Issue #3076365 by k_a_l, maacl, heddn: A more graceful failure for a missing CSV source file?

src/Plugin/migrate/source/CSV.php

@@ -259,7 +259,14 @@ class CSV extends SourcePluginBase implements ConfigurableInterface {
    *   The reader.
    */
   protected function createReader() {
-    return Reader::createFromStream(fopen($this->configuration['path'], 'r'));
+    if (!file_exists($this->configuration['path'])) {
+      throw new \RuntimeException(sprintf('File "%s" was not found.', $this->configuration['path']));
+    }
+    $csv = fopen($this->configuration['path'], 'r');
+    if (!$csv) {
+      throw new \RuntimeException(sprintf('File "%s" could not be opened.', $this->configuration['path']));
+    }
+    return Reader::createFromStream($csv);
   }
 
 }

tests/src/Unit/Plugin/migrate/source/CSVUnitTest.php

@@ -359,8 +359,8 @@ EOD;
     ];
 
     $csv = new CSV($configuration, $this->pluginId, $this->pluginDefinition, $this->migration);
-    $this->expectException(Warning::class);
-    $this->expectExceptionMessage('fopen(non-existent-path): failed to open stream: No such file or directory');
+    $this->expectException(\RuntimeException::class);
+    $this->expectExceptionMessage('File "non-existent-path" was not found.');
     $csv->initializeIterator();
   }