Add platform rule to define a platform as a collection of constraint

values.

Part of ongoing work on bazelbuild#2219.

Change-Id: Ie4e842a5d8218e47f41a954c2b955ab24237aa65

src/main/java/com/google/devtools/build/lib/bazel/rules/BazelRuleClassProvider.java

@@ -161,6 +161,7 @@
 import com.google.devtools.build.lib.rules.objc.XcTestAppProvider;
 import com.google.devtools.build.lib.rules.platform.ConstraintSettingRule;
 import com.google.devtools.build.lib.rules.platform.ConstraintValueRule;
+import com.google.devtools.build.lib.rules.platform.PlatformRule;
 import com.google.devtools.build.lib.rules.proto.BazelProtoLibraryRule;
 import com.google.devtools.build.lib.rules.proto.ProtoConfiguration;
 import com.google.devtools.build.lib.rules.proto.ProtoLangToolchainRule;
@@ -343,6 +344,7 @@ public ImmutableList<RuleSet> requires() {
         public void init(Builder builder) {
           builder.addRuleDefinition(new ConstraintSettingRule());
           builder.addRuleDefinition(new ConstraintValueRule());
+          builder.addRuleDefinition(new PlatformRule());
         }
 
         @Override

src/main/java/com/google/devtools/build/lib/rules/platform/Platform.java

@@ -0,0 +1,60 @@
+package com.google.devtools.build.lib.rules.platform;
+
+import com.google.common.collect.ArrayListMultimap;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Multimap;
+import com.google.devtools.build.lib.analysis.ConfiguredTarget;
+import com.google.devtools.build.lib.analysis.FileProvider;
+import com.google.devtools.build.lib.analysis.FilesToRunProvider;
+import com.google.devtools.build.lib.analysis.RuleConfiguredTarget.Mode;
+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;
+
+/** Defines a platform for execution contexts. */
+public class Platform implements RuleConfiguredTargetFactory {
+  @Override
+  public ConfiguredTarget create(RuleContext ruleContext)
+      throws InterruptedException, RuleErrorException {
+
+    // TODO(katre): Create platform provider with correct data.
+    Iterable<ConstraintValueProvider> constraintValues =
+        ruleContext.getPrerequisites(
+            PlatformRule.CONSTRAINTS_ATTR, Mode.DONT_CHECK, ConstraintValueProvider.class);
+
+    // TODO(katre): Verify the constraints - no two settings.
+    ImmutableMap<ConstraintSettingProvider, ConstraintValueProvider> constraints = validateConstraints(ruleContext, constraintValues);
+    if (constraints == null) {
+      // An error occurred, return null.
+      return null;
+    }
+
+    PlatformProvider provider = PlatformProvider.create(constraints);
+
+    return new RuleConfiguredTargetBuilder(ruleContext)
+        .addProvider(RunfilesProvider.class, RunfilesProvider.EMPTY)
+        .addProvider(FileProvider.class, FileProvider.EMPTY)
+        .addProvider(FilesToRunProvider.class, FilesToRunProvider.EMPTY)
+        .addProvider(PlatformProvider.class, provider)
+        .build();
+  }
+
+  private ImmutableMap<ConstraintSettingProvider, ConstraintValueProvider> validateConstraints(RuleContext ruleContext,
+      Iterable<ConstraintValueProvider> constraintValues) {
+    Multimap<ConstraintSettingProvider, ConstraintValueProvider> constraints = ArrayListMultimap.create();
+
+    for (ConstraintValueProvider constraintValue : constraintValues) {
+      constraints.put(constraintValue.constraint(), constraintValue);
+    }
+
+    // Are there any settings with more than one value?
+    for (ConstraintSettingProvider constraintSetting : constraints.keySet()) {
+      if (constraints.get(constraintSetting).size() > 1) {
+        // error
+      }
+    }
+
+    return null;
+  }
+}

src/main/java/com/google/devtools/build/lib/rules/platform/PlatformProvider.java

@@ -0,0 +1,43 @@
+// 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.
+
+package com.google.devtools.build.lib.rules.platform;
+
+import com.google.auto.value.AutoValue;
+import com.google.common.collect.ImmutableMap;
+import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+
+/** Provider for a platform, which is a group of constraints and values. */
+@AutoValue
+@Immutable
+public abstract class PlatformProvider implements TransitiveInfoProvider {
+  public abstract ImmutableMap<ConstraintSettingProvider, ConstraintValueProvider> constraints();
+
+  public static PlatformProvider create(
+      ImmutableMap<ConstraintSettingProvider, ConstraintValueProvider> constraints) {
+    return new AutoValue_PlatformProvider(constraints);
+  }
+
+  public static PlatformProvider create(Iterable<ConstraintValueProvider> constraintValues) {
+    ImmutableMap.Builder<ConstraintSettingProvider, ConstraintValueProvider> builder =
+        new ImmutableMap.Builder<>();
+
+    for (ConstraintValueProvider constraintValue : constraintValues) {
+      builder.put(constraintValue.constraint(), constraintValue);
+    }
+
+    return create(builder.build());
+  }
+}

