diff -u b/core/includes/install.core.inc b/core/includes/install.core.inc
--- b/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -305,6 +305,7 @@
   // Before having installed the system module and being able to do a module
   // rebuild, prime the drupal_get_filename() static cache with the module's
   // exact location.
+  // @todo Remove as part of https://www.drupal.org/node/2186491
   drupal_get_filename('module', 'system', 'core/modules/system/system.info.yml');
 
   // If the hash salt leaks, it becomes possible to forge a valid testing user
@@ -1036,6 +1037,7 @@
 
   // Before installing the user module, perform a module rebuild so we know
   // where the user module is located.
+  // @todo Remove as part of https://www.drupal.org/node/2186491
   system_rebuild_module_data();
   // Enable the user module so that sessions can be recorded during the
   // upcoming bootstrap step.
diff -u b/core/includes/install.inc b/core/includes/install.inc
--- b/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -925,6 +925,7 @@
 
   // Performs an ExtensionDiscovery scan as the system module is unavailable and
   // we don't yet know where all the modules are located.
+  // @todo Remove as part of https://www.drupal.org/node/2186491
   $listing = new ExtensionDiscovery(\Drupal::root());
   $module_list = $listing->scan('module');
   foreach ($info['dependencies'] as $module) {
diff -u b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
--- b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
+++ b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
@@ -85,6 +85,7 @@
 
       $install_profile = Settings::get('install_profile');
       $extensions = $this->configStorage->read('core.extension');
+      // @todo Remove as part of https://www.drupal.org/node/2186491
       $listing = new ExtensionDiscovery(\Drupal::root());
       if (!empty($extensions['module'])) {
         $modules = $extensions['module'];
diff -u b/core/lib/Drupal/Core/Config/InstallStorage.php b/core/lib/Drupal/Core/Config/InstallStorage.php
--- b/core/lib/Drupal/Core/Config/InstallStorage.php
+++ b/core/lib/Drupal/Core/Config/InstallStorage.php
@@ -161,6 +161,7 @@
       $this->folders += $this->getCoreNames();
       // Perform an ExtensionDiscovery scan as we cannot use drupal_get_path()
       // yet because the system module may not yet be enabled during install.
+      // @todo Remove as part of https://www.drupal.org/node/2186491
       $listing = new ExtensionDiscovery(\Drupal::root());
       if ($profile = drupal_get_profile()) {
         $profile_list = $listing->scan('profile');
@@ -168,6 +169,7 @@
           $this->folders += $this->getComponentNames(array($profile_list[$profile]));
         }
       }
+      // @todo Remove as part of https://www.drupal.org/node/2186491
       $this->folders += $this->getComponentNames($listing->scan('module'));
       $this->folders += $this->getComponentNames($listing->scan('theme'));
     }
diff -u b/core/modules/config/src/Tests/ConfigDependencyTest.php b/core/modules/config/src/Tests/ConfigDependencyTest.php
--- b/core/modules/config/src/Tests/ConfigDependencyTest.php
+++ b/core/modules/config/src/Tests/ConfigDependencyTest.php
@@ -186,6 +186,7 @@
     $entity2->save();
     // Perform a module rebuild so we can know where the node module is located.
     // and uninstall it.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     system_rebuild_module_data();
     // Test that doing a config uninstall of the node module deletes entity2
     // since it is dependent on entity1 which is dependent on the node module.
diff -u b/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
--- b/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -487,6 +487,7 @@
     // Perform an ExtensionDiscovery scan as this function may receive a
     // profile that is not the current profile, and we don't yet have a cached
     // way to receive inactive profile information.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     $listing = new ExtensionDiscovery(\Drupal::root());
     $module_list = $listing->scan('module');
     // In ModuleHandlerTest we pass in a profile as if it were a module.
diff -u b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
--- b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
@@ -26,6 +26,7 @@
     $install_state['parameters']['profile'] = 'testing';
 
     // Rebuild system.module.files state data.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     drupal_static_reset('system_rebuild_module_data');
     system_rebuild_module_data();
 
diff -u b/core/modules/system/src/Tests/Extension/ModuleHandlerTest.php b/core/modules/system/src/Tests/Extension/ModuleHandlerTest.php
--- b/core/modules/system/src/Tests/Extension/ModuleHandlerTest.php
+++ b/core/modules/system/src/Tests/Extension/ModuleHandlerTest.php
@@ -27,6 +27,7 @@
     parent::setUp();
     // Set up the state values so we know where to find the files when running
     // drupal_get_filename().
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     system_rebuild_module_data();
   }
 
