Add a new toolchain type for c++. In order to do this, PlatformConfiguration is made a legal configuration fragment for every rule class.

Add a default "dummy" c++ toolchain to prevent resolution errors when legacy toolchain selection logic is used.  Add toolchain mocks to java and shell tests.

PiperOrigin-RevId: 167901210

25 files changed, 285 insertions, 59 deletions

diff --git a/compile.sh b/compile.sh
index dc414b18b6..c72a8026d1 100755
--- a/compile.sh
+++ b/compile.sh
@@ -81,7 +81,11 @@ source scripts/bootstrap/bootstrap.sh
 new_step 'Building Bazel with Bazel'
 display "."
 log "Building output/bazel"
+# We set host and target platform directly since the defaults in @bazel_tools
+# have not yet been generated.
 bazel_build "src:bazel${EXE_EXT}" \
+  --experimental_host_platform=//tools/platforms:host_platform \
+  --experimental_platforms=//tools/platforms:target_platform \
   || fail "Could not build Bazel"
 bazel_bin_path="$(get_bazel_bin_path)/src/bazel${EXE_EXT}"
 [ -e "$bazel_bin_path" ] \
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/BaseRuleClasses.java b/src/main/java/com/google/devtools/build/lib/analysis/BaseRuleClasses.java
index 817f4d163e..f52d66f209 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/BaseRuleClasses.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/BaseRuleClasses.java
@@ -182,41 +182,60 @@ public class BaseRuleClasses {
    * Share common attributes across both base and Skylark base rules.
    */
   public static RuleClass.Builder commonCoreAndSkylarkAttributes(RuleClass.Builder builder) {
-    return builder
+    return PlatformSemantics.platformAttributes(builder)
         // The visibility attribute is special: it is a nodep label, and loading the
         // necessary package groups is handled by {@link LabelVisitor#visitTargetVisibility}.
         // Package groups always have the null configuration so that they are not duplicated
         // needlessly.
-        .add(attr("visibility", NODEP_LABEL_LIST).orderIndependent().cfg(HOST)
-            .nonconfigurable("special attribute integrated more deeply into Bazel's core logic"))
-        .add(attr("deprecation", STRING).value(deprecationDefault)
-            .nonconfigurable("Used in core loading phase logic with no access to configs"))
-        .add(attr("tags", STRING_LIST).orderIndependent().taggable()
-            .nonconfigurable("low-level attribute, used in TargetUtils without configurations"))
-        .add(attr("generator_name", STRING).undocumented("internal")
-            .nonconfigurable("static structure of a rule"))
-        .add(attr("generator_function", STRING).undocumented("internal")
-            .nonconfigurable("static structure of a rule"))
-        .add(attr("generator_location", STRING).undocumented("internal")
-            .nonconfigurable("static structure of a rule"))
-        .add(attr("testonly", BOOLEAN).value(testonlyDefault)
-            .nonconfigurable("policy decision: rules testability should be consistent"))
+        .add(
+            attr("visibility", NODEP_LABEL_LIST)
+                .orderIndependent()
+                .cfg(HOST)
+                .nonconfigurable(
+                    "special attribute integrated more deeply into Bazel's core logic"))
+        .add(
+            attr("deprecation", STRING)
+                .value(deprecationDefault)
+                .nonconfigurable("Used in core loading phase logic with no access to configs"))
+        .add(
+            attr("tags", STRING_LIST)
+                .orderIndependent()
+                .taggable()
+                .nonconfigurable("low-level attribute, used in TargetUtils without configurations"))
+        .add(
+            attr("generator_name", STRING)
+                .undocumented("internal")
+                .nonconfigurable("static structure of a rule"))
+        .add(
+            attr("generator_function", STRING)
+                .undocumented("internal")
+                .nonconfigurable("static structure of a rule"))
+        .add(
+            attr("generator_location", STRING)
+                .undocumented("internal")
+                .nonconfigurable("static structure of a rule"))
+        .add(
+            attr("testonly", BOOLEAN)
+                .value(testonlyDefault)
+                .nonconfigurable("policy decision: rules testability should be consistent"))
         .add(attr("features", STRING_LIST).orderIndependent())
         .add(attr(":action_listener", LABEL_LIST).cfg(HOST).value(ACTION_LISTENER))
-        .add(attr(RuleClass.COMPATIBLE_ENVIRONMENT_ATTR, LABEL_LIST)
-            .allowedRuleClasses(EnvironmentRule.RULE_NAME)
-            .cfg(Attribute.ConfigurationTransition.HOST)
-            .allowedFileTypes(FileTypeSet.NO_FILE)
-            .dontCheckConstraints()
-            .nonconfigurable("special logic for constraints and select: see ConstraintSemantics")
-        )
-        .add(attr(RuleClass.RESTRICTED_ENVIRONMENT_ATTR, LABEL_LIST)
-            .allowedRuleClasses(EnvironmentRule.RULE_NAME)
-            .cfg(Attribute.ConfigurationTransition.HOST)
-            .allowedFileTypes(FileTypeSet.NO_FILE)
-            .dontCheckConstraints()
-            .nonconfigurable("special logic for constraints and select: see ConstraintSemantics")
-        );
+        .add(
+            attr(RuleClass.COMPATIBLE_ENVIRONMENT_ATTR, LABEL_LIST)
+                .allowedRuleClasses(EnvironmentRule.RULE_NAME)
+                .cfg(Attribute.ConfigurationTransition.HOST)
+                .allowedFileTypes(FileTypeSet.NO_FILE)
+                .dontCheckConstraints()
+                .nonconfigurable(
+                    "special logic for constraints and select: see ConstraintSemantics"))
+        .add(
+            attr(RuleClass.RESTRICTED_ENVIRONMENT_ATTR, LABEL_LIST)
+                .allowedRuleClasses(EnvironmentRule.RULE_NAME)
+                .cfg(Attribute.ConfigurationTransition.HOST)
+                .allowedFileTypes(FileTypeSet.NO_FILE)
+                .dontCheckConstraints()
+                .nonconfigurable(
+                    "special logic for constraints and select: see ConstraintSemantics"));
   }
 
