confutil: fix toml rewriting in new package

Seems marshalling the typed struct causes empty fields
e.g. gcpolicy = [] that (old versions of?) BuildKit do no allow.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

util/confutil/container_test.go

@@ -0,0 +1,62 @@
+package confutil
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestLoadConfigFilesMirrorOnlyPreservesTOML(t *testing.T) {
+	dir := t.TempDir()
+	cfgPath := filepath.Join(dir, "buildkitd.toml")
+	cfg := `[registry."docker.io"]
+mirrors=["127.0.0.1:5000"]
+`
+	require.NoError(t, os.WriteFile(cfgPath, []byte(cfg), 0644))
+
+	m, err := LoadConfigFiles(cfgPath)
+	require.NoError(t, err)
+
+	got := string(m["buildkitd.toml"])
+	require.Equal(t, `[registry]
+[registry.'docker.io']
+mirrors = ['127.0.0.1:5000']
+`, got)
+}
+
+func TestLoadConfigFilesRewritesRegistryCertPaths(t *testing.T) {
+	dir := t.TempDir()
+	caPath := filepath.Join(dir, "myca.pem")
+	keyPath := filepath.Join(dir, "mykey.pem")
+	certPath := filepath.Join(dir, "mycert.pem")
+	require.NoError(t, os.WriteFile(caPath, []byte("ca"), 0644))
+	require.NoError(t, os.WriteFile(keyPath, []byte("key"), 0644))
+	require.NoError(t, os.WriteFile(certPath, []byte("cert"), 0644))
+
+	cfgPath := filepath.Join(dir, "buildkitd.toml")
+	cfg := `[registry."myregistry.io"]
+ca=['` + caPath + `']
+[[registry."myregistry.io".keypair]]
+key='` + keyPath + `'
+cert='` + certPath + `'
+`
+	require.NoError(t, os.WriteFile(cfgPath, []byte(cfg), 0644))
+
+	m, err := LoadConfigFiles(cfgPath)
+	require.NoError(t, err)
+
+	got := string(m["buildkitd.toml"])
+	require.Equal(t, `[registry]
+[registry.'myregistry.io']
+ca = ['/etc/buildkit/certs/myregistry.io/myca.pem']
+
+[[registry.'myregistry.io'.keypair]]
+cert = '/etc/buildkit/certs/myregistry.io/mycert.pem'
+key = '/etc/buildkit/certs/myregistry.io/mykey.pem'
+`, got)
+	require.Equal(t, []byte("ca"), m["certs/myregistry.io/myca.pem"])
+	require.Equal(t, []byte("key"), m["certs/myregistry.io/mykey.pem"])
+	require.Equal(t, []byte("cert"), m["certs/myregistry.io/mycert.pem"])
+}