Redesign xcode_config rule to be evaluated at the level of configuration instead of target depss

--
MOS_MIGRATED_REVID=113398355

12 files changed, 229 insertions, 206 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 5ad748a217..de868a123f 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
@@ -131,6 +131,7 @@ public class AppleCommandLineOptions extends FragmentOptions {
     if (getPlatform() == Platform.IOS_DEVICE) {
       labelMap.put("default_provisioning_profile", defaultProvisioningProfile);
     }
+    labelMap.put("xcode_version_config", xcodeVersionConfig);
   }
   
   /**
@@ -193,6 +194,7 @@ public class AppleCommandLineOptions extends FragmentOptions {
     AppleCommandLineOptions host = (AppleCommandLineOptions) super.getHost(fallback);
 
     // Set options needed in the host configuration.
+    host.xcodeVersionConfig = xcodeVersionConfig;
     host.xcodeVersion = xcodeVersion;
     host.appleBitcodeMode = appleBitcodeMode;
 
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 73096ec15a..01265a618f 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
@@ -48,17 +48,20 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
    **/
   public static final String APPLE_SDK_PLATFORM_ENV_NAME = "APPLE_SDK_PLATFORM";
 
+  private static final DottedVersion MINIMUM_BITCODE_XCODE_VERSION = DottedVersion.fromString("7");
+
   private final DottedVersion iosSdkVersion;
   private final String iosCpu;
-  private final Optional<DottedVersion> xcodeVersionOverride;
+  private final Optional<DottedVersion> xcodeVersion;
   private final List<String> iosMultiCpus;
   private final AppleBitcodeMode bitcodeMode;
   private final Label xcodeConfigLabel;
   @Nullable private final Label defaultProvisioningProfileLabel;
 
-  AppleConfiguration(AppleCommandLineOptions appleOptions) {
+  AppleConfiguration(AppleCommandLineOptions appleOptions,
+      Optional<DottedVersion> xcodeVersionOverride) {
     this.iosSdkVersion = Preconditions.checkNotNull(appleOptions.iosSdkVersion, "iosSdkVersion");
-    this.xcodeVersionOverride = Optional.fromNullable(appleOptions.xcodeVersion);
+    this.xcodeVersion = Preconditions.checkNotNull(xcodeVersionOverride);
     this.iosCpu = Preconditions.checkNotNull(appleOptions.iosCpu, "iosCpu");
     this.iosMultiCpus = Preconditions.checkNotNull(appleOptions.iosMultiCpus, "iosMultiCpus");
     this.bitcodeMode = appleOptions.appleBitcodeMode;
@@ -76,14 +79,12 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
   }
 
   /**
-   * Returns the value of the xcode version build flag if available. This is obtained directly from
-   * the {@code --xcode_version} build flag.
-   * 
-   * <p>Most rules should avoid using this flag value, and instead obtain the appropriate xcode
-   * version from {@link XcodeConfigProvider#getXcodeVersion}.
+   * Returns the value of the xcode version, if available. This is determined based on a combination
+   * of the {@code --xcode_version} build flag and the {@code xcode_config} target defined in the
+   * {@code --xcode_version_config} flag.
    */
-  public Optional<DottedVersion> getXcodeVersionOverrideFlag() {
-    return xcodeVersionOverride;
+  public Optional<DottedVersion> getXcodeVersion() {
+    return xcodeVersion;
   }
 
   /**
@@ -97,6 +98,20 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
     mapBuilder.putAll(appleTargetPlatformEnv(Platform.forIosArch(getIosCpu())));
     return mapBuilder.build();
   }
+  
+  /**
+   * Returns a map of environment variables that should be propagated for actions that build on an
+   * apple host system. These environment variables are needed by the apple toolchain. Keys are
+   * variable names and values are their corresponding values.
+   */
+  public Map<String, String> getAppleHostSystemEnv() {
+    Optional<DottedVersion> xcodeVersion = getXcodeVersion();
+    ImmutableMap.Builder<String, String> builder = ImmutableMap.builder();
+    if (xcodeVersion.isPresent()) {
+      builder.put(AppleConfiguration.XCODE_VERSION_ENV_NAME, xcodeVersion.get().toString());
+    }
+    return builder.build();   
+  }
 
   /**
    * Returns a map of environment variables (derived from configuration) that should be propagated
@@ -198,8 +213,23 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
     public AppleConfiguration create(ConfigurationEnvironment env, BuildOptions buildOptions)
         throws InvalidConfigurationException {
       AppleCommandLineOptions appleOptions = buildOptions.get(AppleCommandLineOptions.class);
+      Optional<DottedVersion> xcodeVersionFlag = getXcodeVersion(env, appleOptions);
+      AppleConfiguration configuration = new AppleConfiguration(appleOptions, xcodeVersionFlag);
 
