Emit additionalProperties: false for records with string keys and Schema.Never values

.changeset/json-schema-never-additional-properties.md

@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Emit `additionalProperties: false` for records with string keys and `Schema.Never` values.

packages/effect/src/JSONSchema.ts

@@ -843,7 +843,7 @@ function go(
         const parameter = is.parameter
         switch (parameter._tag) {
           case "StringKeyword": {
-            output.additionalProperties = go(
+            const additionalProperties = go(
               pruned,
               $defs,
               "handle-identifier",
@@ -852,6 +852,9 @@ function go(
               "handle-annotation",
               errors
             )
+            output.additionalProperties = isNeverWithoutCustomAnnotations(additionalProperties)
+              ? false
+              : additionalProperties
             break
           }
           case "TemplateLiteral": {

packages/effect/test/Schema/JSONSchema.test.ts

@@ -2149,6 +2149,18 @@ details: Cannot encode Symbol(effect/Schema/test/a) key to JSON Schema`
       })
     })
 
+    it("Record(string, never)", () => {
+      const jsonSchema = expectJSONSchema(Schema.Record({ key: Schema.String, value: Schema.Never }), {
+        "type": "object",
+        "properties": {},
+        "required": [],
+        "additionalProperties": false
+      })
+      const validate = getAjvValidate(jsonSchema)
+      assertTrue(validate({}))
+      assertFalse(validate({ a: null }))
+    })
+
     it("Record('a' | 'b', number)", () => {
       expectJSONSchemaAnnotations(
         Schema.Record(