types: add offset and size options to Bun.mmap

packages/bun-types/bun.d.ts

@@ -4551,6 +4551,16 @@ declare module "bun" {
      * @default true
      */
     shared?: boolean;
+    /**
+     * Byte offset into the file where the mapping starts.
+     * @default 0
+     */
+    offset?: number;
+    /**
+     * Maximum number of bytes to map. Clamped to the file size
+     * (minus `offset`). Defaults to mapping the rest of the file.
+     */
+    size?: number;
   }
   /**
    * Open a file as a live-updating `Uint8Array` without copying memory

test/integration/bun-types/bun-types.test.ts

@@ -358,6 +358,39 @@ describe("@types/bun integration test", () => {
     });
   });
 
+  // Runs on debug builds too: spawning tsc over a single file is cheap,
+  // unlike the in-process LanguageService runs above.
+  describe("Bun.mmap", () => {
+    test("MMapOptions accepts offset and size", async () => {
+      const checkDir = join(TEMP_DIR, "mmap-options-check");
+      const tsconfig = structuredClone(sourceTsconfig);
+      tsconfig.include = ["mmap-options.ts"];
+      tsconfig.compilerOptions.typeRoots = [join(BASE_FIXTURE_DIR, "node_modules", "@types")];
+      await mkdir(checkDir, { recursive: true });
+      await makeTree(checkDir, {
+        "tsconfig.json": JSON.stringify(tsconfig, null, 2),
+        "mmap-options.ts": `const view = Bun.mmap("./data.bin", { shared: true, sync: false, offset: 4096, size: 1024 });
+           view satisfies Uint8Array<ArrayBuffer>;
+           Bun.mmap("./data.bin", { offset: 4096 }) satisfies Uint8Array<ArrayBuffer>;
+           Bun.mmap("./data.bin", { size: 1024 }) satisfies Uint8Array<ArrayBuffer>;`,
+      });
+
+      await using proc = Bun.spawn({
+        cmd: [bunExe(), join(BASE_FIXTURE_DIR, "node_modules", "typescript", "bin", "tsc"), "-p", "."],
+        env: bunEnv,
+        cwd: checkDir,
+        stdout: "pipe",
+        stderr: "pipe",
+      });
+
+      const [stdout, stderr, exitCode] = await Promise.all([proc.stdout.text(), proc.stderr.text(), proc.exited]);
+
+      expect(stderr.trim()).toBe("");
+      expect(stdout.trim()).toBe("");
+      expect(exitCode).toBe(0);
+    });
+  });
+
   describe("Test Globals", () => {
     const code = `
       const test_shouldBeAFunction: Function = test;

test/integration/bun-types/fixture/bun.ts

@@ -79,3 +79,17 @@ tsd
     }),
   )
   .is<Promise<boolean>>();
+
+tsd
+  .expectType(
+    Bun.mmap("./data.bin", {
+      shared: true,
+      sync: false,
+      offset: 4096,
+      size: 1024,
+    }),
+  )
+  .is<Uint8Array<ArrayBuffer>>();
+
+tsd.expectType(Bun.mmap("./data.bin", { offset: 4096 })).is<Uint8Array<ArrayBuffer>>();
+tsd.expectType(Bun.mmap("./data.bin", { size: 1024 })).is<Uint8Array<ArrayBuffer>>();