nixos/mattermost: add preferNixConfig option and tests

One use case for Mattermost configuration is doing a "mostly
mutable" configuration where NixOS module options take priority
over Mattermost's config JSON.

Add a preferNixConfig option that prefers configured Nix options
over what's configured in Mattermost config if mutableConfig is set.

Remove the reliance on readFile (it's flake incompatible) and use
jq instead.

Merge Mattermost configs together on Mattermost startup, depending
on configured module options.

Write tests for mutable, mostly mutable, and immutable configurations.

1 files changed, 26 insertions, 16 deletions

diff --git a/nixos/modules/services/web-apps/mattermost.nix b/nixos/modules/services/web-apps/mattermost.nix
index f5c2c356afc..a3127aed692 100644
--- a/nixos/modules/services/web-apps/mattermost.nix
+++ b/nixos/modules/services/web-apps/mattermost.nix
@@ -6,23 +6,18 @@ let
 
   cfg = config.services.mattermost;
 
-  defaultConfig = builtins.fromJSON (builtins.replaceStrings [ "\\u0026" ] [ "&" ]
-    (readFile "${pkgs.mattermost}/config/config.json")
-  );
-
   database = "postgres://${cfg.localDatabaseUser}:${cfg.localDatabasePassword}@localhost:5432/${cfg.localDatabaseName}?sslmode=disable&connect_timeout=10";
 
-  mattermostConf = foldl recursiveUpdate defaultConfig
-    [ { ServiceSettings.SiteURL = cfg.siteUrl;
-        ServiceSettings.ListenAddress = cfg.listenAddress;
-        TeamSettings.SiteName = cfg.siteName;
-        SqlSettings.DriverName = "postgres";
-        SqlSettings.DataSource = database;
-      }
-      cfg.extraConfig
-    ];
+  mattermostConf = recursiveUpdate
+    { ServiceSettings.SiteURL = cfg.siteUrl;
+      ServiceSettings.ListenAddress = cfg.listenAddress;
+      TeamSettings.SiteName = cfg.siteName;
+      SqlSettings.DriverName = "postgres";
+      SqlSettings.DataSource = database;
+    }
+    cfg.extraConfig;
 
-  mattermostConfJSON = pkgs.writeText "mattermost-config-raw.json" (builtins.toJSON mattermostConf);
+  mattermostConfJSON = pkgs.writeText "mattermost-config.json" (builtins.toJSON mattermostConf);
 
 in
 
@@ -77,6 +72,16 @@ in
         '';
       };
 
+      preferNixConfig = mkOption {
+        type = types.bool;
+        default = false;
+        description = ''
+          If both mutableConfig and this option are set, the Nix configuration
+          will take precedence over any settings configured in the server
+          console.
+        '';
+      };
+
       extraConfig = mkOption {
         type = types.attrs;
         default = { };
@@ -180,14 +185,19 @@ in
           ln -sf ${pkgs.mattermost}/{bin,fonts,i18n,templates,client} ${cfg.statePath}
         '' + lib.optionalString (!cfg.mutableConfig) ''
           rm -f ${cfg.statePath}/config/config.json
-          cp ${mattermostConfJSON} ${cfg.statePath}/config/config.json
+          ${pkgs.jq}/bin/jq -s '.[0] * .[1]' ${pkgs.mattermost}/config/config.json ${mattermostConfJSON} > ${cfg.statePath}/config/config.json
           ${pkgs.mattermost}/bin/mattermost config migrate ${cfg.statePath}/config/config.json ${database}
         '' + lib.optionalString cfg.mutableConfig ''
           if ! test -e "${cfg.statePath}/config/.initial-created"; then
             rm -f ${cfg.statePath}/config/config.json
-            cp ${mattermostConfJSON} ${cfg.statePath}/config/config.json
+            ${pkgs.jq}/bin/jq -s '.[0] * .[1]' ${pkgs.mattermost}/config/config.json ${mattermostConfJSON} > ${cfg.statePath}/config/config.json
             touch ${cfg.statePath}/config/.initial-created
           fi
+        '' + lib.optionalString (cfg.mutableConfig && cfg.preferNixConfig) ''
+          newConfig="$(${pkgs.jq}/bin/jq -s '.[0] * .[1]' ${cfg.statePath}/config/config.json ${mattermostConfJSON})"
+
+          rm -f ${cfg.statePath}/config/config.json
+          echo "$newConfig" > ${cfg.statePath}/config/config.json
         '' + lib.optionalString cfg.localDatabaseCreate ''
           if ! test -e "${cfg.statePath}/.db-created"; then
             ${pkgs.sudo}/bin/sudo -u ${config.services.postgresql.superUser} \