1 files changed, 111 insertions, 0 deletions
diff --git a/cli/internal/scm/git_go.go b/cli/internal/scm/git_go.go
new file mode 100644
index 0000000..0dac2bf
--- /dev/null
+++ b/cli/internal/scm/git_go.go
@@ -0,0 +1,111 @@
+//go:build go || !rust
+// +build go !rust
+
+// 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 (
+	"fmt"
+	"github.com/vercel/turbo/cli/internal/turbopath"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"github.com/pkg/errors"
+)
+
+// git implements operations on a git repository.
+type git struct {
+	repoRoot turbopath.AbsoluteSystemPath
+}
+
+// ChangedFiles returns a list of modified files since the given commit, optionally including untracked files.
+func (g *git) ChangedFiles(fromCommit string, toCommit string, relativeTo string) ([]string, error) {
+	if relativeTo == "" {
+		relativeTo = g.repoRoot.ToString()
+	}
+	relSuffix := []string{"--", relativeTo}
+	command := []string{"diff", "--name-only", toCommit}
+
+	out, err := exec.Command("git", append(command, relSuffix...)...).CombinedOutput()
+	if err != nil {
+		return nil, errors.Wrapf(err, "finding changes relative to %v", relativeTo)
+	}
+	files := strings.Split(string(out), "\n")
+
+	if fromCommit != "" {
+		// Grab the diff from the merge-base to HEAD using ... syntax.  This ensures we have just
+		// the changes that have occurred on the current branch.
+		command = []string{"diff", "--name-only", fromCommit + "..." + toCommit}
+		out, err = exec.Command("git", append(command, relSuffix...)...).CombinedOutput()
+		if err != nil {
+			// Check if we can provide a better error message for non-existent commits.
+			// If we error on the check or can't find it, fall back to whatever error git
+			// reported.
+			if exists, err := commitExists(fromCommit); err == nil && !exists {
+				return nil, fmt.Errorf("commit %v does not exist", fromCommit)
+			}
+			return nil, errors.Wrapf(err, "git comparing with %v", fromCommit)
+		}
+		committedChanges := strings.Split(string(out), "\n")
+		files = append(files, committedChanges...)
+	}
+	command = []string{"ls-files", "--other", "--exclude-standard"}
+	out, err = exec.Command("git", append(command, relSuffix...)...).CombinedOutput()
+	if err != nil {
+		return nil, errors.Wrap(err, "finding untracked files")
+	}
+	untracked := strings.Split(string(out), "\n")
+	files = append(files, untracked...)
+	// git will report changed files relative to the worktree: re-relativize to relativeTo
+	normalized := make([]string, 0)
+	for _, f := range files {
+		if f == "" {
+			continue
+		}
+		normalizedFile, err := g.fixGitRelativePath(strings.TrimSpace(f), relativeTo)
+		if err != nil {
+			return nil, err
+		}
+		normalized = append(normalized, normalizedFile)
+	}
+	return normalized, nil
+}
+
+func (g *git) PreviousContent(fromCommit string, filePath string) ([]byte, error) {
+	if fromCommit == "" {
+		return nil, fmt.Errorf("Need commit sha to inspect file contents")
+	}
+
+	out, err := exec.Command("git", "show", fmt.Sprintf("%s:%s", fromCommit, filePath)).CombinedOutput()
+	if err != nil {
+		return nil, errors.Wrapf(err, "unable to get contents of %s", filePath)
+	}
+
+	return out, nil
+}
+
+func commitExists(commit string) (bool, error) {
+	err := exec.Command("git", "cat-file", "-t", commit).Run()
+	if err != nil {
+		exitErr := &exec.ExitError{}
+		if errors.As(err, &exitErr) && exitErr.ExitCode() == 128 {
+			return false, nil
+		}
+		return false, err
+	}
+	return true, nil
+}
+
+func (g *git) fixGitRelativePath(worktreePath, relativeTo string) (string, error) {
+	p, err := filepath.Rel(relativeTo, filepath.Join(g.repoRoot, worktreePath))
+	if err != nil {
+		return "", errors.Wrapf(err, "unable to determine relative path for %s and %s", g.repoRoot, relativeTo)
+	}
+	return p, nil
+}