configure tests are done using wrong compilers

[s-u]

The configure tests are preformed using different compilers than the actual compilation yielding invalid results.

Example based on macOS R release:

$ R CMD config CXX
clang++ -mmacosx-version-min=10.13 -std=gnu++14

tiledb source installation:

* installing *source* package ‘tiledb’ ...
** using staged installation
checking for g++... g++
[...]
** libs
clang++ -mmacosx-version-min=10.13 -std=gnu++17 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I../inst/include/ -I../inst/tiledb/include -I'/Volumes/Builds/packages/high-sierra-x86_64/Rlib/4.1/Rcpp/include' -I/usr/local/include   -fPIC  -Wall -g -O2  -c RcppExports.cpp -o RcppExports.o

configure fails to set CC and CXX correctly, see R-exts 1.2:

Packages written with C++ need to pick up the details for the C++ compiler and switch the current language to C++ by something like

CXX=`"${R_HOME}/bin/R" CMD config CXX`
if test -z "$CXX"; then
  AC_MSG_ERROR([No C++ compiler is available])
fi
CXXFLAGS=`"${R_HOME}/bin/R" CMD config CXXFLAGS`
CPPFLAGS=`"${R_HOME}/bin/R" CMD config CPPFLAGS`
AC_LANG(C++)

[eddelbuettel]

But AFAIK we don't use CC and CXX for anything. And CXXFLAGS is irrelvant as we turn on CXX17 so you wanted to test with R CMD config CXX17 (not that matters on my Linux box).

So I am not sure what this would be helping with.

[s-u]

It is used in the ## Part 3:

TileDB-R/configure.ac

Lines 141 to 157 in 3310f07

	## -- Part 3: Check for TileDB --------------------------------------------------
	##
	## Check for TileDB -- either just probing the header, or by compilations (~ 1 second)
	checkTileDBViaHeader="yes"
	## Use either one of the tests
	if test x"${checkTileDBViaHeader}" = x"yes"; then
	## simply check for tiledb C-api header
	AC_CHECK_HEADER([tiledb/tiledb.h], [have_tiledb="yes"], [have_tiledb="no"])
	else
	## formally check we can build
	AC_MSG_CHECKING([compilation with TileDB])
	AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <tiledb/tiledb>
	tiledb::Context ctx;])],
	[have_tiledb="yes"; AC_MSG_RESULT(yes); ],
	[have_tiledb="no"; AC_MSG_RESULT(no, need to install TileDB)])
	fi

to check whether tiledb links so it will help those with tiledb available.

[eddelbuettel]

But you need to follow the flow; that code never gets turned on at CRAN because we don't find a header and hence turn on the artifact download. After that is it back to default R settings via src/Makevars.{in,win,ucrt}. It would matter say here for me where I have tiledb.h in /usr/local. So still a non-issue AFAICT. (And it passes 1 1/2 years of KH tests so ...)

[eddelbuettel]

While I think it is immaterial, I added a few more in 25afce7.

The ticket should close when we merge the branch with the TileDB 2.5.0 release.