Add export command documentation

modules/cli/src/main/scala/scala/cli/commands/export0/ExportOptions.scala

@@ -54,7 +54,8 @@ object ExportOptions {
   implicit lazy val parser: Parser[ExportOptions] = Parser.derive
   implicit lazy val help: Help[ExportOptions]     = Help.derive
 
-  private val helpHeader = "Export current project to an external build tool (like SBT or Mill)."
+  private val helpHeader =
+    "Export current project to an external build tool (like SBT or Mill) or to JSON."
   val helpMessage: String =
     s"""$helpHeader
        |

website/docs/commands/export.md

@@ -0,0 +1,157 @@
+---
+title: Export ⚡️
+sidebar_position: 27
+---
+
+In case your project outgrows the cabapilities of Scala CLI (e.g support for modules) it may be beneficial
+to switch to a build tool such as SBT or Mill.
+The `export` sub-command allows to do that by converting a Scala CLI project into an SBT or Mill configuration.
+Additionally the sub-command supports the JSON format for custom analysis of projects.
+
+Results of running the sub-command are, by default, put in `./dest/`,
+that behaviour can be modified by specifying a path with the `--output` option.
+
+:::caution
+The `export` sub-command is restricted and requires setting the `--power` option to be used.
+You can pass it explicitly or set it globally by running:
+scala-cli config power true
+:::
+
+The project configuration is read both from information specified in source files
+as well as options passed to the `export` sub-command.
+
+Let's take a simple one-file project as an example:
+```scala title=Hello.scala
+//> using scala "3.1.3"
+//> using option "-Xasync"
+//> using dep "com.lihaoyi::os-lib:0.9.0"
+
+object Hello {
+  def main(args: Array[String]): Unit =
+    println(os.pwd)
+}
+```
+
+# Exporting to SBT:
+
+```bash
+scala-cli --power export Hello.scala --sbt
+```
+Note that `--sbt` is not required here since it's the default.
+
+The result is an sbt-compliant project created in the `dest/` directory:
+
+```
+dest
+├── project
+│   └── build.properties
+├── src
+│   └── main
+│       └── scala
+│           └── Hello.scala
+└── build.sbt
+```
+
+All the project's configuration resides now in `dest/build.sbt`:
+
+
+```scala title=dest/build.sbt
+scalaVersion := "3.1.3"
+
+scalacOptions ++= Seq("-Xasync")
+
+libraryDependencies += "com.lihaoyi" %% "os-lib" % "0.9.0" 
+
+libraryDependencies += "com.lihaoyi" %% "os-lib" % "0.9.0" % Test
+
+```
+
+
+To configure the version of SBT used in the new project provide the `--sbtVersion` option to the `export` sub-command.
+
+# Exporting to Mill:
+
+```bash
+scala-cli --power export Hello.scala --mill --output=dest_mill
+```
+Mill is not the default `export` format, so passing the `--mill` option is required.
+
+By specifying the path with `--output` option the results are now created in `dest_mill/` directory:
+
+```
+dest_mill
+├── project
+│   └── src
+│       └── Hello.scala
+├── .mill-version
+├── build.sc
+├── mill
+└── mill.bat
+```
+
+And all the project's configuration resides now in `dest_mill/build.sc`:
+
+```scala title=dest_mill/build.sc
+import mill._
+import mill.scalalib._
+object project extends ScalaModule {
+  def scalaVersion = "3.1.3"
+  def scalacOptions = super.scalacOptions() ++ Seq("-Xasync")
+  def ivyDeps = super.ivyDeps() ++ Seq(
+    ivy"com.lihaoyi::os-lib:0.9.0"
+  )
+
+  object test extends Tests {
+    def ivyDeps = super.ivyDeps() ++ Seq(
+      ivy"com.lihaoyi::os-lib:0.9.0"
+    )
+  }
+}
+
+```
+
+The script files `mill` and `mill.bat` are mill wrappers fetched from [lefou/millw repository](https://github.com/lefou/millw/tree/166bcdf5741de8569e0630e18c3b2ef7e252cd96).
+To change the build tool version used override the contents of `dest_mill/.mill-version`.
+
+
+# Exporting to JSON:
+
+To export project information in a human-comprehensible format, use the `--json` flag.
+
+```bash
+scala-cli --power export Hello.scala --json --output=dest_json
+```
+
+The result is the `dest_json/export.json` file:
+
+```json title=dest_json/export.json
+{
+ "scalaVersion": "3.1.3",
+ "platform": "JVM",
+ "scopes": {
+  "main": {
+   "sources": [
+    "Foo.scala"
+   ],
+   "scalacOptions": [
+    "-Xasync"
+   ],
+   "dependencies": [
+    {
+     "groupId": "com.lihaoyi",
+     "artifactId": {
+      "name": "os-lib",
+      "fullName": "os-lib_3"
+     },
+     "version": "0.9.0"
+    }
+   ],
+   "resolvers": [
+    "https://repo1.maven.org/maven2",
+    "ivy:file:///Users/mgajek/Library/Caches/ScalaCli/local-repo/v0.1.20-111-648755-DIRTY2ba64fdc//[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext]",
+    "ivy:file:/Users/mgajek/.ivy2/local/[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/[artifact](-[classifier]).[ext]"
+   ]
+  }
+ }
+}
+```

website/docs/reference/commands.md

@@ -54,7 +54,7 @@ Accepts option groups: [compilation server](./cli-options.md#compilation-server-
 
 ## export
 
-Export current project to an external build tool (like SBT or Mill).
+Export current project to an external build tool (like SBT or Mill) or to JSON.
 
 Detailed documentation can be found on our website: https://scala-cli.virtuslab.org