-      return new AppleConfiguration(appleOptions);
+      validate(configuration);
+      return configuration;
+    }
+
+    private void validate(AppleConfiguration config)
+        throws InvalidConfigurationException {
+      Optional<DottedVersion> xcodeVersion = config.getXcodeVersion();
+      if (config.getBitcodeMode() != AppleBitcodeMode.NONE
+          && xcodeVersion.isPresent()
+          && xcodeVersion.get().compareTo(MINIMUM_BITCODE_XCODE_VERSION) < 0) {
+        throw new InvalidConfigurationException(
+            String.format("apple_bitcode mode '%s' is unsupported for xcode version '%s'",
+                config.getBitcodeMode(), xcodeVersion.get()));
+      }
     }
 
     @Override
@@ -211,5 +241,26 @@ public class AppleConfiguration extends BuildConfiguration.Fragment {
     public ImmutableSet<Class<? extends FragmentOptions>> requiredOptions() {
       return ImmutableSet.<Class<? extends FragmentOptions>>of(AppleCommandLineOptions.class);
     }
+    
+    /**
+     * Uses the {@link AppleCommandLineOptions#xcodeVersion} and
+     * {@link AppleCommandLineOptions#xcodeVersionConfig} command line options to determine and
+     * return the effective xcode version. Returns absent if no explicit xcode version is
+     * declared, and host system defaults should be used.
+     *
+     * @param env the current configuration environment
+     * @param appleOptions the command line options
+     * @throws InvalidConfigurationException if the options given (or configuration targets) were
+     *     malformed and thus the xcode version could not be determined
+     */
+    private Optional<DottedVersion> getXcodeVersion(ConfigurationEnvironment env,
+        AppleCommandLineOptions appleOptions) throws InvalidConfigurationException {
+      Optional<DottedVersion> xcodeVersionCommandLineFlag = 
+          Optional.fromNullable(appleOptions.xcodeVersion);
+      Label xcodeVersionConfigLabel = appleOptions.xcodeVersionConfig;
+
+      return XcodeConfig.resolveXcodeVersion(env, xcodeVersionConfigLabel,
+          xcodeVersionCommandLineFlag, "xcode_version_config");
+    }
   }
 }
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleToolchain.java b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleToolchain.java
index e05b686760..bf55f10a67 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/AppleToolchain.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/AppleToolchain.java
@@ -20,7 +20,6 @@ import static com.google.devtools.build.lib.packages.BuildType.LABEL;
 
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.Function;
-import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.analysis.RuleDefinition;
@@ -34,8 +33,6 @@ import com.google.devtools.build.lib.packages.RuleClass.Builder;
 import com.google.devtools.build.lib.packages.RuleClass.Builder.RuleClassType;
 import com.google.devtools.build.xcode.xcodegen.proto.XcodeGenProtos.XcodeprojBuildSetting;
 
-import java.util.Map;
-
 /**
  * Utility class for resolving items for the Apple toolchain (such as common tool flags, and paths).
  */
@@ -168,25 +165,7 @@ public class AppleToolchain {
       }
     });
   }
-  
-  /**
-   * Returns a map of environment variables (derived from configuration) that should be propagated
-   * for actions that build on an apple host system. These environment variables are needed by
-   * the apple toolchain. Keys are variable names and values are their corresponding values.
-   * 
-   * @param configProvider info derived from the {@code xcode_config} rule targeted by the label
-   *     of the build flag {@code --xcode_config}
-   */
-  public static Map<String, String> appleHostSystemEnv(XcodeConfigProvider configProvider) {
-    Preconditions.checkNotNull(configProvider);
-    ImmutableMap.Builder<String, String> builder = ImmutableMap.builder();
-    if (configProvider.getXcodeVersion().isPresent()) {
-      builder.put(AppleConfiguration.XCODE_VERSION_ENV_NAME,
-          configProvider.getXcodeVersion().get().toString());
-    }
-    return builder.build();
-  }
-  
+
   /**
    * Base rule definition to be ancestor for rules which may require an xcode toolchain.
    */
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java
index eb789b3c50..1740a12de1 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfig.java
@@ -14,21 +14,28 @@
 
 package com.google.devtools.build.lib.rules.apple;
 
