1 files changed, 71 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/packages/ProviderFromFunction.java b/src/main/java/com/google/devtools/build/lib/packages/ProviderFromFunction.java
new file mode 100644
index 0000000000..134ed49175
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/packages/ProviderFromFunction.java
@@ -0,0 +1,71 @@
+// Copyright 2018 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.packages;
+
+import com.google.devtools.build.lib.concurrent.ThreadSafety.Immutable;
+import com.google.devtools.build.lib.events.Location;
+import com.google.devtools.build.lib.syntax.BaseFunction;
+import com.google.devtools.build.lib.syntax.Environment;
+import com.google.devtools.build.lib.syntax.EvalException;
+import com.google.devtools.build.lib.syntax.FuncallExpression;
+import com.google.devtools.build.lib.syntax.FunctionSignature;
+import com.google.devtools.build.lib.syntax.SkylarkType;
+import javax.annotation.Nullable;
+
+/**
+ * Implementation of {@link Provider} that is represented by a {@link BaseFunction}, and thus
+ * callable from Skylark.
+ */
+@Immutable
+abstract class ProviderFromFunction extends BaseFunction implements Provider {
+
+  /**
+   * Constructs a provider.
+   *
+   * @param name provider name; should be null iff the subclass overrides {@link #getName}
+   * @param signature the signature for calling this provider as a Skylark function (to construct an
+   *     instance of the provider)
+   * @param location the location of this provider's Skylark definition. Use {@link
+   *     Location#BUILTIN} if it is a native provider.
+   */
+  protected ProviderFromFunction(
+      @Nullable String name,
+      FunctionSignature.WithValues<Object, SkylarkType> signature,
+      Location location) {
+    super(name, signature, location);
+  }
+
+  public SkylarkProviderIdentifier id() {
+    return SkylarkProviderIdentifier.forKey(getKey());
+  }
+
+  @Override
+  protected Object call(Object[] args, @Nullable FuncallExpression ast, Environment env)
+      throws EvalException, InterruptedException {
+    Location loc = ast != null ? ast.getLocation() : Location.BUILTIN;
+    return createInstanceFromSkylark(args, env, loc);
+  }
+
+  /**
+   * Override this method to provide logic that is used to instantiate a declared provider from
+   * Skylark.
+   *
+   * <p>This is a method that is called when a constructor {@code c} is invoked as<br>
+   * {@code c(arg1 = val1, arg2 = val2, ...)}.
+   *
+   * @param args an array of argument values sorted as per the signature ({@see BaseFunction#call})
+   */
+  protected abstract Info createInstanceFromSkylark(Object[] args, Environment env, Location loc)
+      throws EvalException;
+}