Enable specifying directories in plugin-files.

doc/manual/command-ref/conf-file.xml

@@ -764,6 +764,10 @@ builtins.fetchurl {
         should not be linked to any Nix libs directly, as those will
         be available already at load time.
       </para>
+      <para>
+	If an entry in the list is a directory, all files in the
+	directory are loaded as plugins (non-recursively).
+      </para>
     </listitem>
 
   </varlistentry>

src/libstore/globals.cc

@@ -142,12 +142,24 @@ void MaxBuildJobsSetting::set(const std::string & str)
 void initPlugins()
 {
     for (const auto & pluginFile : settings.pluginFiles.get()) {
+        Paths pluginFiles;
+        try {
+            auto ents = readDirectory(pluginFile);
+            for (const auto & ent : ents)
+                pluginFiles.emplace_back(pluginFile + "/" + ent.name);
+        } catch (SysError & e) {
+            if (e.errNo != ENOTDIR)
+                throw;
+            pluginFiles.emplace_back(pluginFile);
+        }
+        for (const auto & file : pluginFiles) {
             /* handle is purposefully leaked as there may be state in the
                DSO needed by the action of the plugin. */
             void *handle =
-            dlopen(pluginFile.c_str(), RTLD_LAZY | RTLD_LOCAL);
+                dlopen(file.c_str(), RTLD_LAZY | RTLD_LOCAL);
             if (!handle)
-            throw Error(format("could not dynamically open plugin file '%1%': %2%") % pluginFile % dlerror());
+                throw Error("could not dynamically open plugin file '%s%': %s%", file, dlerror());
+        }
     }
 }