Issue #3029625 by tim.plunkett: Do not throw an exception when a context is...

Issue #3029625 by tim.plunkett: Do not throw an exception when a context is missing while applying context mapping to a plugin if that context was previously set

core/lib/Drupal/Core/Plugin/Context/ContextHandler.php

@@ -111,6 +111,10 @@ public function applyContextMapping(ContextAwarePluginInterface $plugin, $contex
           $missing_value[] = $plugin_context_id;
         }
       }
+      elseif (($context = $plugin->getContext($context_id)) && $context->hasContextValue()) {
+        // Ignore mappings if the plugin has a value for a missing context.
+        unset($mappings[$plugin_context_id]);
+      }
       elseif ($plugin_context_definition->isRequired()) {
         // Collect required contexts that are missing.
         $missing_value[] = $plugin_context_id;

core/tests/Drupal/KernelTests/Core/Plugin/ContextHandlerTest.php

@@ -42,6 +42,25 @@ public function testApplyContextMapping() {
     $this->assertSame($context, $result);
   }
 
+  /**
+   * @covers ::applyContextMapping
+   */
+  public function testApplyContextMappingAlreadyApplied() {
+    $entity = EntityTest::create([]);
+    $context_definition = EntityContextDefinition::fromEntity($entity);
+    $context = EntityContext::fromEntity($entity);
+
+    $definition = ['context_definitions' => ['a_context_id' => $context_definition]];
+    $plugin = new TestContextAwarePlugin([], 'test_plugin_id', $definition);
+    $plugin->setContext('a_context_id', $context);
+    (new ContextHandler())->applyContextMapping($plugin, []);
+
+    $result = $plugin->getContext('a_context_id');
+
+    $this->assertInstanceOf(EntityContext::class, $result);
+    $this->assertSame($context, $result);
+  }
+
 }
 
 /**

core/tests/Drupal/Tests/Core/Plugin/ContextHandlerTest.php

@@ -18,6 +18,7 @@
 use Drupal\Core\DependencyInjection\ClassResolverInterface;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\Context\Context;
 use Drupal\Core\Plugin\Context\ContextDefinition;
 use Drupal\Core\Plugin\Context\ContextHandler;
 use Drupal\Core\Plugin\ContextAwarePluginInterface;
@@ -378,8 +379,9 @@ public function testApplyContextMappingMissingRequired() {
       ->method('setContext');
 
     // No context, so no cacheability metadata can be passed along.
-    $plugin->expects($this->never())
-      ->method('getContext');
+    $plugin->expects($this->once())
+      ->method('getContext')
+      ->willReturn(new Context($context_definition));
 
     $this->setExpectedException(MissingValueContextException::class, 'Required contexts without a value: hit');
     $this->contextHandler->applyContextMapping($plugin, $contexts);
@@ -413,8 +415,9 @@ public function testApplyContextMappingMissingNotRequired() {
       ->method('setContext');
 
     // No context, so no cacheability metadata can be passed along.
-    $plugin->expects($this->never())
-      ->method('getContext');
+    $plugin->expects($this->once())
+      ->method('getContext')
+      ->willReturn(new Context($context_definition));
 
     $this->contextHandler->applyContextMapping($plugin, $contexts);
   }