• paste() and paste0() gain a new optional argument recycle0. When
  set to true, zero-length arguments are recycled leading to
  character(0) after the sep-concatenation, i.e., to the empty
  string "" if collapse is a string and to the zero-length value
  character(0) when collapse = NULL.

  A package whose code uses this should depend on R (>= 4.0.1).

• The summary(<warnings>) method now maps the counts correctly to
  the warning messages.

BUG FIXES:

• aov(frml, ...) now also works where the formula deparses to more
  than 500 characters, thanks to a report and patch proposal by Jan
  Hauffa.

• Fix a dozen places (code, examples) as Sys.setlocale() returns
  the new rather than the previous setting.

• Fix for adding two complex grid units via sum(). Thanks to Gu
  Zuguang for the report and Thomas Lin Pedersen for the patch.

• Fix parallel::mclapply(..., mc.preschedule=FALSE) to handle raw
  vector results correctly. PR#17779

• Computing the base value, i.e., 2, "everywhere", now uses
  FLT_RADIX, as the original machar code looped indefinitely on the
  ppc64 architecture for the longdouble case.

• In R 4.0.0, sort.list(x) when is.object(x) was true, e.g., for x <- I(letters), was accidentally using method = "radix".
  Consequently, e.g., merge(<data.frame>) was much slower than
  previously; reported in PR#17794.

• plot(y ~ x, ylab = quote(y[i])) now works, as e.g., for xlab;
  related to PR#10525.

• parallel::detect.cores(all.tests = TRUE) tries a matching OS name
  before the other tests (which were intended only for unknown
  OSes).

• Parse data for raw strings is now recorded correctly. Reported by
  Gabor Csardi.