improve example created by package init --type executable

motivation: example is out of date with best practices

changes:
* use @main istead of main.swift
* test executable directly instead of shelling out to a process

rdar://82119401

Author: tomerd

Sources/Workspace/InitPackage.swift

@@ -286,7 +286,7 @@ public final class InitPackage {
         let moduleDir = sources.appending(component: "\(pkgname)")
         try makeDirectories(moduleDir)
 
-        let sourceFileName = (packageType == .executable) ? "main.swift" : "\(typeName).swift"
+        let sourceFileName = "\(typeName).swift"
         let sourceFile = moduleDir.appending(RelativePath(sourceFileName))
 
         let content: String
@@ -303,7 +303,14 @@ public final class InitPackage {
                 """
         case .executable:
             content = """
-                print("Hello, world!")
+                @main
+                public struct \(typeName) {
+                    public private(set) var text = "Hello, World!"
+
+                    public static func main() {
+                        print(\(typeName)().text)
+                    }
+                }
 
                 """
         case .systemModule, .empty, .manifest, .`extension`:
@@ -377,50 +384,14 @@ public final class InitPackage {
         try writePackageFile(path) { stream in
             stream <<< """
                 import XCTest
-                import class Foundation.Bundle
+                @testable import \(moduleName)
 
                 final class \(moduleName)Tests: XCTestCase {
                     func testExample() throws {
                         // This is an example of a functional test case.
                         // Use XCTAssert and related functions to verify your tests produce the correct
                         // results.
-
-                        // Some of the APIs that we use below are available in macOS 10.13 and above.
-                        guard #available(macOS 10.13, *) else {
-                            return
-                        }
-
-                        // Mac Catalyst won't have `Process`, but it is supported for executables.
-                        #if !targetEnvironment(macCatalyst)
-
-                        let fooBinary = productsDirectory.appendingPathComponent("\(pkgname)")
-
-                        let process = Process()
-                        process.executableURL = fooBinary
-
-                        let pipe = Pipe()
-                        process.standardOutput = pipe
-
-                        try process.run()
-                        process.waitUntilExit()
-
-                        let data = pipe.fileHandleForReading.readDataToEndOfFile()
-                        let output = String(data: data, encoding: .utf8)
-
-                        XCTAssertEqual(output, "Hello, world!\\n")
-                        #endif
-                    }
-
-                    /// Returns path to the built products directory.
-                    var productsDirectory: URL {
-                      #if os(macOS)
-                        for bundle in Bundle.allBundles where bundle.bundlePath.hasSuffix(".xctest") {
-                            return bundle.bundleURL.deletingLastPathComponent()
-                        }
-                        fatalError("couldn't find the products directory")
-                      #else
-                        return Bundle.main.bundleURL
-                      #endif
+                        XCTAssertEqual(\(typeName)().text, "Hello, World!")
                     }
                 }