Add "default" command

Giving the content of default .gitignore or .github/workflows/ci.yml
files. Use like
```
$ scala-cli default gitignore
/.bsp/
/.scala-build/

$ scala-cli default workflow --write
$ cat .github/workflows/ci.yml
…
```

build.sc

@@ -21,6 +21,7 @@ import $file.project.deps, deps.customRepositories
 import $file.project.website
 
 import java.io.File
+import java.net.URL
 import java.nio.charset.Charset
 import java.util.Locale
 
@@ -29,7 +30,7 @@ import io.github.alexarchambault.millnativeimage.upload.Upload
 import mill._, scalalib.{publish => _, _}
 import mill.contrib.bloop.Bloop
 
-import _root_.scala.util.Properties
+import _root_.scala.util.{Properties, Using}
 
 // Tell mill modules are under modules/
 implicit def millModuleBasePath: define.BasePath =
@@ -644,6 +645,7 @@ trait Cli extends SbtModule with ProtoBuildModule with CliLaunchers
          |/** Build-time constants. Generated by mill. */
          |object Constants {
          |  def launcherTypeResourcePath = "${launcherTypeResourcePath.toString}"
+         |  def defaultFilesResourcePath = "$defaultFilesResourcePath"
          |}
          |""".stripMargin
     if (!os.isFile(dest) || os.read(dest) != code)
@@ -652,6 +654,25 @@ trait Cli extends SbtModule with ProtoBuildModule with CliLaunchers
   }
   def generatedSources = super.generatedSources() ++ Seq(constantsFile())
 
+  def defaultFilesResources = T.persistent {
+    val dir = T.dest / "resources"
+    val resources = Seq(
+      "https://raw.githubusercontent.com/scala-cli/default-workflow/main/.github/workflows/ci.yml" -> (os.sub / "workflows" / "default.yml"),
+      "https://raw.githubusercontent.com/scala-cli/default-workflow/main/.gitignore" -> (os.sub / "gitignore")
+    )
+    for ((srcUrl, destRelPath) <- resources) {
+      val dest = dir / defaultFilesResourcePath / destRelPath
+      if (!os.isFile(dest)) {
+        val content = Using.resource(new URL(srcUrl).openStream())(_.readAllBytes())
+        os.write(dest, content, createFolders = true)
+      }
+    }
+    PathRef(dir)
+  }
+  override def resources = T.sources {
+    super.resources() ++ Seq(defaultFilesResources())
+  }
+
   def myScalaVersion: String
 
   def scalaVersion = T(myScalaVersion)

modules/cli-options/src/main/scala/scala/cli/commands/default/DefaultFileOptions.scala

@@ -0,0 +1,30 @@
+package scala.cli.commands.default
+
+import caseapp._
+
+import scala.cli.commands.LoggingOptions
+
+// format: off
+final case class DefaultFileOptions(
+  @Recurse
+    logging: LoggingOptions = LoggingOptions(),
+  @Group("Default")
+  @HelpMessage("Write result to files rather than to stdout")
+    write: Boolean = false,
+  @Group("Default")
+  @HelpMessage("List available default files")
+    list: Boolean = false,
+  @Group("Default")
+  @HelpMessage("List available default file ids")
+    listIds: Boolean = false,
+  @Group("Default")
+  @HelpMessage("Force overwriting destination files")
+  @ExtraName("f")
+    force: Boolean = false
+)
+// format: on
+
+object DefaultFileOptions {
+  implicit lazy val parser: Parser[DefaultFileOptions] = Parser.derive
+  implicit lazy val help: Help[DefaultFileOptions]     = Help.derive
+}

modules/cli/src/main/scala/scala/cli/ScalaCliCommands.scala

@@ -7,6 +7,7 @@ import java.nio.file.InvalidPathException
 
 import scala.cli.commands._
 import scala.cli.commands.bloop.BloopOutput
+import scala.cli.commands.default.DefaultFile
 import scala.cli.commands.github.{SecretCreate, SecretList}
 import scala.cli.commands.pgp.{PgpCommands, PgpCommandsSubst, PgpPull, PgpPush}
 import scala.cli.commands.publish.{Publish, PublishLocal}
@@ -33,6 +34,7 @@ class ScalaCliCommands(
     Bsp,
     Clean,
     Compile,
+    DefaultFile,
     Directories,
     Doc,
     Doctor,

