Issue #3202665 by danflanagan8, Ratan Priya, rupertj, longwave, smustgrave,...

Issue #3202665 by danflanagan8, Ratan Priya, rupertj, longwave, smustgrave, thursday_bw: "A(n) object was thrown while attempting to stub." Hard to debug migration message

(cherry picked from commit 2e76fda4)

core/modules/migrate/src/Plugin/migrate/process/MigrationLookup.php

@@ -263,7 +263,7 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
         throw $e;
       }
       catch (\Exception $e) {
-        throw new MigrateException(sprintf('A(n) %s was thrown while attempting to stub.', gettype($e)), $e->getCode(), $e);
+        throw new MigrateException(sprintf('%s was thrown while attempting to stub: %s', get_class($e), $e->getMessage()), $e->getCode(), $e);
       }
     }
     if ($destination_ids) {

core/modules/migrate/tests/src/Unit/process/MigrationLookupTest.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\Tests\migrate\Unit\process;
 
+use Drupal\migrate\MigrateException;
 use Drupal\migrate\MigrateSkipProcessException;
 use Drupal\migrate\Plugin\MigrationInterface;
 use Drupal\migrate\Plugin\migrate\process\MigrationLookup;
@@ -60,6 +61,12 @@ public function testTransformWithStubbing() {
     $migration = MigrationLookup::create($this->prepareContainer(), $configuration, '', [], $migration_plugin->reveal());
     $result = $migration->transform(1, $this->migrateExecutable, $this->row, '');
     $this->assertEquals(2, $result);
+
+    $this->migrateStub->createStub('destination_migration', [1], [], FALSE)->willThrow(new \Exception('Oh noes!'));
+    $migration = MigrationLookup::create($this->prepareContainer(), $configuration, '', [], $migration_plugin->reveal());
+    $this->expectException(MigrateException::class);
+    $this->expectExceptionMessage('Exception was thrown while attempting to stub: Oh noes!');
+    $migration->transform(1, $this->migrateExecutable, $this->row, '');
   }
 
   /**