Support enum-like objects with numeric literal values

TypeDoc already supports enum-like objects with string literal values
via TypeStrong#1675 and TypeStrong#1740. Enum-like objects with numeric literal values
should also be supported, as they are a popular choice for developers
wishing to avoid use of TypeScript enums.

This PR adds support for such objects. Tests and a new example have
been added to cover this type of object.

Resolves TypeStrong#1918.

example/src/enums.ts

@@ -51,3 +51,27 @@ export const EnumLikeObject = {
 
     Completed: "completed",
 } as const;
+
+/**
+ * Since TypeScript's `enum` can be inconvenient to work with, some packages define their own enum-like objects:
+ *
+ * ```
+ * export const EnumLikeObjectNumValues = {
+ *     Pending: 1,
+ *     InProgress: 2,
+ *     Completed: 3
+ * } as const
+ * ```
+ *
+ * Use the `@enum` tag to make TypeDoc document this object as an enum.
+ *
+ * @enum
+ */
+export const EnumLikeObjectNumValues = {
+    Pending: 1,
+
+    /** Indicates that a courier is en route delivering this order. */
+    InProgress: 2,
+
+    Completed: 3,
+} as const;

src/lib/converter/symbols.ts

@@ -881,7 +881,7 @@ function isEnumLike(checker: ts.TypeChecker, type: ts.Type, location: ts.Node) {
 
     return type.getProperties().every((prop) => {
         const propType = checker.getTypeOfSymbolAtLocation(prop, location);
-        return propType.isStringLiteral();
+        return propType.isStringLiteral() || propType.isNumberLiteral();
     });
 }
 
@@ -912,7 +912,7 @@ function convertVariableAsEnum(
             prop,
             declaration
         );
-        assert(propType.isStringLiteral());
+        assert(propType.isStringLiteral() || propType.isNumberLiteral());
 
         reflection.defaultValue = JSON.stringify(propType.value);
 

src/test/converter2/behavior/asConstEnum.ts

@@ -1,3 +1,5 @@
+/* Enum-like objects with string literal values */
+
 export const SomeEnumLike = {
     a: "a",
     b: "b",
@@ -23,3 +25,31 @@ export const ManualEnumHelper: Readonly<{ a: "a" }> = {
 export const WithoutReadonly = {
     a: "a",
 } as { a: "a" };
+
+/* Enum-like objects with numeric literal values */
+
+export const SomeEnumLikeNumeric = {
+    a: 0,
+    b: 1,
+} as const;
+
+/** @enum */
+export const SomeEnumLikeTaggedNumeric = {
+    a: 0,
+    b: 1,
+} as const;
+
+/** @enum */
+export const ManualEnumNumeric: { readonly a: 0 } = {
+    a: 0,
+};
+
+/** @enum */
+export const ManualEnumHelperNumeric: Readonly<{ a: 0 }> = {
+    a: 0,
+};
+
+/** @enum */
+export const WithoutReadonlyNumeric = {
+    a: 0,
+} as { a: 0 };