builder: explicitly set CWD for all git commands

Keep It Simple! Set the working directory for git commands by...setting
the git process's working directory. Git commands can be run in the
parent process's working directory by passing the empty string.

Signed-off-by: Cory Snider <csnider@mirantis.com>

builder/remotecontext/git/gitutils.go

@@ -193,12 +193,9 @@ func checkoutGit(root, ref, subdir string) (string, error) {
 }
 
 func gitWithinDir(dir string, args ...string) ([]byte, error) {
-	a := []string{"--work-tree", dir, "--git-dir", filepath.Join(dir, ".git")}
-	return git(append(a, args...)...)
-}
-
-func git(args ...string) ([]byte, error) {
-	return exec.Command("git", args...).CombinedOutput()
+	cmd := exec.Command("git", args...)
+	cmd.Dir = dir
+	return cmd.CombinedOutput()
 }
 
 // isGitTransport returns true if the provided str is a git transport by inspecting

builder/remotecontext/git/gitutils_test.go

@@ -6,7 +6,6 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
@@ -160,7 +159,7 @@ func TestCloneArgsGit(t *testing.T) {
 }
 
 func gitGetConfig(name string) string {
-	b, err := git([]string{"config", "--get", name}...)
+	b, err := gitWithinDir("", "config", "--get", name)
 	if err != nil {
 		// since we are interested in empty or non empty string,
 		// we can safely ignore the err here.
@@ -191,7 +190,7 @@ func TestCheckoutGit(t *testing.T) {
 	}
 
 	gitDir := filepath.Join(root, "repo")
-	must(git("-c", "init.defaultBranch=master", "init", gitDir))
+	must(gitWithinDir(root, "-c", "init.defaultBranch=master", "init", gitDir))
 	must(gitWithinDir(gitDir, "config", "user.email", "test@docker.com"))
 	must(gitWithinDir(gitDir, "config", "user.name", "Docker test"))
 	assert.NilError(t, os.WriteFile(filepath.Join(gitDir, "Dockerfile"), []byte("FROM scratch"), 0644))
@@ -218,7 +217,7 @@ func TestCheckoutGit(t *testing.T) {
 
 	// set up submodule
 	subrepoDir := filepath.Join(root, "subrepo")
-	must(git("-c", "init.defaultBranch=master", "init", subrepoDir))
+	must(gitWithinDir(root, "-c", "init.defaultBranch=master", "init", subrepoDir))
 	must(gitWithinDir(subrepoDir, "config", "user.email", "test@docker.com"))
 	must(gitWithinDir(subrepoDir, "config", "user.name", "Docker test"))
 
@@ -227,10 +226,7 @@ func TestCheckoutGit(t *testing.T) {
 	must(gitWithinDir(subrepoDir, "add", "-A"))
 	must(gitWithinDir(subrepoDir, "commit", "-am", "Subrepo initial"))
 
-	cmd := exec.Command("git", "submodule", "add", subrepoDir, "sub") // this command doesn't work with --work-tree
-	cmd.Dir = gitDir
-	must(cmd.CombinedOutput())
-
+	must(gitWithinDir(gitDir, "submodule", "add", subrepoDir, "sub"))
 	must(gitWithinDir(gitDir, "add", "-A"))
 	must(gitWithinDir(gitDir, "commit", "-am", "With submodule"))