Read settings for a config-form module that mesh-config holds, not only for one with a settings row (issue 1493)

cmd/mesh-controller/compose_input.go

@@ -375,7 +375,7 @@ func readLicences(ctx context.Context, open *stores) ([]compose.Licence, error)
 	return out, nil
 }
 
-// readSettings is each node's settings layers for every module that has any, read BEFORE any node is resolved: the first pass
+// readSettings is each node's settings layers for every module that has any (a row, or config in mesh-config), read BEFORE any node is resolved: the first pass
 // resolves a node whose set takes a provider's served facts from the node that runs it, with that node's settings on them
 // (servedOnNode), so a mesh whose provider says ${setting:domain} resolves only with the settings in the Input. A module's
 // settings that fail to read are returned in unread, by node and module, and are an error only for a module a node resolves to
@@ -385,13 +385,12 @@ func readSettings(ctx context.Context, open *stores, in *compose.Input) (unread
 	if err != nil {
 		return nil, err
 	}
-	names := make([]string, 0, len(have))
-	for module := range have {
-		if _, onShelf := in.Catalogue[module]; onShelf {
-			names = append(names, module)
-		}
+	names, err := modulesToRead(in.Catalogue, have, func(module string) (bool, error) {
+		return open.inventory.ReadsConfig(ctx, module)
+	})
+	if err != nil {
+		return nil, err
 	}
-	sort.Strings(names)
 	for i := range in.Nodes {
 		n := &in.Nodes[i]
 		for _, module := range names {
@@ -418,6 +417,32 @@ func readSettings(ctx context.Context, open *stores, in *compose.Input) (unread
 	return unread, nil
 }
 
+// modulesToRead is the modules on the shelf whose settings are read for a node: those with a settings row, and those in
+// the config form whose values mesh-config holds (readsConfig), which have no row when they were never in the settings
+// form (issue 1493: brother's scanner and printer, set only in mesh-config, composed empty). SettingsFor is where
+// mesh-config's values are laid in, so a gate on the settings table alone leaves them out.
+func modulesToRead(shelf map[string]catalogue.Manifest, have map[string]bool, readsConfig func(string) (bool, error)) ([]string, error) {
+	names := make([]string, 0, len(have))
+	for module, m := range shelf {
+		if have[module] {
+			names = append(names, module)
+			continue
+		}
+		if !m.DeclaresConfig() {
+			continue
+		}
+		reads, err := readsConfig(module)
+		if err != nil {
+			return nil, err
+		}
+		if reads {
+			names = append(names, module)
+		}
+	}
+	sort.Strings(names)
+	return names, nil
+}
+
 // unreadSettings is the error of a module's settings that did not read, for a module the node resolves to.
 func unreadSettings(unread map[string]map[string]error, plans map[string]compose.Resolved) error {
 	names := make([]string, 0, len(plans))