feat: add "deno init" subcommand (#15469)

This adds an init subcommand to that creates a project starter similar to cargo init.

```
$ deno init my_project
Project initialized
Run these commands to get started:
  cd my_project
  deno run main.ts
  deno run main_test.ts
$ deno run main.ts
Add 2 + 3 5
$ cat main.ts
export function add(a: number, b: number): number {
  return a + b;
}
if (import.meta.main) {
  console.log("Add 2 + 3", add(2, 3));
}
$ cat main_test.ts
import { assertEquals } from "https://deno.land/std@0.151.0/testing/asserts.ts";
import { add } from "./main.ts";
Deno.test(function addTest() {
    assertEquals(add(2, 3), 5);
});
```

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

4 files changed, 64 insertions, 0 deletions

diff --git a/cli/tools/init/mod.rs b/cli/tools/init/mod.rs
new file mode 100644
index 000000000..e47b88702
--- /dev/null
+++ b/cli/tools/init/mod.rs
@@ -0,0 +1,49 @@
+// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.
+
+use crate::args::InitFlags;
+use crate::compat;
+use deno_core::{anyhow::Context, error::AnyError};
+use std::io::Write;
+use std::path::Path;
+
+fn create_file(
+  dir: &Path,
+  filename: &str,
+  content: &str,
+) -> Result<(), AnyError> {
+  let mut file = std::fs::OpenOptions::new()
+    .write(true)
+    .create_new(true)
+    .open(dir.join(filename))
+    .with_context(|| format!("Failed to create {} file", filename))?;
+  file.write_all(content.as_bytes())?;
+  Ok(())
+}
+
+pub async fn init_project(init_flags: InitFlags) -> Result<(), AnyError> {
+  let cwd =
+    std::env::current_dir().context("Can't read current working directory.")?;
+  let dir = if let Some(dir) = &init_flags.dir {
+    let dir = cwd.join(dir);
+    std::fs::create_dir_all(&dir)?;
+    dir
+  } else {
+    cwd
+  };
+
+  let main_ts = include_str!("./templates/main.ts");
+  create_file(&dir, "main.ts", main_ts)?;
+
+  let main_test_ts = include_str!("./templates/main_test.ts")
+    .replace("{CURRENT_STD_URL}", compat::STD_URL_STR);
+  create_file(&dir, "main_test.ts", &main_test_ts)?;
+
+  println!("✅ Project initialized");
+  println!("Run these commands to get started");
+  if let Some(dir) = init_flags.dir {
+    println!("  cd {}", dir);
+  }
+  println!("  deno run main.ts");
+  println!("  deno test");
+  Ok(())
+}
diff --git a/cli/tools/init/templates/main.ts b/cli/tools/init/templates/main.ts
new file mode 100644
index 000000000..be043e97c
--- /dev/null
+++ b/cli/tools/init/templates/main.ts
@@ -0,0 +1,8 @@
+export function add(a: number, b: number): number {
+  return a + b;
+}
+
+// Learn more at https://deno.land/manual/examples/module_metadata#concepts
+if (import.meta.main) {
+  console.log("Add 2 + 3 =", add(2, 3));
+}
diff --git a/cli/tools/init/templates/main_test.ts b/cli/tools/init/templates/main_test.ts
new file mode 100644
index 000000000..5f60b571c
--- /dev/null
+++ b/cli/tools/init/templates/main_test.ts
@@ -0,0 +1,6 @@
+import { assertEquals } from "{CURRENT_STD_URL}testing/asserts.ts";
+import { add } from "./main.ts";
+
+Deno.test(function addTest() {
+  assertEquals(add(2, 3), 5);
+});
diff --git a/cli/tools/mod.rs b/cli/tools/mod.rs
index 7c5d79744..11c904776 100644
--- a/cli/tools/mod.rs
+++ b/cli/tools/mod.rs
@@ -4,6 +4,7 @@ pub mod bench;
 pub mod coverage;
 pub mod doc;
 pub mod fmt;
+pub mod init;
 pub mod installer;
 pub mod lint;
 pub mod repl;