This page should be used to keep track of items which should be added to the migration guide. It's a living document for the life of a development cycle and by M4 should represent a significant proportion of items that are worthy of note in the migration guide. Once the migration guide for a release has been completed the contents of this page should be cleared out.

2.3 Migration Guide items

Recipe-specific sysroots
The previously deprecated bb.data.getVar(), bb.data.setVar() and related functions have now been removed in favour of d.getVar(), d.setVar() etc. Any references to the old functions will now need to be tidied up.
package-depends.dot and pn-depends.dot as previously generated by bitbake -g have been removed, and a recipe-depends.dot file is now generated as a collapsed version of task-depends.dot. This was done because package-depends.dot and pn-depends.dot largely date back to a time before task-based execution and don't take into account task-level dependencies between recipes, and thus can be misleading.
depexp UI replaced by taskexp
Absolute symlinks within staged files are no longer permitted and will trigger an error.
RPM package management has moved from RPM5 with the no-longer maintained SMART to RPM4 and the DNF stack from RedHat/Fedora.
PATH is filtered to allow only whitelisted tools from the host during a build, user configurable with HOSTTOOLS variable.

FutureMigrationGuide