   public static RuleClass.Builder nameAttribute(RuleClass.Builder builder) {
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java b/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
index 3376e9609d..e2bf25b98b 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/PlatformOptions.java
@@ -60,7 +60,7 @@ public class PlatformOptions extends FragmentOptions {
   @Option(
     name = "extra_toolchains",
     converter = LabelListConverter.class,
-    defaultValue = "",
+    defaultValue = "@bazel_tools//tools/cpp:dummy_cc_toolchain",
     documentationCategory = OptionDocumentationCategory.UNDOCUMENTED,
     effectTags = {OptionEffectTag.UNKNOWN},
     metadataTags = {OptionMetadataTag.HIDDEN},
@@ -98,6 +98,8 @@ public class PlatformOptions extends FragmentOptions {
   public PlatformOptions getHost(boolean fallback) {
     PlatformOptions host = (PlatformOptions) getDefault();
     host.platforms = ImmutableList.of(this.hostPlatform);
+    host.hostPlatform = this.hostPlatform;
+    host.extraToolchains = this.extraToolchains;
     return host;
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/PlatformSemantics.java b/src/main/java/com/google/devtools/build/lib/analysis/PlatformSemantics.java
index bc47c69d57..45c967e551 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/PlatformSemantics.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/PlatformSemantics.java
@@ -26,6 +26,7 @@ import com.google.devtools.build.lib.packages.AttributeMap;
 import com.google.devtools.build.lib.packages.Rule;
 import com.google.devtools.build.lib.packages.RuleClass;
 import java.util.List;
+import javax.annotation.Nullable;
 
 /** Helper class to manage rules' use of platforms. */
 public class PlatformSemantics {
@@ -49,6 +50,7 @@ public class PlatformSemantics {
       };
 
   /** Implementation for the :execution_platform attribute. */
+  @Nullable
   public static final Attribute.LateBoundLabel<BuildConfiguration> EXECUTION_PLATFORM =
       new Attribute.LateBoundLabel<BuildConfiguration>(PlatformConfiguration.class) {
         @Override
diff --git a/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkRuleClassFunctions.java b/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkRuleClassFunctions.java
index 3e850d966d..6c8487364d 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkRuleClassFunctions.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/skylark/SkylarkRuleClassFunctions.java
@@ -39,7 +39,6 @@ import com.google.devtools.build.lib.analysis.ActionsProvider;
 import com.google.devtools.build.lib.analysis.BaseRuleClasses;
 import com.google.devtools.build.lib.analysis.DefaultInfo;
 import com.google.devtools.build.lib.analysis.OutputGroupProvider;
-import com.google.devtools.build.lib.analysis.PlatformSemantics;
 import com.google.devtools.build.lib.analysis.TransitiveInfoCollection;
 import com.google.devtools.build.lib.analysis.skylark.SkylarkAttr.Descriptor;
 import com.google.devtools.build.lib.analysis.test.TestConfiguration;
@@ -129,10 +128,9 @@ public class SkylarkRuleClassFunctions {
   /** Parent rule class for non-executable non-test Skylark rules. */
   public static final RuleClass baseRule =
       BaseRuleClasses.commonCoreAndSkylarkAttributes(
-              PlatformSemantics.platformAttributes(
-                  BaseRuleClasses.nameAttribute(
-                          new RuleClass.Builder("$base_rule", RuleClassType.ABSTRACT, true))
-                      .add(attr("expect_failure", STRING))))
+              BaseRuleClasses.nameAttribute(
+                      new RuleClass.Builder("$base_rule", RuleClassType.ABSTRACT, true))
+                  .add(attr("expect_failure", STRING)))
           .build();
 
