From da20fc94c33649f5ba26651ea3c2841ba1f9dfac Mon Sep 17 00:00:00 2001
From: Duncan Beevers <duncan@dweebd.com>
Date: Mon, 16 Dec 2024 08:03:00 -0800
Subject: [PATCH] Simplify minItems / maxItems tuple generation

Closes #2048
---
 .changeset/clean-phones-deliver.md            |  5 +++
 .../src/transform/schema-object.ts            | 40 ++++++-------------
 .../transform/schema-object/array.test.ts     | 16 ++++++++
 3 files changed, 34 insertions(+), 27 deletions(-)
 create mode 100644 .changeset/clean-phones-deliver.md

diff --git a/.changeset/clean-phones-deliver.md b/.changeset/clean-phones-deliver.md
new file mode 100644
index 000000000..878466f42
--- /dev/null
+++ b/.changeset/clean-phones-deliver.md
@@ -0,0 +1,5 @@
+---
+"openapi-typescript": patch
+---
+
+Simplify minItems / maxItems tuple generation.
diff --git a/packages/openapi-typescript/src/transform/schema-object.ts b/packages/openapi-typescript/src/transform/schema-object.ts
index 80ec56b51..6b9836a00 100644
--- a/packages/openapi-typescript/src/transform/schema-object.ts
+++ b/packages/openapi-typescript/src/transform/schema-object.ts
@@ -339,40 +339,26 @@ function transformSchemaObjectCore(schemaObject: SchemaObject, options: Transfor
         typeof schemaObject.maxItems === "number" && schemaObject.maxItems >= 0 && min <= schemaObject.maxItems
           ? schemaObject.maxItems
           : undefined;
-      const estimateCodeSize = typeof max !== "number" ? min : (max * (max + 1) - min * (min - 1)) / 2;
+      const estimateCodeSize = max === undefined ? min : (max * (max + 1) - min * (min - 1)) / 2;
       if (
         options.ctx.arrayLength &&
         (min !== 0 || max !== undefined) &&
         estimateCodeSize < 30 // "30" is an arbitrary number but roughly around when TS starts to struggle with tuple inference in practice
       ) {
-        if (min === max) {
-          const elements: ts.TypeNode[] = [];
-          for (let i = 0; i < min; i++) {
-            elements.push(itemType);
-          }
-          return tsUnion([ts.factory.createTupleTypeNode(elements)]);
-        } 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++) {
-            const elements: ts.TypeNode[] = [];
-            for (let j = min; j < i + min; j++) {
-              elements.push(itemType);
-            }
-            members.push(ts.factory.createTupleTypeNode(elements));
-          }
-          return tsUnion(members);
-        }
         // if maxItems not set, then return a simple tuple type the length of `min`
-        else {
-          const elements: ts.TypeNode[] = [];
-          for (let i = 0; i < min; i++) {
-            elements.push(itemType);
-          }
-          elements.push(ts.factory.createRestTypeNode(ts.factory.createArrayTypeNode(itemType)));
-          return ts.factory.createTupleTypeNode(elements);
+        if (max === undefined) {
+          return ts.factory.createTupleTypeNode([
+            ...Array.from({ length: min }).map(() => itemType),
+            ts.factory.createRestTypeNode(ts.factory.createArrayTypeNode(itemType)),
+          ]);
         }
+
+        // if maxItems is set, then return a union of all permutations of possible tuple types
+        return tsUnion(
+          Array.from({ length: max === undefined ? min : max - min + 1 }).map((_, index) =>
+            ts.factory.createTupleTypeNode(Array.from({ length: index + min }).map(() => itemType)),
+          ),
+        );
       }
 
       const finalType =
diff --git a/packages/openapi-typescript/test/transform/schema-object/array.test.ts b/packages/openapi-typescript/test/transform/schema-object/array.test.ts
index 59a2fddb7..8b48b0b0e 100644
--- a/packages/openapi-typescript/test/transform/schema-object/array.test.ts
+++ b/packages/openapi-typescript/test/transform/schema-object/array.test.ts
@@ -128,6 +128,22 @@ describe("transformSchemaObject > array", () => {
 ] | [
     string,
     string
+]`,
+        options: {
+          ...DEFAULT_OPTIONS,
+          ctx: { ...DEFAULT_OPTIONS.ctx, arrayLength: true },
+        },
+      },
+    ],
+    [
+      "options > arrayLength: true > minItems: 1, maxItems: 2",
+      {
+        given: { type: "array", items: { type: "string" }, minItems: 1, maxItems: 2 },
+        want: `[
+    string
+] | [
+    string,
+    string
 ]`,
         options: {
           ...DEFAULT_OPTIONS,