[build-script] Add an option for cleaning the install destdir

Useful to make sure that one is not hitting weird behavior due to a stale just
built toolchain.

Author: gottesmm

utils/build-script

@@ -664,6 +664,10 @@ def main_normal():
                                         ".build_script_log")
         open(build_script_log, 'w').close()
 
+    if args.clean_install_destdir:
+        sys.stdout.write("Cleaning install destdir!\n")
+        shell.rmtree(args.install_destdir)
+
     # Build ninja if required, which will update the toolchain.
     if args.build_ninja:
         invocation.build_ninja()

utils/build_swift/build_swift/driver_arguments.py

@@ -698,6 +698,9 @@ def create_argument_parser():
     option(['-c', '--clean'], store_true,
            help='do a clean build')
 
+    option(['--clean-install-destdir'], store_true,
+           help='Clean the install destroot before building.')
+
     option('--export-compile-commands', toggle_true,
            help='generate compilation databases in addition to building')
 

utils/build_swift/tests/expected_options.py

@@ -269,6 +269,7 @@
     'watchos': False,
     'watchos_all': False,
     'llvm_install_components': defaults.llvm_install_components(),
+    'clean_install_destdir': False,
 }
 
 
@@ -484,6 +485,7 @@ class BuildScriptImplOption(_BaseOption):
                   dest='install_backdeployconcurrency'),
     SetTrueOption('--benchmark'),
     SetTrueOption('--clean'),
+    SetTrueOption('--clean-install-destdir'),
     SetTrueOption('--dry-run'),
     SetTrueOption('--dump-config'),
     SetTrueOption('--disable-guaranteed-normal-arguments'),

validation-test/BuildSystem/clean_install_destroot.test

@@ -0,0 +1,10 @@
+# REQUIRES: standalone_build
+# REQUIRES: OS=macosx
+
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --cmake %cmake --clean-install-destdir --verbose-build 2>&1 | %FileCheck %s
+
+# CHECK: Cleaning install destdir!
+# CHECK-NEXT: rm -rf
+