From 4373398627c8dffec8ad16a6244bbca37b9bd87c Mon Sep 17 00:00:00 2001
From: Michael Bashurov <accounts@saitonakamura.me>
Date: Sat, 27 Feb 2021 11:24:56 +0200
Subject: [PATCH 1/2] Allow nullish extends in interfaceish

Otherwise code such as

```ts
t.interfaceDeclaration(
  t.identifier('id'),
  undefined,
  undefined,
  t.objectTypeAnnotation([])
)
```

Will fail when priting with ` TypeError: unknown: Cannot read property 'length' of null`
Despite nullish values being allowed in `t.interfaceDeclaration` definitions
---
 packages/babel-generator/src/generators/flow.ts |  2 +-
 packages/babel-generator/test/index.js          | 11 +++++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/packages/babel-generator/src/generators/flow.ts b/packages/babel-generator/src/generators/flow.ts
index c59b2518389f..9bb094698a0a 100644
--- a/packages/babel-generator/src/generators/flow.ts
+++ b/packages/babel-generator/src/generators/flow.ts
@@ -360,7 +360,7 @@ export function _interfaceish(
 ) {
   this.print(node.id, node);
   this.print(node.typeParameters, node);
-  if (node.extends.length) {
+  if (node.extends && node.extends.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..7dcf37f6112f 100644
--- a/packages/babel-generator/test/index.js
+++ b/packages/babel-generator/test/index.js
@@ -462,6 +462,17 @@ describe("programmatic generation", function () {
 }`);
   });
 
+  it("flow interface with nullish extends", () => {
+    const interfaceDeclaration = t.interfaceDeclaration(
+      t.identifier("A"),
+      undefined,
+      undefined,
+      t.objectTypeAnnotation([]),
+    );
+    const output = generate(interfaceDeclaration).code;
+    expect(output).toBe("interface A {}");
+  });
+
   describe("directives", function () {
     it("preserves escapes", function () {
       const directive = t.directive(

From 2676750ed8e54d8a1779c7dc972b37901c34ba7a 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: Sat, 27 Feb 2021 12:05:40 +0200
Subject: [PATCH 2/2] Update packages/babel-generator/src/generators/flow.ts
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>
---
 packages/babel-generator/src/generators/flow.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/babel-generator/src/generators/flow.ts b/packages/babel-generator/src/generators/flow.ts
index 9bb094698a0a..133fec107f37 100644
--- a/packages/babel-generator/src/generators/flow.ts
+++ b/packages/babel-generator/src/generators/flow.ts
@@ -360,7 +360,7 @@ export function _interfaceish(
 ) {
   this.print(node.id, node);
   this.print(node.typeParameters, node);
-  if (node.extends && node.extends.length) {
+  if (node.extends?.length) {
     this.space();
     this.word("extends");
     this.space();