   /** Parent rule class for executable non-test Skylark rules. */
diff --git a/src/main/java/com/google/devtools/build/lib/bazel/rules/cpp/BazelCppRuleClasses.java b/src/main/java/com/google/devtools/build/lib/bazel/rules/cpp/BazelCppRuleClasses.java
index 99abec3c14..8d494c8720 100644
--- a/src/main/java/com/google/devtools/build/lib/bazel/rules/cpp/BazelCppRuleClasses.java
+++ b/src/main/java/com/google/devtools/build/lib/bazel/rules/cpp/BazelCppRuleClasses.java
@@ -57,6 +57,7 @@ import com.google.devtools.build.lib.packages.TriState;
 import com.google.devtools.build.lib.rules.cpp.CcToolchain;
 import com.google.devtools.build.lib.rules.cpp.CppConfiguration;
 import com.google.devtools.build.lib.rules.cpp.CppFileTypes;
+import com.google.devtools.build.lib.rules.cpp.CppHelper;
 import com.google.devtools.build.lib.rules.cpp.CppRuleClasses;
 import com.google.devtools.build.lib.rules.cpp.CppRuleClasses.LipoTransition;
 import com.google.devtools.build.lib.util.FileTypeSet;
@@ -139,6 +140,7 @@ public class BazelCppRuleClasses {
               attr(CcToolchain.CC_TOOLCHAIN_DEFAULT_ATTRIBUTE_NAME, LABEL)
                   .value(CppRuleClasses.ccToolchainAttribute(env)))
           .setPreferredDependencyPredicate(Predicates.<String>or(CPP_SOURCE, C_SOURCE, CPP_HEADER))
+          .addRequiredToolchains(CppHelper.getCcToolchainType(env.getToolsRepository()))
           .build();
     }
 
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index dcf609261e..daa2e8ec1b 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
@@ -28,6 +28,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
+import com.google.common.collect.Lists;
 import com.google.common.collect.Ordering;
 import com.google.devtools.build.lib.cmdline.Label;
 import com.google.devtools.build.lib.cmdline.LabelSyntaxException;
@@ -997,6 +998,11 @@ public class RuleClass {
       return this;
     }
 
+    public Builder addRequiredToolchains(Label... toolchainLabels) {
+      Iterables.addAll(this.requiredToolchains, Lists.newArrayList(toolchainLabels));
+      return this;
+    }
+
     /**
      * Returns an Attribute.Builder object which contains a replica of the
      * same attribute in the parent rule if exists.
diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppHelper.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppHelper.java
index 1100576151..87f43cc057 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CppHelper.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CppHelper.java
@@ -87,6 +87,11 @@ public class CppHelper {
   private static final ImmutableList<String> LINKOPTS_PREREQUISITE_LABEL_KINDS =
       ImmutableList.of("deps", "srcs");
 
+  /** Returns label used to select resolved cc_toolchain instances based on platform. */
+  public static Label getCcToolchainType(String toolsRepository) {
+    return Label.parseAbsoluteUnchecked(toolsRepository + "//tools/cpp:toolchain_type");
+  }
+
   private CppHelper() {
     // prevents construction
   }
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctionEnvironmentForTesting.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctionEnvironmentForTesting.java
index 7df8afddd5..0acb49c1c6 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctionEnvironmentForTesting.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyFunctionEnvironmentForTesting.java
@@ -14,7 +14,9 @@
 
 package com.google.devtools.build.lib.skyframe;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.events.ExtendedEventHandler;
 import com.google.devtools.build.lib.util.ResourceUsage;
 import com.google.devtools.build.skyframe.AbstractSkyFunctionEnvironment;
@@ -33,21 +35,27 @@ public class SkyFunctionEnvironmentForTesting extends AbstractSkyFunctionEnviron
 
   private final BuildDriver buildDriver;
   private final ExtendedEventHandler eventHandler;
+  private final SkyframeExecutor skyframeExecutor;
 