src/main/java/com/google/devtools/build/lib/rules/platform/PlatformRule.java

@@ -0,0 +1,54 @@
+package com.google.devtools.build.lib.rules.platform;
+
+import static com.google.devtools.build.lib.packages.Attribute.attr;
+
+import com.google.common.collect.ImmutableList;
+import com.google.devtools.build.lib.analysis.BaseRuleClasses;
+import com.google.devtools.build.lib.analysis.RuleDefinition;
+import com.google.devtools.build.lib.analysis.RuleDefinitionEnvironment;
+import com.google.devtools.build.lib.analysis.TransitiveInfoProvider;
+import com.google.devtools.build.lib.packages.BuildType;
+import com.google.devtools.build.lib.packages.RuleClass;
+import com.google.devtools.build.lib.syntax.Type;
+import com.google.devtools.build.lib.util.FileTypeSet;
+
+/** Rule definition for {@link Platform}. */
+public class PlatformRule implements RuleDefinition {
+  public static final String RULE_NAME = "platform";
+  public static final String CONSTRAINTS_ATTR = "constraints";
+
+  @Override
+  public RuleClass build(RuleClass.Builder builder, RuleDefinitionEnvironment env) {
+    /* <!-- #BLAZE_RULE(platform).NAME -->
+    <!-- #END_BLAZE_RULE.NAME --> */
+    return builder
+        .override(
+            attr("tags", Type.STRING_LIST)
+                // No need to show up in ":all", etc. target patterns.
+                .value(ImmutableList.of("manual"))
+                .nonconfigurable("low-level attribute, used in platform configuration"))
+
+        // TODO(katre): add constraints attr.
+        .add(
+            attr(CONSTRAINTS_ATTR, BuildType.LABEL_LIST)
+                .allowedFileTypes(FileTypeSet.NO_FILE)
+                .mandatoryNativeProviders(
+                    ImmutableList.<Class<? extends TransitiveInfoProvider>>of(
+                        ConstraintValueProvider.class)))
+        .exemptFromConstraintChecking("this rule *defines* a constraint")
+        .build();
+  }
+
+  @Override
+  public Metadata getMetadata() {
+    return Metadata.builder()
+        .name(RULE_NAME)
+        .ancestors(BaseRuleClasses.RuleBase.class)
+        .factoryClass(Platform.class)
+        .build();
+  }
+}
+/*<!-- #BLAZE_RULE (NAME = platform, TYPE = OTHER, FAMILY = General)[GENERIC_RULE] -->
+
+
+<!-- #END_BLAZE_RULE -->*/

src/test/java/com/google/devtools/build/lib/rules/platform/ConstraintTest.java

@@ -57,4 +57,49 @@ public void testConstraint() throws Exception {
     assertThat(barValue.getProvider(ConstraintValueProvider.class).value())
         .isEqualTo(Label.parseAbsolute("//constraint:bar"));
   }
+
+  @Test
+  public void testPlatform() throws Exception {
+    scratch.file(
+            "constraint/BUILD",
+            "constraint_setting(name = 'basic')",
+            "constraint_value(name = 'foo',",
+            "    constraint=':basic',",
+            "    )",
+            "platform(name = 'plat1',",
+            "    constraints = [",
+            "       ':foo',",
+            "    ])"
+    );
+
+    ConfiguredTarget platform = getConfiguredTarget("//constraint:plat1");
+    assertThat(platform).isNotNull();
+
+    PlatformProvider provider = platform.getProvider(PlatformProvider.class);
+    assertThat(provider).isNotNull();
+    assertThat(provider.constraints()).hasSize(1);
+    assertThat(provider.constraints()).containsKey(ConstraintSettingProvider.create(Label.parseAbsolute("//constraint:basic")));
+    assertThat(provider.constraints().get(ConstraintSettingProvider.create(Label.parseAbsolute("//constraint:basic"))).value())
+        .isEqualTo(Label.parseAbsolute("//constraint:foo"));
+  }
+
+  @Test
+  public void testPlatform_overlappingConstraintValueError() throws Exception {
+    checkError("constraint",
+        "plat1",
+        "Conflicting constraint values for //constraint:basic",
+        "constraint_setting(name = 'basic')",
+        "constraint_value(name = 'foo',",
+        "    constraint=':basic',",
+        "    )",
+        "constraint_value(name = 'bar',",
+        "    constraint=':basic',",
+        "    )",
+        "platform(name = 'plat1',",
+        "    constraints = [",
+        "       ':foo',",
+        "       ':bar',",
+        "    ])"
+    );
+  }
 }