feat(typescript-estree): handle 3.9's non-null assertion changes

[TS 3.9 introduced a breaking change for how non-null assertions are handled in optional chains](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-3-9.html#parsing-differences-in-optional-chaining-and-non-null-assertions).

Pre-3.9,  `x?.y!.z` means `(x?.y).z` - i.e. it essentially scrubbed the optionality from the chain
Post-3.9, `x?.y!.z` means `x?.y!.z`  - i.e. it just asserts that the property `y` is non-null, not the result of `x?.y`

This PR:

**updates the AST so it matches this**

Previously `x?.y!.z` produced `MemberExpression > TSNonNullAssertion > OptionalMemberExpression`.
Now it produces `OptionalMemberExpression > TSNonNullAssertion > OptionalMemberExpression`.

Note that
`(x?.y)!.z` still produces `MemberExpression > TSNonNullAssertion > OptionalMemberExpression`.

Same results apply for call expressions.

**updates `no-non-null-asserted-optional-chain` to handle this**

With the above AST change, the only change needed was a simple "is parent optional chain" check.

Both of these changes are gated behind a version check, so they are completely backwards compatible.

package.json

@@ -78,7 +78,7 @@
     "ts-jest": "^25.5.1",
     "ts-node": "^8.10.1",
     "tslint": "^6.1.2",
-    "typescript": ">=3.2.1 <3.9.0"
+    "typescript": ">=3.2.1 <4.0.0"
   },
   "resolutions": {
     "typescript": "^3.8.3"

packages/eslint-plugin/package.json

@@ -44,6 +44,7 @@
     "@typescript-eslint/experimental-utils": "2.33.0",
     "functional-red-black-tree": "^1.0.1",
     "regexpp": "^3.0.0",
+    "semver": "^7.3.2",
     "tsutils": "^3.17.1"
   },
   "devDependencies": {

packages/eslint-plugin/src/rules/no-non-null-asserted-optional-chain.ts

@@ -1,8 +1,19 @@
-import { TSESTree, TSESLint } from '@typescript-eslint/experimental-utils';
+import {
+  TSESTree,
+  TSESLint,
+  AST_NODE_TYPES,
+} from '@typescript-eslint/experimental-utils';
+import { version } from 'typescript';
+import * as semver from 'semver';
 import * as util from '../util';
 
 type MessageIds = 'noNonNullOptionalChain' | 'suggestRemovingNonNull';
 
+const is3dot9 = !semver.satisfies(
+  version,
+  '< 3.9.0 || < 3.9.1-rc || < 3.9.0-beta',
+);
+
 export default util.createRule<[], MessageIds>({
   name: 'no-non-null-asserted-optional-chain',
   meta: {
@@ -29,6 +40,24 @@ export default util.createRule<[], MessageIds>({
           | TSESTree.OptionalCallExpression
           | TSESTree.OptionalMemberExpression,
       ): void {
+        if (is3dot9) {
+          // TS3.9 made a breaking change to how non-null works with optional chains.
+          // Pre-3.9,  `x?.y!.z` means `(x?.y).z` - i.e. it essentially scrubbed the optionality from the chain
+          // Post-3.9, `x?.y!.z` means `x?.y!.z`  - i.e. it just asserts that the property `y` is non-null, not the result of `x?.y`.
+          // This means that for > 3.9, x?.y!.z is valid!
+          // NOTE: these cases are still invalid:
+          // - x?.y.z!
+          // - (x?.y)!.z
+          const nnAssertionParent = node.parent?.parent;
+          if (
+            nnAssertionParent?.type ===
+              AST_NODE_TYPES.OptionalMemberExpression ||
+            nnAssertionParent?.type === AST_NODE_TYPES.OptionalCallExpression
+          ) {
+            return;
+          }
+        }
+
         // selector guarantees this assertion
         const parent = node.parent as TSESTree.TSNonNullExpression;
         context.report({

packages/eslint-plugin/tests/rules/no-non-null-asserted-optional-chain.test.ts

@@ -13,6 +13,10 @@ ruleTester.run('no-non-null-asserted-optional-chain', rule, {
     'foo?.bar();',
     '(foo?.bar).baz!;',
     '(foo?.bar()).baz!;',
+    // Valid as of 3.9
+    'foo?.bar!.baz;',
+    'foo?.bar!();',
+    "foo?.['bar']!.baz;",
   ],
   invalid: [
     {
@@ -71,20 +75,6 @@ ruleTester.run('no-non-null-asserted-optional-chain', rule, {
         },
       ],
     },
-    {
-      code: 'foo?.bar!();',
-      errors: [
-        {
-          messageId: 'noNonNullOptionalChain',
-          suggestions: [
-            {
-              messageId: 'suggestRemovingNonNull',
-              output: 'foo?.bar();',
-            },
-          ],
-        },
-      ],
-    },
     {
       code: noFormat`(foo?.bar)!.baz`,
       errors: [
@@ -99,20 +89,6 @@ ruleTester.run('no-non-null-asserted-optional-chain', rule, {
         },
       ],
     },
-    {
-      code: "foo?.['bar']!.baz;",
-      errors: [
-        {
-          messageId: 'noNonNullOptionalChain',
-          suggestions: [
-            {
-              messageId: 'suggestRemovingNonNull',
-              output: "foo?.['bar'].baz;",
-            },
-          ],
-        },
-      ],
-    },
     {
       code: noFormat`(foo?.bar)!().baz`,
       errors: [