-import static com.google.devtools.build.lib.syntax.Type.BOOLEAN;
-
 import com.google.common.base.Joiner;
 import com.google.common.base.Optional;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Maps;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
-import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
+import com.google.devtools.build.lib.analysis.RedirectChaser;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
 import com.google.devtools.build.lib.analysis.RuleContext;
 import com.google.devtools.build.lib.analysis.RunfilesProvider;
+import com.google.devtools.build.lib.analysis.config.ConfigurationEnvironment;
+import com.google.devtools.build.lib.analysis.config.InvalidConfigurationException;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.packages.BuildType;
+import com.google.devtools.build.lib.packages.NoSuchPackageException;
+import com.google.devtools.build.lib.packages.NoSuchTargetException;
+import com.google.devtools.build.lib.packages.NonconfigurableAttributeMapper;
+import com.google.devtools.build.lib.packages.Rule;
+import com.google.devtools.build.lib.packages.Target;
 import com.google.devtools.build.lib.rules.RuleConfiguredTargetFactory;
-import com.google.devtools.build.lib.rules.apple.AppleCommandLineOptions.AppleBitcodeMode;
+import com.google.devtools.build.lib.syntax.Type;
 
+import java.util.List;
 import java.util.Map;
 
 import javax.annotation.Nullable;
@@ -38,43 +45,40 @@ import javax.annotation.Nullable;
  */
 public class XcodeConfig implements RuleConfiguredTargetFactory {
 
-  private static final DottedVersion MINIMUM_BITCODE_XCODE_VERSION = DottedVersion.fromString("7");
-
   @Override
   public ConfiguredTarget create(RuleContext ruleContext) throws InterruptedException {
-    AppleConfiguration configuration = ruleContext.getFragment(AppleConfiguration.class);
-    Optional<DottedVersion> versionOverrideFlag = configuration.getXcodeVersionOverrideFlag();
-
-    DottedVersion targetVersion = resolveExplicitlyDefinedVersion(ruleContext);
-
-    XcodeConfigProvider xcodeConfigProvider;
-    if (targetVersion == null) {
-      if (versionOverrideFlag.isPresent()) {
-        xcodeConfigProvider = new XcodeConfigProvider(versionOverrideFlag.get());
-      } else {
-        xcodeConfigProvider = XcodeConfigProvider.hostSystemDefault();
-      }
-    } else {
-      xcodeConfigProvider = new XcodeConfigProvider(targetVersion);
-    }
-
-    validateXcodeConfig(ruleContext, configuration, xcodeConfigProvider);
-
     return new RuleConfiguredTargetBuilder(ruleContext)
         .addProvider(RunfilesProvider.class, RunfilesProvider.EMPTY)
-        .addProvider(XcodeConfigProvider.class, xcodeConfigProvider)
         .build();
   }
-
-  private void validateXcodeConfig(RuleContext ruleContext, AppleConfiguration config,
-      XcodeConfigProvider xcodeConfigProvider) {
-    Optional<DottedVersion> xcodeVersion = xcodeConfigProvider.getXcodeVersion();
-    if (config.getBitcodeMode() != AppleBitcodeMode.NONE
-        && xcodeVersion.isPresent()
-        && xcodeVersion.get().compareTo(MINIMUM_BITCODE_XCODE_VERSION) < 0) {
-      ruleContext.ruleError(
-          String.format("apple_bitcode mode '%s' is unsupported for xcode version '%s'",
-              config.getBitcodeMode(), xcodeVersion.get()));
+  
+  /**
+   * Uses the {@link AppleCommandLineOptions#xcodeVersion} and
+   * {@link AppleCommandLineOptions#xcodeVersionConfig} command line options to determine and
+   * return the effective xcode version.
+   *
+   * @param env the current configuration environment
+   * @param xcodeConfigLabel the label for the xcode_config target to parse
+   * @param xcodeVersionOverrideFlag the value of the command line flag to override the default
+   *     xcode version, absent if unspecified
+   * @param errorDescription a description of the origin of {@code #xcodeConfigLabel} for messaging
+   *     parse errors
+   * @throws InvalidConfigurationException if the options given (or configuration targets) were
+   *     malformed and thus the xcode version could not be determined
+   */
+  public static Optional<DottedVersion> resolveXcodeVersion(ConfigurationEnvironment env,
+      Label xcodeConfigLabel, Optional<DottedVersion> xcodeVersionOverrideFlag,
+      String errorDescription) throws InvalidConfigurationException {
+    Rule xcodeConfigRule =
+        getRuleForLabel(xcodeConfigLabel, "xcode_config", env, errorDescription);
+
+    DottedVersion dottedVersion =
+        resolveExplicitlyDefinedVersion(env, xcodeConfigRule, xcodeVersionOverrideFlag);
+    
+    if (dottedVersion != null) {
+      return Optional.of(dottedVersion);
+    } else {
+      return xcodeVersionOverrideFlag;
     }
   }
 
