fix(networkmanager): read the automatic DNS switch from a family that takes name servers

clients/networkmanager/iputils.cpp

@@ -197,8 +197,11 @@ Form form(const Settings& settings)
         }
     }
 
-    // The switch stands for both families; IPv4's decides when they differ.
-    form.automaticDns = !toBool(value(group(settings, ipv4Setting), "ignore-auto-dns"));
+    // The switch stands for both families; IPv4's decides when they differ,
+    // unless IPv4 takes no name servers and so keeps a value nothing writes.
+    const std::string& dnsFamily =
+        configurable(form.ipv4Method) || !configurable(form.ipv6Method) ? ipv4Setting : ipv6Setting;
+    form.automaticDns = !toBool(value(group(settings, dnsFamily), "ignore-auto-dns"));
     form.dns = text::join(dnsServers(settings), ", ");
     return form;
 }

clients/networkmanager/tests/iputils_test.cpp

@@ -264,6 +264,30 @@ TEST(IpUtils, WritesNameServers)
     EXPECT_FALSE(toBool(value(cleared->at("ipv4"), "ignore-auto-dns")));
 }
 
+TEST(IpUtils, AutomaticDnsOfAnIpv6OnlyProfile)
+{
+    Settings existing = automaticProfile();
+    existing["ipv4"] = {{"method", Variant(std::string("disabled"))}};
+    ip::Form form = ip::form(existing);
+    EXPECT_TRUE(form.automaticDns);
+    form.automaticDns = false;
+    form.dns = "2606:4700::1111";
+
+    bool changed = false;
+    std::string error;
+    const auto profile = ip::settings(form, existing, &changed, &error);
+    ASSERT_TRUE(profile) << error;
+    EXPECT_TRUE(toBool(value(profile->at("ipv6"), "ignore-auto-dns")));
+
+    // Read back, the switch is off as saved, and another server keeps it off.
+    form = ip::form(*profile);
+    EXPECT_FALSE(form.automaticDns);
+    form.dns = "2001:4860:4860::8888";
+    const auto edited = ip::settings(form, *profile, &changed, &error);
+    ASSERT_TRUE(edited) << error;
+    EXPECT_TRUE(toBool(value(edited->at("ipv6"), "ignore-auto-dns")));
+}
+
 TEST(IpUtils, WritesDnsDataWhereItCameFrom)
 {
     Settings existing = automaticProfile();