pkg/vcs: find base commit by blob sha hashes

Given a git diff, determine the latest commit where the modified files
still have the exact sha hashes they had at the moment the git patch was
created.

1 files changed, 84 insertions, 0 deletions

diff --git a/pkg/vcs/git_test.go b/pkg/vcs/git_test.go
index 5050bcdc0..542b572ac 100644
--- a/pkg/vcs/git_test.go
+++ b/pkg/vcs/git_test.go
@@ -10,7 +10,9 @@ import (
 	"time"
 
 	"github.com/google/go-cmp/cmp"
+	"github.com/google/syzkaller/pkg/debugtracer"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestGitParseCommit(t *testing.T) {
@@ -484,3 +486,85 @@ index f70f10e..0000000
 		},
 	})
 }
+
+func TestGitFileHashes(t *testing.T) {
+	repo := MakeTestRepo(t, t.TempDir())
+	commit1 := repo.commitChangeset("first commit", writeFile{"object.txt", "some text"})
+	commit2 := repo.commitChangeset("second commit", writeFile{"object2.txt", "some text2"})
+
+	map1, err := repo.repo.fileHashes(commit1.Hash, []string{"object.txt", "object2.txt"})
+	require.NoError(t, err)
+	assert.NotEmpty(t, map1["object.txt"])
+
+	map2, err := repo.repo.fileHashes(commit2.Hash, []string{"object.txt", "object2.txt"})
+	require.NoError(t, err)
+	assert.NotEmpty(t, map2["object.txt"])
+	assert.NotEmpty(t, map2["object2.txt"])
+}
+
+func TestBaseForDiff(t *testing.T) {
+	repo := MakeTestRepo(t, t.TempDir())
+	repo.commitChangeset("first commit",
+		writeFile{"a.txt", "content of a.txt"},
+		writeFile{"b.txt", "content of b.txt"},
+	)
+	commit2 := repo.commitChangeset("second commit",
+		writeFile{"c.txt", "content of c.txt"},
+		writeFile{"d.txt", "content of d.txt"},
+	)
+	// Create a diff.
+	commit3 := repo.commitChangeset("third commit",
+		writeFile{"a.txt", "update a.txt"},
+	)
+	diff, err := repo.repo.Diff(commit2.Hash, commit3.Hash)
+	require.NoError(t, err)
+	t.Run("conflicting", func(t *testing.T) {
+		_, err := repo.repo.SwitchCommit(commit2.Hash)
+		require.NoError(t, err)
+		// Create a different change on top of commit2.
+		repo.Git("checkout", "-b", "branch-a")
+		time.Sleep(time.Second)
+		repo.commitChangeset("patch a.txt",
+			writeFile{"a.txt", "another change to a.txt"},
+		)
+		// Yet the patch could only be applied to commit2
+		base, err := repo.repo.BaseForDiff(diff, &debugtracer.TestTracer{T: t})
+		require.NoError(t, err)
+		require.NotNil(t, base)
+		assert.Equal(t, []string{"branch-a", "master"}, base.Branches)
+		assert.Equal(t, commit2.Hash, base.Hash)
+	})
+	t.Run("choose latest", func(t *testing.T) {
+		_, err := repo.repo.SwitchCommit(commit2.Hash)
+		require.NoError(t, err)
+		// Wait a second and add one more commit.
+		// (Otherwise the test might be flaky).
+		time.Sleep(time.Second)
+		repo.Git("checkout", "-b", "branch-b")
+		commit4 := repo.commitChangeset("unrelated commit",
+			writeFile{"new.txt", "create new file"},
+		)
+		// Since the commit did not touch a.txt, it's the expected one.
+		base, err := repo.repo.BaseForDiff(diff, &debugtracer.TestTracer{T: t})
+		require.NoError(t, err)
+		require.NotNil(t, base)
+		assert.Equal(t, []string{"branch-b"}, base.Branches)
+		assert.Equal(t, commit4.Hash, base.Hash)
+	})
+	t.Run("ignore unknown objects", func(t *testing.T) {
+		// It's okay if the diff contains unknown hashes.
+		diff2 := `
+diff --git a/b.txt b/b.txt
+deleted file mode 100644
+index f70f10e..0000000
+--- a/b.txt
++++ /dev/null
+@@ -1 +0,0 @@
+-A`
+		twoDiffs := append(append([]byte{}, diff...), diff2...)
+		base, err := repo.repo.BaseForDiff(twoDiffs, &debugtracer.TestTracer{T: t})
+		require.NoError(t, err)
+		require.NotNil(t, base)
+		assert.Equal(t, []string{"branch-b"}, base.Branches)
+	})
+}