Use BSD tar on windows (#126)

* Use BSD tar on windows

* Linting

* Fallback to which tar if no system tar

* Fix formatting

* Bump prettier and typescript

__tests__/tar.test.ts

@@ -0,0 +1,58 @@
+import * as exec from "@actions/exec";
+import * as io from "@actions/io";
+import * as tar from "../src/tar";
+
+jest.mock("@actions/exec");
+jest.mock("@actions/io");
+
+beforeAll(() => {
+    jest.spyOn(io, "which").mockImplementation(tool => {
+        return Promise.resolve(tool);
+    });
+});
+
+test("extract tar", async () => {
+    const mkdirMock = jest.spyOn(io, "mkdirP");
+    const execMock = jest.spyOn(exec, "exec");
+
+    const archivePath = "cache.tar";
+    const targetDirectory = "~/.npm/cache";
+    await tar.extractTar(archivePath, targetDirectory);
+
+    expect(mkdirMock).toHaveBeenCalledWith(targetDirectory);
+
+    const IS_WINDOWS = process.platform === "win32";
+    const tarPath = IS_WINDOWS
+        ? `${process.env["windir"]}\\System32\\tar.exe`
+        : "tar";
+    expect(execMock).toHaveBeenCalledTimes(1);
+    expect(execMock).toHaveBeenCalledWith(`"${tarPath}"`, [
+        "-xz",
+        "-f",
+        archivePath,
+        "-C",
+        targetDirectory
+    ]);
+});
+
+test("create tar", async () => {
+    const execMock = jest.spyOn(exec, "exec");
+
+    const archivePath = "cache.tar";
+    const sourceDirectory = "~/.npm/cache";
+    await tar.createTar(archivePath, sourceDirectory);
+
+    const IS_WINDOWS = process.platform === "win32";
+    const tarPath = IS_WINDOWS
+        ? `${process.env["windir"]}\\System32\\tar.exe`
+        : "tar";
+    expect(execMock).toHaveBeenCalledTimes(1);
+    expect(execMock).toHaveBeenCalledWith(`"${tarPath}"`, [
+        "-cz",
+        "-f",
+        archivePath,
+        "-C",
+        sourceDirectory,
+        "."
+    ]);
+});