chore: enable unbound-method eslint rule (#165)

Unbound method calls using `this` are likely to have unintended effects.

Here is an example with static methods, but the same thing applies to
object methods:

```ts
class Class {
  public static staticMethod() {
    this.otherStaticMethod()
  }

  public static otherStaticMethod() { }
}

// ✅ valid
Class.staticMethod();

// ❌ boom
const x = Class.staticMethod;
x();
```

When assigning a method to a variable, you need to take extra care and
this linter rule is going to remind you.

---
By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license

Author: rix0rrr

.eslintrc.json

@@ -259,7 +259,7 @@ export class Manifest {
    * Ideally, we would start writing the `camelCased` and translate to how CloudFormation expects it when needed. But this requires nasty
    * backwards-compatibility code and it just doesn't seem to be worth the effort.
    */
-  private static patchStackTagsOnRead(manifest: assembly.AssemblyManifest) {
+  private static patchStackTagsOnRead(this: void, manifest: assembly.AssemblyManifest) {
     return Manifest.replaceStackTags(manifest, (tags) =>
       tags.map((diskTag: any) => ({
         key: diskTag.Key,
@@ -273,6 +273,7 @@ export class Manifest {
    * should have dedicated properties preceding this (e.g `assumeRoleArn` and `assumeRoleExternalId`).
    */
   private static validateAssumeRoleAdditionalOptions(
+    this: void,
     instance: any,
     key: string,
     _schema: jsonschema.Schema,
@@ -301,7 +302,7 @@ export class Manifest {
    *
    * Translate stack tags metadata if it has the "right" casing.
    */
-  private static patchStackTagsOnWrite(manifest: assembly.AssemblyManifest) {
+  private static patchStackTagsOnWrite(this: void, manifest: assembly.AssemblyManifest) {
     return Manifest.replaceStackTags(manifest, (tags) =>
       tags.map(
         (memTag) =>

packages/@aws-cdk/cdk-build-tools/.eslintrc.json

@@ -501,7 +501,7 @@ export class Toolkit extends CloudAssemblySourceBuilder implements AsyncDisposab
 
     const stacksAndTheirAssetManifests = stacks.flatMap((stack) => [
       stack,
-      ...stack.dependencies.filter(cxapi.AssetManifestArtifact.isAssetManifestArtifact),
+      ...stack.dependencies.filter(x => cxapi.AssetManifestArtifact.isAssetManifestArtifact(x)),
     ]);
     const workGraph = new WorkGraphBuilder({ ioHost, action }, prebuildAssets).build(stacksAndTheirAssetManifests);
 

packages/@aws-cdk/cdk-cli-wrapper/.eslintrc.json

@@ -1,4 +1,4 @@
-/* eslint-disable import/no-extraneous-dependencies */
+/* eslint-disable import/no-extraneous-dependencies,@typescript-eslint/unbound-method */
 /**
  * A Jest environment that buffers outputs to `console.log()` and only shows it for failing tests.
  */

packages/@aws-cdk/cli-lib-alpha/.eslintrc.json

@@ -177,8 +177,8 @@ export class WorkGraphBuilder {
 
 function stacksFromAssets(artifacts: cxapi.CloudArtifact[]) {
   const ret = new Map<cxapi.AssetManifestArtifact, cxapi.CloudFormationStackArtifact>();
-  for (const stack of artifacts.filter(cxapi.CloudFormationStackArtifact.isCloudFormationStackArtifact)) {
-    const assetArtifacts = stack.dependencies.filter(cxapi.AssetManifestArtifact.isAssetManifestArtifact);
+  for (const stack of artifacts.filter(x => cxapi.CloudFormationStackArtifact.isCloudFormationStackArtifact(x))) {
+    const assetArtifacts = stack.dependencies.filter((x) => cxapi.AssetManifestArtifact.isAssetManifestArtifact(x));
     for (const art of assetArtifacts) {
       ret.set(art, stack);
     }
@@ -188,5 +188,5 @@ function stacksFromAssets(artifacts: cxapi.CloudArtifact[]) {
 }
 
 function onlyStacks(artifacts: cxapi.CloudArtifact[]) {
-  return artifacts.filter(cxapi.CloudFormationStackArtifact.isCloudFormationStackArtifact);
+  return artifacts.filter(x => cxapi.CloudFormationStackArtifact.isCloudFormationStackArtifact(x));
 }

packages/@aws-cdk/cli-plugin-contract/.eslintrc.json

@@ -581,7 +581,7 @@ export class CdkToolkit {
 
     const stacksAndTheirAssetManifests = stacks.flatMap((stack) => [
       stack,
-      ...stack.dependencies.filter(cxapi.AssetManifestArtifact.isAssetManifestArtifact),
+      ...stack.dependencies.filter(x => cxapi.AssetManifestArtifact.isAssetManifestArtifact(x)),
     ]);
     const workGraph = new WorkGraphBuilder({
       ioHost: this.ioHost,

packages/@aws-cdk/cloud-assembly-schema/.eslintrc.json

@@ -1,4 +1,4 @@
-/* eslint-disable import/no-extraneous-dependencies */
+/* eslint-disable import/no-extraneous-dependencies,@typescript-eslint/unbound-method */
 /**
  * A Jest environment that buffers outputs to `console.log()` and only shows it for failing tests.
  */

packages/@aws-cdk/cloud-assembly-schema/lib/manifest.ts

@@ -165,6 +165,9 @@ export const ESLINT_RULES = {
     ],
   }],
 
+  // Unbound methods are a JavaScript footgun
+  '@typescript-eslint/unbound-method': 'error',
+
   // Overrides for plugin:jest/recommended
   'jest/expect-expect': 'off',
   'jest/no-conditional-expect': 'off',