From 88f08f410760f58fdc2de58ecd9dab9610821642 Mon Sep 17 00:00:00 2001
From: Alexander T <alexander.tarasyuk@outlook.com>
Date: Mon, 20 Jul 2020 08:23:37 +0300
Subject: [PATCH] feat(eslint-plugin): [no-empty-function] add
 `decoratedFunctions` option (#2295)

---
 .../docs/rules/no-empty-function.md           |  2 +-
 .../src/rules/no-empty-function.ts            | 35 ++++++++++++-
 .../tests/rules/no-empty-function.test.ts     | 50 +++++++++++++++++++
 packages/types/src/ts-estree.ts               |  1 +
 4 files changed, 86 insertions(+), 2 deletions(-)

diff --git a/packages/eslint-plugin/docs/rules/no-empty-function.md b/packages/eslint-plugin/docs/rules/no-empty-function.md
index df6a3f82583..43dcf5375b0 100644
--- a/packages/eslint-plugin/docs/rules/no-empty-function.md
+++ b/packages/eslint-plugin/docs/rules/no-empty-function.md
@@ -5,7 +5,7 @@
 This rule extends the base [`eslint/no-empty-function`](https://eslint.org/docs/rules/no-empty-function) rule.
 It adds support for handling TypeScript specific code that would otherwise trigger the rule.
 
-One example of valid TypeScript specific code that would otherwise trigger the `no-empty-function` rule is the use of [parameter properties](https://www.typescriptlang.org/docs/handbook/classes.html#parameter-properties) in constructor functions:
+One example of valid TypeScript specific code that would otherwise trigger the `no-empty-function` rule is the use of [parameter properties](https://www.typescriptlang.org/docs/handbook/classes.html#parameter-properties) in constructor functions.
 
 ## How to use
 
diff --git a/packages/eslint-plugin/src/rules/no-empty-function.ts b/packages/eslint-plugin/src/rules/no-empty-function.ts
index 6dc610941e6..7f5a03a8c39 100644
--- a/packages/eslint-plugin/src/rules/no-empty-function.ts
+++ b/packages/eslint-plugin/src/rules/no-empty-function.ts
@@ -29,6 +29,7 @@ const schema = util.deepMerge(
             'protected-constructors',
             'asyncFunctions',
             'asyncMethods',
+            'decoratedFunctions',
           ],
         },
       },
@@ -61,6 +62,7 @@ export default util.createRule<Options, MessageIds>({
       'protected-constructors',
     );
     const isAllowedPrivateConstructors = allow.includes('private-constructors');
+    const isAllowedDecoratedFunctions = allow.includes('decoratedFunctions');
 
     /**
      * Check if the method body is empty
@@ -117,15 +119,46 @@ export default util.createRule<Options, MessageIds>({
       return false;
     }
 
+    /**
+     * @param node the node to be validated
+     * @returns true if a function has decorators
+     * @private
+     */
+    function isAllowedEmptyDecoratedFunctions(
+      node: TSESTree.FunctionExpression | TSESTree.FunctionDeclaration,
+    ): boolean {
+      if (isAllowedDecoratedFunctions && isBodyEmpty(node)) {
+        const decorators =
+          node.type === AST_NODE_TYPES.FunctionDeclaration
+            ? node.decorators
+            : node.parent?.type === AST_NODE_TYPES.MethodDefinition
+            ? node.parent.decorators
+            : undefined;
+        return !!decorators && !!decorators.length;
+      }
+
+      return false;
+    }
+
     return {
       ...rules,
       FunctionExpression(node): void {
-        if (isAllowedEmptyConstructor(node)) {
+        if (
+          isAllowedEmptyConstructor(node) ||
+          isAllowedEmptyDecoratedFunctions(node)
+        ) {
           return;
         }
 
         rules.FunctionExpression(node);
       },
+      FunctionDeclaration(node): void {
+        if (isAllowedEmptyDecoratedFunctions(node)) {
+          return;
+        }
+
+        rules.FunctionDeclaration(node);
+      },
     };
   },
 });
diff --git a/packages/eslint-plugin/tests/rules/no-empty-function.test.ts b/packages/eslint-plugin/tests/rules/no-empty-function.test.ts
index 9ec4d3c3097..258ef3e0ff5 100644
--- a/packages/eslint-plugin/tests/rules/no-empty-function.test.ts
+++ b/packages/eslint-plugin/tests/rules/no-empty-function.test.ts
@@ -63,6 +63,22 @@ function foo() {
 }
       `,
     },
+    {
+      code: `
+@decorator()
+function foo() {}
+      `,
+      options: [{ allow: ['decoratedFunctions'] }],
+    },
+    {
+      code: `
+class Foo {
+  @decorator()
+  foo() {}
+}
+      `,
+      options: [{ allow: ['decoratedFunctions'] }],
+    },
   ],
 
   invalid: [
@@ -149,5 +165,39 @@ function foo() {}
         },
       ],
     },
+    {
+      code: `
+@decorator()
+function foo() {}
+      `,
+      errors: [
+        {
+          messageId: 'unexpected',
+          data: {
+            name: "function 'foo'",
+          },
+          line: 3,
+          column: 16,
+        },
+      ],
+    },
+    {
+      code: `
+class Foo {
+  @decorator()
+  foo() {}
+}
+      `,
+      errors: [
+        {
+          messageId: 'unexpected',
+          data: {
+            name: "method 'foo'",
+          },
+          line: 4,
+          column: 9,
+        },
+      ],
+    },
   ],
 });
diff --git a/packages/types/src/ts-estree.ts b/packages/types/src/ts-estree.ts
index b72a1f58b09..527e67623f1 100644
--- a/packages/types/src/ts-estree.ts
+++ b/packages/types/src/ts-estree.ts
@@ -946,6 +946,7 @@ export interface ForStatement extends BaseNode {
 export interface FunctionDeclaration extends FunctionDeclarationBase {
   type: AST_NODE_TYPES.FunctionDeclaration;
   body: BlockStatement;
+  decorators?: Decorator[];
 }
 
 export interface FunctionExpression extends FunctionDeclarationBase {