bake: fix BAKE_CMD_CONTEXT relative path resolution

Signed-off-by: Justin Chadwell <me@jedevc.com>

tests/bake.go

@@ -20,6 +20,7 @@ func bakeCmd(sb integration.Sandbox, dir string, args ...string) (string, error)
 
 var bakeTests = []func(t *testing.T, sb integration.Sandbox){
 	testBakeRemote,
+	testBakeRemoteCmdContext,
 }
 
 func testBakeRemote(t *testing.T, sb integration.Sandbox) {
@@ -51,3 +52,37 @@ EOT
 
 	require.FileExists(t, filepath.Join(dirDest, "foo"))
 }
+
+func testBakeRemoteCmdContext(t *testing.T, sb integration.Sandbox) {
+	bakefile := []byte(`
+target "default" {
+	context = BAKE_CMD_CONTEXT
+	dockerfile-inline = <<EOT
+FROM scratch
+COPY foo /foo
+EOT
+}
+`)
+	dirSpec := tmpdir(
+		t,
+		fstest.CreateFile("docker-bake.hcl", bakefile, 0600),
+	)
+	dirSrc := tmpdir(
+		t,
+		fstest.CreateFile("foo", []byte("foo"), 0600),
+	)
+	dirDest := t.TempDir()
+
+	git, err := gitutil.New(gitutil.WithWorkingDir(dirSpec))
+	require.NoError(t, err)
+
+	gitutil.GitInit(git, t)
+	gitutil.GitAdd(git, t, "docker-bake.hcl")
+	gitutil.GitCommit(git, t, "initial commit")
+	addr := gitutil.GitServeHTTP(git, t)
+
+	out, err := bakeCmd(sb, dirSrc, addr, "--set", "*.output=type=local,dest="+dirDest)
+	require.NoError(t, err, out)
+
+	require.FileExists(t, filepath.Join(dirDest, "foo"))
+}