[build-script] Set TOOLCHAIN_PREFIX in Python

Rather than setting the path to the .xctoolchain in the build-script-impl
shellscript, do so in the Python build-script. A small step towards
achieving SR-237.

Author: modocache

utils/build-script

@@ -14,6 +14,7 @@ from __future__ import print_function
 import argparse
 import multiprocessing
 import os
+import platform
 import shutil
 import sys
 import textwrap
@@ -761,6 +762,12 @@ the number of parallel build jobs to use""",
             "--skip-build-benchmarks",
         ]
 
+    if platform.system() == 'Darwin':
+        build_script_impl_inferred_args += [
+            "--toolchain-prefix",
+            swift_build_support.targets.darwin_toolchain_prefix(args.install_prefix),
+        ]
+
     if args.build_subdir is None:
         # Create a name for the build directory.
         args.build_subdir = args.cmake_generator.replace(" ", "_")

utils/build-script-impl

@@ -86,6 +86,7 @@ KNOWN_SETTINGS=(
     cmake-generator             "Unix Makefiles" "kind of build system to generate; see output of 'cmake --help' for choices"
     verbose-build               ""               "print the commands executed during the build"
     install-prefix              ""               "installation prefix"
+    toolchain-prefix            ""               "the path to the .xctoolchain directory that houses the install prefix path"
     install-destdir             ""               "the path to use as the filesystem root for the installation"
     install-symroot             ""               "the path to install debug symbols into"
     swift-install-components    ""               "a semicolon-separated list of Swift components to install"
@@ -714,15 +715,6 @@ function true_false() {
     esac
 }
 
-#
-# Set default values for command-line parameters.
-#
-
-if [[ "$(uname -s)" == "Darwin" ]] ; then
-    TOOLCHAIN_PREFIX=$(echo ${INSTALL_PREFIX} | sed -E 's/\/usr$//')
-fi
-
-
 # A list of deployment targets to cross-compile the Swift host tools for.
 # We can't run the resulting binaries on the build machine.
 CROSS_TOOLS_DEPLOYMENT_TARGETS=()

utils/swift_build_support/swift_build_support/targets.py

@@ -8,6 +8,7 @@
 # See http://swift.org/LICENSE.txt for license information
 # See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
+import os
 import platform
 
 
@@ -56,3 +57,12 @@ def install_prefix():
         return '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr'
     else:
         return '/usr'
+
+
+def darwin_toolchain_prefix(darwin_install_prefix):
+    """
+    Given the install prefix for a Darwin system, and assuming that that path
+    is to a .xctoolchain directory, return the path to the .xctoolchain
+    directory.
+    """
+    return os.path.split(darwin_install_prefix)[0]