Breaking: #111156 - Site sets follow the order a site declares 

Description 

The sets a site lists in its dependencies are now applied in the order the site lists them, each of them preceded by the sets it depends on. A set reached more than once, because several sets depend on it, keeps its first position.

So far, the order came from one global ordering of every installed set. Sets with no dependency relation between them were ordered by the number of dependencies they declare and then by name, and the order the site listed them in had no effect. Installing an extension whose set declares one more dependency could therefore change which of two unrelated sets wins, on sites that do not use that extension's set at all.

\TYPO3\CMS\Core\Site\Set\SetRegistry::getSets() returns the sets in the order described above. All consumers of the set order follow it, which are:

• TypoScript setup and constants
• page TSconfig
• site settings, their definitions and their categories
• route enhancers

The protected method SetRegistry::hasDependency() has been removed.

Impact 

On a site listing two sets without a dependency relation between them, the set listed last now wins: its TypoScript, page TSconfig, settings and route enhancers override those of the set listed before it. A set still always comes after the sets it depends on, so a set that depends on another one keeps overriding it, wherever the site lists them.

Sites where the previous order happened to match the order of their dependencies are not affected.

Affected installations 

Installations with sites listing several sets, where two of those sets, or the sets they depend on, configure the same TypoScript, page TSconfig, setting or route enhancer without one of them depending on the other.

A common case is a theme or site package set that replaces lib.contentElement , listed before a set of another extension that depends on typo3/fluid-styled-content . That set of typo3/fluid-styled-content is now applied after the theme and replaces its lib.contentElement , while it may have been applied before the theme so far.

Extensions extending SetRegistry and calling hasDependency() are affected as well.

Migration 

List the sets of a site in the order they are meant to override each other, the set that is meant to win last:

dependencies:
  - vendor/some-extension
  - myvendor/my-theme

Alternatively, declare the dependency between the sets explicitly in the config.yaml of the set that is meant to win, which makes the order independent of any site.