   /** Creates a SkyFunctionEnvironmentForTesting that uses a BuildDriver to evaluate skykeys. */
   public SkyFunctionEnvironmentForTesting(
-      BuildDriver buildDriver, ExtendedEventHandler eventHandler) {
+      BuildDriver buildDriver,
+      ExtendedEventHandler eventHandler,
+      SkyframeExecutor skyframeExecutor) {
     this.buildDriver = buildDriver;
     this.eventHandler = eventHandler;
+    this.skyframeExecutor = skyframeExecutor;
   }
 
   @Override
   protected Map<SkyKey, ValueOrUntypedException> getValueOrUntypedExceptions(
       Iterable<? extends SkyKey> depKeys) throws InterruptedException {
     ImmutableMap.Builder<SkyKey, ValueOrUntypedException> resultMap = ImmutableMap.builder();
+    Iterable<SkyKey> keysToEvaluate = ImmutableList.copyOf(depKeys);
     EvaluationResult<SkyValue> evaluationResult =
+        skyframeExecutor.evaluateSkyKeys(eventHandler, keysToEvaluate, true);
         buildDriver.evaluate(depKeys, true, ResourceUsage.getAvailableProcessors(), eventHandler);
-    for (SkyKey depKey : depKeys) {
+    for (SkyKey depKey : ImmutableSet.copyOf(depKeys)) {
       resultMap.put(depKey, ValueOrExceptionUtils.ofValue(evaluationResult.get(depKey)));
     }
     return resultMap.build();
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
index f592d39268..9c952acb78 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/SkyframeExecutor.java
@@ -837,7 +837,7 @@ public abstract class SkyframeExecutor implements WalkableGraphFactory {
       Set<Label> requiredToolchains, BuildConfiguration config, ExtendedEventHandler eventHandler)
       throws ToolchainContextException, InterruptedException {
     SkyFunctionEnvironmentForTesting env =
-        new SkyFunctionEnvironmentForTesting(buildDriver, eventHandler);
+        new SkyFunctionEnvironmentForTesting(buildDriver, eventHandler, this);
     return ToolchainUtil.createToolchainContext(env, "", requiredToolchains, config);
   }
 
