pkg/vcs: add tests for automatic backports

Also, slightly refactor the code to facilitate testing.

2 files changed, 118 insertions, 2 deletions

diff --git a/pkg/vcs/linux_patches.go b/pkg/vcs/linux_patches.go
index 2ec3e0c63..88c3741f2 100644
--- a/pkg/vcs/linux_patches.go
+++ b/pkg/vcs/linux_patches.go
@@ -21,8 +21,16 @@ type BackportCommit struct {
 
 // linuxFixBackports() cherry-picks the commits necessary to compile/run older Linux kernel releases.
 func linuxFixBackports(repo *git, extraCommits ...BackportCommit) error {
-	list := append([]BackportCommit{}, pickLinuxCommits...)
-	for _, info := range append(list, extraCommits...) {
+	return applyFixBackports(repo,
+		append(
+			append([]BackportCommit{}, pickLinuxCommits...),
+			extraCommits...,
+		),
+	)
+}
+
+func applyFixBackports(repo *git, commits []BackportCommit) error {
+	for _, info := range commits {
 		if info.GuiltyHash != "" {
 			contains, err := repo.Contains(info.GuiltyHash)
 			if err != nil {
diff --git a/pkg/vcs/linux_patches_test.go b/pkg/vcs/linux_patches_test.go
new file mode 100644
index 000000000..f5a27219d
--- /dev/null
+++ b/pkg/vcs/linux_patches_test.go
@@ -0,0 +1,108 @@
+// Copyright 2023 syzkaller project authors. All rights reserved.
+// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+package vcs
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/google/syzkaller/pkg/osutil"
+)
+
+func TestFixBackport(t *testing.T) {
+	baseDir := t.TempDir()
+	repo := MakeTestRepo(t, baseDir)
+
+	repo.Git("checkout", "-b", "main")
+	repo.Git("commit", "--no-edit", "--allow-empty", "-m", "starting commit")
+
+	// Let the fix stay in a separate branch.
+	repo.Git("checkout", "-b", "branch-with-a-fix")
+	filePath := filepath.Join(baseDir, "object.txt")
+	if err := os.WriteFile(filePath, []byte("content"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	repo.Git("add", "object.txt")
+	repo.Git("commit", "--no-edit", "-m", "fix title")
+	fixCommit, _ := repo.repo.HeadCommit()
+
+	// Return to the original branch.
+	repo.Git("checkout", "main")
+
+	// Check the test is sane.
+	if osutil.IsExist(filePath) {
+		t.Fatalf("we have switched the branch, object.txt should not be present")
+	}
+
+	// Verify that the fix gets backported.
+	err := applyFixBackports(repo.repo, []BackportCommit{
+		{
+			FixHash:  fixCommit.Hash,
+			FixTitle: `fix title`,
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !osutil.IsExist(filePath) {
+		t.Fatalf("the commit was not backported, but should have")
+	}
+}
+
+func TestConditionalFixBackport(t *testing.T) {
+	baseDir := t.TempDir()
+	repo := MakeTestRepo(t, baseDir)
+
+	repo.Git("checkout", "-b", "main")
+	repo.Git("commit", "--no-edit", "--allow-empty", "-m", "starting commit")
+
+	// Let the fix stay in a separate branch.
+	repo.Git("checkout", "-b", "branch-with-fix")
+	filePath := filepath.Join(baseDir, "object.txt")
+	if err := os.WriteFile(filePath, []byte("content"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	repo.Git("add", "object.txt")
+	repo.Git("commit", "--no-edit", "-m", "fix title")
+	fixCommit, _ := repo.repo.HeadCommit()
+
+	// Create a branch without a bug.
+	repo.Git("checkout", "main")
+	repo.Git("checkout", "-b", "branch-no-bug")
+	repo.Git("commit", "--no-edit", "--allow-empty", "-m", "some commit")
+
+	// Create a branch with a bug.
+	repo.Git("checkout", "-b", "branch-with-bug")
+	repo.Git("commit", "--no-edit", "--allow-empty", "-m", "bad commit")
+	badCommit, _ := repo.repo.HeadCommit()
+	repo.Git("commit", "--no-edit", "--allow-empty", "-m", "some other commit")
+
+	// Ensure we do not cherry-pick the fix when there's no bug.
+	repo.Git("checkout", "branch-no-bug")
+	rules := []BackportCommit{
+		{
+			GuiltyHash: badCommit.Hash,
+			FixHash:    fixCommit.Hash,
+			FixTitle:   `fix title`,
+		},
+	}
+	err := applyFixBackports(repo.repo, rules)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if osutil.IsExist(filePath) {
+		t.Fatalf("the commit was backported, but shouldn't have been")
+	}
+
+	// .. but we do cherry-pick otherwise.
+	repo.Git("checkout", "branch-with-bug")
+	err = applyFixBackports(repo.repo, rules)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !osutil.IsExist(filePath) {
+		t.Fatalf("the commit was not backported, but should have been")
+	}
+}