
+import { typescriptVersionIsAtLeast } from './version-check';
 
 const SyntaxKind = ts.SyntaxKind;
 
@@ -452,13 +452,6 @@ export function isOptionalChain(
   );
 }
 
-/**
- * Returns true if the current TS version is TS 3.9
- */
-function isTSv3dot9(): boolean {
-  return !semver.satisfies(ts.version, '< 3.9.0 || < 3.9.1-rc || < 3.9.0-beta');
-}
-
 /**
  * Returns true of the child of property access expression is an optional chain
  */
@@ -477,7 +470,7 @@ export function isChildOptionalChain(
     return true;
   }
 
-  if (!isTSv3dot9()) {
+  if (!typescriptVersionIsAtLeast['3.9']) {
     return false;
   }
 
diff --git a/packages/typescript-estree/src/version-check.ts b/packages/typescript-estree/src/version-check.ts
new file mode 100644
index 00000000000..d26f96bc31a
--- /dev/null
+++ b/packages/typescript-estree/src/version-check.ts
@@ -0,0 +1,28 @@
+import * as semver from 'semver';
+import * as ts from 'typescript';
+
+function semverCheck(version: string): boolean {
+  return semver.satisfies(
+    ts.version,
+    `>= ${version}.0 || >= ${version}.1-rc || >= ${version}.0-beta`,
+    {
+      includePrerelease: true,
+    },
+  );
+}
+
+const versions = [
+  //
+  '3.7',
+  '3.8',
+  '3.9',
+  '4.0',
+] as const;
+type Versions = typeof versions extends ArrayLike<infer U> ? U : never;
+
+const typescriptVersionIsAtLeast = {} as Record<Versions, boolean>;
+for (const version of versions) {
+  typescriptVersionIsAtLeast[version] = semverCheck(version);
+}
+
+export { typescriptVersionIsAtLeast };