feat: add example with go proto codegen

.bazelrc

@@ -1,4 +1,8 @@
 import %workspace%/tools/preset.bazelrc
+common --@protobuf//bazel/toolchains:prefer_prebuilt_protoc
+
+# Cause a build failure when files in the source tree don't match their generated counterparts.
+common --@diff.bzl//diff:validate_diffs
 
 # Don’t want to push a rules author to update their deps if not needed.
 # https://bazel.build/reference/command-line-reference#flag--check_direct_dependencies

MODULE.bazel

@@ -14,6 +14,8 @@ bazel_dep(name = "bazel_lib", version = "3.0.0")
 bazel_dep(name = "diffutils", version = "3.12", dev_dependency = True)
 bazel_dep(name = "buildifier_prebuilt", version = "8.2.1", dev_dependency = True)
 bazel_dep(name = "bazelrc-preset.bzl", version = "1.6.0", dev_dependency = True)
+bazel_dep(name = "protobuf", version = "33.4", dev_dependency = True)
+bazel_dep(name = "rules_go", version = "0.60.0", dev_dependency = True)
 
 register_toolchains(
     "//tools/toolchains:all",

diff/private/diff.bzl

@@ -66,12 +66,11 @@ def _diff_rule_impl(ctx):
 
     # If both inputs are generated, there's no writable file to patch.
     is_copy_to_source = ctx.file.file1.is_source or ctx.file.file2.is_source
-    outputs = [ctx.outputs.patch, ctx.outputs.exit_code]
     ctx.actions.run_shell(
         inputs = [ctx.file.file1, ctx.file.file2] + diffinfo.tool_files,
-        outputs = outputs,
+        outputs = [ctx.outputs.patch, ctx.outputs.exit_code],
         command = command,
-        mnemonic = "DiffutilsDiff",
+        mnemonic = "Diff",
         progress_message = "Diffing %{input} to %{output}",
     )
 
@@ -82,11 +81,11 @@ def _diff_rule_impl(ctx):
         ERROR: diff command exited with non-zero status.
 
         To accept the diff, run:
-        patch -d \\$(bazel info workspace) -p0 < {patch}
-        """.format(patch = ctx.outputs.patch.path)))
+        patch -d \\$(bazel info workspace) -p0 < \\$(bazel info bazel-bin)/{patch}
+        """.format(patch = ctx.outputs.patch.short_path)))
 
     return [
-        DefaultInfo(files = depset(outputs)),
+        DefaultInfo(files = depset([ctx.file.file1])),
         OutputGroupInfo(
             _validation = depset(validation_outputs),
             # By reading the Build Events, a Bazel wrapper can identify this diff output group and apply the patch.

examples/BUILD

@@ -0,0 +1,38 @@
+load("@diff.bzl", "diff")
+load("@protobuf//bazel:proto_library.bzl", "proto_library")
+load("@rules_go//go:def.bzl", "go_test")
+load("@rules_go//proto:def.bzl", "go_proto_library")
+
+proto_library(
+    name = "foo_proto",
+    srcs = ["foo.proto"],
+)
+
+go_proto_library(
+    name = "foo_go_proto",
+    importpath = "github.com/kormide/diff.bzl/examples/foo_go_proto",
+    proto = "foo_proto",
+)
+
+filegroup(
+    name = "go_codegen",
+    srcs = [":foo_go_proto"],
+    output_group = "go_generated_srcs",
+)
+
+diff(
+    name = "go_codegen_diff",
+    args = ["--unified"],
+    file1 = ":foo.pb.go",
+    file2 = ":go_codegen",
+)
+
+go_test(
+    name = "foo_usage_test",
+    srcs = ["foo_test.go"],
+    # we want to trigger the validation action to ensure this test can't run
+    # if the generated code is not up to date
+    # This is an awkward way to do this, maybe improve
+    data = [":go_codegen_diff"],
+    deps = [":foo_go_proto"],
+)