@@ -83,70 +87,126 @@ public class XcodeConfig implements RuleConfiguredTargetFactory {
    * is an available {@code xcode_version} target which recognizes the flag value as either
    * an official version or an alias. Returns null if no such target is found.
    */
-  @Nullable private DottedVersion resolveExplicitlyDefinedVersion(RuleContext ruleContext) {
-    AppleConfiguration configuration = ruleContext.getFragment(AppleConfiguration.class);
-    Optional<DottedVersion> versionOverrideFlag = configuration.getXcodeVersionOverrideFlag();
+  @Nullable private static DottedVersion resolveExplicitlyDefinedVersion(
+      ConfigurationEnvironment env, Rule xcodeConfigTarget,
+      Optional<DottedVersion> versionOverrideFlag) throws InvalidConfigurationException {
     if (versionOverrideFlag.isPresent()) {
       // The version override flag is not necessarily an actual version - it may be a version
       // alias.
-      DottedVersion explicitVerison =
-          aliasesToVersionMap(ruleContext).get(versionOverrideFlag.get().toString());
-      if (explicitVerison != null) {
-        return explicitVerison;
+      DottedVersion explicitVersion =
+          aliasesToVersionMap(env, xcodeConfigTarget).get(versionOverrideFlag.get().toString());
+      if (explicitVersion != null) {
+        return explicitVersion;
       }
     } else { // No override specified. Use default.
-      XcodeVersionProvider defaultProvider = ruleContext.getPrerequisite(
-          XcodeConfigRule.DEFAULT_ATTR_NAME, Mode.TARGET, XcodeVersionProvider.class);
-
-      if (defaultProvider != null) {
-        return defaultProvider.getVersion();
+      DottedVersion defaultVersion = getDefaultVersion(env, xcodeConfigTarget);
+      
+      if (defaultVersion != null) {
+        return defaultVersion;
       }
     }
-
-    boolean requireDefinedVersions = ruleContext.attributes().get(
-        XcodeConfigRule.REQUIRE_DEFINED_VERSIONS_ATTR_NAME, BOOLEAN);
+    
+    boolean requireDefinedVersions = NonconfigurableAttributeMapper.of(xcodeConfigTarget)
+        .get(XcodeConfigRule.REQUIRE_DEFINED_VERSIONS_ATTR_NAME, Type.BOOLEAN);
     if (requireDefinedVersions) {
-      ruleContext.ruleError(
+      throw new InvalidConfigurationException(
           "xcode version config required an explicitly defined version, but none was available");
     }
 
     return null;
   }
 
-  private static Map<String, DottedVersion> aliasesToVersionMap(RuleContext ruleContext) {
-    Iterable<XcodeVersionProvider> xcodeVersionProviders =
-        ruleContext.getPrerequisites(XcodeConfigRule.VERSIONS_ATTR_NAME, Mode.TARGET,
-            XcodeVersionProvider.class);
+  /**
+   * Returns the default xcode version to use, if no {@code --xcode_version} command line flag
+   * was specified.
+   */
+  @Nullable private static DottedVersion getDefaultVersion(ConfigurationEnvironment env,
+      Rule xcodeConfigTarget) throws InvalidConfigurationException {
+    Label defaultVersionLabel = NonconfigurableAttributeMapper.of(xcodeConfigTarget)
+        .get(XcodeConfigRule.DEFAULT_ATTR_NAME, BuildType.LABEL);
+    if (defaultVersionLabel != null) {
+      Rule defaultVersionRule = getRuleForLabel(
+          defaultVersionLabel, "xcode_version", env, "default xcode version");
+      return new XcodeVersionRuleData(defaultVersionLabel, defaultVersionRule).getVersion();
+    } else {
+      return null;
+    }
+  }
+
+  private static Map<String, DottedVersion> aliasesToVersionMap(ConfigurationEnvironment env,
+      Rule xcodeConfigTarget) throws InvalidConfigurationException {
+    List<Label> xcodeVersionLabels = NonconfigurableAttributeMapper.of(xcodeConfigTarget)
+        .get(XcodeConfigRule.VERSIONS_ATTR_NAME, BuildType.LABEL_LIST);
+    ImmutableList.Builder<XcodeVersionRuleData> xcodeVersionRuleListBuilder =
+        ImmutableList.builder();
+    for (Label label : xcodeVersionLabels) {
+      Rule xcodeVersionRule = getRuleForLabel(label, "xcode_version", env, "xcode_version");
+      xcodeVersionRuleListBuilder.add(new XcodeVersionRuleData(label, xcodeVersionRule));
+    }
+    ImmutableList<XcodeVersionRuleData> xcodeVersionRules = xcodeVersionRuleListBuilder.build();
 
