TYPO3 Core

Another reason in favor of removal is the structure of the property names: For compression there are the two properties config.compressCss and config.compressJs, but no config.compressJsAndCss. Question was (might well have been in Core list back in the days), if config.compressJsAndCss should then not be added. And the result was no. No, because what it would do already is available with config.compressCss and config.compressJs. People saw no need for additional properties, which in fact only duplicate functionality. Consequently there should then also not be a config.concatenateJsAndCss property as this one only duplicates config.concatenateJs and config.concatenateCss.

it is still like this in 7.4-dev (latest master)

concatenateJsAndCss is defined on typo3/sysext/frontend/Classes/Page/PageGenerator.php :

        // Backward compatibility for old configuration
        if ($tsfe->config['config']['concatenateJsAndCss']) {
            $pageRenderer->enableConcatenateFiles();
        }

searching for enableConcatenateFiles I found:

typo3/sysext/backend/Classes/Template/DocumentTemplate.php
typo3/sysext/core/Classes/Page/PageRenderer.php
typo3/sysext/form/Classes/View/Wizard/WizardView.php
typo3/sysext/frontend/Classes/Page/PageGenerator.php

still present even on latest 8.2-dev master, AFAICS

Searching for enableConcatenateFiles on TYPO3 8.7-dev (latest master):

typo3/sysext/backend/Classes/Template/DocumentTemplate.php
typo3/sysext/core/Classes/Page/PageRenderer.php
typo3/sysext/frontend/Classes/Page/PageGenerator.php

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/57629

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/57629