fix: allow enum member without initializer after non-literal member

packages/babel-plugin-transform-typescript/src/enum.ts

@@ -108,37 +108,43 @@ export function translateEnumValues(
 ): Array<[name: string, value: t.Expression]> {
   const seen: PreviousEnumMembers = Object.create(null);
   // Start at -1 so the first enum member is its increment, 0.
-  let prev: number | typeof undefined = -1;
+  let constValue: number | string | undefined = -1;
+  let lastName: string;
+
   return path.node.members.map(member => {
     const name = t.isIdentifier(member.id) ? member.id.name : member.id.value;
     const initializer = member.initializer;
     let value: t.Expression;
     if (initializer) {
-      const constValue = evaluate(initializer, seen);
+      constValue = evaluate(initializer, seen);
       if (constValue !== undefined) {
         seen[name] = constValue;
         if (typeof constValue === "number") {
           value = t.numericLiteral(constValue);
-          prev = constValue;
         } else {
           assert(typeof constValue === "string");
           value = t.stringLiteral(constValue);
-          prev = undefined;
         }
       } else {
         value = initializer;
-        prev = undefined;
       }
+    } else if (typeof constValue === "number") {
+      constValue += 1;
+      value = t.numericLiteral(constValue);
+      seen[name] = constValue;
+    } else if (typeof constValue === "string") {
+      throw path.buildCodeFrameError("Enum member must have initializer.");
     } else {
-      if (prev !== undefined) {
-        prev++;
-        value = t.numericLiteral(prev);
-        seen[name] = prev;
-      } else {
-        throw path.buildCodeFrameError("Enum member must have initializer.");
-      }
+      // create dynamic initializer: 1 + ENUM["PREVIOUS"]
+      const lastRef = t.memberExpression(
+        t.cloneNode(path.node.id),
+        t.stringLiteral(lastName),
+        true,
+      );
+      value = t.binaryExpression("+", t.numericLiteral(1), lastRef);
     }
 
+    lastName = name;
     return [name, value];
   });
 }

packages/babel-plugin-transform-typescript/test/fixtures/enum/non-foldable-constant/output.js

@@ -0,0 +1,6 @@
+var E;
+
+(function (E) {
+  E[E["a"] = Math.sin(1)] = "a";
+  E[E["b"] = 1 + E["a"]] = "b";
+})(E || (E = {}));

packages/babel-plugin-transform-typescript/test/fixtures/enum/outer-references/input.ts

@@ -0,0 +1,13 @@
+enum socketType {
+  SOCKET,
+  SERVER,
+  IPC,
+}
+
+enum constants {
+  SOCKET = socketType.SOCKET,
+  SERVER = socketType.SERVER,
+  IPC = socketType.IPC,
+  UV_READABLE,
+  UV_WRITABLE,
+}

packages/babel-plugin-transform-typescript/test/fixtures/enum/outer-references/output.js

@@ -0,0 +1,17 @@
+var socketType;
+
+(function (socketType) {
+  socketType[socketType["SOCKET"] = 0] = "SOCKET";
+  socketType[socketType["SERVER"] = 1] = "SERVER";
+  socketType[socketType["IPC"] = 2] = "IPC";
+})(socketType || (socketType = {}));
+
+var constants;
+
+(function (constants) {
+  constants[constants["SOCKET"] = socketType.SOCKET] = "SOCKET";
+  constants[constants["SERVER"] = socketType.SERVER] = "SERVER";
+  constants[constants["IPC"] = socketType.IPC] = "IPC";
+  constants[constants["UV_READABLE"] = 1 + constants["IPC"]] = "UV_READABLE";
+  constants[constants["UV_WRITABLE"] = 1 + constants["UV_READABLE"]] = "UV_WRITABLE";
+})(constants || (constants = {}));