Have configure check for c++17 compatibility

If tesseract/leptonica is present, check if the the compiler is g++ (or
compatible) and if so, check it understands the -std=c++17 option. If not,
drop the OCR devices, and emit a warning message at the end of configure.

If the compiler is not g++ (or compatible) carry on, but emit a warning to
the effect that it's up to the user to ensure the compiler they use can handle
c++17.

1 files changed, 123 insertions, 102 deletions

diff --git a/configure.ac b/configure.ac
index eddc08e6d..9779331c5 100644
--- a/configure.ac
+++ b/configure.ac
@@ -833,6 +833,9 @@ TESSERACTINCLUDE=
 TESSERACT_LIBS=
 OCR_DEVS=
 
+OCR_DEVS_WARNING_LINE1=
+OCR_DEVS_WARNING_LINE2=
+
 AC_ARG_WITH([tesseract], AS_HELP_STRING([--without-tesseract],
     [do not try to use the Tesseract library for OCR]))
 
@@ -863,120 +866,129 @@ if test x$with_tesseract != xno; then
         CXXFLAGS="$old_cflags"
       done
 
-      CXXFLAGS="$save_cxxflags $CXXFLAGS_TO_USE"
-
-      dnl --------------------------------------------------
-      dnl check for sse4.1, avx, avx2 or fma
-      dnl --------------------------------------------------
-      AC_MSG_CHECKING([sse4.1 support])
-      save_cxxflags=$CXXFLAGS
-      TESS_CXXFLAGS="$CXXFLAGS"
-      CXXFLAGS="$CXXFLAGS -msse4.1"
-
-      TESS_SSE4_1=""
-      AC_LINK_IFELSE(
-        [AC_LANG_PROGRAM([#include <emmintrin.h>
-                          #include <smmintrin.h>],
-                         [__m128i input1;
-                          unsigned char buf1[[128]];
-                          input1 = _mm_loadu_si128((const __m128i *)buf1);
-                          input1 = _mm_hadd_epi32(input1, input1);
-                          return(0);
-                         ])],
-        [TESS_SSE4_1="-msse4.1"],
-        [TESS_SSE4_1=""])
-
-      if test "x$TESS_SSE4_1" != x; then
-        AC_MSG_RESULT(yes)
-        TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_SSE4_1"
-      else
-        AC_MSG_RESULT(no)
-      fi
+      if test x"$GXX" = x"no" || echo $CXXFLAGS_TO_USE | grep "std=c++17" ; then
+        if test x"$GXX" = x"no" ; then
+          OCR_DEVS_WARNING_LINE1="C++ compiler does not appear to be gcc or compatible, attempting to continue anyway"
+          OCR_DEVS_WARNING_LINE2="NOTE: that tesseract requires a C++17 compatible C++ compiler"
+        fi
 
-      AC_MSG_CHECKING([avx support])
-      CXXFLAGS="$save_cxxflags -mavx"
+        CXXFLAGS="$save_cxxflags $CXXFLAGS_TO_USE"
+
+        dnl --------------------------------------------------
+        dnl check for sse4.1, avx, avx2 or fma
+        dnl --------------------------------------------------
+        AC_MSG_CHECKING([sse4.1 support])
+        save_cxxflags=$CXXFLAGS
+        TESS_CXXFLAGS="$CXXFLAGS"
+        CXXFLAGS="$CXXFLAGS -msse4.1"
+
+        TESS_SSE4_1=""
+        AC_LINK_IFELSE(
+          [AC_LANG_PROGRAM([#include <emmintrin.h>
+                            #include <smmintrin.h>],
+                           [__m128i input1;
+                            unsigned char buf1[[128]];
+                            input1 = _mm_loadu_si128((const __m128i *)buf1);
+                            input1 = _mm_hadd_epi32(input1, input1);
+                            return(0);
+                           ])],
+          [TESS_SSE4_1="-msse4.1"],
+          [TESS_SSE4_1=""])
+
+        if test "x$TESS_SSE4_1" != x; then
+          AC_MSG_RESULT(yes)
+          TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_SSE4_1"
+        else
+          AC_MSG_RESULT(no)
+        fi
 
