expand_template: Add an is_executable flag

docs/expand_template_doc.md

@@ -9,7 +9,7 @@ A rule that performs template expansion.
 <pre>
 load("@bazel_skylib//rules:expand_template.bzl", "expand_template")
 
-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-out">out</a>, <a href="#expand_template-is_executable">is_executable</a>, <a href="#expand_template-substitutions">substitutions</a>, <a href="#expand_template-template">template</a>)
 </pre>
 
 Template expansion
@@ -27,6 +27,7 @@ explicitly add delimiters to the key strings, for example "{KEY}" or "@KEY@".
 | :------------- | :------------- | :------------- | :------------- | :------------- |
 | <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-out"></a>out |  The destination of the expanded file.   | <a href="https://bazel.build/concepts/labels">Label</a>; <a href="https://bazel.build/reference/be/common-definitions#configurable-attributes">nonconfigurable</a> | required |  |
+| <a id="expand_template-is_executable"></a>is_executable |  Whether the expanded file is executable   | Boolean | optional |  `False`  |
 | <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 |  |
 

rules/expand_template.bzl

@@ -20,7 +20,10 @@ def _expand_template_impl(ctx):
         template = ctx.file.template,
         output = ctx.outputs.out,
         substitutions = ctx.attr.substitutions,
+        is_executable = ctx.attr.is_executable,
     )
+    if ctx.attr.is_executable:
+        return [DefaultInfo(executable = ctx.outputs.out)]
 
 expand_template = rule(
     implementation = _expand_template_impl,
@@ -45,5 +48,9 @@ explicitly add delimiters to the key strings, for example "{KEY}" or "@KEY@"."""
             mandatory = True,
             doc = "The destination of the expanded file.",
         ),
+        "is_executable": attr.bool(
+            default = False,
+            doc = "Whether the expanded file is executable",
+        ),
     },
 )