From d5ae39f0774e51c3a40924a1b973a7947b5a3212 Mon Sep 17 00:00:00 2001
From: Keith Smiley <keithbsmiley@gmail.com>
Date: Mon, 24 Jun 2024 11:13:39 -0700
Subject: [PATCH] Add support for data in expand_template

This can be useful for encoding the paths to things in your expansions
---
 docs/expand_template_doc.md            |  3 ++-
 rules/expand_template.bzl              | 18 +++++++++++++++++-
 tests/expand_template/BUILD            | 15 +++++++++++++++
 tests/expand_template/template_test.sh |  4 +++-
 tests/expand_template/test.tpl.yaml    |  2 ++
 5 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/docs/expand_template_doc.md b/docs/expand_template_doc.md
index 34bbb3a..b5f4add 100755
--- a/docs/expand_template_doc.md
+++ b/docs/expand_template_doc.md
@@ -7,7 +7,7 @@ A rule that performs template expansion.
 ## expand_template
 
 <pre>
-expand_template(<a href="#expand_template-name">name</a>, <a href="#expand_template-out">out</a>, <a href="#expand_template-substitutions">substitutions</a>, <a href="#expand_template-template">template</a>)
+expand_template(<a href="#expand_template-name">name</a>, <a href="#expand_template-data">data</a>, <a href="#expand_template-out">out</a>, <a href="#expand_template-substitutions">substitutions</a>, <a href="#expand_template-template">template</a>)
 </pre>
 
 Template expansion
@@ -24,6 +24,7 @@ explicitly add delimiters to the key strings, for example "{KEY}" or "@KEY@".
 | Name  | Description | Type | Mandatory | Default |
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <a id="expand_template-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
+| <a id="expand_template-data"></a>data |  data dependencies. See https://bazel.build/reference/be/common-definitions#typical.data   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional |  `[]`  |
 | <a id="expand_template-out"></a>out |  The destination of the expanded file.   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
 | <a id="expand_template-substitutions"></a>substitutions |  A dictionary mapping strings to their substitutions.   | <a href="https://bazel.build/rules/lib/dict">Dictionary: String -> String</a> | required |  |
 | <a id="expand_template-template"></a>template |  The template file to expand.   | <a href="https://bazel.build/concepts/labels">Label</a> | required |  |
diff --git a/rules/expand_template.bzl b/rules/expand_template.bzl
index f95507e..2c1a7e3 100644
--- a/rules/expand_template.bzl
+++ b/rules/expand_template.bzl
@@ -16,10 +16,21 @@
 """
 
 def _expand_template_impl(ctx):
+    expanded_substitutions = {}
+    for key, value in ctx.attr.substitutions.items():
+        expanded_substitutions[key] = ctx.expand_make_variables(
+            "substitutions",
+            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 +43,11 @@ 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,
diff --git a/tests/expand_template/BUILD b/tests/expand_template/BUILD
index 07fc579..6dbe34a 100644
--- a/tests/expand_template/BUILD
+++ b/tests/expand_template/BUILD
@@ -14,6 +14,7 @@
 
 # This package aids testing the 'diff_test' rule.
 
+load("//rules:common_settings.bzl", "string_flag")
 load("//rules:expand_template.bzl", "expand_template")
 
 package(
@@ -21,14 +22,28 @@ package(
     default_testonly = 1,
 )
 
+string_flag(
+    name = "my_string_flag",
+    build_setting_default = "VAR",
+    make_variable = "SOMEVAR",
+)
+
 expand_template(
     name = "filled_template",
     out = "foo/test.yaml",
+    data = [
+        ":version",
+    ],
     substitutions = {
         "@name@": "test",
         "@version@": "1.1.1",
+        "@path@": "$(rlocationpath :version)",
+        "@toolchain@": "prefix$(SOMEVAR)suffix",
     },
     template = "test.tpl.yaml",
+    toolchains = [
+        ":my_string_flag",
+    ],
 )
 
 sh_test(
diff --git a/tests/expand_template/template_test.sh b/tests/expand_template/template_test.sh
index 10099a4..3ab7c12 100755
--- a/tests/expand_template/template_test.sh
+++ b/tests/expand_template/template_test.sh
@@ -32,6 +32,8 @@ 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 'tests/expand_template/version.h'
+  expect_log 'toolchain: prefixVARsuffix'
 }
 
-run_suite "expand_template_tests test suite"
\ No newline at end of file
+run_suite "expand_template_tests test suite"
diff --git a/tests/expand_template/test.tpl.yaml b/tests/expand_template/test.tpl.yaml
index 03d9fdd..1c8636d 100644
--- a/tests/expand_template/test.tpl.yaml
+++ b/tests/expand_template/test.tpl.yaml
@@ -1,2 +1,4 @@
 name: @name@
 version: @version@
+path: @path@
+toolchain: @toolchain@