     Map<String, DottedVersion> aliasesToVersionMap = Maps.newLinkedHashMap();
-    for (XcodeVersionProvider versionProvider : xcodeVersionProviders) {
-      for (String alias : versionProvider.getAliases()) {
-        if (aliasesToVersionMap.put(alias, versionProvider.getVersion()) != null) {
-          ruleErrorDuplicateAlias(alias, ruleContext);
+    for (XcodeVersionRuleData xcodeVersionRule : xcodeVersionRules) {
+      for (String alias : xcodeVersionRule.getAliases()) {
+        if (aliasesToVersionMap.put(alias, xcodeVersionRule.getVersion()) != null) {
+          configErrorDuplicateAlias(alias, xcodeVersionRules);
         }
       }
       if (aliasesToVersionMap.put(
-          versionProvider.getVersion().toString(), versionProvider.getVersion()) != null) {
-        ruleErrorDuplicateAlias(versionProvider.getVersion().toString(), ruleContext);
+          xcodeVersionRule.getVersion().toString(), xcodeVersionRule.getVersion()) != null) {
+        configErrorDuplicateAlias(xcodeVersionRule.getVersion().toString(), xcodeVersionRules);
       }
     }
     return aliasesToVersionMap;
   }
   
-  private static void ruleErrorDuplicateAlias(String alias, RuleContext ruleContext) {
-    Iterable<XcodeVersionProvider> xcodeVersionProviders =
-        ruleContext.getPrerequisites(XcodeConfigRule.VERSIONS_ATTR_NAME, Mode.TARGET,
-            XcodeVersionProvider.class);
-    
+  /**
+   * Convenience method for throwing an {@link InvalidConfigurationException} due to presence
+   * of duplicate aliases in an {@code xcode_config} target definition. 
+   */
+  private static void configErrorDuplicateAlias(String alias,
+      List<XcodeVersionRuleData> xcodeVersionRules) throws InvalidConfigurationException {
+
     ImmutableList.Builder<Label> labelsContainingAlias = ImmutableList.builder();
-    for (XcodeVersionProvider versionProvider : xcodeVersionProviders) {
-      if (versionProvider.getAliases().contains(alias)
-          || versionProvider.getVersion().toString().equals(alias)) {
-        labelsContainingAlias.add(versionProvider.getLabel());
+    for (XcodeVersionRuleData xcodeVersionRule : xcodeVersionRules) {
+      if (xcodeVersionRule.getAliases().contains(alias)
+          || xcodeVersionRule.getVersion().toString().equals(alias)) {
+        labelsContainingAlias.add(xcodeVersionRule.getLabel());
+      }
+    }
+
+    throw new InvalidConfigurationException(
+        String.format("'%s' is registered to multiple labels (%s) in a single xcode_config rule",
+            alias, Joiner.on(", ").join(labelsContainingAlias.build())));
+  }
+
+  /**
+   * If the given label (following redirects) is a target for a rule of type {@code type},
+   * then returns the {@link Rule} representing that target. Otherwise, throws a
+   * {@link InvalidConfigurationException}.
+   */
+  private static Rule getRuleForLabel(Label label, String type, ConfigurationEnvironment env,
+      String description) throws InvalidConfigurationException {
+    label = RedirectChaser.followRedirects(env, label, description);
+
+    if (label == null) {
+      throw new InvalidConfigurationException(String.format(
+          "Expected value of %s (%s) to resolve to a target of type %s",
+          description, label, type));
+    }
+
+    try {
+      Target target = env.getTarget(label);
+      
+      if (target instanceof Rule && ((Rule) target).getRuleClass().equals(type)) {
+        return (Rule) target;
+      } else {
+        throw new InvalidConfigurationException(String.format(
+            "Expected value of %s (%s) to resolve to a target of type %s",
+            description, label, type));
       }
+    } catch (NoSuchPackageException | NoSuchTargetException exception) {
+      throw new InvalidConfigurationException(exception);
     }
-    ruleContext.ruleError(String.format(
-        "'%s' is registered to multiple labels (%s) in a single xcode version "
-        + "configuration", alias, Joiner.on(", ").join(labelsContainingAlias.build())));
   }
 }
\ No newline at end of file
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigProvider.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigProvider.java
deleted file mode 100644
index 5241e04867..0000000000
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigProvider.java
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright 2015 The Bazel Authors. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//    http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package com.google.devtools.build.lib.rules.apple;
-
-import com.google.common.base.Optional;
-import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
-import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
-
-/**
- * Provides a version of xcode based on a combination of the {@code --xcode_version} build flag
- * and a {@code xcode_config} target. This version of xcode should be used for selecting apple
- * toolchains and SDKs.
- */
-@Immutable
-public final class XcodeConfigProvider implements TransitiveInfoProvider {
-  private final Optional<DottedVersion> xcodeVersion;
-  
-  XcodeConfigProvider(DottedVersion xcodeVersion) {
-    this.xcodeVersion = Optional.of(xcodeVersion);
-  }
-  
-  private XcodeConfigProvider() {
-    this.xcodeVersion = Optional.absent();
-  }
-  
-  /**
-   * Returns a {@link XcodeConfigProvider} with no xcode version specified. The host system
-   * default xcode should be used. See {@link #getXcodeVersion}.
-   */
-  static XcodeConfigProvider hostSystemDefault() {
-    return new XcodeConfigProvider();
-  }
-
-  /**
-   * Returns either an explicit xcode version which should be used in actions which require an
-   * apple toolchain, or {@link Optional#absent} if the host system default should be used.
-   */
-  public Optional<DottedVersion> getXcodeVersion() {
-    return xcodeVersion;
-  }
-}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigRule.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigRule.java
index 58275f034f..ecfb643458 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeConfigRule.java
@@ -47,7 +47,8 @@ public class XcodeConfigRule implements RuleDefinition {
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
         .add(attr(DEFAULT_ATTR_NAME, LABEL)
             .allowedRuleClasses("xcode_version")
-            .allowedFileTypes())
+            .allowedFileTypes()
+            .nonconfigurable("this rule determines configuration"))
         /* <!-- #BLAZE_RULE(proto_library).ATTRIBUTE(version) -->
         Accepted <code>xcode_version<code> targets that may be used.
         If the value of the <code>xcode_version</code> build flag matches one of the aliases
@@ -56,14 +57,17 @@ public class XcodeConfigRule implements RuleDefinition {
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
         .add(attr(VERSIONS_ATTR_NAME, LABEL_LIST)
             .allowedRuleClasses("xcode_version")
-            .allowedFileTypes())
+            .allowedFileTypes()
+            .nonconfigurable("this rule determines configuration"))
         /* <!-- #BLAZE_RULE(proto_library).ATTRIBUTE(version) -->
         Whether to require the build's xcode version match one of the declared targets.
         If true, this will raise an error if either the <code>xcode_version</code> flag value
         or <code>default</code> attribute value do not match one of the versions declared
         among <code>xcode_verison</code> targets.
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
-        .add(attr(REQUIRE_DEFINED_VERSIONS_ATTR_NAME, BOOLEAN).value(false))
+        .add(attr(REQUIRE_DEFINED_VERSIONS_ATTR_NAME, BOOLEAN)
+            .value(false)
+            .nonconfigurable("this rule determines configuration"))
         .build();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersion.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersion.java
index 2b363e6c62..f7e321f285 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersion.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersion.java
@@ -14,17 +14,12 @@
 
