[R-pkg-devel] Alternative to ifeq for Makevars

[Josiah Parry]

I am working on refactoring some Makevars files and I am quite stuck. I
want to conditionally set the value of CRAN_FLAGS like so in my Makevars
files

ifeq ($(NOT_CRAN), false)
  CRAN_FLAGS = -j 2 --offline
else
  CRAN_FLAGS =
endif

Using ifeq appears to be the only way to get the value of CRAN_FLAGS to
persist within the $(STATILIB) portion of the Makevars file.

However, this results in a Warning

checking for GNU extensions in Makefiles ... WARNING
  Found the following file(s) containing GNU extensions:
    src/Makevars
  Portable Makefiles do not use GNU extensions such as +=, :=, $(shell),
  $(wildcard), ifeq ... endif, .NOTPARALLEL See section ‘Writing portable
  packages’ in the ‘Writing R Extensions’ manual.

How do other people address this?

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