modules/cli/src/main/scala/scala/cli/commands/default/DefaultFile.scala

@@ -0,0 +1,111 @@
+package scala.cli.commands.default
+
+import caseapp.core.RemainingArgs
+
+import java.io.File
+
+import scala.build.Logger
+import scala.cli.commands.ScalaCommand
+import scala.cli.commands.util.CommonOps._
+import scala.cli.internal.Constants
+import scala.util.Using
+
+object DefaultFile extends ScalaCommand[DefaultFileOptions] {
+
+  override def hidden     = true
+  override def inSipScala = false
+
+  private def readDefaultFile(path: String): Array[Byte] = {
+    val resourcePath = Constants.defaultFilesResourcePath + "/" + path
+    val cl           = Thread.currentThread().getContextClassLoader
+    val resUrl       = cl.getResource(resourcePath)
+    if (resUrl == null)
+      sys.error(s"Should not happen - resource $resourcePath not found")
+    Using.resource(resUrl.openStream())(_.readAllBytes())
+  }
+
+  final case class DefaultFile(
+    path: os.SubPath,
+    content: () => Array[Byte]
+  ) {
+    def printablePath = path.segments.mkString(File.separator)
+  }
+
+  def defaultWorkflow: Array[Byte] =
+    readDefaultFile("workflows/default.yml")
+  def defaultGitignore: Array[Byte] =
+    readDefaultFile("gitignore")
+
+  val defaultFiles = Map(
+    "workflow"  -> DefaultFile(os.sub / ".github" / "workflows" / "ci.yml", () => defaultWorkflow),
+    "gitignore" -> DefaultFile(os.sub / ".gitignore", () => defaultGitignore)
+  )
+  val defaultFilesByRelPath = defaultFiles.flatMap {
+    case (_, d) =>
+      // d.path.toString and d.printablePath differ on Windows (one uses '/', the other '\')
+      Seq(
+        d.path.toString -> d,
+        d.printablePath -> d
+      )
+  }
+
+  private def unrecognizedFile(name: String, logger: Logger): Nothing = {
+    logger.error(
+      s"Error: unrecognized default file $name (available: ${defaultFiles.keys.toVector.sorted.mkString(", ")})"
+    )
+    sys.exit(1)
+  }
+
+  def run(options: DefaultFileOptions, args: RemainingArgs): Unit = {
+
+    val logger = options.logging.logger
+
+    lazy val allArgs = {
+      val l = args.all
+      if (l.isEmpty) {
+        logger.error("No default file asked")
+        sys.exit(1)
+      }
+      l
+    }
+
+    if (options.list || options.listIds)
+      for ((name, d) <- defaultFiles.toVector.sortBy(_._1)) {
+        if (options.listIds)
+          println(name)
+        if (options.list)
+          println(d.printablePath)
+      }
+    else if (options.write)
+      for (arg <- allArgs)
+        defaultFiles.get(arg).orElse(defaultFilesByRelPath.get(arg)) match {
+          case Some(f) =>
+            val dest = os.pwd / f.path
+            if (!options.force && os.exists(dest)) {
+              logger.error(
+                s"Error: ${f.path} already exists. Pass --force to force erasing it."
+              )
+              sys.exit(1)
+            }
+            if (options.force)
+              os.write.over(dest, f.content(), createFolders = true)
+            else
+              os.write(dest, f.content(), createFolders = true)
+            logger.message(s"Wrote ${f.path}")
+          case None =>
+            unrecognizedFile(arg, logger)
+        }
+    else {
+      if (allArgs.length > 1) {
+        logger.error(s"Error: expected only one argument, got ${allArgs.length}")
+        sys.exit(1)
+      }
+
+      val arg = allArgs.head
+      val f = defaultFiles.get(arg).orElse(defaultFilesByRelPath.get(arg)).getOrElse {
+        unrecognizedFile(arg, logger)
+      }
+      System.out.write(f.content())
+    }
+  }
+}

modules/integration/src/test/scala/scala/cli/integration/DefaultFileTests.scala

@@ -0,0 +1,25 @@
+package scala.cli.integration
+
+import com.eed3si9n.expecty.Expecty.expect
+
+class DefaultFileTests extends munit.FunSuite {
+
+  test("Print .gitignore") {
+    val res = os.proc(TestUtil.cli, "default-file", ".gitignore")
+      .call()
+    val output = res.out.text()
+    expect(output.linesIterator.toVector.contains("/.scala-build/"))
+  }
+
+  test("Write .gitignore") {
+    TestInputs(Nil).fromRoot { root =>
+      os.proc(TestUtil.cli, "default-file", ".gitignore", "--write")
+        .call(cwd = root, stdout = os.Inherit)
+      val dest = root / ".gitignore"
+      expect(os.isFile(dest))
+      val content = os.read(dest)
+      expect(content.linesIterator.toVector.contains("/.scala-build/"))
+    }
+  }
+
+}

