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

README.md

@@ -97,6 +97,22 @@ This also works for directories.
 
 To validate all `diff`, `cmp`, etc. actions by default, set `common --@diff.bzl//diff:validate=true` in your bazelrc.
 
-### Support automatic patch workflows for CI
+### Support automatic patch workflows
 
-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.
+This ruleset outputs patches for source tree files into the `diff_bzl__patch` output group by default, making it easier to collect and apply patches in an automated fashion. See the [build & patch](./examples/build-and-patch.sh) example script.
+
+The output groups for source patches can be customized via the `source_patch_output_groups` attribute. This can be used to categorize types of patches. For example, `diff` targets with `source_patch_output_groups = ["autopatch"]` might identify patches that should automatically be applied if the build fails on CI, whereas a `"snapshot_test"` group could identify patches that require human review, etc.
+
+```starlark
+diff(
+    name = "foo",
+    srcs = [
+      "foo.pb.go",
+      ":foo_generated",
+    ],
+    validate = 1,
+    source_patch_output_groups = ["autopatch"],
+)
+```
+
+NB: Only patches for files in the source tree are placed in the above output group(s). Patches for files in the output tree are not included as they should not be modified outside of Bazel.

diff/defs.bzl

@@ -55,7 +55,7 @@ def cmp(name, srcs, args = [], out = None, **kwargs):
         **kwargs
     )
 
-def diff(name, srcs, args = ["--unified"], patch = None, **kwargs):
+def diff(name, srcs, args = ["--unified"], patch = None, source_patch_output_groups = ["diff_bzl__patch"], **kwargs):
     """Runs a diff between files and return a patch.
 
     Examples:
@@ -98,9 +98,10 @@ def diff(name, srcs, args = ["--unified"], patch = None, **kwargs):
 
     Args:
         name: The name of the rule
-        srcs: The files to compare.
+        srcs: The files to compare
         args: Additional arguments to pass to diff
         patch: The output file to write the diff to. Defaults to ${name}.patch.
+        source_patch_output_groups: Additional output groups to add source file patches to
         **kwargs: Additional arguments to pass to the underlying rule
     """
     for i in range(len(srcs)):
@@ -114,6 +115,7 @@ def diff(name, srcs, args = ["--unified"], patch = None, **kwargs):
         args = args,
         srcs = srcs,
         patch = patch or name + ".patch",
+        source_patch_output_groups = source_patch_output_groups,
         **kwargs
     )
 

diff/private/diff.bzl

@@ -229,18 +229,28 @@ 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_output_groups = {group: source_patches_depset for group in ctx.attr.source_patch_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),
+            **source_patch_output_groups
         ),
     ]
 
 diff_rule = rule(
     implementation = _diff_rule_impl,
     attrs = {
+        "source_patch_output_groups": attr.string_list(
+            doc = """\
+            Additional output groups to add source file patches to. Output groups can be used to categorize sets of patches
+            that a Bazel wrapper can identify and apply by reading build events.
+            """,
+            default = ["diff_bzl__patch"],
+        ),
         "args": attr.string_list(
             doc = """\
               Additional arguments to pass to the diff command.

diff/tests/BUILD.bazel

@@ -265,6 +265,53 @@ diff(
     validate = 1,
 )
 
+diff(
+    name = "case_source_patch_default_output_group",
+    srcs = [
+        "case_source_patch_default_output_group.a",
+        "case_source_patch_default_output_group.b",
+    ],
+)
+
+filegroup(
+    name = "case_source_patch_default_output_group_output",
+    srcs = [":case_source_patch_default_output_group"],
+    output_group = "diff_bzl__patch",
+)
+
+diff(
+    name = "case_source_patch_default_output_group_assert_patch",
+    srcs = [
+        "case_source_patch_default_output_group.golden.patch",
+        ":case_source_patch_default_output_group_output",
+    ],
+    validate = 1,
+)
+
+diff(
+    name = "case_source_patch_custom_output_group",
+    srcs = [
+        "case_source_patch_custom_output_group.a",
+        "case_source_patch_custom_output_group.b",
+    ],
+    source_patch_output_groups = ["autopatch"],
+)
+
+filegroup(
+    name = "case_source_patch_custom_output_group_output",
+    srcs = [":case_source_patch_custom_output_group"],
+    output_group = "autopatch",
+)
+
+diff(
+    name = "case_source_patch_custom_output_group_assert_patch",
+    srcs = [
+        "case_source_patch_custom_output_group.golden.patch",
+        ":case_source_patch_custom_output_group_output",
+    ],
+    validate = 1,
+)
+
 genrule(
     name = "case_diff_genrule",
     srcs = [],
@@ -536,6 +583,12 @@ build_test(
         ":case_to_file_directory_assert_patch",
         ":case_to_file_directory_newfile",
         ":case_to_file_directory_newfile_assert_patch",
+        ":case_source_patch_default_output_group",
+        ":case_source_patch_default_output_group_output",
+        ":case_source_patch_default_output_group_assert_patch",
+        ":case_source_patch_custom_output_group",
+        ":case_source_patch_custom_output_group_output",
+        ":case_source_patch_custom_output_group_assert_patch",
         ":case_diff_genrule",
         ":case_cmp_genrule",
         ":case_cmp_same_binary",

diff/tests/case_source_patch_custom_output_group.a

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

diff/tests/case_source_patch_custom_output_group.b

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

diff/tests/case_source_patch_custom_output_group.golden.patch

@@ -0,0 +1,5 @@
+--- diff/tests/case_source_patch_custom_output_group.a 1970-01-01 00:00:00.000000000 +0000
++++ diff/tests/case_source_patch_custom_output_group.b 1970-01-01 00:00:00.000000000 +0000
+@@ -1 +1 @@
+-moo
++cow

diff/tests/case_source_patch_default_output_group.a

@@ -0,0 +1 @@
+foo

diff/tests/case_source_patch_default_output_group.b

@@ -0,0 +1 @@
+bar

diff/tests/case_source_patch_default_output_group.golden.patch

@@ -0,0 +1,5 @@
+--- diff/tests/case_source_patch_default_output_group.a 1970-01-01 00:00:00.000000000 +0000
++++ diff/tests/case_source_patch_default_output_group.b 1970-01-01 00:00:00.000000000 +0000
+@@ -1 +1 @@
+-foo
++bar