bazel: support linking accumulated libraries into C++ binaries

This CL permits a cc_binary to have a set of dependencies that are all
gathered together when the cc_binary is linked, producing a set of
LibraryToLink objects to link into the cc_binary.  Each such
dependency will an instance of a class that extends BuildLibraryToLink
to a CcLinkParams.  All instances of the same class will be gathered
together.  At link time the BuildLibraryToLink method buildLibraries
will be called to build the LibraryToLink objects.

--
MOS_MIGRATED_REVID=107242331

1 files changed, 63 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/ExtraLinkTimeLibrary.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/ExtraLinkTimeLibrary.java
new file mode 100644
index 0000000000..52b2a0822a
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/ExtraLinkTimeLibrary.java
@@ -0,0 +1,63 @@
+// Copyright 2015 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.cpp;
+
+import com.google.devtools.build.lib.analysis.RuleContext;
+import com.google.devtools.build.lib.collect.nestedset.NestedSet;
+import com.google.devtools.build.lib.rules.cpp.LinkerInputs.LibraryToLink;
+
+/**
+ * An extra library to include in a link.  The actual library is built
+ * at link time.
+ *
+ * <p>This can be used for non-C++ inputs to a C++ link.  A class that
+ * implements this interface will support transitively gathering all
+ * inputs from link dependencies, and then combine them all together
+ * into a set of C++ libraries.
+ *
+ * <p>Any implementations must be immutable (and therefore thread-safe),
+ * because this is passed between rules and accessed in a multi-threaded
+ * context.
+ */
+public interface ExtraLinkTimeLibrary {
+  /**
+   * Build the LibraryToLink inputs to pass to the C++ linker.
+   */
+  NestedSet<LibraryToLink> buildLibraries(RuleContext context);
+
+  /**
+   * Get a new Builder for this ExtraLinkTimeLibrary class.  This acts
+   * like a static method, in that the result does not depend on the
+   * current state of the object, and the new Builder starts out
+   * empty.
+   */
+  Builder getBuilder();
+
+  /**
+   * The Builder interface builds an ExtraLinkTimeLibrary.
+   */
+  public interface Builder {
+    /**
+     * Add the inputs associated with another instance of the same
+     * underlying ExtraLinkTimeLibrary type.
+     */
+    void addTransitive(ExtraLinkTimeLibrary dep);
+
+    /**
+     * Build the ExtraLinkTimeLibrary based on the inputs.
+     */
+    ExtraLinkTimeLibrary build();
+  }
+}