build: add an initial CMake based build system for DocC (#818)

* build: add an initial CMake based build system for DocC

This allows us to cross-compile DocC and reduce the size of the binary
by sharing the toolchain artifacts.

* Update CONTRIBUTING.md

Co-authored-by: David Rönnqvist <ronnqvist@apple.com>

---------

Co-authored-by: David Rönnqvist <ronnqvist@apple.com>

Author: compnerd

CMakeLists.txt

@@ -0,0 +1,42 @@
+#[[
+This source file is part of the Swift open source project
+
+Copyright © 2014 - 2025 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 3.24)
+
+project(SwiftDocC
+  LANGUAGES Swift)
+
+set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
+set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
+
+set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/swift)
+set(CMAKE_Swift_COMPILE_OPTIONS_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
+set(CMAKE_Swift_LANGUAGE_VERSION 5)
+
+enable_language(C)
+include(GNUInstallDirs)
+
+# NOTE(compnerd) workaround CMake issues
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-swift-version 5>")
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-upcoming-feature ConciseMagicFile>")
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-upcoming-feature ExistentialAny>")
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:SHELL:-enable-upcoming-feature InternalImportsByDefault>")
+
+find_package(ArgumentParser)
+find_package(SwiftASN1)
+find_package(SwiftCrypto)
+find_package(SwiftMarkdown)
+find_package(LMDB)
+find_package(SymbolKit)
+find_package(cmark-gfm)
+
+add_compile_options("$<$<COMPILE_LANGUAGE:Swift>:-package-name;SwiftDocC>")
+
+add_subdirectory(Sources)

CONTRIBUTING.md

@@ -350,7 +350,32 @@ by running the test suite in a Docker environment that simulates Swift on Linux.
     cd swift-docc
     swift run docc
     ```
-    
+
+## Updating Build Rules
+
+In order to build DocC as part of the Windows toolchain distribution uniformly,
+a parallel CMake based build exists. Note that this is **not** supported for
+development purposes (you cannot execute the test suite with this build).
+
+CMake requires that the full file list is kept up-to-date. When adding or
+removing files in a given module, the `CMakeLists.txt` list must be updated to
+the file list.
+
+The 1-line script below lists all the Swift files in the current directory tree. 
+You can use the script's output to replace the list of files in the CMakeLists.txt file for each target that you added files to or removed files from.
+
+```bash
+python -c "print('\n'.join((f'{chr(34)}{path}{chr(34)}' if ' ' in path else path) for path in sorted(str(path) for path in __import__('pathlib').Path('.').rglob('*.swift'))))"
+```
+
+This should provide the listing of files in the module that can be used to
+update the `CMakeLists.txt` associated with the target.
+
+In the case that a new target is added to the project, the new directory would
+need to add the new library or executable target (`add_library` and
+`add_executable` respectively) and the new target subdirectory must be listed in
+the `Sources/CMakeLists.txt` (via `add_subdirectory`).
+
 ## Continuous Integration
 
 Swift-DocC uses [swift-ci](https://ci.swift.org) infrastructure for its continuous integration

Sources/CMakeLists.txt

@@ -0,0 +1,12 @@
+#[[
+This source file is part of the Swift open source project
+
+Copyright © 2014 - 2025 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_subdirectory(SwiftDocC)
+add_subdirectory(SwiftDocCUtilities)
+add_subdirectory(docc)