@@ -1534,7 +1534,7 @@ public abstract class SkyframeExecutor implements WalkableGraphFactory {
    * Evaluates the given sky keys, blocks, and returns their evaluation results. Enables/disables
    * "keep going" on evaluation errors as specified.
    */
-  private EvaluationResult<SkyValue> evaluateSkyKeys(
+  EvaluationResult<SkyValue> evaluateSkyKeys(
       final ExtendedEventHandler eventHandler,
       final Iterable<SkyKey> skyKeys,
       final boolean keepGoing) {
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/BuildViewTest.java b/src/test/java/com/google/devtools/build/lib/analysis/BuildViewTest.java
index 183c8c05f7..83bcdad904 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/BuildViewTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/BuildViewTest.java
@@ -1238,8 +1238,8 @@ public class BuildViewTest extends BuildViewTestBase {
     useConfiguration("--experimental_dynamic_configs=on");
     AnalysisResult res = update("//foo:x");
     ConfiguredTarget topLevelTarget = Iterables.getOnlyElement(res.getTargetsToBuild());
-    assertThat(topLevelTarget.getConfiguration().getAllFragments().keySet()).containsExactly(
-        ruleClassProvider.getUniversalFragment());
+    assertThat(topLevelTarget.getConfiguration().getAllFragments().keySet())
+        .containsExactly(ruleClassProvider.getUniversalFragment(), PlatformConfiguration.class);
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/packages/util/BazelMockCcSupport.java b/src/test/java/com/google/devtools/build/lib/packages/util/BazelMockCcSupport.java
index 0defa523b1..b938e5fe93 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/util/BazelMockCcSupport.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/util/BazelMockCcSupport.java
@@ -77,7 +77,6 @@ public final class BazelMockCcSupport extends MockCcSupport {
     config.create(
         "/bazel_tools_workspace/tools/cpp/BUILD",
         "package(default_visibility=['//visibility:public'])",
-        "toolchain_type(name = 'toolchain_type')",
         "cc_library(name = 'stl')",
         "cc_library(name = 'malloc')",
         "cc_toolchain_suite(",
@@ -123,7 +122,7 @@ public final class BazelMockCcSupport extends MockCcSupport {
         "    linker_files = ':empty',",
         "    module_map = 'crosstool.cppmap', supports_header_parsing = 1,",
         "    objcopy_files = ':empty', static_runtime_libs = [':empty'], strip_files = ':empty',",
-        ")", 
+        ")",
         "cc_toolchain(name = 'cc-compiler-armeabi-v7a', all_files = ':empty', ",
         "    compiler_files = ':empty',",
         "    cpu = 'local', dwp_files = ':empty', dynamic_runtime_libs = [':empty'], ",
@@ -145,8 +144,27 @@ public final class BazelMockCcSupport extends MockCcSupport {
         "filegroup(",
         "    name = 'link_dynamic_library',",
         "    srcs = ['link_dynamic_library.sh'],",
-        ")");
-
+        ")",
+        "toolchain_type(name = 'toolchain_type')",
+        "toolchain(",
+        "   name = 'toolchain_cc-compiler-piii',",
+        "   toolchain_type = ':toolchain_type',",
+        "   toolchain = '//third_party/crosstool/mock:cc-compiler-piii',",
+        "   target_compatible_with = [':mock_value'],",
+        ")",
+        "toolchain(",
+        "   name = 'dummy_cc_toolchain',",
+        "   toolchain_type = ':toolchain_type',",
+        "   toolchain = ':dummy_cc_toolchain_impl',",
+        ")",
+        "load(':dummy_toolchain.bzl', 'dummy_toolchain')",
+        "dummy_toolchain(name = 'dummy_cc_toolchain_impl')");
+    config.create(
+        "/bazel_tools_workspace/tools/cpp/dummy_toolchain.bzl",
+        "def _dummy_toolchain_impl(ctx):",
+        "   toolchain = platform_common.ToolchainInfo()",
+        "   return [toolchain]",
+        "dummy_toolchain = rule(_dummy_toolchain_impl, attrs = {})");
     config.create(
         "/bazel_tools_workspace/tools/cpp/CROSSTOOL",
         readCrosstoolFile());
@@ -156,6 +174,7 @@ public final class BazelMockCcSupport extends MockCcSupport {
       config.create("tools/cpp/link_dynamic_library.sh", "");
     }
     MockObjcSupport.setup(config);
+    MockPlatformSupport.setup(config, "/bazel_tools_workspace/platforms");
   }
 
   @Override
diff --git a/src/test/java/com/google/devtools/build/lib/packages/util/MockPlatformSupport.java b/src/test/java/com/google/devtools/build/lib/packages/util/MockPlatformSupport.java
index dd0b5463dd..f2d89fbbe4 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/util/MockPlatformSupport.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/util/MockPlatformSupport.java
@@ -11,7 +11,6 @@
 // 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.packages.util;
 
 import java.io.IOException;
@@ -20,9 +19,10 @@ import java.io.IOException;
 public class MockPlatformSupport {
 
   /** Adds mocks for basic host and target platform. */
-  public static void setup(MockToolsConfig mockToolsConfig) throws IOException {
+  public static void setup(MockToolsConfig mockToolsConfig, String platformsPath)
+      throws IOException {
     mockToolsConfig.create(
-        "buildenv/platforms/BUILD",
+        platformsPath + "/BUILD",
         "package(default_visibility=['//visibility:public'])",
         "platform(",
         "   name = 'target_platform',",
diff --git a/src/test/java/com/google/devtools/build/lib/rules/cpp/CcCommonTest.java b/src/test/java/com/google/devtools/build/lib/rules/cpp/CcCommonTest.java
index 2547d354f3..2ff18b4379 100644
--- a/src/test/java/com/google/devtools/build/lib/rules/cpp/CcCommonTest.java
+++ b/src/test/java/com/google/devtools/build/lib/rules/cpp/CcCommonTest.java
@@ -977,6 +977,7 @@ public class CcCommonTest extends BuildViewTestCase {
           BazelRuleClassProvider.BAZEL_SETUP.init(builder);
           CoreRules.INSTANCE.init(builder);
           BazelRuleClassProvider.CORE_WORKSPACE_RULES.init(builder);
+          BazelRuleClassProvider.PLATFORM_RULES.init(builder);
           BazelRuleClassProvider.GENERIC_RULES.init(builder);
           BazelRuleClassProvider.CPP_RULES.init(builder);
           builder.addRuleDefinition(new OnlyCppToolchainTypeRule());
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java
index 86bbf073f6..1c0f5697f1 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/RegisteredToolchainsFunctionTest.java
@@ -57,9 +57,10 @@ public class RegisteredToolchainsFunctionTest extends ToolchainTestCase {
     assertThatEvaluationResult(result).hasEntryThat(toolchainsKey).isNotNull();
 
