Allow building R backend with MSVC

src/backends/R/CMakeLists.txt

@@ -31,6 +31,13 @@ add_backend(rbackend ${RBackend_SRCS})
 
 set_target_properties( cantor_rbackend PROPERTIES INSTALL_RPATH_USE_LINK_PATH false)
 target_link_libraries( cantor_rbackend cantor_help ${R_USED_LIBS} KF5::SyntaxHighlighting)
+if(MSVC)
+# When compiling with MSVC, we have to create a .lib file for R.dll, first
+find_package(Python3 COMPONENTS Interpreter REQUIRED)
+add_custom_target(R_lib COMMAND ${Python3_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/GenLibFile.py ${R_R_LIBRARY} ${CMAKE_BINARY_DIR} ${CMAKE_SYSTEM_PROCESSOR}
+                        COMMENT "Generate .lib file for R.dll")
+add_dependencies(cantor_rbackend R_lib)
+endif(MSVC)
 
 if(BUILD_TESTING)
   add_executable( testr testr.cpp)

src/backends/R/GenLibFile.py

+import subprocess
+import os
+import sys
+
+# Generate a .lib file for a given .dll
+# This assumed dumpbin and lib to be in the path, which they should be, when compiling with MSVC (and that's what this is needed for)
+#
+# Usage: python3 GenLibFile.py XYZ.dll output_directory architecture
+
+dllfile = sys.argv[1]
+workdir = sys.argv[2]
+arch = sys.argv[3]
+base = os.path.basename(dllfile).replace(".dll", "")
+deffile = base + ".def"
+libfile = base + ".lib"
+
+dump = subprocess.check_output(["dumpbin", "/exports", dllfile]).decode("latin1").splitlines()
+exports = []
+for line in dump:
+    fields = line.split()
+    if len(fields) != 4:
+        continue
+    exports.append(fields[3])
+os.chdir(workdir)
+with open(os.path.join(workdir, deffile), "wt+") as outdef:
+    outdef.write("EXPORTS\n")
+    outdef.write("\n".join(exports))
+subprocess.call(["lib", f"/def:{deffile}", f"/out:{libfile}", f"/machine:{arch}"])