(Visual C++) Added CMake option to link CRT

Previously Visual C++ users were forced to link CRT statically,
i.e. use /MT flag whenever they want to use the static library.
Linker have an error if user tries to link a /MT static library
to a /MD executable.

This commit defaults the build to statically link with CRT, but
may be turned off if needed.

runtime/Cpp/CMakeLists.txt

@@ -20,6 +20,8 @@ if(NOT WITH_DEMO)
 endif(NOT WITH_DEMO)
 
 option(WITH_LIBCXX "Building with clang++ and libc++(in Linux). To enable with: -DWITH_LIBCXX=On" On)
+option(WITH_STATIC_CRT "(Visual C++) Enable to statically link CRT, which avoids requiring users to install the redistribution package.
+ To disable with: -DWITH_STATIC_CRT=Off" On)
 
 project(LIBANTLR4)
 

runtime/Cpp/cmake/ExternalAntlr4Cpp.cmake

@@ -60,6 +60,10 @@ else()
           --target)
 endif()
 
+if(NOT DEFINED ANTLR4_WITH_STATIC_CRT)
+  set(ANTLR4_WITH_STATIC_CRT ON)
+endif()
+
 ExternalProject_Add(
     antlr4_runtime
     PREFIX antlr4_runtime
@@ -72,6 +76,7 @@ ExternalProject_Add(
     SOURCE_SUBDIR runtime/Cpp
     CMAKE_CACHE_ARGS
         -DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}
+        -DWITH_STATIC_CRT:BOOL=${ANTLR4_WITH_STATIC_CRT}
     INSTALL_COMMAND ""
     EXCLUDE_FROM_ALL 1)
 

runtime/Cpp/cmake/README.md

@@ -22,6 +22,8 @@ set(CMAKE_CXX_STANDARD 11)
 # required if linking to static library
 add_definitions(-DANTLR4CPP_STATIC)
 
+# using /MD flag for antlr4_runtime (for Visual C++ compilers only)
+set(ANTLR4_WITH_STATIC_CRT OFF)
 # add external build for antlrcpp
 include(ExternalAntlr4Cpp)
 # add antrl4cpp artifacts to project environment
@@ -114,6 +116,8 @@ ANTLR4_TAG - branch/tag used for building antlr4 library
 ```
 `ANTLR4_TAG` is set to master branch by default to keep antlr4 updated. However, it will be required to rebuild after every `clean` is called. Set `ANTLR4_TAG` to a desired commit hash value to avoid rebuilding after every `clean` and keep the build stable, at the cost of not automatically update to latest commit.
 
+Visual C++ compiler users may want to additionally define `ANTLR4_WITH_STATIC_CRT` before including the file. Set `ANTLR4_WITH_STATIC_CRT` to true if ANTLR4 C++ runtime library should be compiled with `/MT` flag, otherwise will be compiled with `/MD` flag. This variable has a default value of `OFF`. Changing `ANTLR4_WITH_STATIC_CRT` after building the library may require reinitialization of CMake or `clean` for the library to get rebuilt.
+
 #### Examples
 To build and link ANTLR4 static library to a target one may call:
 ```cmake

runtime/Cpp/runtime/CMakeLists.txt

@@ -64,8 +64,13 @@ if (WIN32)
   set(extra_static_compile_flags "-DANTLR4CPP_STATIC")
 endif(WIN32)
 if (CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
-  target_compile_options(antlr4_shared PRIVATE "/MD$<$<CONFIG:Debug>:d>")
+  if(WITH_STATIC_CRT)
-  target_compile_options(antlr4_static PRIVATE "/MT$<$<CONFIG:Debug>:d>")
+    target_compile_options(antlr4_shared PRIVATE "/MT$<$<CONFIG:Debug>:d>")
+    target_compile_options(antlr4_static PRIVATE "/MT$<$<CONFIG:Debug>:d>")
+  else()
+    target_compile_options(antlr4_shared PRIVATE "/MD$<$<CONFIG:Debug>:d>")
+    target_compile_options(antlr4_static PRIVATE "/MD$<$<CONFIG:Debug>:d>")
+  endif()
 endif()
 
 set(static_lib_suffix "")