     RegisteredToolchainsValue value = result.get(toolchainsKey);
-    assertThat(value.registeredToolchains()).hasSize(2);
+    // We have two registered toolchains, and one default for c++
+    assertThat(value.registeredToolchains()).hasSize(3);
 
-    DeclaredToolchainInfo registeredToolchain1 = value.registeredToolchains().get(0);
+    DeclaredToolchainInfo registeredToolchain1 = value.registeredToolchains().get(1);
     assertThat(registeredToolchain1).isNotNull();
 
     assertThat(registeredToolchain1.toolchainType()).isEqualTo(testToolchainType);
@@ -68,7 +69,7 @@ public class RegisteredToolchainsFunctionTest extends ToolchainTestCase {
     assertThat(registeredToolchain1.toolchainLabel())
         .isEqualTo(makeLabel("//toolchain:test_toolchain_1"));
 
-    DeclaredToolchainInfo registeredToolchain2 = value.registeredToolchains().get(1);
+    DeclaredToolchainInfo registeredToolchain2 = value.registeredToolchains().get(2);
     assertThat(registeredToolchain2).isNotNull();
 
     assertThat(registeredToolchain2.toolchainType()).isEqualTo(testToolchainType);
@@ -137,7 +138,7 @@ public class RegisteredToolchainsFunctionTest extends ToolchainTestCase {
         requestToolchainsFromSkyframe(toolchainsKey);
     assertThatEvaluationResult(result).hasNoError();
     assertToolchainLabels(result.get(toolchainsKey))
-        .containsExactly(makeLabel("//toolchain:test_toolchain_1"));
+        .contains(makeLabel("//toolchain:test_toolchain_1"));
 
     // Re-write the WORKSPACE.
     rewriteWorkspace("register_toolchains('//toolchain:toolchain_2')");
@@ -146,7 +147,7 @@ public class RegisteredToolchainsFunctionTest extends ToolchainTestCase {
     result = requestToolchainsFromSkyframe(toolchainsKey);
     assertThatEvaluationResult(result).hasNoError();
     assertToolchainLabels(result.get(toolchainsKey))
-        .containsExactly(makeLabel("//toolchain:test_toolchain_2"));
+        .contains(makeLabel("//toolchain:test_toolchain_2"));
   }
 
   @Test
diff --git a/src/test/java/com/google/devtools/build/lib/skyframe/RuleContextTest.java b/src/test/java/com/google/devtools/build/lib/skyframe/RuleContextTest.java
index 5ba165b4ed..1eeec40c78 100644
--- a/src/test/java/com/google/devtools/build/lib/skyframe/RuleContextTest.java
+++ b/src/test/java/com/google/devtools/build/lib/skyframe/RuleContextTest.java
@@ -18,7 +18,6 @@ import static com.google.common.truth.Truth.assertThat;
 
 import com.google.devtools.build.lib.analysis.RuleContext;
 import com.google.devtools.build.lib.cmdline.Label;
-import com.google.devtools.build.lib.packages.util.MockPlatformSupport;
 import com.google.devtools.build.lib.rules.platform.ToolchainTestCase;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -30,7 +29,6 @@ public class RuleContextTest extends ToolchainTestCase {
 
