Support TypeScript 3.0's support for rest elements as the trailing parameter of tuples

Author: rpetrich

Diff for: test/programs/type-aliases-tuple-with-rest-element/main.ts

@@ -0,0 +1 @@
+export type MyTuple = [string, ...number[]];

Diff for: test/programs/type-aliases-tuple-with-rest-element/schema.json

@@ -0,0 +1,13 @@
+{
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "type": "array",
+    "items": [
+        {
+            "type": "string"
+        }
+    ],
+    "additionalItems": {
+        "type": "number"
+    },
+    "minItems": 1
+}

Diff for: test/schema.test.ts

@@ -161,6 +161,7 @@ describe("schema", () => {
         assertSchema("type-aliases-recursive-export", "MyObject");
         */
         assertSchema("type-aliases-tuple-of-variable-length", "MyTuple");
+        assertSchema("type-aliases-tuple-with-rest-element", "MyTuple");
     });
 
     describe("enums", () => {

Diff for: typescript-json-schema.ts

@@ -80,7 +80,7 @@ export type Definition = {
     minItems?: number,
     additionalItems?: {
         anyOf: Definition[]
-    },
+    } | Definition,
     enum?: PrimitiveType[] | Definition[],
     default?: PrimitiveType | Object,
     additionalProperties?: Definition | boolean,
@@ -380,9 +380,14 @@ export class JsonSchemaGenerator {
             definition.items = fixedTypes;
             const targetTupleType = (propertyType as ts.TupleTypeReference).target;
             definition.minItems = targetTupleType.minLength;
-            definition.additionalItems = {
-                anyOf: fixedTypes
-            };
+            if (targetTupleType.hasRestElement) {
+                definition.additionalItems = fixedTypes[fixedTypes.length - 1];
+                fixedTypes.splice(fixedTypes.length - 1, 1);
+            } else {
+                definition.additionalItems = {
+                    anyOf: fixedTypes
+                };
+            }
         } else {
             const propertyTypeString = this.tc.typeToString(propertyType, undefined, ts.TypeFormatFlags.UseFullyQualifiedType);
             const flags = propertyType.flags;