embind_ts: handle empty enumerators case (#20398)

Author: shrinktofit

src/embind/embind_ts.js

@@ -143,11 +143,15 @@ var LibraryEmbind = {
       out.push(`export interface ${this.name}Value<T extends number> {\n`);
       out.push('  value: T;\n}\n');
       out.push(`export type ${this.name} = `);
-      const outItems = [];
-      for (const [name, value] of this.items) {
-        outItems.push(`${this.name}Value<${value}>`);
+      if (this.items.length === 0) {
+        out.push('never/* Empty Enumerator */');
+      } else {
+        const outItems = [];
+        for (const [name, value] of this.items) {
+          outItems.push(`${this.name}Value<${value}>`);
+        }
+        out.push(outItems.join('|'));
       }
-      out.push(outItems.join('|'));
       out.push(';\n\n');
     }
 

test/other/embind_tsgen.cpp

@@ -41,6 +41,8 @@ class Foo {
 
 enum Bar { kValueOne, kValueTwo, kValueThree };
 
+enum EmptyEnum {};
+
 Bar enum_returning_fn() { return kValueOne; }
 
 struct ValArr {
@@ -120,6 +122,7 @@ EMSCRIPTEN_BINDINGS(Test) {
       .value("valueOne", Bar::kValueOne)
       .value("valueTwo", Bar::kValueTwo)
       .value("valueThree", Bar::kValueThree);
+  enum_<EmptyEnum>("EmptyEnum");
 
   function("enum_returning_fn", &enum_returning_fn);
 

test/other/embind_tsgen.d.ts

@@ -16,6 +16,11 @@ export interface BarValue<T extends number> {
 }
 export type Bar = BarValue<0>|BarValue<1>|BarValue<2>;
 
+export interface EmptyEnumValue<T extends number> {
+  value: T;
+}
+export type EmptyEnum = never/* Empty Enumerator */;
+
 export type ValArrIx = [ Bar, Bar, Bar, Bar ];
 
 export interface IntVec {
@@ -66,6 +71,7 @@ export interface MainModule {
   a_class_instance: Test;
   an_enum: Bar;
   Bar: {valueOne: BarValue<0>, valueTwo: BarValue<1>, valueThree: BarValue<2>};
+  EmptyEnum: {};
   enum_returning_fn(): Bar;
   IntVec: {new(): IntVec};
   Foo: {new(): Foo};