config-loader: resolve config files suffixed with local and NODE_ENV

.gitignore

@@ -125,3 +125,6 @@ dist
 
 # MkDocs build output
 site
+
+# Local configuration files
+*.local.yaml

packages/config-loader/src/lib/resolver.ts

@@ -24,18 +24,34 @@ type ResolveOptions = {
 
 /**
  * Resolves all configuration files that should be loaded in the given environment.
+ *
+ * For each root directory, search for the default app-config.yaml, along with suffixed
+ * NODE_ENV and local variants, e.g. app-config.production.yaml or app-config.development.local.yaml
+ *
+ * The priority order of config loaded through suffixes is `env > local > none`, meaning that
+ * for example app-config.development.yaml has higher priority than `app-config.local.yaml`.
+ *
  */
 export async function resolveStaticConfig(
   options: ResolveOptions,
 ): Promise<string[]> {
-  // TODO: We'll want this to be a bit more elaborate, probably adding configs for
-  //       specific env, and maybe local config for plugins.
+  const env = process.env.NODE_ENV ?? 'development';
+
+  const filePaths = [
+    `app-config.${env}.local.yaml`,
+    `app-config.${env}.yaml`,
+    `app-config.local.yaml`,
+    `app-config.yaml`,
+  ];
+
   const resolvedPaths = [];
 
   for (const rootPath of options.rootPaths) {
-    const path = resolvePath(rootPath, 'app-config.yaml');
-    if (await pathExists(path)) {
-      resolvedPaths.push(path);
+    for (const filePath of filePaths) {
+      const path = resolvePath(rootPath, filePath);
+      if (await pathExists(path)) {
+        resolvedPaths.push(path);
+      }
     }
   }