 package com.google.devtools.build.lib.rules.apple;
 
-import static com.google.devtools.build.lib.syntax.Type.STRING;
-import static com.google.devtools.build.lib.syntax.Type.STRING_LIST;
-
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
 import com.google.devtools.build.lib.analysis.RuleContext;
 import com.google.devtools.build.lib.analysis.RunfilesProvider;
 import com.google.devtools.build.lib.rules.RuleConfiguredTargetFactory;
 
-import java.util.List;
-
 /**
  * Implementation for the {@code xcode_version} rule.
  */
@@ -32,15 +27,8 @@ public class XcodeVersion implements RuleConfiguredTargetFactory {
 
   @Override
   public ConfiguredTarget create(RuleContext ruleContext) throws InterruptedException {
-    DottedVersion version = DottedVersion.fromString(
-        ruleContext.attributes().get(XcodeVersionRule.VERSION_ATTR_NAME, STRING));
-    List<String> aliases = 
-        ruleContext.attributes().get(XcodeVersionRule.ALIASES_ATTR_NAME, STRING_LIST);
-    
     return new RuleConfiguredTargetBuilder(ruleContext)
         .addProvider(RunfilesProvider.class, RunfilesProvider.EMPTY)
-        .addProvider(XcodeVersionProvider.class,
-            new XcodeVersionProvider(ruleContext.getLabel(), version, aliases))
         .build();
   }
 }
\ No newline at end of file
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionRule.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionRule.java
index d78337bcdf..f6e8274902 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionRule.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionRule.java
@@ -41,13 +41,16 @@ public class XcodeVersionRule implements RuleDefinition {
         /* <!-- #BLAZE_RULE(proto_library).ATTRIBUTE(version) -->
         The official version number of a version of Xcode.
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
-        .add(attr(VERSION_ATTR_NAME, STRING).mandatory())
+        .add(attr(VERSION_ATTR_NAME, STRING)
+            .mandatory()
+            .nonconfigurable("this rule determines configuration"))
         /* <!-- #BLAZE_RULE(proto_library).ATTRIBUTE(version) -->
         Accepted aliases for this version of Xcode.
         If the value of the <code>xcode_version</code> build flag matches any of the given
         alias strings, this xcode version will be used.
         <!-- #END_BLAZE_RULE.ATTRIBUTE --> */
-        .add(attr(ALIASES_ATTR_NAME, STRING_LIST))
+        .add(attr(ALIASES_ATTR_NAME, STRING_LIST)
+            .nonconfigurable("this rule determines configuration"))
         .build();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionProvider.java b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionRuleData.java
index f7b15b60d6..02bf38dc48 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionProvider.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/apple/XcodeVersionRuleData.java
@@ -15,30 +15,35 @@
 package com.google.devtools.build.lib.rules.apple;
 
