From d05fdbc3c7fa0baae813e1394843ccf2874b4161 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20=E3=82=B5=E3=82=A4=E3=83=88=E3=83=BC=20=E4=B8=AD?=
 =?UTF-8?q?=E6=9D=91=20Bashurov?= <accounts@saitonakamura.me>
Date: Mon, 1 Mar 2021 17:43:24 +0200
Subject: [PATCH] Fix invalid print output when empty array is passed to
 t.tsInterfaceDeclaration (#12921)

If you pass an empty array as `extends` in `t.tsInterfaceDeclaration` you'll get an invalid code printed

```ts
t.tsInterfaceDeclaration(
  t.identifier('x'),
  undefined,
  [],
  t.tsInterfaceBody([])
)
```

You will get
```ts
interface A extends {}
```

Which is an invalid TS, this PR fixes that
---
 .../babel-generator/src/generators/typescript.ts    |  2 +-
 packages/babel-generator/test/index.js              | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/packages/babel-generator/src/generators/typescript.ts b/packages/babel-generator/src/generators/typescript.ts
index 14375b0beac5..0945de55ad5f 100644
--- a/packages/babel-generator/src/generators/typescript.ts
+++ b/packages/babel-generator/src/generators/typescript.ts
@@ -435,7 +435,7 @@ export function TSInterfaceDeclaration(
   this.space();
   this.print(id, node);
   this.print(typeParameters, node);
-  if (extendz) {
+  if (extendz?.length) {
     this.space();
     this.word("extends");
     this.space();
diff --git a/packages/babel-generator/test/index.js b/packages/babel-generator/test/index.js
index 7dcf37f6112f..8c597b818db7 100644
--- a/packages/babel-generator/test/index.js
+++ b/packages/babel-generator/test/index.js
@@ -735,6 +735,19 @@ describe("programmatic generation", function () {
       }
     });
   });
+
+  describe("typescript interface declaration", () => {
+    it("empty extends array", () => {
+      const tsInterfaceDeclaration = t.tsInterfaceDeclaration(
+        t.identifier("A"),
+        undefined,
+        [],
+        t.tsInterfaceBody([]),
+      );
+      const output = generate(tsInterfaceDeclaration).code;
+      expect(output).toBe("interface A {}");
+    });
+  });
 });
 
 describe("CodeGenerator", function () {