Initial Commit: Adding initial projects

 - The first project is a single-file "Hello World" program written in
   Swift.

 - The second project is a library and executable, both are written in
   Swift.

 - The third project demonstrates Swift/C++ interop, where a library
   containing mixes C++ and Swift sources is linked into a C++
   executable and a Swift executable.

Author: etcwilde

.mailmap

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+Evan Wilde <[email protected]> <[email protected]>

1_single_executable/CMakeLists.txt

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+# This source file is part of the Swift open source project
+#
+# Copyright (c) 2023 Apple Inc. and the Swift project authors.
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See https://swift.org/LICENSE.txt for license information
+
+cmake_minimum_required(VERSION 3.22)
+
+project(hello LANGUAGES Swift)
+
+add_executable(hello hello.swift)

1_single_executable/Readme.md

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+# Hello World
+
+This is the simplest usage of Swift and CMake, building a single swift
+executable.
+
+## Build Instructions
+
+### macOS and Linux:
+
+```sh
+$ mkdir build && cd build
+$ cmake -G 'Ninja' ../
+$ ninja hello
+$ ./hello
+Hello, world!
+```
+
+## Build Results
+
+Building this project results in a single executable, `hello` in the build
+directory.

1_single_executable/hello.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift project authors.
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+print("Hello, world!")

2_executable_library/CMakeLists.txt

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+# This source file is part of the Swift open source project
+#
+# Copyright (c) 2023 Apple Inc. and the Swift project authors.
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See https://swift.org/LICENSE.txt for license information
+
+cmake_minimum_required(VERSION 3.22)
+project(Project2 LANGUAGES Swift)
+
+add_subdirectory("lib/")
+add_subdirectory("src/")

2_executable_library/Readme.md

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+# Factorials
+
+This program demonstrates using CMake to build a Swift executable that uses a
+Swift library.
+
+## Build Instructions
+
+### macOS and Linux:
+
+```sh
+$ mkdir build && cd build
+$ cmake -G 'Ninja' ../
+$ ninja factorials
+$ ./src/factorials
+
+factorial(0) = 1
+factorial(1) = 1
+factorial(2) = 2
+factorial(3) = 6
+factorial(4) = 24
+factorial(5) = 120
+factorial(6) = 720
+factorial(7) = 5040
+factorial(8) = 40320
+factorial(9) = 362880
+factorial(10) = 3628800
+```
+
+## Build Results
+
+This project results in two primary build products, the `factorial` library, and
+the `factorials` executable The library and the corresponding swiftmodule live
+under the `lib/` directory, while the executable lives under the `src/`
+directory.

2_executable_library/lib/CMakeLists.txt

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+# This source file is part of the Swift open source project
+#
+# Copyright (c) 2023 Apple Inc. and the Swift project authors.
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See https://swift.org/LICENSE.txt for license information
+
+add_library(factorial factorial.swift)

2_executable_library/lib/factorial.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift project authors.
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+public func factorial(x: Int) -> Int {
+    if x <= 0 {
+        return 1
+    }
+    return x * factorial(x: x - 1)
+}

2_executable_library/src/CMakeLists.txt

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+# This source file is part of the Swift open source project
+#
+# Copyright (c) 2023 Apple Inc. and the Swift project authors.
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See https://swift.org/LICENSE.txt for license information
+
+add_executable(factorials main.swift)
+target_link_libraries(factorials PRIVATE factorial)

2_executable_library/src/main.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2023 Apple Inc. and the Swift project authors.
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import factorial
+
+for x in 0...10 {
+    print("factorial(\(x)) = \(factorial(x: x))")
+}