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=135033093

2 files changed, 24 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java
index 5d2830a049..3d71ca5ad8 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleCommandLineOptions.java
@@ -227,6 +227,17 @@ public class AppleCommandLineOptions extends FragmentOptions {
     }
   }
 
+  @Option(
+    name = "xcode_toolchain",
+    defaultValue = "null",
+    category = "flags",
+    help = "The identifier of an Xcode toolchain to use for builds. Currently only the toolchains "
+           + "that ship with Xcode are supported. For example, in addition to the default toolchain"
+           + " Xcode 8 has 'com.apple.dt.toolchain.Swift_2_3' which can be used for building legacy"
+           + " Swift code."
+  )
+  public String xcodeToolchain;
+
   @Option(name = "apple_bitcode",
       converter = AppleBitcodeMode.Converter.class,
       // TODO(blaze-team): Default to embedded_markers when fully implemented.
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java
index 59a6fc1403..e0d242703f 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleConfiguration.java
@@ -84,6 +84,7 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
   private final ImmutableList<String> tvosCpus;
   private final AppleBitcodeMode bitcodeMode;
   private final Label xcodeConfigLabel;
+  @Nullable private final String xcodeToolchain;
   @Nullable private final Label defaultProvisioningProfileLabel;
   private final boolean disableNativeSwiftRules;
 
@@ -127,6 +128,7 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
     this.xcodeConfigLabel =
         Preconditions.checkNotNull(appleOptions.xcodeVersionConfig, "xcodeConfigLabel");
     this.defaultProvisioningProfileLabel = appleOptions.defaultProvisioningProfile;
+    this.xcodeToolchain = appleOptions.xcodeToolchain;
     this.disableNativeSwiftRules = appleOptions.disableNativeSwiftRules;
   }
 
@@ -519,6 +521,17 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
     return Joiner.on('-').join(components);
   }
 
+  /** Returns the identifier for an Xcode toolchain to use with tools. */
+  @SkylarkCallable(
+    name = "xcode_toolchain",
+    doc = "Identifier for the custom Xcode toolchain to use in build or None if not specified",
+    allowReturnNones = true,
+    structField = true
+  )
+  public String getXcodeToolchain() {
+    return xcodeToolchain;
+  }
+
   /**
    * Whether the native Swift support should be disabled. Used to deprecate said functionality.
    */