CMake: set C++17 standard for benchmarks (required by newer re2).

This fixes https://github.com/skvadrik/re2c/issues/455 "Test for C++11
compiler at configure time".

BUILD.md

@@ -5,9 +5,9 @@ How to build
 Dependencies
 ------------
 
-To build re2c from a release tarball one needs only a C++ compiler and Python 3
-(for build-time scripts and for testing). Building on Windows additionally
-requires either CMake or a Mingw build environment.
+To build re2c from a release tarball one needs only a C++ compiler (supporting
+at least C++11) and Python 3 for build-time scripts and for testing. Building on
+Windows additionally requires either CMake or a Mingw build environment.
 
 To develop re2c one also needs CMake or Autotools (both build systems are
 maintained). Other dependencies include Bison (to rebuild parsers), Python 3

CMakeLists.txt

@@ -53,6 +53,7 @@ endif()
 # -std=gnu++11, not -std=c++11. Extensions are needed to enable POSIX functions on
 # Cygwin and NetBSD.
 set(CMAKE_CXX_STANDARD 11)
+set(CMAKE_CXX_STANDARD_REQUIRED ON) # fail if the C++ compiler does not support this standard
 set(CMAKE_POSITION_INDEPENDENT_CODE ON) # make sure object libraries work with shared libraries
 
 # needed for POSIX file API

Makefile.am

@@ -311,17 +311,28 @@ man_MANS = $(DOCS)
 # include files (stdlib)
 dist_stdlib_DATA = include/unicode_categories.re
 
+BAZELFILES := \
+	BUILD.bazel \
+	WORKSPACE \
+	bazel
+
 CMAKEFILES := \
 	CMakeLists.txt \
+	CMakePresets.json \
 	cmake
 
 EXTRA_DIST = \
 	$(re2c_BOOT) \
 	$(re2c_CUSTOM) \
 	$(re2c_SRC_DOC_EXT) \
+	$(BAZELFILES) \
 	$(CMAKEFILES) \
+	BUILD.md \
 	CHANGELOG \
+	CONTRIBUTING.md \
+	IDEAS.md \
 	LICENSE \
+	MAINTAINERS.md \
 	NO_WARRANTY \
 	README.md \
 	autogen.sh \

benchmarks/submatch_dfa_jit/CMakeLists.txt

@@ -12,6 +12,9 @@ target_link_libraries(bench_submatch_dfa_jit benchmark::benchmark)
 find_path(RE2_INCLUDE_DIRECTORY "re2/re2.h")
 find_library(RE2_LIBRARY re2)
 if(RE2_INCLUDE_DIRECTORY AND RE2_LIBRARY)
+    set_target_properties(bench_submatch_dfa_jit PROPERTIES
+        CXX_STANDARD 17
+        CXX_STANDARD_REQUIRED ON)
     target_compile_definitions(bench_submatch_dfa_jit PRIVATE "HAVE_RE2_RE2_H=1")
     target_include_directories(bench_submatch_dfa_jit PRIVATE "${RE2_INCLUDE_DIRECTORY}")
     target_link_libraries(bench_submatch_dfa_jit "${RE2_LIBRARY}")

benchmarks/submatch_nfa/CMakeLists.txt

@@ -12,6 +12,9 @@ target_link_libraries(bench_submatch_nfa benchmark::benchmark)
 find_path(RE2_INCLUDE_DIRECTORY "re2/re2.h")
 find_library(RE2_LIBRARY re2)
 if(RE2_INCLUDE_DIRECTORY AND RE2_LIBRARY)
+    set_target_properties(bench_submatch_nfa PROPERTIES
+        CXX_STANDARD 17
+        CXX_STANDARD_REQUIRED ON)
     target_compile_definitions(bench_submatch_nfa PRIVATE "HAVE_RE2_RE2_H=1")
     target_include_directories(bench_submatch_nfa PRIVATE "${RE2_INCLUDE_DIRECTORY}")
     target_link_libraries(bench_submatch_nfa "${RE2_LIBRARY}")

configure.ac

@@ -124,13 +124,18 @@ AC_DEFUN([TRY_CXXFLAG], [
             AS_VAR_SET([TRY_CXXFLAG_RESULT], [yes])
             AS_VAR_SET([CXXFLAGSDEFAULT], ["$CXXFLAGSDEFAULT $1 $2"])
         ],
-        [AS_VAR_SET([TRY_CXXFLAG_RESULT], [no])]
+        [
+            AS_VAR_SET([TRY_CXXFLAG_RESULT], [no])
+            AS_IF([test "x$3" = "xrequired"], [
+                AC_MSG_ERROR([C++ compiler flag $1 is required to build re2c])
+            ])
+        ]
     )
     AC_LANG_POP([C++])
     AS_VAR_SET([CXXFLAGS], ["$CXXFLAGS_BACKUP"])
     AC_MSG_RESULT([$TRY_CXXFLAG_RESULT])
 ])
-TRY_CXXFLAG([-std=c++11])
+TRY_CXXFLAG([-std=c++11], [], [required])
 TRY_CXXFLAG([-W])
 TRY_CXXFLAG([-Wall])
 TRY_CXXFLAG([-Wextra])