feat: allow source patches to be placed in user-defined output groups

README.md

@@ -100,3 +100,17 @@ To validate all `diff`, `cmp`, etc. actions by default, set `common --@diff.bzl/
 ### Support automatic patch workflows for CI
 
 This ruleset outputs patches into a distinct `diff_bzl__patch` output group making it easier for patches to be collected and then applied using automation. See the [build & patch](./examples/build-and-patch.sh) example script.
+
+Patches can be placed in separately identifiable output groups via the `source_patch_extra_output_groups` attr. For example, you may want all patches in the "autopatch" group to be automatically applied on a CI build failure, while patches from snapshot tests ought to be reviewed by a human first.
+
+```starlark
+diff(
+    name = "foo",
+    srcs = [
+      "foo.pb.go",
+      ":foo_generated",
+    ],
+    validate = 1,
+    source_patch_extra_output_groups = ["autopatch"],
+)
+```

diff/private/diff.bzl

@@ -229,18 +229,31 @@ def _diff_rule_impl(ctx):
     ERROR: diff command exited with non-zero status.
     {}""".format(patch_msg)))
 
+    source_patches_depset = depset(source_patch_outputs)
+    source_patch_extra_output_groups = {group: source_patches_depset for group in ctx.attr.source_patch_extra_output_groups}
+
     return [
         DefaultInfo(files = depset(outputs)),
         OutputGroupInfo(
             _validation = depset(validation_outputs),
             # By reading the Build Events, a Bazel wrapper can identify this diff output group and apply the patch.
-            diff_bzl__patch = depset(source_patch_outputs),
+            diff_bzl__patch = source_patches_depset,
+            **source_patch_extra_output_groups
         ),
     ]
 
 diff_rule = rule(
     implementation = _diff_rule_impl,
     attrs = {
+        "source_patch_extra_output_groups": attr.string_list(
+            doc = """\
+            Additional output groups to add non-empty source file patches to, in addition to the default
+            diff_bzl__patch group. Groups can be used to identify sets of patches, for example, patches
+            that should be automatically applied after a failing CI build might be placed in an "autopatch"
+            group.
+            """,
+            default = [],
+        ),
         "args": attr.string_list(
             doc = """\
               Additional arguments to pass to the diff command.

diff/tests/BUILD.bazel

@@ -265,6 +265,15 @@ diff(
     validate = 1,
 )
 
+diff(
+    name = "case_source_patch_extra_output_groups",
+    srcs = [
+        "case_extra_output_group.a",
+        "case_extra_output_group.b",
+    ],
+    source_patch_extra_output_groups = ["autopatch"],
+)
+
 genrule(
     name = "case_diff_genrule",
     srcs = [],
@@ -536,6 +545,7 @@ build_test(
         ":case_to_file_directory_assert_patch",
         ":case_to_file_directory_newfile",
         ":case_to_file_directory_newfile_assert_patch",
+        ":case_source_patch_extra_output_groups",
         ":case_diff_genrule",
         ":case_cmp_genrule",
         ":case_cmp_same_binary",

diff/tests/case_extra_output_group.a

@@ -0,0 +1 @@
+moo

diff/tests/case_extra_output_group.b

@@ -0,0 +1 @@
+cow