project/settings.sc

@@ -141,6 +141,7 @@ def getGhToken(): String =
 trait CliLaunchers extends SbtModule { self =>
 
   def launcherTypeResourcePath = os.rel / "scala" / "cli" / "internal" / "launcher-type.txt"
+  def defaultFilesResourcePath = os.rel / "scala" / "cli" / "commands" / "publish"
 
   trait CliNativeImage extends NativeImage {
     def launcherKind: String
@@ -155,6 +156,7 @@ trait CliLaunchers extends SbtModule { self =>
       Seq(
         s"-H:IncludeResources=$localRepoResourcePath",
         s"-H:IncludeResources=$launcherTypeResourcePath",
+        s"-H:IncludeResources=$defaultFilesResourcePath/.*",
         "-H:-ParseRuntimeOptions",
         s"-H:CLibraryPath=$cLibPath"
       )

website/docs/commands/misc/_category_.json

@@ -0,0 +1,4 @@
+{
+  "label": "Miscellaneous",
+  "position": 17
+}

website/docs/commands/misc/default-file.md

@@ -0,0 +1,28 @@
+---
+title: Default File
+sidebar_position: 1
+---
+
+The `default-file` sub-command provides sensible default content for files
+such as `.gitignore` or for GitHub actions workflows, for Scala CLI projects.
+
+To list the available files, pass it `--list`:
+```text
+$ scala-cli default-file --list
+.gitignore
+.github/workflows/ci.yml
+```
+
+Get the content of a default file with
+```text
+$ scala-cli default-file .gitignore
+/.bsp/
+/.scala-build/
+```
+
+Optionally, write the content of one or more default files by passing `--write`:
+```text
+$ scala-cli default-file --write .gitignore .github/workflows/ci.yml
+Wrote .gitignore
+Wrote .github/workflows/ci.yml
+```

website/docs/reference/cli-options.md

@@ -266,6 +266,32 @@ Available in commands:
 
 Aliases: `-X`
 
+## Default file options
+
+Available in commands:
+- [`default-file`](./commands.md#default-file)
+
+
+<!-- Automatically generated, DO NOT EDIT MANUALLY -->
+
+#### `--write`
+
+Write result to files rather than to stdout
+
+#### `--list`
+
+List available default files
+
+#### `--list-ids`
+
+List available default file ids
+
+#### `--force`
+
+Aliases: `-f`
+
+Force overwriting destination files
+
 ## Dependency options
 
 Available in commands:
@@ -433,6 +459,7 @@ Available in commands:
 - [`bsp`](./commands.md#bsp)
 - [`clean`](./commands.md#clean)
 - [`compile`](./commands.md#compile)
+- [`default-file`](./commands.md#default-file)
 - [`directories`](./commands.md#directories)
 - [`doc`](./commands.md#doc)
 - [`doctor`](./commands.md#doctor)
@@ -661,6 +688,7 @@ Available in commands:
 - [`bsp`](./commands.md#bsp)
 - [`clean`](./commands.md#clean)
 - [`compile`](./commands.md#compile)
+- [`default-file`](./commands.md#default-file)
 - [`doc`](./commands.md#doc)
 - [`export`](./commands.md#export)
 - [`fmt` / `format` / `scalafmt`](./commands.md#fmt)
@@ -1568,6 +1596,7 @@ Available in commands:
 - [`bsp`](./commands.md#bsp)
 - [`clean`](./commands.md#clean)
 - [`compile`](./commands.md#compile)
+- [`default-file`](./commands.md#default-file)
 - [`directories`](./commands.md#directories)
 - [`doc`](./commands.md#doc)
 - [`doctor`](./commands.md#doctor)

website/docs/reference/commands.md

@@ -444,6 +444,13 @@ Accepts options:
 - [verbosity](./cli-options.md#verbosity-options)
 - [workspace](./cli-options.md#workspace-options)
 
+### `default-file`
+
+Accepts options:
+- [default file](./cli-options.md#default-file-options)
+- [logging](./cli-options.md#logging-options)
+- [verbosity](./cli-options.md#verbosity-options)
+
 ### `directories`
 
 Prints directories used by `scala-cli`