1 files changed, 158 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java
new file mode 100644
index 0000000000..afa107a327
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+++ b/src/main/java/com/google/devtools/build/lib/syntax/SkylarkMutable.java
@@ -0,0 +1,158 @@
+// Copyright 2016 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.syntax;
+
+import com.google.devtools.build.lib.events.Location;
+import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;
+import com.google.devtools.build.lib.syntax.Mutability.Freezable;
+import com.google.devtools.build.lib.syntax.Mutability.MutabilityException;
+
+import java.util.Collection;
+import java.util.Iterator;
+
+import javax.annotation.Nullable;
+
+/**
+ * Base class for data structures that are only mutable with a proper Mutability.
+ */
+abstract class SkylarkMutable implements Freezable, SkylarkValue {
+
+  protected SkylarkMutable() {}
+
+  /**
+   * Check whether this object is mutable in the current evaluation Environment.
+   * @throws EvalException if the object was not mutable.
+   */
+  protected void checkMutable(Location loc, Environment env) throws EvalException {
+    try {
+      Mutability.checkMutable(this, env);
+    } catch (MutabilityException ex) {
+      throw new EvalException(loc, ex);
+    }
+  }
+
+  @Override
+  public String toString() {
+    return Printer.repr(this);
+  }
+
+  abstract static class MutableCollection<E> extends SkylarkMutable implements Collection<E> {
+
+    protected MutableCollection() {}
+
+    /**
+     * Return the underlying contents of this collection,
+     * that may be of a more specific class with its own methods.
+     * This object MUST NOT be mutated.
+     * If possible, the implementation should make this object effectively immutable,
+     * by throwing {@link UnsupportedOperationException} if attemptedly mutated;
+     * but it need not be an instance of {@link com.google.common.collect.ImmutableCollection}.
+     */
+    public abstract Collection<Object> getContents();
+
+    /**
+     * The underlying contents is a (usually) mutable data structure.
+     * Read access is forwarded to these contents.
+     * This object must not be modified outside an {@link Environment}
+     * with a correct matching {@link Mutability},
+     * which should be checked beforehand using {@link #checkMutable}.
+     * it need not be an instance of {@link com.google.common.collect.ImmutableCollection}.
+     */
+    protected abstract Collection<E> getContentsUnsafe();
+
+    @Override
+    public Iterator<E> iterator() {
+      return getContentsUnsafe().iterator();
+    };
+
+    @Override
+    public int size() {
+      return getContentsUnsafe().size();
+    }
+
+    @Override
+    public final Object[] toArray() {
+      return getContentsUnsafe().toArray();
+    }
+
+    @Override
+    public final <Object> Object[] toArray(Object[] other) {
+      return getContentsUnsafe().toArray(other);
+    }
+
+    @Override
+    public boolean isEmpty() {
+      return getContentsUnsafe().isEmpty();
+    }
+
+    @Override
+    public final boolean contains(@Nullable Object object) {
+      return getContentsUnsafe().contains(object);
+    }
+
+    @Override
+    public final boolean containsAll(Collection<?> collection) {
+      return getContentsUnsafe().containsAll(collection);
+    }
+
+    // Disable all mutation interfaces without a mutation context.
+
+    @Deprecated
+    @Override
+    public final boolean add(E element) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Deprecated
+    @Override
+    public final boolean addAll(Collection<? extends E> collection) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Deprecated
+    @Override
+    public final boolean remove(Object object) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Deprecated
+    @Override
+    public final boolean removeAll(Collection<?> collection) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Deprecated
+    @Override
+    public final boolean retainAll(Collection<?> collection) {
+      throw new UnsupportedOperationException();
+    }
+
+    @Deprecated
+    @Override
+    public final void clear() {
+      throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+      return getContentsUnsafe().equals(o);
+    }
+
+    @Override
+    public int hashCode() {
+      return getContentsUnsafe().hashCode();
+    }
+  }
+}