Allow .scl files in bzl_library (#450)

See bazelbuild/bazel@a0cd355

Author: tetromino

bzl_library.bzl

@@ -46,19 +46,19 @@ bzl_library = rule(
     implementation = _bzl_library_impl,
     attrs = {
         "srcs": attr.label_list(
-            allow_files = [".bzl"],
-            doc = "List of `.bzl` files that are processed to create this target.",
+            allow_files = [".bzl", ".scl"],
+            doc = "List of `.bzl` and `.scl` files that are processed to create this target.",
         ),
         "deps": attr.label_list(
-            allow_files = [".bzl"],
+            allow_files = [".bzl", ".scl"],
             providers = [
                 [StarlarkLibraryInfo],
             ],
             doc = """List of other `bzl_library` targets that are required by the
 Starlark files listed in `srcs`.""",
         ),
     },
-    doc = """Creates a logical collection of Starlark .bzl files.
+    doc = """Creates a logical collection of Starlark .bzl and .scl files.
 
 Example:
   Suppose your project has the following structure:

docs/BUILD

@@ -14,6 +14,12 @@ stardoc_with_diff_test(
     out_label = "//docs:build_test_doc.md",
 )
 
+stardoc_with_diff_test(
+    name = "bzl_library",
+    bzl_library_target = "//:bzl_library",
+    out_label = "//docs:bzl_library.md",
+)
+
 stardoc_with_diff_test(
     name = "collections",
     bzl_library_target = "//lib:collections",

docs/bzl_library.md

@@ -0,0 +1,88 @@
+<!-- Generated with Stardoc: http://skydoc.bazel.build -->
+
+Skylib module containing a library rule for aggregating rules files.
+
+<a id="bzl_library"></a>
+
+## bzl_library
+
+<pre>
+bzl_library(<a href="#bzl_library-name">name</a>, <a href="#bzl_library-deps">deps</a>, <a href="#bzl_library-srcs">srcs</a>)
+</pre>
+
+Creates a logical collection of Starlark .bzl and .scl files.
+
+Example:
+  Suppose your project has the following structure:
+
+  ```
+  [workspace]/
+      WORKSPACE
+      BUILD
+      checkstyle/
+          BUILD
+          checkstyle.bzl
+      lua/
+          BUILD
+          lua.bzl
+          luarocks.bzl
+  ```
+
+  In this case, you can have `bzl_library` targets in `checkstyle/BUILD` and
+  `lua/BUILD`:
+
+  `checkstyle/BUILD`:
+
+  ```python
+  load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+
+  bzl_library(
+      name = "checkstyle-rules",
+      srcs = ["checkstyle.bzl"],
+  )
+  ```
+
+  `lua/BUILD`:
+
+  ```python
+  load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+
+  bzl_library(
+      name = "lua-rules",
+      srcs = [
+          "lua.bzl",
+          "luarocks.bzl",
+      ],
+  )
+  ```
+
+
+**ATTRIBUTES**
+
+
+| Name  | Description | Type | Mandatory | Default |
+| :------------- | :------------- | :------------- | :------------- | :------------- |
+| <a id="bzl_library-name"></a>name |  A unique name for this target.   | <a href="https://bazel.build/concepts/labels#target-names">Name</a> | required |  |
+| <a id="bzl_library-deps"></a>deps |  List of other <code>bzl_library</code> targets that are required by the Starlark files listed in <code>srcs</code>.   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional | <code>[]</code> |
+| <a id="bzl_library-srcs"></a>srcs |  List of <code>.bzl</code> and <code>.scl</code> files that are processed to create this target.   | <a href="https://bazel.build/concepts/labels">List of labels</a> | optional | <code>[]</code> |
+
+
+<a id="StarlarkLibraryInfo"></a>
+
+## StarlarkLibraryInfo
+
+<pre>
+StarlarkLibraryInfo(<a href="#StarlarkLibraryInfo-srcs">srcs</a>, <a href="#StarlarkLibraryInfo-transitive_srcs">transitive_srcs</a>)
+</pre>
+
+Information on contained Starlark rules.
+
+**FIELDS**
+
+
+| Name  | Description |
+| :------------- | :------------- |
+| <a id="StarlarkLibraryInfo-srcs"></a>srcs |  Top level rules files.    |
+| <a id="StarlarkLibraryInfo-transitive_srcs"></a>transitive_srcs |  Transitive closure of rules files required for interpretation of the srcs    |
+
+