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diff --git a/rules/expand_template.bzl b/rules/expand_template.bzl
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+# Copyright 2022 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.
+
+"""A rule that performs template expansion.
+"""
+
+def _expand_template_impl(ctx):
+    ctx.actions.expand_template(
+        template = ctx.file.template,
+        output = ctx.outputs.out,
+        substitutions = ctx.attr.substitutions,
+    )
+
+expand_template = rule(
+    implementation = _expand_template_impl,
+    doc = """Template expansion
+
+This performs a simple search over the template file for the keys in
+substitutions, and replaces them with the corresponding values.
+
+There is no special syntax for the keys. To avoid conflicts, you would need to
+explicitly add delimiters to the key strings, for example "{KEY}" or "@KEY@".""",
+    attrs = {
+        "template": attr.label(
+            mandatory = True,
+            allow_single_file = True,
+            doc = "The template file to expand.",
+        ),
+        "substitutions": attr.string_dict(
+            mandatory = True,
+            doc = "A dictionary mapping strings to their substitutions.",
+        ),
+        "out": attr.output(
+            mandatory = True,
+            doc = "The destination of the expanded file.",
+        ),
+    },
+    output_to_genfiles = True,
+)