build-script: allow non-zero exit codes from 'xcodebuild -version -sdk'

Under certain obscure circumstances (incomplete SDKs), xcodebuild can
successfully work with the SDK and print its version number, but will
still exit with a non-zero code.  This change works around the issue by
ignoring the exit code.

Author: gribozavr

utils/swift_build_support/swift_build_support/debug.py

@@ -29,8 +29,12 @@ def print_xcodebuild_versions(file=sys.stdout):
     """
     version = shell.capture(
         ['xcodebuild', '-version'], dry_run=False, echo=False).rstrip()
+    # Allow non-zero exit codes.  Under certain obscure circumstances
+    # xcodebuild can exit with an non-zero exit code even when the SDK is
+    # usable.
     sdks = shell.capture(
-        ['xcodebuild', '-version', '-sdk'], dry_run=False, echo=False).rstrip()
+        ['xcodebuild', '-version', '-sdk'], dry_run=False, echo=False,
+        allow_non_zero_exit=True).rstrip()
     fmt = """\
 {version}
 

utils/swift_build_support/swift_build_support/shell.py

@@ -92,7 +92,7 @@ def call(command, stderr=None, env=None, dry_run=None, echo=True):
 
 
 def capture(command, stderr=None, env=None, dry_run=None, echo=True,
-            optional=False):
+            optional=False, allow_non_zero_exit=False):
     """
     capture(command, ...) -> str
 
@@ -114,6 +114,8 @@ def capture(command, stderr=None, env=None, dry_run=None, echo=True,
         # Coerce to `str` hack. not py3 `byte`, not py2 `unicode`.
         return str(out.decode())
     except subprocess.CalledProcessError as e:
+        if allow_non_zero_exit:
+            return e.output
         if optional:
             return None
         diagnostics.fatal(

utils/swift_build_support/tests/test_shell.py

@@ -71,6 +71,10 @@ def test_capture(self):
 
         self.assertIsNone(shell.capture(["false"], optional=True))
 
+        self.assertEqual(
+            shell.capture(["sh", "-c", "echo foo && false"],
+                          allow_non_zero_exit=True), "foo\n")
+
         with self.assertRaises(SystemExit):
             shell.capture(["**not-a-command**"], optional=True)