Polish JSON Schema for patterns

Author: colinhacks

packages/zod/src/v4/classic/tests/json-schema.test.ts

@@ -361,54 +361,64 @@ describe("toJSONSchema", () => {
     expect(z.toJSONSchema(z.string().regex(/asdf/))).toMatchInlineSnapshot(`
       {
         "$schema": "https://json-schema.org/draft/2020-12/schema",
-        "format": "regex",
         "pattern": "asdf",
         "type": "string",
       }
     `);
   });
 
   test("string patterns", () => {
-    expect(z.toJSONSchema(z.string().startsWith("hello").includes("cruel").endsWith("world"))).toMatchInlineSnapshot(`
-  {
-    "$schema": "https://json-schema.org/draft/2020-12/schema",
-    "allOf": [
-      {
-        "pattern": "^hello.*",
-      },
-      {
-        "pattern": "cruel",
-      },
+    expect(
+      z.toJSONSchema(z.string().startsWith("hello").includes("cruel").endsWith("world").regex(/stuff/))
+    ).toMatchInlineSnapshot(`
       {
-        "pattern": ".*world$",
-      },
-    ],
-    "type": "string",
-  }
-`);
+        "$schema": "https://json-schema.org/draft/2020-12/schema",
+        "allOf": [
+          {
+            "pattern": "^hello.*",
+          },
+          {
+            "pattern": "cruel",
+          },
+          {
+            "pattern": ".*world$",
+          },
+          {
+            "pattern": "stuff",
+          },
+        ],
+        "type": "string",
+      }
+    `);
 
     expect(
-      z.toJSONSchema(
-        z
-          .string()
-          .regex(/^hello/)
-          .regex(/world$/)
-      )
+      z.toJSONSchema(z.string().startsWith("hello").includes("cruel").endsWith("world").regex(/stuff/), {
+        target: "draft-7",
+      })
     ).toMatchInlineSnapshot(`
-  {
-    "$schema": "https://json-schema.org/draft/2020-12/schema",
-    "allOf": [
-      {
-        "pattern": "^hello",
-      },
       {
-        "pattern": "world$",
-      },
-    ],
-    "format": "regex",
-    "type": "string",
-  }
-`);
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "allOf": [
+          {
+            "pattern": "^hello.*",
+            "type": "string",
+          },
+          {
+            "pattern": "cruel",
+            "type": "string",
+          },
+          {
+            "pattern": ".*world$",
+            "type": "string",
+          },
+          {
+            "pattern": "stuff",
+            "type": "string",
+          },
+        ],
+        "type": "string",
+      }
+    `);
   });
 
   test("number constraints", () => {

packages/zod/src/v4/core/to-json-schema.ts

@@ -48,11 +48,12 @@ interface EmitParams {
     | undefined;
 }
 
-const formatMap: Partial<Record<checks.$ZodStringFormats, string>> = {
+const formatMap: Partial<Record<checks.$ZodStringFormats, string | undefined>> = {
   guid: "uuid",
   url: "uri",
   datetime: "date-time",
   json_string: "json-string",
+  regex: "", // do not set
 };
 
 interface Seen {
@@ -156,15 +157,16 @@ export class JSONSchemaGenerator {
           // custom pattern overrides format
           if (format) {
             json.format = formatMap[format as checks.$ZodStringFormats] ?? format;
+            if (json.format === "") delete json.format; // empty format is not valid
           }
           if (contentEncoding) json.contentEncoding = contentEncoding;
           if (patterns && patterns.size > 0) {
             const regexes = [...patterns];
-            if (regexes.length === 1) {
-              json.pattern = regexes[0].source;
-            } else {
-              json.allOf = [
+            if (regexes.length === 1) json.pattern = regexes[0].source;
+            else if (regexes.length > 1) {
+              result.schema.allOf = [
                 ...regexes.map((regex) => ({
+                  ...(this.target === "draft-7" ? { type: "string" } : {}),
                   pattern: regex.source,
                 })),
               ];