Introduce a QlPackGenerator class

This will receive a folder name and language.

It will generate:
- a `codeql-pack.yml` file
- an `example.ql` file
- a `codeql-pack.lock.yml` file

It will also install dependencies listed in `codeql-pack.lock.yml`
file.

We were initially planning to call the `packInstall` command once
we generate `codeql-pack.yml` in order to install dependencies.

However, the `packAdd` command does this for us, as well as
generating a lock file.

Rather than trying to craft the lock file by hand, we're opting
to use the cli command.

NB: We're introducing a new `QueryLanguage` type which is identical
to the `VariantAnalysisQueryLanguage`. In a subsequent PR we'll
unify these two types.

extensions/ql-vscode/src/qlpack-generator.ts

@@ -0,0 +1,85 @@
+import { mkdir, writeFile } from "fs-extra";
+import { dump } from "js-yaml";
+import { join } from "path";
+import { CodeQLCliServer } from "./cli";
+
+export type QueryLanguage =
+  | "csharp"
+  | "cpp"
+  | "go"
+  | "java"
+  | "javascript"
+  | "python"
+  | "ruby"
+  | "swift";
+
+export class QlPackGenerator {
+  private readonly qlpackName: string;
+  private readonly qlpackVersion: string;
+  private readonly header: string;
+  private readonly qlpackFileName: string;
+
+  constructor(
+    private readonly folderName: string,
+    private readonly queryLanguage: QueryLanguage,
+    private readonly cliServer: CodeQLCliServer,
+  ) {
+    this.qlpackName = `getting-started/codeql-extra-queries-${this.queryLanguage}`;
+    this.qlpackVersion = "1.0.0";
+    this.header = "# This is an automatically generated file.\n\n";
+
+    this.qlpackFileName = "qlpack.yml";
+  }
+
+  public async generate() {
+    await mkdir(this.folderName);
+
+    // create qlpack.yml
+    await this.createQlPackYaml();
+
+    // create example.ql
+    await this.createExampleQlFile();
+
+    // create codeql-pack.lock.yml
+    await this.createCodeqlPackLockYaml();
+  }
+
+  private async createQlPackYaml() {
+    const qlPackFile = join(this.folderName, this.qlpackFileName);
+
+    const qlPackYml = {
+      name: this.qlpackName,
+      version: this.qlpackVersion,
+      dependencies: {
+        [`codeql/${this.queryLanguage}-all`]: "*",
+      },
+    };
+
+    await writeFile(qlPackFile, this.header + dump(qlPackYml), "utf8");
+  }
+
+  private async createExampleQlFile() {
+    const exampleQlFile = join(this.folderName, "example.ql");
+
+    const exampleQl = `
+/**
+ * @name Empty block
+ * @kind problem
+ * @problem.severity warning
+ * @id ${this.queryLanguage}/example/empty-block
+ */
+
+import ${this.queryLanguage}
+
+from BlockStmt b
+where b.getNumStmt() = 0
+select b, "This is an empty block."
+`.trim();
+
+    await writeFile(exampleQlFile, exampleQl, "utf8");
+  }
+
+  private async createCodeqlPackLockYaml() {
+    await this.cliServer.packAdd(this.folderName, this.queryLanguage);
+  }
+}

extensions/ql-vscode/test/vscode-tests/minimal-workspace/qlpack-generator.test.ts

@@ -0,0 +1,53 @@
+import { join } from "path";
+import { existsSync, rmdirSync } from "fs";
+import { QlPackGenerator, QueryLanguage } from "../../../src/qlpack-generator";
+import { CodeQLCliServer } from "../../../src/cli";
+
+describe("QlPackGenerator", () => {
+  let packfolderName: string;
+  let qlPackYamlFilePath: string;
+  let exampleQlFilePath: string;
+  let language: string;
+  let generator: QlPackGenerator;
+  let packAddSpy: jest.SpyInstance;
+
+  beforeEach(async () => {
+    language = "ruby";
+    packfolderName = `test-ql-pack-${language}`;
+    qlPackYamlFilePath = join(packfolderName, "qlpack.yml");
+    exampleQlFilePath = join(packfolderName, "example.ql");
+
+    packAddSpy = jest.fn();
+    const mockCli = {
+      packAdd: packAddSpy,
+    } as unknown as CodeQLCliServer;
+
+    generator = new QlPackGenerator(
+      packfolderName,
+      language as QueryLanguage,
+      mockCli,
+    );
+  });
+
+  afterEach(async () => {
+    try {
+      rmdirSync(packfolderName, { recursive: true });
+    } catch (e) {
+      // ignore
+    }
+  });
+
+  it("should generate a QL pack", async () => {
+    expect(existsSync(packfolderName)).toBe(false);
+    expect(existsSync(qlPackYamlFilePath)).toBe(false);
+    expect(existsSync(exampleQlFilePath)).toBe(false);
+
+    await generator.generate();
+
+    expect(existsSync(packfolderName)).toBe(true);
+    expect(existsSync(qlPackYamlFilePath)).toBe(true);
+    expect(existsSync(exampleQlFilePath)).toBe(true);
+
+    expect(packAddSpy).toHaveBeenCalledWith(packfolderName, language);
+  });
+});