[bootstrap] Use a prebuilt swift-build from the Swift toolchain if one exists

Rather than building with CMake and then using that freshly built swift-build
to build it with itself, use a prebuilt swift-build next to swiftc if there is
one. The PackageDescription libraries are still built using CMake, as this
repo's Package.swift only builds the latest 4_2 version.

Author: finagolfin

CMakeLists.txt

@@ -37,18 +37,20 @@ option(USE_CMAKE_INSTALL
   "Install build products using cmake's install() instead of the bootstrap script's install()"
   ${CMAKE_INSTALL_DEFAULT})
 
-find_package(TSC CONFIG REQUIRED)
+if(BOOTSTRAP)
+  find_package(TSC CONFIG REQUIRED)
 
-find_package(LLBuild CONFIG)
-if(NOT LLBuild_FOUND)
-  find_package(LLBuild REQUIRED)
+  find_package(LLBuild CONFIG)
+  if(NOT LLBuild_FOUND)
+    find_package(LLBuild REQUIRED)
+  endif()
+
+  find_package(ArgumentParser CONFIG REQUIRED)
+  find_package(SwiftDriver CONFIG REQUIRED)
 endif()
 
 find_package(dispatch QUIET)
 find_package(Foundation QUIET)
 
-find_package(ArgumentParser CONFIG REQUIRED)
-find_package(SwiftDriver CONFIG REQUIRED)
-
 add_subdirectory(Sources)
 add_subdirectory(cmake/modules)

Utilities/bootstrap

@@ -292,14 +292,19 @@ def build(args):
     """Builds SwiftPM using a two-step process: first using CMake, then with itself."""
     parse_build_args(args)
 
+    # Don't bootstrap if the Swift toolchain already has a pre-built swift-build.
+    args.bootstrap = not os.path.exists(os.path.join(os.path.split(args.swiftc_path)[0], "swift-build"))
+
     # Build llbuild if its build path is not passed in.
     if not args.llbuild_build_dir:
         build_llbuild(args)
 
-    build_tsc(args)
-    build_yams(args)
-    build_swift_argument_parser(args)
-    build_swift_driver(args)
+    if args.bootstrap:
+        build_tsc(args)
+        build_yams(args)
+        build_swift_argument_parser(args)
+        build_swift_driver(args)
+
     build_swiftpm_with_cmake(args)
     build_swiftpm_with_swiftpm(args,integrated_swift_driver=False)
 
@@ -433,7 +438,7 @@ def install_binary(args, binary, dest_dir):
 # Build functions
 # -----------------------------------------------------------
 
-def build_with_cmake(args, cmake_args, source_path, build_dir):
+def build_with_cmake(args, cmake_args, source_path, build_dir, targets=[]):
     """Runs CMake if needed, then builds with Ninja."""
     cache_path = os.path.join(build_dir, "CMakeCache.txt")
     if args.reconfigure or not os.path.isfile(cache_path) or not args.swiftc_path in open(cache_path).read():
@@ -461,6 +466,8 @@ def build_with_cmake(args, cmake_args, source_path, build_dir):
     if args.verbose:
         ninja_cmd.append("-v")
 
+    ninja_cmd += targets
+
     call(ninja_cmd, cwd=build_dir, verbose=args.verbose)
 
 def build_llbuild(args):
@@ -558,19 +565,27 @@ def build_swiftpm_with_cmake(args):
     """Builds SwiftPM using CMake."""
     note("Building SwiftPM (with CMake)")
 
-    cmake_flags = [
-        get_llbuild_cmake_arg(args),
-        "-DTSC_DIR=" + os.path.join(args.tsc_build_dir, "cmake/modules"),
-        "-DYams_DIR=" + os.path.join(args.yams_build_dir, "cmake/modules"),
-        "-DArgumentParser_DIR=" + os.path.join(args.swift_argument_parser_build_dir, "cmake/modules"),
-        "-DSwiftDriver_DIR=" + os.path.join(args.swift_driver_build_dir, "cmake/modules"),
-    ]
+    if args.bootstrap:
+        cmake_flags = [
+            get_llbuild_cmake_arg(args),
+            "-DTSC_DIR=" + os.path.join(args.tsc_build_dir, "cmake/modules"),
+            "-DYams_DIR=" + os.path.join(args.yams_build_dir, "cmake/modules"),
+            "-DArgumentParser_DIR=" + os.path.join(args.swift_argument_parser_build_dir, "cmake/modules"),
+            "-DSwiftDriver_DIR=" + os.path.join(args.swift_driver_build_dir, "cmake/modules"),
+            "-DBOOTSTRAP:BOOL=ON",
+        ]
+    else:
+        cmake_flags = [ "-DBOOTSTRAP:BOOL=OFF" ]
 