 import com.google.common.collect.ImmutableList;
-import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
 import com.google.devtools.build.lib.cmdline.Label;
-import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.packages.NonconfigurableAttributeMapper;
+import com.google.devtools.build.lib.packages.Rule;
+import com.google.devtools.build.lib.syntax.Type;
 
 import java.util.List;
 
 /**
- * Provides the information in a single {@code xcode_version} target. A single target of this rule
- * contains an official version label decided by Apple and a number of supported aliases one might
- * use to reference this version.
+ * A tuple containing the information in a single target of the {@code xcode_version} rule.
+ * A single target of this rule contains an official version label decided by Apple and a number
+ *  of supported aliases one might use to reference this version.
  *
  * <p>For example, one may want to reference official xcode version 7.0.1 using the "7" or
  * "7.0" aliases.
  */
-@Immutable
-public final class XcodeVersionProvider implements TransitiveInfoProvider {
+public class XcodeVersionRuleData {
   private final Label label;
   private final DottedVersion version;
   private final ImmutableList<String> aliases;
-  
-  XcodeVersionProvider(Label label, DottedVersion version, List<String> aliases) {
+
+  XcodeVersionRuleData(Label label, Rule rule) {
+    NonconfigurableAttributeMapper attrMapper =
+        NonconfigurableAttributeMapper.of(rule);
+
     this.label = label;
-    this.version = version;
-    this.aliases = ImmutableList.copyOf(aliases);
+    this.version = DottedVersion.fromString(
+        attrMapper.get(XcodeVersionRule.VERSION_ATTR_NAME, Type.STRING));
+    this.aliases = ImmutableList.copyOf(
+        attrMapper.get(XcodeVersionRule.ALIASES_ATTR_NAME, Type.STRING_LIST));
   }
 
   /**
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
index 54bfe47c41..01d1899595 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppCompileAction.java
@@ -36,7 +36,6 @@ import com.google.devtools.build.lib.actions.PackageRootResolver;
 import com.google.devtools.build.lib.actions.ResourceSet;
 import com.google.devtools.build.lib.actions.extra.CppCompileInfo;
 import com.google.devtools.build.lib.actions.extra.ExtraActionInfo;
-import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
 import com.google.devtools.build.lib.analysis.RuleContext;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.config.PerLabelOptions;
@@ -51,9 +50,7 @@ import com.google.devtools.build.lib.events.EventKind;
 import com.google.devtools.build.lib.profiler.Profiler;
 import com.google.devtools.build.lib.profiler.ProfilerTask;
 import com.google.devtools.build.lib.rules.apple.AppleConfiguration;
-import com.google.devtools.build.lib.rules.apple.AppleToolchain;
 import com.google.devtools.build.lib.rules.apple.Platform;
-import com.google.devtools.build.lib.rules.apple.XcodeConfigProvider;
 import com.google.devtools.build.lib.rules.cpp.CcToolchainFeatures.FeatureConfiguration;
 import com.google.devtools.build.lib.rules.cpp.CppCompileActionContext.Reply;
 import com.google.devtools.build.lib.rules.cpp.CppConfiguration.Tool;
@@ -157,9 +154,6 @@ public class CppCompileAction extends AbstractAction implements IncludeScannable
   private final Iterable<IncludeScannable> lipoScannables;
   private final CppCompileCommandLine cppCompileCommandLine;
   private final boolean usePic;
-  // TODO(bazel-team): Needed for lazily evaluating xcode configuration attribute. Remove when
-  // this logic is refactored into crosstool expansion.
-  private final RuleContext ruleContext;
 
