Allow nullish extends in interfaceish (#12920)

* 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 * Update packages/babel-generator/src/generators/flow.ts Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com> Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>
babel · Mar 1, 2021 · 4c343ac · 4c343ac
1 parent b62fc3d
commit 4c343ac
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diff --git 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?.length) {
     this.space();
     this.word("extends");
     this.space();

diff --git 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(