Support Flow Enums with unknown members (#9432)

changelog_unreleased/flow/pr-9432.md

@@ -0,0 +1,22 @@
+#### Flow Enums with unknown members (#9432 by @gkz)
+
+Previously, was not supported. Now, the following is formatted:
+
+<!-- prettier-ignore -->
+```jsx
+// Input
+enum E {
+  A,
+  B,
+  ...
+}
+
+// Prettier stable: parse error
+
+// Prettier master
+enum E {
+  A,
+  B,
+  ...
+}
+```

src/language-js/printer-estree.js

@@ -2472,7 +2472,7 @@ function printPathNoParens(path, options, print, args) {
         }
         parts.push("of ", type, " ");
       }
-      if (n.members.length === 0) {
+      if (n.members.length === 0 && !n.hasUnknownMembers) {
         parts.push(
           group(
             concat([
@@ -2484,15 +2484,22 @@ function printPathNoParens(path, options, print, args) {
           )
         );
       } else {
+        const members = n.members.length
+          ? [
+              hardline,
+              printArrayItems(path, options, "members", print),
+              n.hasUnknownMembers || shouldPrintComma(options) ? "," : "",
+            ]
+          : [];
+
         parts.push(
           group(
             concat([
               "{",
               indent(
                 concat([
-                  hardline,
-                  printArrayItems(path, options, "members", print),
-                  shouldPrintComma(options) ? "," : "",
+                  ...members,
+                  ...(n.hasUnknownMembers ? [hardline, "..."] : []),
                 ])
               ),
               comments.printDanglingComments(

tests/flow/enums-unknown-members/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,51 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`enum-unknown-members.js - {"trailingComma":"all"} format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+trailingComma: "all"
+                                                                                | printWidth
+=====================================input======================================
+// @flow
+
+enum E {
+  A,
+  B,
+  ...
+}
+
+=====================================output=====================================
+// @flow
+
+enum E {
+  A,
+  B,
+  ...
+}
+
+================================================================================
+`;
+
+exports[`enum-unknown-members-empty.js - {"trailingComma":"all"} format 1`] = `
+====================================options=====================================
+parsers: ["flow"]
+printWidth: 80
+trailingComma: "all"
+                                                                                | printWidth
+=====================================input======================================
+// @flow
+
+enum E {
+  ...
+}
+
+=====================================output=====================================
+// @flow
+
+enum E {
+  ...
+}
+
+================================================================================
+`;

tests/flow/enums-unknown-members/enum-unknown-members-empty.js

@@ -0,0 +1,5 @@
+// @flow
+
+enum E {
+  ...
+}

tests/flow/enums-unknown-members/enum-unknown-members.js

@@ -0,0 +1,7 @@
+// @flow
+
+enum E {
+  A,
+  B,
+  ...
+}

tests/flow/enums-unknown-members/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname, ["flow"], { trailingComma: "all" });