Roll forward of commit deeeb31f8ba0f196fbc9ca2a177d59d57ea50b32.

* Fixed breakage in shell tools with an old bazel binary.

Rollback of commit deeeb31f8ba0f196fbc9ca2a177d59d57ea50b32.

*** Reason for rollback ***

Breaks builds with current blaze

*** Original change description ***

Add a way to select non-default Xcode toolchain

* Adds a flag --xcode_toolchain which sets TOOLCHAINS env variable for xcrun.
* Updates swift_library to work with this flag when selecting Swift runtime
location.
* By default the flag has a null value and is not set in env.

--
MOS_MIGRATED_REVID=135238820

1 files changed, 36 insertions, 2 deletions

diff --git a/tools/build_defs/apple/swift.bzl b/tools/build_defs/apple/swift.bzl
index 9b496688a7..3cc22fe44b 100644
--- a/tools/build_defs/apple/swift.bzl
+++ b/tools/build_defs/apple/swift.bzl
@@ -78,6 +78,39 @@ def _module_name(ctx):
   """Returns a module name for the given rule context."""
   return ctx.label.package.lstrip("//").replace("/", "_") + "_" + ctx.label.name
 
+def _swift_lib_dir(ctx):
+  """Returns the location of swift runtime directory to link against."""
+  # TODO(dmishe): Expose this template from native code.
+  developer_dir = "__BAZEL_XCODE_DEVELOPER_DIR__"
+  platform_str = ctx.fragments.apple.single_arch_platform.name_in_plist.lower()
+
+  toolchain_name = "XcodeDefault"
+  if hasattr(ctx.fragments.apple, "xcode_toolchain"):
+    toolchain = ctx.fragments.apple.xcode_toolchain
+
+    # We cannot use non Xcode-packaged toolchains, and the only one non-default
+    # toolchain known to exist (as of Xcode 8.1) is this one.
+    # TODO(b/29338444): Write an integration test when Xcode 8 is available.
+    if toolchain == "com.apple.dt.toolchain.Swift_2_3":
+      toolchain_name = "Swift_2.3"
+
+  return "{0}/Toolchains/{1}.xctoolchain/usr/lib/swift/{2}".format(
+      developer_dir, toolchain_name, platform_str)
+
+def _swift_linkopts(ctx):
+  """Returns additional linker arguments for the given rule context."""
+  return set(["-L" + _swift_lib_dir(ctx)])
+
+def _swift_xcrun_args(ctx):
+  """Returns additional arguments that should be passed to xcrun."""
+  # TODO(dmishe): Remove this check when xcode_toolchain is available by default
+  args = []
+  if hasattr(ctx.fragments.apple, "xcode_toolchain"):
+    if ctx.fragments.apple.xcode_toolchain:
+      args += ["--toolchain", ctx.fragments.apple.xcode_toolchain]
+
+  return args
+
 def _swift_library_impl(ctx):
   """Implementation for swift_library Skylark rule."""
   # TODO(b/29772303): Assert xcode version.
@@ -202,7 +235,7 @@ def _swift_library_impl(ctx):
       # https://llvm.org/bugs/show_bug.cgi?id=19501
       + ["-fmodule-map-file=%s" % x.path for x in objc_module_maps])
 
-  args = [
+  args = _swift_xcrun_args(ctx) + [
       "swiftc",
       "-emit-object",
       "-emit-module-path",
@@ -253,7 +286,8 @@ def _swift_library_impl(ctx):
       library=set([output_lib] + dep_libs),
       header=set([output_header]),
       providers=objc_providers,
-      uses_swift=True)
+      linkopt=_swift_linkopts(ctx),
+      uses_swift=True,)
 
   return struct(
       swift=struct(