meson/docs/markdown/snippets/subsubproject.md

Sub-subprojects

It is not required to promote wrap files for subprojects into the main project any more. When configuring a subproject, meson will look for any wrap file or directory in the subproject's subprojects/ directory and add them into the global list of available subprojects, to be used by any future subproject() call or dependency() fallback. If a subproject with the same name already exists, the new wrap file or directory is ignored. That means that the main project can always override any subproject's wrap files by providing their own, it also means the ordering in which subprojects are configured matters, if 2 subprojects provide foo.wrap only the one from the first subproject to be configured will be used.