-      TESS_AVX=""
-      AC_LINK_IFELSE(
-        [AC_LANG_PROGRAM([#include <immintrin.h>],
-	                 [__m256d input1 = _mm256_setzero_pd();
-                          input1 = _mm256_hadd_pd(input1, input1);
-                          return(0);])],
-        [TESS_AVX="-mavx"],
-        [TESS_AVX=""])
+        AC_MSG_CHECKING([avx support])
+        CXXFLAGS="$save_cxxflags -mavx"
 
-      if test "x$TESS_AVX" != x; then
-        AC_MSG_RESULT(yes)
-        TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_AVX"
-      else
-        AC_MSG_RESULT(no)
-      fi
+        TESS_AVX=""
+        AC_LINK_IFELSE(
+          [AC_LANG_PROGRAM([#include <immintrin.h>],
+                           [__m256d input1 = _mm256_setzero_pd();
+                            input1 = _mm256_hadd_pd(input1, input1);
+                            return(0);])],
+          [TESS_AVX="-mavx"],
+          [TESS_AVX=""])
 
-      AC_MSG_CHECKING([avx2 support])
-      CXXFLAGS="$save_cxxflags -mavx2"
-
-      TESS_AVX2=""
-      AC_LINK_IFELSE(
-        [AC_LANG_PROGRAM([#include <immintrin.h>],
-	                 [__m256i input1;
-                          unsigned char buf1[[256]];
-                          input1 = _mm256_loadu_si256((const __m256i *)buf1);
-                          input1 = _mm256_adds_epu8(input1, input1);
-                          return(0);])],
-        [TESS_AVX2="-mavx2"],
-        [TESS_AVX2=""])
-
-      if test "x$TESS_AVX2" != x; then
-        AC_MSG_RESULT(yes)
-        TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_AVX2"
-      else
-        AC_MSG_RESULT(no)
-      fi
+        if test "x$TESS_AVX" != x; then
+          AC_MSG_RESULT(yes)
+          TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_AVX"
+        else
+          AC_MSG_RESULT(no)
+        fi
+
+        AC_MSG_CHECKING([avx2 support])
+        CXXFLAGS="$save_cxxflags -mavx2"
+
+        TESS_AVX2=""
+        AC_LINK_IFELSE(
+          [AC_LANG_PROGRAM([#include <immintrin.h>],
+                           [__m256i input1;
+                            unsigned char buf1[[256]];
+                            input1 = _mm256_loadu_si256((const __m256i *)buf1);
+                            input1 = _mm256_adds_epu8(input1, input1);
+                            return(0);])],
+          [TESS_AVX2="-mavx2"],
+          [TESS_AVX2=""])
+
+        if test "x$TESS_AVX2" != x; then
+          AC_MSG_RESULT(yes)
+          TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_AVX2"
+        else
+          AC_MSG_RESULT(no)
+        fi
 
-      AC_MSG_CHECKING([fma support])
-      CXXFLAGS="$save_cxxflags -mfma"
+        AC_MSG_CHECKING([fma support])
+        CXXFLAGS="$save_cxxflags -mfma"
 
-      TESS_FMA=""
-      AC_LINK_IFELSE(
-        [AC_LANG_PROGRAM([#include <immintrin.h>],
-	                 [__m256d input1 = _mm256_setzero_pd();
-                          input1 = _mm256_fmadd_pd(input1, input1, input1);
-                          return(0);])],
-        [TESS_FMA="-mfma"],
-        [TESS_FMA=""])
+        TESS_FMA=""
+        AC_LINK_IFELSE(
+          [AC_LANG_PROGRAM([#include <immintrin.h>],
+                           [__m256d input1 = _mm256_setzero_pd();
+                            input1 = _mm256_fmadd_pd(input1, input1, input1);
+                            return(0);])],
+          [TESS_FMA="-mfma"],
+          [TESS_FMA=""])
 