   @Test
   public void testMockRuleContextHasToolchains() throws Exception {
-    MockPlatformSupport.setup(mockToolsConfig);
     mockToolsConfig.create("x/BUILD", "mock_toolchain_rule(name='x')");
     useConfiguration(
         "--experimental_host_platform=//constraint:linux_plat",
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/TestRuleClassProvider.java b/src/test/java/com/google/devtools/build/lib/testutil/TestRuleClassProvider.java
index e69cb7ec0a..9391aa7b4a 100644
--- a/src/test/java/com/google/devtools/build/lib/testutil/TestRuleClassProvider.java
+++ b/src/test/java/com/google/devtools/build/lib/testutil/TestRuleClassProvider.java
@@ -27,7 +27,6 @@ import com.google.devtools.build.lib.analysis.ConfiguredRuleClassProvider;
 import com.google.devtools.build.lib.analysis.ConfiguredTarget;
 import com.google.devtools.build.lib.analysis.MakeVariableInfo;
 import com.google.devtools.build.lib.analysis.PlatformConfiguration;
-import com.google.devtools.build.lib.analysis.PlatformSemantics;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetBuilder;
 import com.google.devtools.build.lib.analysis.RuleConfiguredTargetFactory;
 import com.google.devtools.build.lib.analysis.RuleContext;
@@ -151,7 +150,7 @@ public class TestRuleClassProvider {
   public static class MockToolchainRule implements RuleDefinition {
     @Override
     public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env) {
-      return PlatformSemantics.platformAttributes(builder)
+      return builder
           .requiresConfigurationFragments(PlatformConfiguration.class)
           .addRequiredToolchains(
               ImmutableList.of(Label.parseAbsoluteUnchecked("//toolchain:test_toolchain")))
diff --git a/src/test/shell/integration/discard_graph_edges_test.sh b/src/test/shell/integration/discard_graph_edges_test.sh
index 3259566ece..aeedbeba90 100755
--- a/src/test/shell/integration/discard_graph_edges_test.sh
+++ b/src/test/shell/integration/discard_graph_edges_test.sh
@@ -193,7 +193,7 @@ function test_packages_cleared() {
       || fail "env extension count $env_count too low: did you move/rename the class?"
   local ct_count="$(extract_histogram_count "$histo_file" \
        'RuleConfiguredTarget$')"
-  [[ "ct_count" -ge 18 ]] \
+  [[ "ct_count" -ge 40 ]] \
       || fail "RuleConfiguredTarget count $ct_count too low: did you move/rename the class?"
   local histo_file="$(prepare_histogram "$BUILD_FLAGS")"
   package_count="$(extract_histogram_count "$histo_file" \
diff --git a/tools/BUILD b/tools/BUILD
index 61e9abc1a2..0432b126cb 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -51,7 +51,7 @@ filegroup(
         "//tools/jdk:package-srcs",
         "//tools/jdk:srcs",
         "//tools/launcher:srcs",
-        "//tools/platforms:package-srcs",
+        "//tools/platforms:srcs",
         "//tools/objc:srcs",
         "//tools/python:srcs",
         "//tools/test:srcs",
diff --git a/tools/cpp/BUILD b/tools/cpp/BUILD
index 1a4dc674ea..eb75333e75 100644
--- a/tools/cpp/BUILD
+++ b/tools/cpp/BUILD
@@ -204,3 +204,18 @@ filegroup(
     name = "link_dynamic_library",
     srcs = ["link_dynamic_library.sh"],
 )
+
+toolchain_type(name = "toolchain_type")
+
+# A dummy toolchain is necessary to satisfy toolchain resolution until platforms
+# are used in c++ by default.
+# TODO(b/64754003): Remove once platforms are used in c++ by default.
+toolchain(
+    name = "dummy_cc_toolchain",
+    toolchain = "dummy_cc_toolchain_impl",
+    toolchain_type = ":toolchain_type",
+)
+
+load(":dummy_toolchain.bzl", "dummy_toolchain")
+
+dummy_toolchain(name = "dummy_cc_toolchain_impl")
diff --git a/tools/cpp/BUILD.static b/tools/cpp/BUILD.static
index 9ae4950d80..aaadc5bad8 100644
--- a/tools/cpp/BUILD.static
+++ b/tools/cpp/BUILD.static
@@ -115,3 +115,18 @@ filegroup(
     name = "link_dynamic_library",
     srcs = ["link_dynamic_library.sh"],
 )
+
+toolchain_type(name = "toolchain_type")
+
+# A dummy toolchain is necessary to satisfy toolchain resolution until platforms
+# are used in c++ by default.
+# TODO(b/64754003): Remove once platforms are used in c++ by default.
+toolchain(
+    name = "dummy_cc_toolchain",
+    toolchain = "dummy_cc_toolchain_impl",
+    toolchain_type = ":toolchain_type",
+)
+
+load(":dummy_toolchain.bzl", "dummy_toolchain")
+
+dummy_toolchain(name = "dummy_cc_toolchain_impl")
diff --git a/tools/cpp/BUILD.tpl b/tools/cpp/BUILD.tpl
index 5ea5368c62..170fe3f91d 100644
--- a/tools/cpp/BUILD.tpl
+++ b/tools/cpp/BUILD.tpl
@@ -75,3 +75,18 @@ cc_toolchain(
     strip_files = ":empty",
     supports_param_files = 1,
 )
+
+toolchain_type(name = "toolchain_type")
+
+# A dummy toolchain is necessary to satisfy toolchain resolution until platforms
+# are used in c++ by default.
+# TODO(b/64754003): Remove once platforms are used in c++ by default.
+toolchain(
+    name = "dummy_cc_toolchain",
+    toolchain = "dummy_cc_toolchain_impl",
+    toolchain_type = ":toolchain_type",
+)
+
+load(":dummy_toolchain.bzl", "dummy_toolchain")
+
+dummy_toolchain(name = "dummy_cc_toolchain_impl")
diff --git a/tools/cpp/cc_configure.bzl b/tools/cpp/cc_configure.bzl
index 70e2fd0ff1..9d6d29fc82 100644
--- a/tools/cpp/cc_configure.bzl
+++ b/tools/cpp/cc_configure.bzl
@@ -20,6 +20,8 @@ load("@bazel_tools//tools/cpp:unix_cc_configure.bzl", "configure_unix_toolchain"
 load("@bazel_tools//tools/cpp:lib_cc_configure.bzl", "get_cpu_value")
 
