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A general description is here.
The long-standing environment variable ‘PKG_BUILD_DIR’
to control where ‘R CMD INSTALL’ unpacks source tarballs is now documented in the R Internals manual. This is supplemented by ‘PKG_BUILD_DIR_BARE’ to use ‘PKG_BUILD_DIR’ as the unpacking directory without adding a random path component.
Long stringed error messages are now protected from premature garbage collection, fixing PR#19210, reported and analyzed by Yuancheng Jiang.