MDL-58970 themes: Fix references to core/loginform template

lib/outputrenderers.php

@@ -4294,7 +4294,7 @@ EOD;
         $context->cookieshelpiconformatted = $this->help_icon('cookiesenabled');
         $context->errorformatted = $this->error_text($context->error);
 
-        return $this->render_from_template('core/login', $context);
+        return $this->render_from_template('core/loginform', $context);
     }
 
     /**

lib/templates/loginform.mustache

@@ -15,7 +15,7 @@
     along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 }}
 {{!
-    @template core/login
+    @template core/loginform
 
     Moodle template for the login page.
 

theme/boost/classes/output/core_renderer.php

@@ -465,7 +465,7 @@ class core_renderer extends \core_renderer {
         $context->logourl = $url;
         $context->sitename = format_string($SITE->fullname, true, ['context' => context_course::instance(SITEID), "escape" => false]);
 
-        return $this->render_from_template('core/login', $context);
+        return $this->render_from_template('core/loginform', $context);
     }
 
     /**

theme/boost/templates/core/loginform.mustache

@@ -15,7 +15,7 @@
     along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
 }}
 {{!
-    @template core/login
+    @template core/loginform
 
     Moodle template for the login page.
 

theme/upgrade.txt

@@ -7,6 +7,10 @@ information provided here is intended especially for theme designer.
   setup for this module have been moved from core standard_head_html to the bootstrapbase
   renderer. If your theme needs this javascript you will need to ensure the bootstrap renderer
   is called, or require the JS yourself
+* There was a mustache template login.mustache in /lib/templates/ rendering the login form
+  and a template with the same name in /theme/boost/templates/ rendering the pagelayout "login".
+  To prevent misunderstanding when overriding one of these templates in a Boost child theme,
+  the first one was renamed to loginform.mustache - see MDL-58970.
 
 === 3.2 ===