@@ -47,6 +48,7 @@
     // Prime the drupal_get_filename() static cache with the location of the
     // testing profile as it is not the currently active profile and we don't
     // yet have any cached way to retrieve its location.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     drupal_get_filename('profile', 'testing', 'core/profiles/testing/testing.info.yml');
     // Build a list of modules, sorted alphabetically.
     $profile_info = install_profile_info('testing', 'en');
@@ -198,6 +200,7 @@
     // Prime the drupal_get_filename() static cache with the location of the
     // minimal profile as it is not the currently active profile and we don't
     // yet have any cached way to retrieve its location.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     drupal_get_filename('profile', 'minimal', 'core/profiles/' . $profile . '/' . $profile . '.info.yml');
     $this->enableModules(array('module_test', $profile));
 
diff -u b/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php b/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php
--- b/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php
+++ b/core/modules/system/src/Tests/Extension/ThemeHandlerTest.php
@@ -317,6 +317,7 @@
     $this->assertFalse(isset($themes[$name]->info['regions']['test_region']));
 
     // Rebuild module data so we know where module_test is located.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     system_rebuild_module_data();
     $this->moduleInstaller()->install(array('module_test'), FALSE);
     $this->assertTrue($this->moduleHandler()->moduleExists('module_test'));
diff -u b/core/modules/system/src/Tests/File/ScanDirectoryTest.php b/core/modules/system/src/Tests/File/ScanDirectoryTest.php
--- b/core/modules/system/src/Tests/File/ScanDirectoryTest.php
+++ b/core/modules/system/src/Tests/File/ScanDirectoryTest.php
@@ -31,6 +31,7 @@
     // Hardcode the location of the simpletest files as it is already known
     // and shouldn't change, and we don't yet have a way to retreive their
     // location from drupal_get_filename() in a cached way.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     $this->path = 'core/modules/simpletest/files';
   }
 
diff -u b/core/modules/system/src/Tests/Installer/InstallerLanguageTest.php b/core/modules/system/src/Tests/Installer/InstallerLanguageTest.php
--- b/core/modules/system/src/Tests/Installer/InstallerLanguageTest.php
+++ b/core/modules/system/src/Tests/Installer/InstallerLanguageTest.php
@@ -30,6 +30,8 @@
       'it' => array(),
     );
 
+    // Hardcode the simpletest module location as we don't yet know where it is.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     $file_translation = new FileTranslation('core/modules/simpletest/files/translations');
     foreach ($expected_translation_files as $langcode => $files_expected) {
       $files_found = $file_translation->findTranslationFiles($langcode);
diff -u b/core/modules/system/src/Tests/Path/UrlAliasFixtures.php b/core/modules/system/src/Tests/Path/UrlAliasFixtures.php
--- b/core/modules/system/src/Tests/Path/UrlAliasFixtures.php
+++ b/core/modules/system/src/Tests/Path/UrlAliasFixtures.php
@@ -82,6 +82,7 @@
 
     // Prime the drupal_get_filename() cache with the location of the system
     // module as its location is known and shouldn't change.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     drupal_get_filename('module', 'system', 'core/modules/system/system.info.yml');
     module_load_install('system');
     $schema = system_schema();
diff -u b/core/modules/system/system.module b/core/modules/system/system.module
--- b/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -884,15 +884,16 @@
 function _system_rebuild_module_data() {
   $listing = new ExtensionDiscovery(\Drupal::root());
 
-  // Find installation profiles. This needs to happen before
-  // performing a module scan as the module scan requires knowing
-  // what the active profile is.
-  $profiles = $listing->scan('profile');
+  // Find installation profiles. This needs to happen before performing a
+  // module scan as the module scan requires knowing what the active profile is.
+  // @todo Remove as part of https://www.drupal.org/node/2186491
+  $profiles = $liseing->scan('profile');
   $profile = drupal_get_profile();
   if ($profile && isset($profiles[$profile])) {
     // Prime the drupal_get_filename() static cache with the profile info file
     // location so we can use drupal_get_path() on the active profile during
     // the module scan.
+    // @todo Remove as part of https://www.drupal.org/node/2186491
     drupal_get_filename('profile', $profile, $profiles[$profile]->getPathname());
   }