build: introduce a CMake based build

This enables building DocC as a CMake project. Doing so is motivated by
toolchain build times. By using CMake instead of SPM, we see an overall
reduction of ~7% in the total toolchain build time on Windows.

CMakeLists.txt

@@ -0,0 +1,23 @@
+#[[
+This source file is part of the DocC open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC 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(SymbolKit
+  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)
+
+add_subdirectory(Sources)
+add_subdirectory(cmake/modules)

Sources/CMakeLists.txt

@@ -0,0 +1,10 @@
+#[[
+This source file is part of the DocC open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+#]]
+
+add_subdirectory(SymbolKit)

Sources/SymbolKit/CMakeLists.txt

@@ -0,0 +1,69 @@
+#[[
+This source file is part of the DocC open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+#]]
+
+add_library(SymbolKit
+  Mixin/Mixin+Equals.swift
+  Mixin/Mixin+Hash.swift
+  Mixin/Mixin.swift
+  SymbolGraph/AnyScalar.swift
+  SymbolGraph/LineList/LineList.swift
+  SymbolGraph/LineList/SourceRange/Position.swift
+  SymbolGraph/LineList/SourceRange/SourceRange.swift
+  SymbolGraph/Metadata.swift
+  SymbolGraph/Module.swift
+  SymbolGraph/OperatingSystem.swift
+  SymbolGraph/Platform.swift
+  SymbolGraph/Relationship/ReferenceLocation.swift
+  SymbolGraph/Relationship/Relationship.swift
+  SymbolGraph/Relationship/RelationshipKind.swift
+  SymbolGraph/Relationship/SourceOrigin.swift
+  SymbolGraph/Relationship/Swift/GenericConstraints.swift
+  SymbolGraph/Relationship/Swift/Swift.swift
+  SymbolGraph/SemanticVersion.swift
+  SymbolGraph/Symbol/AccessControl.swift
+  SymbolGraph/Symbol/AlternateDeclarations.swift
+  SymbolGraph/Symbol/Availability/Availability.swift
+  SymbolGraph/Symbol/Availability/AvailabilityItem.swift
+  SymbolGraph/Symbol/Availability/Domain.swift
+  SymbolGraph/Symbol/DeclarationFragments/DeclarationFragments+Simplify.swift
+  SymbolGraph/Symbol/DeclarationFragments/DeclarationFragments.swift
+  SymbolGraph/Symbol/DeclarationFragments/Fragment/Fragment.swift
+  SymbolGraph/Symbol/DeclarationFragments/Fragment/FragmentKind.swift
+  SymbolGraph/Symbol/FunctionSignature/FunctionParameter.swift
+  SymbolGraph/Symbol/FunctionSignature/FunctionSignature.swift
+  SymbolGraph/Symbol/HTTP/HTTP.swift
+  SymbolGraph/Symbol/Identifier.swift
+  SymbolGraph/Symbol/KindIdentifier.swift
+  SymbolGraph/Symbol/Location.swift
+  SymbolGraph/Symbol/Mutability.swift
+  SymbolGraph/Symbol/Names.swift
+  SymbolGraph/Symbol/OverloadData.swift
+  SymbolGraph/Symbol/PlistDetails.swift
+  SymbolGraph/Symbol/Snippet.swift
+  SymbolGraph/Symbol/SPI.swift
+  SymbolGraph/Symbol/Swift/Extension.swift
+  SymbolGraph/Symbol/Swift/GenericConstraint.swift
+  SymbolGraph/Symbol/Swift/GenericParameter.swift
+  SymbolGraph/Symbol/Swift/Generics.swift
+  SymbolGraph/Symbol/Swift/Namespace.swift
+  SymbolGraph/Symbol/Symbol.swift
+  SymbolGraph/Symbol/SymbolKind.swift
+  SymbolGraph/Symbol/ValueConstraints.swift
+  SymbolGraph/SymbolGraph+Overloads.swift
+  SymbolGraph/SymbolGraph.swift
+  UnifiedSymbolGraph/GraphCollector.swift
+  UnifiedSymbolGraph/UnifiedSymbol+Encodable.swift
+  UnifiedSymbolGraph/UnifiedSymbol.swift
+  UnifiedSymbolGraph/UnifiedSymbolGraph+Encodable.swift
+  UnifiedSymbolGraph/UnifiedSymbolGraph+Overloads.swift
+  UnifiedSymbolGraph/UnifiedSymbolGraph.swift)
+set_target_properties(SymbolKit PROPERTIES
+  INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_Swift_MODULE_DIRECTORY})
+
+set_property(GLOBAL APPEND PROPERTY SYMBOLKIT_EXPORTS SymbolKit)

cmake/modules/CMakeLists.txt

@@ -0,0 +1,19 @@
+#[[
+This source file is part of the DocC open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+#]]
+
+set(SYMBOLKIT_EXPORTS_FILE
+  ${CMAKE_CURRENT_BINARY_DIR}/SymbolKitExports.cmake)
+configure_file(SymbolKitConfig.cmake.in
+  ${CMAKE_CURRENT_BINARY_DIR}/SymbolKitConfig.cmake)
+
+get_property(SYMBOLKIT_EXPORTS GLOBAL PROPERTY SYMBOLKIT_EXPORTS)
+export(TARGETS ${SYMBOLKIT_EXPORTS}
+  NAMESPACE DocC::
+  FILE ${SYMBOLKIT_EXPORTS_FILE}
+  EXPORT_LINK_INTERFACE_LIBRARIES)

cmake/modules/SymbolKitConfig.cmake.in

@@ -0,0 +1,12 @@
+#[[
+This source file is part of the DocC open source project
+
+Copyright (c) 2024 Apple Inc. and the DocC project authors
+Licensed under Apache License v2.0 with Runtime Library Exception
+
+See https://swift.org/LICENSE.txt for license information
+#]]
+
+if(NOT TARGET DocC::SymbolKit)
+  include("@SYMBOLKIT_EXPORTS_FILE@")
+endif()