From 878dd4ae8c408f1eb42790a8fac37f85040b7f3c Mon Sep 17 00:00:00 2001
From: Ryota Kameoka <kameoka.ryota@gmail.com>
Date: Thu, 26 Nov 2020 05:28:44 +0900
Subject: [PATCH] feat(eslint-plugin): [unbound-method] add support for methods
 with a `this: void` parameter (#2796)

---
 .../docs/rules/unbound-method.md              | 16 ++++++++++++
 .../eslint-plugin/src/rules/unbound-method.ts | 25 ++++++++++++++-----
 .../tests/rules/unbound-method.test.ts        | 16 +++++++++---
 3 files changed, 47 insertions(+), 10 deletions(-)

diff --git a/packages/eslint-plugin/docs/rules/unbound-method.md b/packages/eslint-plugin/docs/rules/unbound-method.md
index 0de7b17abcf..a9a4fe396a2 100644
--- a/packages/eslint-plugin/docs/rules/unbound-method.md
+++ b/packages/eslint-plugin/docs/rules/unbound-method.md
@@ -23,6 +23,14 @@ myLog();
 
 // This log might later be called with an incorrect scope
 const { log } = instance;
+
+// arith.double may refer to `this` internally
+const arith = {
+  double(x: number): number {
+    return x * 2;
+  },
+};
+const { double } = arith;
 ```
 
 Examples of **correct** code for this rule
@@ -45,6 +53,14 @@ logBound();
 // .bind and lambdas will also add a correct scope
 const dotBindLog = instance.logBound.bind(instance);
 const innerLog = () => instance.logBound();
+
+// arith.double explicitly declares that it does not refer to `this` internally
+const arith = {
+  double(this: void, x: number): number {
+    return x * 2;
+  },
+};
+const { double } = arith;
 ```
 
 ## Options
diff --git a/packages/eslint-plugin/src/rules/unbound-method.ts b/packages/eslint-plugin/src/rules/unbound-method.ts
index 246023fce10..407d04c11ec 100644
--- a/packages/eslint-plugin/src/rules/unbound-method.ts
+++ b/packages/eslint-plugin/src/rules/unbound-method.ts
@@ -248,14 +248,27 @@ function isDangerousMethod(symbol: ts.Symbol, ignoreStatic: boolean): boolean {
         ts.SyntaxKind.FunctionExpression
       );
     case ts.SyntaxKind.MethodDeclaration:
-    case ts.SyntaxKind.MethodSignature:
-      return !(
-        ignoreStatic &&
-        tsutils.hasModifier(
-          valueDeclaration.modifiers,
-          ts.SyntaxKind.StaticKeyword,
+    case ts.SyntaxKind.MethodSignature: {
+      const decl = valueDeclaration as
+        | ts.MethodDeclaration
+        | ts.MethodSignature;
+      const firstParam = decl.parameters[0];
+      const thisArgIsVoid =
+        firstParam?.name.kind === ts.SyntaxKind.Identifier &&
+        firstParam?.name.escapedText === 'this' &&
+        firstParam?.type?.kind === ts.SyntaxKind.VoidKeyword;
+
+      return (
+        !thisArgIsVoid &&
+        !(
+          ignoreStatic &&
+          tsutils.hasModifier(
+            valueDeclaration.modifiers,
+            ts.SyntaxKind.StaticKeyword,
+          )
         )
       );
+    }
   }
 
   return false;
diff --git a/packages/eslint-plugin/tests/rules/unbound-method.test.ts b/packages/eslint-plugin/tests/rules/unbound-method.test.ts
index 4c0cb8f58d3..83f3b93524c 100644
--- a/packages/eslint-plugin/tests/rules/unbound-method.test.ts
+++ b/packages/eslint-plugin/tests/rules/unbound-method.test.ts
@@ -25,6 +25,12 @@ class ContainsMethods {
 
 let instance = new ContainsMethods();
 
+const arith = {
+  double(this: void, x: number): number {
+    return x * 2;
+  }
+};
+
 ${code}
   `;
 }
@@ -35,7 +41,7 @@ function addContainsMethodsClassInvalid(
     code: addContainsMethodsClass(c),
     errors: [
       {
-        line: 12,
+        line: 18,
         messageId: 'unbound',
       },
     ],
@@ -153,6 +159,8 @@ ruleTester.run('unbound-method', rule, {
       'if (!!instance.unbound) {}',
       'void instance.unbound',
       'delete instance.unbound',
+
+      'const { double } = arith;',
     ].map(addContainsMethodsClass),
     `
 interface RecordA {
@@ -300,15 +308,15 @@ function foo(arg: ContainsMethods | null) {
       `),
       errors: [
         {
-          line: 14,
+          line: 20,
           messageId: 'unbound',
         },
         {
-          line: 15,
+          line: 21,
           messageId: 'unbound',
         },
         {
-          line: 16,
+          line: 22,
           messageId: 'unbound',
         },
       ],