 def _impl(repository_ctx):
+  repository_ctx.symlink(
+      Label("@bazel_tools//tools/cpp:dummy_toolchain.bzl"), "dummy_toolchain.bzl")
   cpu_value = get_cpu_value(repository_ctx)
   if cpu_value == "freebsd":
     # This is defaulting to the static crosstool, we should eventually
diff --git a/tools/cpp/dummy_toolchain.bzl b/tools/cpp/dummy_toolchain.bzl
new file mode 100644
index 0000000000..c787f7315d
--- /dev/null
+++ b/tools/cpp/dummy_toolchain.bzl
@@ -0,0 +1,23 @@
+# pylint: disable=g-bad-file-header
+# Copyright 2017 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.
+
+"""Skylark rule that stubs a toolchain."""
+def _dummy_toolchain_impl(ctx):
+  ctx = ctx  # unused argument
+  toolchain = platform_common.ToolchainInfo()
+  return [toolchain]
+
+dummy_toolchain = rule(_dummy_toolchain_impl, attrs = {})
+
diff --git a/tools/platforms/BUILD b/tools/platforms/BUILD
index 4e788aea2c..1b74f106eb 100644
--- a/tools/platforms/BUILD
+++ b/tools/platforms/BUILD
@@ -13,3 +13,95 @@ filegroup(
     name = "srcs",
     srcs = glob(["**"]),
 )
+
+# These match values in //src/main/java/com/google/build/lib/util:CPU.java
+constraint_setting(name = "cpu")
+
+constraint_value(
+    name = "x86_32",
+    constraint_setting = ":cpu",
+)
+
+constraint_value(
+    name = "x86_64",
+    constraint_setting = ":cpu",
+)
+
+constraint_value(
+    name = "ppc",
+    constraint_setting = ":cpu",
+)
+
+constraint_value(
+    name = "arm",
+    constraint_setting = ":cpu",
+)
+
+constraint_value(
+    name = "s390x",
+    constraint_setting = ":cpu",
+)
+
+# These match values in //src/main/java/com/google/build/lib/util:OS.java
+constraint_setting(name = "os")
+
+constraint_value(
+    name = "osx",
+    constraint_setting = ":os",
+)
+
+constraint_value(
+    name = "freebsd",
+    constraint_setting = ":os",
+)
+
+constraint_value(
+    name = "linux",
+    constraint_setting = ":os",
+)
+
+constraint_value(
+    name = "windows",
+    constraint_setting = ":os",
+)
+
+# A default platform with nothing defined.
+platform(name = "default_platform")
+
+# A default platform referring to the host system. This only exists for
+# internal build configurations, and so shouldn't be accessed by other packages.
+platform(
+    name = "host_platform",
+    cpu_constraints = [
+        ":x86_32",
+        ":x86_64",
+        ":ppc",
+        ":arm",
+        ":s390x",
+    ],
+    host_platform = True,
+    os_constraints = [
+        ":osx",
+        ":freebsd",
+        ":linux",
+        ":windows",
+    ],
+)
+
+platform(
+    name = "target_platform",
+    cpu_constraints = [
+        ":x86_32",
+        ":x86_64",
+        ":ppc",
+        ":arm",
+        ":s390x",
+    ],
+    os_constraints = [
+        ":osx",
+        ":freebsd",
+        ":linux",
+        ":windows",
+    ],
+    target_platform = True,
+)