1 files changed, 43 insertions, 0 deletions
diff --git a/third_party/common.bzl b/third_party/common.bzl
new file mode 100644
index 0000000000..db981a5e31
--- /dev/null
+++ b/third_party/common.bzl
@@ -0,0 +1,43 @@
+# Rule for simple expansion of template files. This performs a simple
+# search over the template file for the keys in substitutions,
+# and replaces them with the corresponding values.
+#
+# Typical usage:
+#   load("/tools/build_rules/template_rule", "expand_header_template")
+#   template_rule(
+#       name = "ExpandMyTemplate",
+#       src = "my.template",
+#       out = "my.txt",
+#       substitutions = {
+#         "$VAR1": "foo",
+#         "$VAR2": "bar",
+#       }
+#   )
+#
+# Args:
+#   name: The name of the rule.
+#   template: The template file to expand
+#   out: The destination of the expanded file
+#   substitutions: A dictionary mapping strings to their substitutions
+
+def template_rule_impl(ctx):
+  ctx.template_action(
+      template = ctx.file.src,
+      output = ctx.outputs.out,
+      substitutions = ctx.attr.substitutions,
+  )
+
+template_rule = rule(
+    attrs = {
+        "src": attr.label(
+            mandatory = True,
+            allow_files = True,
+            single_file = True,
+        ),
+        "substitutions": attr.string_dict(mandatory = True),
+        "out": attr.output(mandatory = True),
+    },
+    # output_to_genfiles is required for header files.
+    output_to_genfiles = True,
+    implementation = template_rule_impl,
+)