     if platform.system() == 'Darwin':
         cmake_flags.append("-DCMAKE_C_FLAGS=-target %s%s" % (get_build_target(args), g_macos_deployment_target))
         cmake_flags.append("-DCMAKE_OSX_DEPLOYMENT_TARGET=%s" % g_macos_deployment_target)
 
-    build_with_cmake(args, cmake_flags, args.project_root, args.bootstrap_dir)
+    targets = []
+    if not args.bootstrap:
+        targets = ["PD4", "PD4_2"]
+
+    build_with_cmake(args, cmake_flags, args.project_root, args.bootstrap_dir, targets)
 
     if args.llbuild_link_framework:
         add_rpath_for_cmake_build(args, args.llbuild_build_dir)
@@ -582,15 +597,22 @@ def build_swiftpm_with_cmake(args):
 
 def build_swiftpm_with_swiftpm(args, integrated_swift_driver):
     """Builds SwiftPM using the version of SwiftPM built with CMake."""
-    note("Building SwiftPM (with swift-build)")
 
     swiftpm_args = [
         "SWIFT_EXEC=" + args.swiftc_path,
         "SWIFT_DRIVER_SWIFT_EXEC=" + args.swiftc_path,
-        "SWIFTPM_PD_LIBS=" + os.path.join(args.bootstrap_dir, "pm"),
-        os.path.join(args.bootstrap_dir, "bin/swift-build"),
-        "--disable-sandbox",
     ]
+
+    if args.bootstrap:
+        note("Building SwiftPM (with a freshly built swift-build)")
+        swiftpm_args.append("SWIFTPM_PD_LIBS=" + os.path.join(args.bootstrap_dir, "pm"))
+        swiftpm_args.append(os.path.join(args.bootstrap_dir, "bin/swift-build"))
+    else:
+        note("Building SwiftPM (with a prebuilt swift-build)")
+        swiftpm_args.append(os.path.join(os.path.split(args.swiftc_path)[0], "swift-build"))
+
+    swiftpm_args.append("--disable-sandbox")
+
     if integrated_swift_driver:
         swiftpm_args.append("--use-integrated-swift-driver")
 
@@ -660,18 +682,19 @@ def get_swiftpm_env_cmd(args):
     env_cmd.append("SWIFTCI_USE_LOCAL_DEPS=1")
     env_cmd.append("SWIFTPM_MACOS_DEPLOYMENT_TARGET=%s" % g_macos_deployment_target)
 
-    libs_joined = ":".join([
-        os.path.join(args.bootstrap_dir, "lib"),
-        os.path.join(args.tsc_build_dir, "lib"),
-        os.path.join(args.llbuild_build_dir, "lib"),
-        os.path.join(args.yams_build_dir, "lib"),
-        os.path.join(args.swift_argument_parser_build_dir, "lib"),
-        os.path.join(args.swift_driver_build_dir, "lib"),
-    ] + args.target_info["paths"]["runtimeLibraryPaths"])
+    if args.bootstrap:
+        libs_joined = ":".join([
+            os.path.join(args.bootstrap_dir, "lib"),
+            os.path.join(args.tsc_build_dir, "lib"),
+            os.path.join(args.llbuild_build_dir, "lib"),
+            os.path.join(args.yams_build_dir, "lib"),
+            os.path.join(args.swift_argument_parser_build_dir, "lib"),
+            os.path.join(args.swift_driver_build_dir, "lib"),
+        ] + args.target_info["paths"]["runtimeLibraryPaths"])
 
     if platform.system() == 'Darwin':
         env_cmd.append("DYLD_LIBRARY_PATH=%s" % libs_joined)
-    else:
+    elif args.bootstrap:
         env_cmd.append("LD_LIBRARY_PATH=%s" % libs_joined)
 
     return env_cmd