feat(typescript-zod): emit literals for single-value enums

packages/quicktype-core/src/language/TypeScriptZod/TypeScriptZodRenderer.ts

@@ -376,13 +376,26 @@ export class TypeScriptZodRenderer extends ConvenienceRenderer {
     protected emitEnum(e: EnumType, enumName: Name): void {
         this.ensureBlankLine();
         this.emitDescription(this.descriptionForType(e));
-        this.emitLine("\nexport const ", enumName, "Schema = ", "z.enum([");
-        this.indent(() =>
-            this.forEachEnumCase(e, "none", (_, jsonName) => {
-                this.emitLine('"', stringEscape(jsonName), '",');
-            }),
-        );
-        this.emitLine("]);");
+
+        if (e.cases.size === 1) {
+            const value = e.cases.values().next().value;
+            if (value === undefined) panic("Single-value enum has no case.");
+            this.emitLine(
+                "\nexport const ",
+                enumName,
+                "Schema = z.literal(",
+                JSON.stringify(value),
+                ");",
+            );
+        } else {
+            this.emitLine("\nexport const ", enumName, "Schema = ", "z.enum([");
+            this.indent(() =>
+                this.forEachEnumCase(e, "none", (_, jsonName) => {
+                    this.emitLine('"', stringEscape(jsonName), '",');
+                }),
+            );
+            this.emitLine("]);");
+        }
         if (!this._options.justSchema) {
             this.emitLine(
                 "export type ",

test/inputs/schema/single-value-enum.1.fail.enum.json

@@ -0,0 +1,3 @@
+{
+  "kind": "other"
+}

test/inputs/schema/single-value-enum.1.json

@@ -0,0 +1,3 @@
+{
+  "kind": "only"
+}

test/inputs/schema/single-value-enum.schema

@@ -0,0 +1,10 @@
+{
+  "type": "object",
+  "properties": {
+    "kind": {
+      "type": "string",
+      "enum": ["only"]
+    }
+  },
+  "required": ["kind"]
+}

test/unit/typescript-zod-const-enum.test.ts

@@ -0,0 +1,31 @@
+import { InputData, JSONSchemaInput, quicktype } from "quicktype-core";
+import { expect, test } from "vitest";
+
+async function render(): Promise<string> {
+    const schemaInput = new JSONSchemaInput(undefined);
+    await schemaInput.addSource({
+        name: "TopLevel",
+        schema: JSON.stringify({
+            type: "object",
+            properties: {
+                kind: { type: "string", enum: ["only"] },
+            },
+            required: ["kind"],
+        }),
+    });
+    const inputData = new InputData();
+    inputData.addInput(schemaInput);
+
+    const result = await quicktype({
+        inputData,
+        lang: "typescript-zod",
+    });
+    return result.lines.join("\n");
+}
+
+test("TypeScript Zod emits a literal for a single-value enum", async () => {
+    const output = await render();
+
+    expect(output).toContain('z.literal("only")');
+    expect(output).not.toContain("z.enum([");
+});