1 files changed, 53 insertions, 0 deletions
diff --git a/cli/internal/scm/scm.go b/cli/internal/scm/scm.go
new file mode 100644
index 0000000..e7f17c8
--- /dev/null
+++ b/cli/internal/scm/scm.go
@@ -0,0 +1,53 @@
+// Package scm abstracts operations on various tools like git
+// Currently, only git is supported.
+//
+// Adapted from https://github.com/thought-machine/please/tree/master/src/scm
+// Copyright Thought Machine, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+package scm
+
+import (
+	"github.com/pkg/errors"
+
+	"github.com/vercel/turbo/cli/internal/turbopath"
+)
+
+var ErrFallback = errors.New("cannot find a .git folder. Falling back to manual file hashing (which may be slower). If you are running this build in a pruned directory, you can ignore this message. Otherwise, please initialize a git repository in the root of your monorepo")
+
+// An SCM represents an SCM implementation that we can ask for various things.
+type SCM interface {
+	// ChangedFiles returns a list of modified files since the given commit, including untracked files
+	ChangedFiles(fromCommit string, toCommit string, relativeTo string) ([]string, error)
+	// PreviousContent Returns the content of the file at fromCommit
+	PreviousContent(fromCommit string, filePath string) ([]byte, error)
+}
+
+// newGitSCM returns a new SCM instance for this repo root.
+// It returns nil if there is no known implementation there.
+func newGitSCM(repoRoot turbopath.AbsoluteSystemPath) SCM {
+	if repoRoot.UntypedJoin(".git").Exists() {
+		return &git{repoRoot: repoRoot}
+	}
+	return nil
+}
+
+// newFallback returns a new SCM instance for this repo root.
+// If there is no known implementation it returns a stub.
+func newFallback(repoRoot turbopath.AbsoluteSystemPath) (SCM, error) {
+	if scm := newGitSCM(repoRoot); scm != nil {
+		return scm, nil
+	}
+
+	return &stub{}, ErrFallback
+}
+
+// FromInRepo produces an SCM instance, given a path within a
+// repository. It does not need to be a git repository, and if
+// it is not, the given path is assumed to be the root.
+func FromInRepo(repoRoot turbopath.AbsoluteSystemPath) (SCM, error) {
+	dotGitDir, err := repoRoot.Findup(".git")
+	if err != nil {
+		return nil, err
+	}
+	return newFallback(dotGitDir.Dir())
+}