fix: add diff_test to docs (#296)

docs/BUILD.bazel

@@ -27,6 +27,11 @@ stardoc_with_diff_test(
     bzl_library_target = "//lib:docs",
 )
 
+stardoc_with_diff_test(
+    name = "diff_test",
+    bzl_library_target = "//lib:diff_test",
+)
+
 stardoc_with_diff_test(
     name = "expand_make_vars",
     bzl_library_target = "//lib:expand_make_vars",

docs/diff_test.md

@@ -0,0 +1,37 @@
+<!-- Generated with Stardoc: http://skydoc.bazel.build -->
+
+A test rule that compares two binary files or two directories.
+
+Similar to `bazel-skylib`'s [`diff_test`](https://github.com/bazelbuild/bazel-skylib/blob/main/rules/diff_test.bzl)
+but also supports comparing directories.
+
+The rule uses a Bash command (diff) on Linux/macOS/non-Windows, and a cmd.exe
+command (fc.exe) on Windows (no Bash is required).
+
+
+<a id="diff_test"></a>
+
+## diff_test
+
+<pre>
+diff_test(<a href="#diff_test-name">name</a>, <a href="#diff_test-file1">file1</a>, <a href="#diff_test-file2">file2</a>, <a href="#diff_test-size">size</a>, <a href="#diff_test-timeout">timeout</a>, <a href="#diff_test-kwargs">kwargs</a>)
+</pre>
+
+A test that compares two files.
+
+The test succeeds if the files' contents match.
+
+
+**PARAMETERS**
+
+
+| Name  | Description | Default Value |
+| :------------- | :------------- | :------------- |
+| <a id="diff_test-name"></a>name |  The name of the test rule.   |  none |
+| <a id="diff_test-file1"></a>file1 |  Label of the file to compare to &lt;code&gt;file2&lt;/code&gt;.   |  none |
+| <a id="diff_test-file2"></a>file2 |  Label of the file to compare to &lt;code&gt;file1&lt;/code&gt;.   |  none |
+| <a id="diff_test-size"></a>size |  standard attribute for tests   |  <code>None</code> |
+| <a id="diff_test-timeout"></a>timeout |  standard attribute for tests. Defaults to "short" if both timeout and size are unspecified.   |  <code>None</code> |
+| <a id="diff_test-kwargs"></a>kwargs |  The &lt;a href="https://docs.bazel.build/versions/main/be/common-definitions.html#common-attributes-tests"&gt;common attributes for tests&lt;/a&gt;.   |  none |
+
+

lib/private/docs/BUILD.bazel

@@ -166,7 +166,11 @@ bzl_library(
 
 bzl_library(
     name = "diff_test",
-    srcs = ["//lib/private:diff_test.bzl"],
+    srcs = [
+        "//lib:utils",
+        "//lib/private:diff_test.bzl",
+        "//lib/private:directory_path.bzl",
+    ],
 )
 
 bzl_library(