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A general description is here.
Most functions with file-path inputs will give an explicit error if a file-path input in a marked encoding cannot be translated (to the native encoding or in some cases on Windows to UTF-8), rather than translate to a different file path using escapes. Some (such as ‘dir.exists()’, ‘file.exists()’, ‘file.access()’, ‘file.info()’, ‘list.files()’, ‘normalizePath()’ and ‘path.expand()’) treat this like any other non-existent file, often with a warning.
There is a new function ‘infoRDS()’ providing information about the serialization format of a serialized object.
A package with Fortran source code and perhaps C (but not C++) sources can request for its shared object/DLL to be linked by the Fortran compiler by including a line ‘USE_FC_TO_LINK=’ in ‘src/Makevars[.win]’.
The known reason for doing so is a package which uses Fortran (only) OpenMP on a platform where the Fortran OpenMP runtime is incompatible with the C one (e.g. ‘gfortran’ 9.x with ‘clang’).