   @VisibleForTesting
   final CppConfiguration cppConfiguration;
@@ -274,7 +268,6 @@ public class CppCompileAction extends AbstractAction implements IncludeScannable
     this.lipoScannables = lipoScannables;
     this.actionClassId = actionClassId;
     this.usePic = usePic;
-    this.ruleContext = ruleContext;
 
     // We do not need to include the middleman artifact since it is a generated
     // artifact and will definitely exist prior to this action execution.
@@ -612,9 +605,7 @@ public class CppCompileAction extends AbstractAction implements IncludeScannable
     // evaluation here.
     AppleConfiguration appleConfiguration = configuration.getFragment(AppleConfiguration.class);
     if (CppConfiguration.MAC_SYSTEM_NAME.equals(getHostSystemName())) {
-      XcodeConfigProvider xcodeConfigProvider =
-          ruleContext.getPrerequisite(":xcode_config", Mode.HOST, XcodeConfigProvider.class);
-      environment.putAll(AppleToolchain.appleHostSystemEnv(xcodeConfigProvider));
+      environment.putAll(appleConfiguration.getAppleHostSystemEnv());
     }
     if (Platform.isApplePlatform(cppConfiguration.getTargetCpu())) {
       environment.putAll(appleConfiguration.appleTargetPlatformEnv(
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java
index 99c880f8b6..23acbd12ad 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/ObjcRuleClasses.java
@@ -53,7 +53,6 @@ import com.google.devtools.build.lib.rules.apple.AppleToolchain;
 import com.google.devtools.build.lib.rules.apple.AppleToolchain.RequiresXcodeConfigRule;
 import com.google.devtools.build.lib.rules.apple.DottedVersion;
 import com.google.devtools.build.lib.rules.apple.Platform;
-import com.google.devtools.build.lib.rules.apple.XcodeConfigProvider;
 import com.google.devtools.build.lib.syntax.Type;
 import com.google.devtools.build.lib.util.FileType;
 import com.google.devtools.build.lib.util.FileTypeSet;
@@ -165,12 +164,10 @@ public class ObjcRuleClasses {
    */
   static SpawnAction.Builder spawnXcrunActionBuilder(RuleContext ruleContext) {
     AppleConfiguration appleConfiguration = ruleContext.getFragment(AppleConfiguration.class);
-    XcodeConfigProvider xcodeConfigProvider =
-        ruleContext.getPrerequisite(":xcode_config", Mode.HOST, XcodeConfigProvider.class);
 
     ImmutableMap.Builder<String, String> envBuilder = ImmutableMap.<String, String>builder()
         .putAll(appleConfiguration.getEnvironmentForIosAction())
-        .putAll(AppleToolchain.appleHostSystemEnv(xcodeConfigProvider));
+        .putAll(appleConfiguration.getAppleHostSystemEnv());
 
     return spawnOnDarwinActionBuilder()
         .setEnvironment(envBuilder.build());
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/TestSupport.java b/src/main/java/com/google/devtools/build/lib/rules/objc/TestSupport.java
index aca9e11dd5..ce49995630 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/TestSupport.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/TestSupport.java
@@ -32,8 +32,6 @@ import com.google.devtools.build.lib.analysis.actions.TemplateExpansionAction.Su
 import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.lib.collect.nestedset.NestedSetBuilder;
 import com.google.devtools.build.lib.rules.apple.AppleConfiguration;
-import com.google.devtools.build.lib.rules.apple.AppleToolchain;
-import com.google.devtools.build.lib.rules.apple.XcodeConfigProvider;
 import com.google.devtools.build.lib.rules.test.TestEnvironmentProvider;
 import com.google.devtools.build.lib.syntax.Type;
 import com.google.devtools.build.lib.util.FileType;
@@ -234,13 +232,11 @@ public class TestSupport {
    */
   public Map<Class<? extends TransitiveInfoProvider>, TransitiveInfoProvider> getExtraProviders() {
     AppleConfiguration configuration = ruleContext.getFragment(AppleConfiguration.class);
-    XcodeConfigProvider xcodeConfigProvider =
-        ruleContext.getPrerequisite(":xcode_config", Mode.HOST, XcodeConfigProvider.class);
 
     ImmutableMap.Builder<String, String> envBuilder = ImmutableMap.builder();
 
     envBuilder.putAll(configuration.getEnvironmentForIosAction());
-    envBuilder.putAll(AppleToolchain.appleHostSystemEnv(xcodeConfigProvider));
+    envBuilder.putAll(configuration.getAppleHostSystemEnv());
 
     if (ruleContext.getConfiguration().isCodeCoverageEnabled()) {
       envBuilder.put("COVERAGE_GCOV_PATH",