-      if test "x$TESS_FMA" != x; then
-        AC_MSG_RESULT(yes)
-        TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_FMA"
-      else
-        AC_MSG_RESULT(no)
-      fi
+        if test "x$TESS_FMA" != x; then
+          AC_MSG_RESULT(yes)
+          TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_FMA"
+        else
+          AC_MSG_RESULT(no)
+        fi
 
-      AC_MSG_CHECKING([neon support])
-      CXXFLAGS="$save_cxxflags -mfpu=neon -mcpu=cortex-a53"
+        AC_MSG_CHECKING([neon support])
+        CXXFLAGS="$save_cxxflags -mfpu=neon -mcpu=cortex-a53"
 
-      TESS_NEON=""
-      AC_LINK_IFELSE(
-       [AC_LANG_PROGRAM([#include "arm_neon.h"],
-                        [int32x4_t round = vdupq_n_s32(10);
-                         return(0);])],
-       [TESS_NEON="-mfpu=neon -mcpu=cortex-a53 -D__ARM_NEON__"],
-       [TESS_NEON=""])
+        TESS_NEON=""
+        AC_LINK_IFELSE(
+         [AC_LANG_PROGRAM([#include "arm_neon.h"],
+                          [int32x4_t round = vdupq_n_s32(10);
+                           return(0);])],
+         [TESS_NEON="-mfpu=neon -mcpu=cortex-a53 -D__ARM_NEON__"],
+         [TESS_NEON=""])
 
-      if test "x$TESS_NEON" != x; then
-        AC_MSG_RESULT(yes)
-        TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_NEON"
-      else
-        AC_MSG_RESULT(no)
-      fi
+        if test "x$TESS_NEON" != x; then
+          AC_MSG_RESULT(yes)
+          TESS_CXXFLAGS="$TESS_CXXFLAGS -DHAVE_NEON"
+        else
+          AC_MSG_RESULT(no)
+        fi
 
-      CXXFLAGS="$save_cxxflags"
+        CXXFLAGS="$save_cxxflags"
 
-      OCR_VERSION=1
-      OCR_DEVS="\$(DD)ocr.dev \$(DD)hocr.dev \$(DD)pdfocr8.dev \$(DD)pdfocr24.dev \$(DD)pdfocr32.dev"
-      LEPTONICAINCLUDE="include base/leptonica.mak"
-      TESSERACTINCLUDE="include base/tesseract.mak"
-      TESSERACT_LIBS="-lstdc++"
+        OCR_VERSION=1
+        OCR_DEVS="\$(DD)ocr.dev \$(DD)hocr.dev \$(DD)pdfocr8.dev \$(DD)pdfocr24.dev \$(DD)pdfocr32.dev"
+        LEPTONICAINCLUDE="include base/leptonica.mak"
+        TESSERACTINCLUDE="include base/tesseract.mak"
+        TESSERACT_LIBS="-lstdc++"
+      else
+        OCR_DEVS_WARNING_LINE1="OCR devices disabled due to incompatible compiler: tesseract requires a C++17 compatible compiler"
+      fi
     fi
     AC_LANG_POP()
   else
@@ -3750,6 +3762,15 @@ if test "x$NTS_EXCLUDES" != "x" ; then
    echo "$NTS_EXCLUDES"
 fi
 
+if test x"$OCR_DEVS_WARNING_LINE1" != x"" ; then
+    echo ""
+    AC_MSG_WARN([$OCR_DEVS_WARNING_LINE1])
+    if test x"$OCR_DEVS_WARNING_LINE2" != x"" ; then
+      AC_MSG_WARN([$OCR_DEVS_WARNING_LINE2])
+    fi
+    echo ""
+fi
+
 AC_CONFIG_FILES($CONFIG_FILES_LIST)
 
 AC_OUTPUT