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diff --git a/examples/vendor/constant_gen/defs.bzl b/examples/vendor/constant_gen/defs.bzl
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+"""A trivial rule to turn a string into a C++ constant."""
+
+# Copyright 2020 Google LLC
+#
+# 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
+#
+# https://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.
+
+def _constant_gen_impl(ctx):
+    # Turn text into a C++ constant.
+    outputs = [ctx.outputs.src_out]
+    ctx.actions.run(
+        mnemonic = "GenerateConstant",
+        progress_message = "Generating %s" % ctx.attr.var,
+        outputs = outputs,
+        executable = ctx.executable._generator,
+        arguments = [ctx.outputs.src_out.path, ctx.attr.var, ctx.attr.text],
+    )
+    return [DefaultInfo(files = depset(outputs))]
+
+_constant_gen = rule(
+    implementation = _constant_gen_impl,
+    attrs = {
+        "src_out": attr.output(mandatory = True),
+        "text": attr.string(mandatory = True),
+        "var": attr.string(mandatory = False),
+        "_generator": attr.label(
+            default = Label("@rules_license//examples/vendor/constant_gen:constant_generator"),
+            executable = True,
+            allow_files = True,
+            cfg = "host",
+        ),
+    },
+)
+
+def constant_gen(name, text, var):
+    # Generate the code
+    _constant_gen(
+        name = name + "_src_",
+        src_out = name + "_src_.cc",
+        text = text,
+        var = var,
+        applicable_licenses = ["@rules_license//examples/vendor/constant_gen:license_for_emitted_code"],
+    )
+
+    # And turn it into a library we can link against
+    native.cc_library(
+        name = name,
+        srcs = [name + "_src_"],
+        applicable_licenses = ["@rules_license//examples/vendor/constant_gen:license_for_emitted_code"],
+    )