Add linux support

Author: finestructure

Package.swift

@@ -36,7 +36,7 @@ let package = Package(
             ]
         ),
         .testTarget(
-            name: "ReleaseNotesCoreTests",
+            name: "ReleaseNotesTests",
             dependencies: ["ReleaseNotesCore"]
         ),
     ]

Sources/ReleaseNotesCore/App.swift

@@ -1,9 +1,8 @@
 import ArgumentParser
 
 
-@main
-struct App {
-    static func main() async {
+public struct App {
+    public static func main() async {
         await ReleaseNotes.main()
     }
 }

Sources/ReleaseNotesCore/Parser.swift

@@ -1,6 +1,5 @@
 import Parsing
 import SemanticVersion
-import Darwin
 
 
 enum Parser {

Sources/swift-release-notes/main.swift

@@ -0,0 +1,12 @@
+import Foundation
+import ReleaseNotesCore
+
+
+let group = DispatchGroup()
+group.enter()
+Task {
+    defer { group.leave() }
+    await App.main()
+}
+
+group.wait()

Sources/swift-release-notes/release-notes.swift

@@ -0,0 +1,47 @@
+import XCTest
+import class Foundation.Bundle
+
+
+final class LaunchTests: XCTestCase {
+
+    func test_launch() throws {
+        let process = Process()
+        process.executableURL = productsDirectory
+            .appendingPathComponent("swift-release-notes")
+        process.arguments = ["--help"]
+
+        let pipe = Pipe()
+        process.standardOutput = pipe
+
+        try process.run()
+        process.waitUntilExit()
+
+        let data = pipe.fileHandleForReading.readDataToEndOfFile()
+        let output = try XCTUnwrap(String(data: data, encoding: .utf8))
+
+        XCTAssertEqual(output, """
+            USAGE: release-notes [<working-direcory>]
+
+            ARGUMENTS:
+              <working-direcory>      (default: .)
+
+            OPTIONS:
+              -h, --help              Show help information.
+
+
+            """)
+    }
+
+    /// 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
+    }
+
+}