[build] Make it possible to actually build the stdlib with a prebuilt clang

Author: finagolfin

CMakeLists.txt

@@ -487,6 +487,14 @@ else()
   set(SWIFT_CROSS_COMPILING TRUE)
 endif()
 
+# Check if a prebuilt clang path was passed in, as this variable will be
+# assigned if not, in SwiftSharedCMakeConfig.
+if("${SWIFT_NATIVE_CLANG_TOOLS_PATH}" STREQUAL "")
+  set(SWIFT_PREBUILT_CLANG FALSE)
+else()
+  set(SWIFT_PREBUILT_CLANG TRUE)
+endif()
+
 include(SwiftSharedCMakeConfig)
 
 # NOTE: We include this before SwiftComponents as it relies on some LLVM CMake

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -1669,7 +1669,8 @@ function(add_swift_target_library name)
     list(APPEND SWIFTLIB_SWIFT_COMPILE_FLAGS "-warn-implicit-overrides")
   endif()
 
-  if(NOT SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER AND NOT BUILD_STANDALONE)
+  if(NOT SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER AND NOT BUILD_STANDALONE AND
+     NOT SWIFT_PREBUILT_CLANG)
     list(APPEND SWIFTLIB_DEPENDS clang)
   endif()
 

stdlib/public/SwiftShims/CMakeLists.txt

@@ -111,7 +111,8 @@ endif()
 # First extract the "version" used for Clang's resource directory.
 string(REGEX MATCH "[0-9]+\\.[0-9]+(\\.[0-9]+)?" CLANG_VERSION
   "${LLVM_PACKAGE_VERSION}")
-if(NOT SWIFT_INCLUDE_TOOLS AND SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER)
+if(NOT SWIFT_INCLUDE_TOOLS AND
+   (SWIFT_BUILD_RUNTIME_WITH_HOST_COMPILER OR SWIFT_PREBUILT_CLANG))
   if(SWIFT_COMPILER_IS_MSVC_LIKE)
     execute_process(COMMAND ${CMAKE_C_COMPILER} /clang:-print-resource-dir
       OUTPUT_VARIABLE clang_headers_location

utils/build-presets.ini

@@ -2283,10 +2283,9 @@ skip-build-cmark
 skip-build-benchmarks
 skip-test-cmark
 
-# This triggers the stdlib standalone build: Don't build tools (the compiler),
-# assume we are working with the host compiler.
+# This triggers the stdlib standalone build: don't build the native tools from
+# scratch, ie the compiler.
 build-swift-tools=0
-build-runtime-with-host-compiler=1
 
 # Then set the paths to our native tools. If compiling against a toolchain,
 # these should all be the ./usr/bin directory.

utils/build-script-impl

@@ -1485,13 +1485,6 @@ for host in "${ALL_HOSTS[@]}"; do
         fi
     fi
 
-    if [[ "${NATIVE_CLANG_TOOLS_PATH}" ]] ; then
-        common_cmake_options_host+=(
-                -DCMAKE_C_COMPILER="${NATIVE_CLANG_TOOLS_PATH}/clang"
-                -DCMAKE_CXX_COMPILER="${NATIVE_CLANG_TOOLS_PATH}/clang++"
-            )
-    fi
-
     llvm_cmake_options=(
         "${llvm_cmake_options[@]}"
         -DCMAKE_INSTALL_PREFIX:PATH="$(get_host_install_prefix ${host})"