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

Part of ongoing work on #2219.

--
Change-Id: Ie4e842a5d8218e47f41a954c2b955ab24237aa65
Reviewed-on: https://cr.bazel.build/9116
PiperOrigin-RevId: 148976893
MOS_MIGRATED_REVID=148976893

3 files changed, 226 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/platform/Platform.java b/src/main/java/com/google/devtools/build/lib/rules/platform/Platform.java
new file mode 100644
index 0000000000..f652383757
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/platform/Platform.java
@@ -0,0 +1,101 @@
+// 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.common.collect.ArrayListMultimap;
+import com.google.common.collect.ImmutableMap;
+import com.google.common.collect.Iterables;
+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 {
+
+    Iterable<ConstraintValueProvider> constraintValues =
+        ruleContext.getPrerequisites(
+            PlatformRule.CONSTRAINT_VALUES_ATTR, Mode.DONT_CHECK, ConstraintValueProvider.class);
+
+    // Verify the constraints - no two values for the same setting, and construct the map.
+    ImmutableMap<ConstraintSettingProvider, ConstraintValueProvider> constraints =
+        validateConstraints(ruleContext, constraintValues);
+    if (constraints == null) {
+      // An error occurred, return null.
+      return null;
+    }
+
+    return new RuleConfiguredTargetBuilder(ruleContext)
+        .addProvider(RunfilesProvider.class, RunfilesProvider.EMPTY)
+        .addProvider(FileProvider.class, FileProvider.EMPTY)
+        .addProvider(FilesToRunProvider.class, FilesToRunProvider.EMPTY)
+        .addProvider(PlatformProvider.class, PlatformProvider.create(constraints))
+        .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?
+    boolean foundError = false;
+    for (ConstraintSettingProvider constraintSetting : constraints.keySet()) {
+      if (constraints.get(constraintSetting).size() > 1) {
+        foundError = true;
+        // error
+        StringBuilder constraintValuesDescription = new StringBuilder();
+        for (ConstraintValueProvider constraintValue : constraints.get(constraintSetting)) {
+          if (constraintValuesDescription.length() > 0) {
+            constraintValuesDescription.append(", ");
+          }
+          constraintValuesDescription.append(constraintValue.value());
+        }
+        ruleContext.attributeError(
+            PlatformRule.CONSTRAINT_VALUES_ATTR,
+            String.format(
+                "Duplicate constraint_values for constraint_setting %s: %s",
+                constraintSetting.constraintSetting(), constraintValuesDescription.toString()));
+      }
+    }
+
+    if (foundError) {
+      return null;
+    }
+
+    // Convert to a flat map.
+    ImmutableMap.Builder<ConstraintSettingProvider, ConstraintValueProvider> builder =
+        new ImmutableMap.Builder<>();
+    for (ConstraintSettingProvider constraintSetting : constraints.keySet()) {
+      ConstraintValueProvider constraintValue =
+          Iterables.getOnlyElement(constraints.get(constraintSetting));
+      builder.put(constraintSetting, constraintValue);
+    }
+
+    return builder.build();
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/platform/PlatformProvider.java b/src/main/java/com/google/devtools/build/lib/rules/platform/PlatformProvider.java
new file mode 100644
index 0000000000..7a06c1f138
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/platform/PlatformProvider.java
@@ -0,0 +1,32 @@
+// 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);
+  }
+}
diff --git a/src/main/java/com/google/devtools/build/lib/rules/platform/PlatformRule.java b/src/main/java/com/google/devtools/build/lib/rules/platform/PlatformRule.java
new file mode 100644
index 0000000000..29537a4fb0
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/platform/PlatformRule.java
@@ -0,0 +1,93 @@
+// 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 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 CONSTRAINT_VALUES_ATTR = "constraint_values";
+
+  @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"))
+        .add(
+            attr(CONSTRAINT_VALUES_ATTR, BuildType.LABEL_LIST)
+                .allowedFileTypes(FileTypeSet.NO_FILE)
+                .mandatoryNativeProviders(
+                    ImmutableList.<Class<? extends TransitiveInfoProvider>>of(
+                        ConstraintValueProvider.class)))
+        .removeAttribute("deps")
+        .removeAttribute("data")
+        .exemptFromConstraintChecking("this rule is part of constraint definition")
+        .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 = Platform)[GENERIC_RULE] -->
+
+<p>This rule defines a platform, as a collection of constraint_values.
+
+<h4 id="platform_examples">Examples</h4>
+<p>
+  This defines two possible platforms, each targeting a different CPU type.
+</p>
+<pre class="code">
+constraint_setting(name="cpu")
+constraint_value(
+    name="arm64",
+    constraint=":cpu")
+constraint_value(
+    name="k8",
+    constraint=":cpu")
+platform(
+    name="mobile_device",
+    constraints = [
+        ":arm64",
+    ])
+platform(
+    name="devel",
+    constraints = [
+        ":k8",
+    ])
+</pre>
+
+<!-- #END_BLAZE_RULE -->*/