Issue #3136041 by jweowu: drupal_static() edge case bug and inconsistent comments

core/includes/bootstrap.inc

@@ -429,37 +429,42 @@ function drupal_maintenance_theme() {
  * @see drupal_static_reset()
  */
 function &drupal_static($name, $default_value = NULL, $reset = FALSE) {
-  static $data = [], $default = [];
+  static $data = [], $defaults = [];
-  // First check if dealing with a previously defined static variable.
+  if (isset($name)) {
-  if (isset($data[$name]) || array_key_exists($name, $data)) {
+    // Check if we're dealing with a previously defined static variable.
-    // Non-NULL $name and both $data[$name] and $default[$name] statics exist.
+    if (\array_key_exists($name, $data)) {
+      // Both $data[$name] and (implicitly) $defaults[$name] statics exist.
       if ($reset) {
         // Reset pre-existing static variable to its default value.
-      $data[$name] = $default[$name];
+        $data[$name] = $defaults[$name];
       }
-    return $data[$name];
     }
-  // Neither $data[$name] nor $default[$name] static variables exist.
+    else {
-  if (isset($name)) {
+      // Neither $data[$name] nor $defaults[$name] static variables exist.
       if ($reset) {
-      // Reset was called before a default is set and yet a variable must be
+        // Reset was called before any value for $name was set, so we should
-      // returned.
+        // not set anything ($default_value is not reliable in this case). As
+        // the function returns a reference, we must still return a variable.
+        // (Code using $reset does not use the return value).
         return $data;
       }
       // First call with new non-NULL $name. Initialize a new static variable.
-    $default[$name] = $data[$name] = $default_value;
+      $defaults[$name] = $data[$name] = $default_value;
+    }
+    // Return a reference to the named variable.
     return $data[$name];
   }
+  else {
     // Reset all: ($name == NULL). This needs to be done one at a time so that
     // references returned by earlier invocations of drupal_static() also get
     // reset.
-  foreach ($default as $name => $value) {
+    foreach ($defaults as $name => $value) {
       $data[$name] = $value;
     }
-  // As the function returns a reference, the return should always be a
+    // As the function returns a reference, we must still return a variable.
-  // variable.
     return $data;
   }
+}
 
 /**
  * Resets one or all centrally stored static variable(s).

core/tests/Drupal/KernelTests/Core/Bootstrap/ResettableStaticTest.php

@@ -36,6 +36,25 @@ class ResettableStaticTest extends KernelTestBase {
     $var = 'bar';
     drupal_static_reset();
     $this->assertEquals('foo', $var, 'Variable was reset after second invocation of global reset.');
+
+    // Test calling drupal_static() with no arguments (empty string).
+    $name1 = __CLASS__ . '_' . __METHOD__ . '1';
+    $name2 = '';
+    $var1 = &drupal_static($name1, 'initial1');
+    $var2 = &drupal_static($name2, 'initial2');
+    $this->assertEquals('initial1', $var1, 'Variable 1 returned by drupal_static() was set to its default.');
+    $this->assertEquals('initial2', $var2, 'Variable 2 returned by drupal_static() was set to its default.');
+    $var1 = 'modified1';
+    $var2 = 'modified2';
+    drupal_static_reset($name1);
+    drupal_static_reset($name2);
+    $this->assertEquals('initial1', $var1, 'Variable 1 was reset after invocation of name-specific reset.');
+    $this->assertEquals('initial2', $var2, 'Variable 2 was reset after invocation of name-specific reset.');
+    $var1 = 'modified1';
+    $var2 = 'modified2';
+    drupal_static_reset();
+    $this->assertEquals('initial1', $var1, 'Variable 1 was reset after invocation of global reset.');
+    $this->assertEquals('initial2', $var2, 'Variable 2 was reset after invocation of global reset.');
   }
 
 }