Init template cleanup

Improve the `swift package init` experience using the following criteria:

- Simplify the templates to include only the minimum necessary to get started
  without making assumptions.
- Use documentation links instead of template content to teach people
  about Swift.
- Improve the "front door" experience with the help usage.

Detailed list of changes:

- Remove the `system-module` template.
- Remove the `manifest` template
- Add a new `tool` template, an executable that uses ArgumentParser
a manifest instead.
- Remove README generation.
- Don't generate empty directories.
- Don't emit empty dependencies array in manifests.
- Update `library` template content:
  - Remove struct definition, use a simple public function instead.
  - Include documentation links for TSPL and the Standard Library.
  - Include documentation links for XCTest in the generated test case.
- Update `executable` template content
  - Use simpler top-level code instead of an `@main` struct.
  - Remove executable tests.
  - Put sources directly in `./Sources`.
- Clean up and align `type` argument help text
- Update Usage.md documentation
-  Update CHANGELOG to reflect init template changes in #6144

rdar://98999734

Author: bitjammer

CHANGELOG.md

@@ -17,7 +17,6 @@ Swift Next
   }
   ```
 
-
 Swift 5.9
 -----------
 
@@ -29,6 +28,9 @@ Swift 5.9
 
   Support for building plugin dependencies for the host when cross-compiling.
 
+* [#6144]
+
+  Remove the `system-module` and `manifest` templates and clean up the remaining `empty`, `library`, and `executable` templates so they include the minimum information needed to get started, with links to documentation in the generated library, executable, and test content.
 
 Swift 5.8
 -----------

Documentation/Usage.md

@@ -158,9 +158,9 @@ initialize it as a package that builds a system module:
     example$ cd ..
     $ mkdir Clibgit
     $ cd Clibgit
-    Clibgit$ swift package init --type system-module
+    Clibgit$ swift package init --type empty
 
-This creates `Package.swift` and `module.modulemap` files in the directory.
+This creates a `Package.swift` file in the directory.
 Edit `Package.swift` and add `pkgConfig` parameter:
 
 ```swift
@@ -181,7 +181,7 @@ parameter you can pass the path of a directory containing the library using the
 
     example$ swift build -Xlinker -L/usr/local/lib/
 
-Edit `module.modulemap` so it consists of the following:
+Create a `module.modulemap` file so it consists of the following:
 
     module Clibgit [system] {
       header "/usr/local/include/git2.h"
@@ -258,10 +258,10 @@ initialize it as a package that builds a system module:
     example$ cd ..
     $ mkdir CJPEG
     $ cd CJPEG
-    CJPEG$ swift package init --type system-module
+    CJPEG$ swift package init --type empty
 
-This creates `Package.swift` and `module.modulemap` files in the directory.
-Edit `module.modulemap` so it consists of the following:
+This creates `Package.swift` file in the directory.
+Create a `module.modulemap` file so it consists of the following:
 
     module CJPEG [system] {
         header "shim.h"

IntegrationTests/Tests/IntegrationTests/BasicTests.swift

@@ -234,11 +234,11 @@ final class BasicTests: XCTestCase {
             try localFileSystem.createDirectory(packagePath)
             try sh(swiftPackage, "--package-path", packagePath, "init", "--type", "executable")
             // delete any files generated
-            for entry in try localFileSystem.getDirectoryContents(packagePath.appending(components: "Sources", "secho")) {
-                try localFileSystem.removeFileTree(packagePath.appending(components: "Sources", "secho", entry))
+            for entry in try localFileSystem.getDirectoryContents(packagePath.appending(components: "Sources")) {
+                try localFileSystem.removeFileTree(packagePath.appending(components: "Sources", entry))
             }
             try localFileSystem.writeFileContents(
-                packagePath.appending(components: "Sources", "secho", "main.swift"),
+                packagePath.appending(components: "Sources", "secho.swift"),
                 bytes: ByteString(encodingAsUTF8: """
                     import Foundation
                     print(CommandLine.arguments.dropFirst().joined(separator: " "))

IntegrationTests/Tests/IntegrationTests/SwiftPMTests.swift

@@ -59,10 +59,10 @@ final class SwiftPMTests: XCTestCase {
             try localFileSystem.createDirectory(packagePath)
             try sh(swiftPackage, "--package-path", packagePath, "init", "--type", "executable")
             // delete any files generated
-            for entry in try localFileSystem.getDirectoryContents(packagePath.appending(components: "Sources", "foo")) {
-                try localFileSystem.removeFileTree(packagePath.appending(components: "Sources", "foo", entry))
+            for entry in try localFileSystem.getDirectoryContents(packagePath.appending(components: "Sources")) {
+                try localFileSystem.removeFileTree(packagePath.appending(components: "Sources", entry))
             }
-            try localFileSystem.writeFileContents(AbsolutePath(validating: "Sources/foo/main.m", relativeTo: packagePath)) {
+            try localFileSystem.writeFileContents(AbsolutePath(validating: "Sources/main.m", relativeTo: packagePath)) {
                 $0 <<< "int main() {}"
             }
             let archs = ["x86_64", "arm64"]

Sources/Commands/PackageTools/Init.swift

@@ -25,12 +25,13 @@ extension SwiftPackageTool {
 
         @Option(
             name: .customLong("type"),
-            help: ArgumentHelp("Package type: empty | library | executable | system-module | manifest", discussion: """
-                empty - Create an empty package
-                library - Create a package that contains a library
-                executable - Create a package that contains a binary executable
-                system-module - Create a package that contains a system module
-                manifest - Create a Package.swift file
+            help: ArgumentHelp("Package type:", discussion: """
+                library           - A package with a library.
+                executable        - A package with an executable.
+                tool              - A package with an executable that uses
+                                    Swift Argument Parser. Use this template if you
+                                    plan to have a rich set of command-line arguments.
+                empty             - An empty package with a Package.swift manifest.
                 """))
         var initMode: InitPackage.PackageType = .library