Warn about XFT and about Cairo without HarfBuzz

* configure.ac: Warn about libXFT usage.  Warn about using Cairo
without HarfBuzz.

* etc/NEWS: Announce XFT and HarfBuzz warnings.

Author: rpluim

configure.ac

@@ -5891,6 +5891,20 @@ you can continue to support by using '$0 --with-pop'.])
   esac
 fi
 
+if test "${HAVE_XFT}" = yes; then
+AC_MSG_WARN([This configuration uses libXft,
+    which has a number of font rendering issues, and is being considered for
+    removal in the next release of Emacs.  Please consider using Cairo + HarfBuzz
+    instead (they are auto-detected if the relevant development headers are
+    installed).])
+fi
+
+if test "${HAVE_CAIRO}" = "yes" && test "${HAVE_HARFBUZZ}" = no; then
+   AC_MSG_WARN([This configuration uses Cairo, but not HarfBuzz.  We
+    recommend the use of HarfBuzz when using Cairo, please install
+    HarfBuzz development packages.])
+fi
+
 # Let plain 'make' work.
 test "$MAKE" = make || test -f makefile || cat >makefile <<EOF
 .POSIX:

etc/NEWS

@@ -41,6 +41,19 @@ available when HarfBuzz is supported, but will not be used by default.
 We strongly recommend building with HarBuzz support. 'x' is still a
 valid backend.
 
+---
+** 'configure' now warns about building with libXft support.
+libXft is unmaintained, and causes a number of problems with modern
+fonts including but not limited to crashes; support for it may be
+removed in a future version of Emacs.  Please consider using
+Cairo + HarfBuzz instead.
+
+---
+** 'configure' now warns about not using HarfBuzz if using Cairo.
+We want to encourage people to use the most modern font features
+available, and this is Cairo + HarfBuzz, so 'configure' now recommends
+that combination.
+
 ---
 ** The ftx font backend driver has been removed.
 It was declared obsolete in Emacs 27.1.