From 775544ee58fb70750d2af50ba8926cbf2da443fb Mon Sep 17 00:00:00 2001
From: Michael Bashurov <accounts@saitonakamura.me>
Date: Sat, 27 Feb 2021 12:12:55 +0200
Subject: [PATCH] Fix a bug with invalid print output when empty array is
 passed to t.tsInterfaceDeclaration

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 0993e5c352b8..c053162fa500 100644
--- a/packages/babel-generator/test/index.js
+++ b/packages/babel-generator/test/index.js
@@ -724,6 +724,19 @@ 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 () {