Merge pull request moby#5098 from daghack/env-lint-test

dockerfile: Add integration test for ARG with empty value and default

Author: tonistiigi

frontend/dockerfile/dockerfile_test.go

@@ -192,6 +192,7 @@ var allTests = integration.TestFuncs(
 	testFrontendDeduplicateSources,
 	testDuplicateLayersProvenance,
 	testSourcePolicyWithNamedContext,
+	testEmptyStringArgInEnv,
 	testInvalidJSONCommands,
 	testHistoryError,
 	testHistoryFinalizeTrace,
@@ -273,6 +274,50 @@ func TestIntegration(t *testing.T) {
 	)...)
 }
 
+func testEmptyStringArgInEnv(t *testing.T, sb integration.Sandbox) {
+	integration.SkipOnPlatform(t, "windows")
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox AS build
+ARG FOO
+ARG BAR=
+RUN env > env.txt
+
+FROM scratch
+COPY --from=build env.txt .
+`)
+	dir := integration.Tmpdir(
+		t,
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	c, err := client.New(sb.Context(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	destDir := t.TempDir()
+	_, err = f.Solve(sb.Context(), c, client.SolveOpt{
+		Exports: []client.ExportEntry{
+			{
+				Type:      client.ExporterLocal,
+				OutputDir: destDir,
+			},
+		},
+		LocalMounts: map[string]fsutil.FS{
+			dockerui.DefaultLocalNameDockerfile: dir,
+			dockerui.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	dt, err := os.ReadFile(filepath.Join(destDir, "env.txt"))
+	require.NoError(t, err)
+
+	envStr := string(dt)
+	require.Contains(t, envStr, "BAR=")
+	require.NotContains(t, envStr, "FOO=")
+}
+
 func testDefaultEnvWithArgs(t *testing.T, sb integration.Sandbox) {
 	integration.SkipOnPlatform(t, "windows")
 	f := getFrontend(t, sb)