fix(openapi-typescript): fix array minItems/maxItems tuple generation algorithm

The loop was incorrectly generating tuples from 0 to (max-min) elements
instead of min to max elements. For example, minItems: 1, maxItems: 3
was producing [] | [T] | [T, T] instead of [T] | [T, T] | [T, T, T].

Author: simonsolnes

packages/openapi-typescript/src/transform/schema-object.ts

@@ -381,10 +381,9 @@ function transformSchemaObjectCore(schemaObject: SchemaObject, options: Transfor
         } else if ((schemaObject.maxItems as number) > 0) {
           // if maxItems is set, then return a union of all permutations of possible tuple types
           const members: ts.TypeNode[] = [];
-          // populate 1 short of min …
-          for (let i = 0; i <= (max ?? 0) - min; i++) {
+          for (let i = min; i <= (max ?? 0); i++) {
             const elements: ts.TypeNode[] = [];
-            for (let j = min; j < i + min; j++) {
+            for (let j = 0; j < i; j++) {
               elements.push(itemType);
             }
             members.push(ts.factory.createTupleTypeNode(elements));

packages/openapi-typescript/test/transform/schema-object/array.test.ts

@@ -161,6 +161,102 @@ describe("transformSchemaObject > array", () => {
         want: `[
     string,
     string
+]`,
+        options: {
+          ...DEFAULT_OPTIONS,
+          ctx: { ...DEFAULT_OPTIONS.ctx, arrayLength: true },
+        },
+      },
+    ],
+    [
+      "options > arrayLength: true > minItems: 1, maxItems: 3",
+      {
+        given: { type: "array", items: { type: "string" }, minItems: 1, maxItems: 3 },
+        want: `[
+    string
+] | [
+    string,
+    string
+] | [
+    string,
+    string,
+    string
+]`,
+        options: {
+          ...DEFAULT_OPTIONS,
+          ctx: { ...DEFAULT_OPTIONS.ctx, arrayLength: true },
+        },
+      },
+    ],
+    [
+      "options > arrayLength: true > minItems: 0, maxItems: 2 (starts from empty)",
+      {
+        given: { type: "array", items: { type: "string" }, minItems: 0, maxItems: 2 },
+        want: `[
+] | [
+    string
+] | [
+    string,
+    string
+]`,
+        options: {
+          ...DEFAULT_OPTIONS,
+          ctx: { ...DEFAULT_OPTIONS.ctx, arrayLength: true },
+        },
+      },
+    ],
+    [
+      "options > arrayLength: true > minItems: 3, maxItems: 5 (larger range)",
+      {
+        given: { type: "array", items: { type: "number" }, minItems: 3, maxItems: 5 },
+        want: `[
+    number,
+    number,
+    number
+] | [
+    number,
+    number,
+    number,
+    number
+] | [
+    number,
+    number,
+    number,
+    number,
+    number
+]`,
+        options: {
+          ...DEFAULT_OPTIONS,
+          ctx: { ...DEFAULT_OPTIONS.ctx, arrayLength: true },
+        },
+      },
+    ],
+    [
+      "options > arrayLength: true > minItems: 2, maxItems: 3 with object items",
+      {
+        given: {
+          type: "array",
+          items: { type: "object", properties: { id: { type: "string" } } },
+          minItems: 2,
+          maxItems: 3,
+        },
+        want: `[
+    {
+        id?: string;
+    },
+    {
+        id?: string;
+    }
+] | [
+    {
+        id?: string;
+    },
+    {
+        id?: string;
+    },
+    {
+        id?: string;
+    }
 ]`,
         options: {
           ...DEFAULT_OPTIONS,