feat(eslint): add rule no-optional-inputs

eslint-rules/src/rules/no-optional-inputs.ts

@@ -0,0 +1,40 @@
+import { Selectors } from '@angular-eslint/utils';
+import { AST_NODE_TYPES, TSESLint, TSESTree } from '@typescript-eslint/utils';
+
+const messages = {
+  doNotUseOptionalOperatorOnInputs: 'Angular @Input() properties are optional by default.',
+};
+
+const noOptionalInputsRule: TSESLint.RuleModule<keyof typeof messages> = {
+  meta: {
+    messages,
+    type: 'problem',
+    fixable: 'code',
+    schema: [],
+    docs: {
+      description: 'Disallow optional inputs',
+      recommended: 'warn',
+    },
+  },
+  create: context => ({
+    [Selectors.INPUT_DECORATOR](node: TSESTree.Decorator): void {
+      if (
+        node.parent.type === AST_NODE_TYPES.PropertyDefinition &&
+        node.parent.key.type === AST_NODE_TYPES.Identifier &&
+        node.parent.key.parent.type === AST_NODE_TYPES.PropertyDefinition &&
+        node.parent.key.parent.optional
+      ) {
+        const loc = node.parent.key.range[1];
+        context.report({
+          node: node.parent.key.parent,
+          messageId: 'doNotUseOptionalOperatorOnInputs',
+          fix(fixer) {
+            return fixer.removeRange([loc, loc + 1]);
+          },
+        });
+      }
+    },
+  }),
+};
+
+export default noOptionalInputsRule;

eslint-rules/tests/no-optional-inputs.spec.ts

@@ -0,0 +1,24 @@
+import noOptionalInputsRule from '../src/rules/no-optional-inputs';
+
+import testRule from './rule-tester';
+
+testRule(noOptionalInputsRule, {
+  valid: [
+    {
+      name: 'should not report when inputs do not use the optional operator',
+      code: 'export class MyComponent { @Input() foo: string; }',
+    },
+  ],
+  invalid: [
+    {
+      name: 'should report when inputs use the optional operator',
+      code: 'export class MyComponent { @Input() foo?: string; }',
+      errors: [
+        {
+          messageId: 'doNotUseOptionalOperatorOnInputs',
+        },
+      ],
+      output: 'export class MyComponent { @Input() foo: string; }',
+    },
+  ],
+});