Handle the error properly when LESS source file is empty or having compilation error, and make the error message clear and clean.

Author: Hailong

app/code/Magento/Deploy/Package/Package.php

@@ -320,7 +320,10 @@ public function getFilesByType($type)
      */
     public function deleteFile($fileId)
     {
+        $file = $this->files[$fileId];
+        $deployedFileId = $file->getDeployedFileId();
         unset($this->files[$fileId]);
+        unset($this->map[$deployedFileId]);
     }
 
     /**

app/code/Magento/Deploy/Service/DeployPackage.php

@@ -134,9 +134,10 @@ public function deployEmulated(Package $package, array $options, $skipLogging =
             } catch (ContentProcessorException $exception) {
                 $errorMessage = __('Compilation from source: ')
                     . $file->getSourcePath()
-                    . PHP_EOL . $exception->getMessage();
+                    . PHP_EOL . $exception->getMessage() . PHP_EOL;
                 $this->errorsCount++;
                 $this->logger->critical($errorMessage);
+                $package->deleteFile($file->getFileId());
             } catch (\Exception $exception) {
                 $this->logger->critical(
                     'Compilation from source ' . $file->getSourcePath() . ' failed' . PHP_EOL . (string)$exception

dev/tests/integration/testsuite/Magento/Email/Model/Template/FilterTest.php

@@ -9,6 +9,7 @@
 use Magento\Framework\App\State;
 use Magento\Framework\App\TemplateTypesInterface;
 use Magento\Framework\Phrase;
+use Magento\Framework\View\Asset\ContentProcessorInterface;
 use Magento\Setup\Module\I18n\Locale;
 use Magento\Theme\Block\Html\Footer;
 
@@ -267,7 +268,7 @@ public function cssDirectiveDataProvider()
             'Empty or missing file' => [
                 TemplateTypesInterface::TYPE_HTML,
                 'file="css/non-existent-file.css"',
-                '/* Contents of the specified CSS file could not be loaded or is empty */'
+                '/*' . PHP_EOL . ContentProcessorInterface::ERROR_MESSAGE_PREFIX . 'LESS file is empty: ',
             ],
             'File with compilation error results in error message' => [
                 TemplateTypesInterface::TYPE_HTML,

lib/internal/Magento/Framework/Css/PreProcessor/Adapter/Less/Processor.php

@@ -77,7 +77,7 @@ public function processContent(File $asset)
             $content = $this->assetSource->getContent($asset);
 
             if (trim($content) === '') {
-                return '';
+                throw new ContentProcessorException(new Phrase(ContentProcessorInterface::ERROR_MESSAGE_PREFIX . 'LESS file is empty: ' . $path));
             }
 
             $tmpFilePath = $this->temporaryFile->createFile($path, $content);
@@ -88,8 +88,7 @@ public function processContent(File $asset)
             gc_enable();
 
             if (trim($content) === '') {
-                $this->logger->warning('Parsed less file is empty: ' . $path);
-                return '';
+                throw new ContentProcessorException(new Phrase(ContentProcessorInterface::ERROR_MESSAGE_PREFIX . 'LESS file is empty: ' . $path));
             } else {
                 return $content;
             }

lib/internal/Magento/Framework/Css/Test/Unit/PreProcessor/Adapter/Less/ProcessorTest.php

@@ -111,6 +111,9 @@ public function testProcessContentException()
 
     /**
      * Test for processContent method (empty content)
+     *
+     * @expectedException \Magento\Framework\View\Asset\ContentProcessorException
+     * @expectedExceptionMessageRegExp (Compilation from source: LESS file is empty: test-path)
      */
     public function testProcessContentEmpty()
     {