Fix determining ZXING_CFLAGS for --with-system-zxing

While at least Linux distros typically provide the zxing include files in a
dedicated ZXing sub-directory (i.e., /usr/include/ZXing/), the bundled
external/zxing does not (it rather provides them in
workdir/UnpackedTarball/zxing/core/src/, cf. RepositoryExternal.mk).  Therefore,
source files like cui/source/dialogs/QrCodeGenDialog.cxx

#include <BarcodeFormat.h>

etc. rather than

#include <ZXing/BarcodeFormat.h>

etc., and for --with-system-zxing ad92c7dfa64c9e08aa2bcf612a9a4a68e9deae22 "fix
system zxing build" simply hardcoded ZXING_CFLAGS=-I/usr/include/ZXing (i.e.,
the typical location for these include files).

However, for e.g. a Fedora Flatpak-from-RPM build of --with-system-zxing
LibreOffice, the include files will be in /app/include/ZXing/ rather than in
/usr/include/ZXing/.  (And which AC_CHECK_HEADER would find via
CPLUS_INCLUDE_PATH containing /app/include for such a build.  But the hardcoded
ZXING_CFLAGS then caused compiling e.g. cui/source/dialogs/QrCodeGenDialog.cxx
to fail because it didn't find BarcodeFormat.h etc. in the hardcoded
/usr/include/ZXing/.)

So when checking for the sample zxing include file (MultiFormatWriter.h), try
any $CPLUS_INCLUDE_PATH paths one by one (and with a fallback to /usr/include).
(The explicit unset ac_cv_header_MultiFormatWriter_h is needed so that the
second and later iterations of the for loop don't erroneously reuse a cached
"no" result.)

Change-Id: Id85f9960ffd3759c7960ef3a81982b85bc3c04c1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133189
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 25 insertions, 3 deletions

diff --git a/configure.ac b/configure.ac
index 1d432bc77a7b..a43d6bddd344 100644
--- a/configure.ac
+++ b/configure.ac
@@ -11143,10 +11143,32 @@ else
     if test "$with_system_zxing" = "yes"; then
         AC_MSG_RESULT([external])
         SYSTEM_ZXING=TRUE
+        ZXING_CFLAGS=
         AC_LANG_PUSH([C++])
-        AC_CHECK_HEADER(ZXing/MultiFormatWriter.h, [],
-            [AC_MSG_ERROR(zxing headers not found.)], [#include <stdexcept>])
-        ZXING_CFLAGS=-I/usr/include/ZXing
+        save_CXXFLAGS=$CXXFLAGS
+        save_IFS=$IFS
+        IFS=$P_SEP
+        for i in $CPLUS_INCLUDE_PATH /usr/include; do
+            dnl Reset IFS as soon as possible, to avoid unexpected side effects (and the
+            dnl "/usr/include" fallback makes sure we get here at least once; resetting rather than
+            dnl unsetting follows the advice at <http://git.savannah.gnu.org/gitweb/?p=autoconf.git;
+            dnl a=commit;h=e51c9919f2cf70185b7916ac040bc0bbfd0f743b> "Add recommendation on (not)
+            dnl unsetting IFS."):
+            IFS=$save_IFS
+            dnl TODO: GCC and Clang treat empty paths in CPLUS_INCLUDE_PATH like ".", but we simply
+            dnl ignore them here:
+            if test -z "$i"; then
+                continue
+            fi
+            dnl TODO: White space in $i would cause problems:
+            CXXFLAGS="$save_CXXFLAGS -I$i/ZXing"
+            AC_CHECK_HEADER(MultiFormatWriter.h, [ZXING_CFLAGS=-I$i/ZXing; break],
+                [unset ac_cv_header_MultiFormatWriter_h], [#include <stdexcept>])
+        done
+        CXXFLAGS=$save_CXXFLAGS
+        if test -z "$ZXING_CFLAGS"; then
+            AC_MSG_ERROR(zxing headers not found.)
+        fi
         AC_CHECK_LIB([ZXing], [main], [ZXING_LIBS=-lZXing],
             [ AC_CHECK_LIB([ZXingCore], [main], [ZXING_LIBS=-lZXingCore],
             [ AC_MSG_ERROR(zxing C++ library not found.) ])], [])