feat: print warning on some unsupported compose features (#288)

* feat: error on unsupported compose features

This implements a check for the unimplemented features of the uncloud
support matrix and points to the matrix in the error.

Fixes: #237

This redos #277, as I messed up my branch, (basically rebase gone
wrong).

Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix tests by capturing stderr

The error should be nil, but we _do_ want to know if the user saw an
warning. Redirect stderr to capture this as the error is emited by
printing to stderr.

Signed-off-by: Miek Gieben <miek@miek.nl>

---------

Signed-off-by: Miek Gieben <miek@miek.nl>

pkg/client/compose/service.go

@@ -422,3 +422,52 @@ func validateServicesExtensions(project *types.Project) error {
 
 	return nil
 }
+
+// validateServicesFeatures checks the service for unsupported features and returns an error for this first one found.
+func validateServicesFeatures(project *types.Project) error {
+	err := func(service, feature string) error {
+		return fmt.Errorf("service: '%s': unsupported feature: '%s', see %s", service, feature, "https://uncloud.run/docs/compose-file-reference/support-matrix")
+	}
+
+	for _, service := range project.Services {
+		if service.SecurityOpt != nil {
+			return err(service.Name, "security_opt")
+		}
+		if service.DNS != nil {
+			return err(service.Name, "dns")
+		}
+		if service.DNSSearch != nil {
+			return err(service.Name, "dns_search")
+		}
+		if service.Labels != nil {
+			return err(service.Name, "labels")
+		}
+		if service.Links != nil {
+			return err(service.Name, "links")
+		}
+		if service.MemSwappiness > 0 {
+			return err(service.Name, "mem_swappiness")
+		}
+		if service.MemSwapLimit > 0 {
+			return err(service.Name, "memswap_limit")
+		}
+		if service.Secrets != nil {
+			return err(service.Name, "secrets")
+		}
+		if service.StorageOpt != nil {
+			return err(service.Name, "storage_opt")
+		}
+		// we only allow the 'default' network, nothing else.
+		if x := service.Networks; x != nil {
+			if len(x) != 1 {
+				return err(service.Name, "networks")
+			}
+			config, ok := x["default"]
+			if !ok || config != nil {
+				return err(service.Name, "networks")
+			}
+		}
+	}
+
+	return nil
+}