Add support for data in expand_template

This can be useful for encoding the paths to things in your expansions

Author: keith

rules/expand_template.bzl

@@ -16,10 +16,17 @@
 """
 
 def _expand_template_impl(ctx):
+    expanded_substitutions = {}
+    for key, value in ctx.attr.substitutions.items():
+        expanded_substitutions[key] = ctx.expand_location(
+            value,
+            targets = ctx.attr.data,
+        )
+
     ctx.actions.expand_template(
         template = ctx.file.template,
         output = ctx.outputs.out,
-        substitutions = ctx.attr.substitutions,
+        substitutions = expanded_substitutions,
     )
 
 expand_template = rule(
@@ -32,6 +39,11 @@ 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 = {
+        "data": attr.label_list(
+            allow_files = True,
+            doc = "data dependencies. See" +
+                  " https://bazel.build/reference/be/common-definitions#typical.data",
+        ),
         "template": attr.label(
             mandatory = True,
             allow_single_file = True,

tests/expand_template/BUILD

@@ -24,9 +24,13 @@ package(
 expand_template(
     name = "filled_template",
     out = "foo/test.yaml",
+    data = [
+        ":version",
+    ],
     substitutions = {
         "@name@": "test",
         "@version@": "1.1.1",
+        "@path@": "$(rlocationpath :version)",
     },
     template = "test.tpl.yaml",
 )

tests/expand_template/template_test.sh

@@ -32,6 +32,7 @@ function test_expand_template() {
   cat "$(rlocation $TEST_WORKSPACE/tests/expand_template/foo/test.yaml)" >"$TEST_log"
   expect_log 'name: test'
   expect_log 'version: 1.1.1'
+  expect_log 'path: _main/tests/expand_template/version.h'
 }
 
-run_suite "expand_template_tests test suite"
+run_suite "expand_template_tests test suite"

tests/expand_template/test.tpl.yaml

@@ -1,2 +1,3 @@
 name: @name@
 version: @version@
+path: @path@