Fix compilation of NIFs on Windows

Thanks to two users of the ninenines/esdl2 project,
a correct way to build NIFs on Windows has been found.

At the moment we require a specific compiler (MingW's
gcc). Maybe we can change this in the future and allow
Visual Studio and others.

Some small changes have been made to the documentation,
and the meaning of one configuration variable has changed
to not include the extension (which is decided automatically
by Erlang.mk; and configurable separately).

Enjoy!

doc/src/guide/installation.asciidoc

@@ -95,6 +95,13 @@ to find all packages related to GCC:
 [source,bash]
 $ pacman -Ss gcc
 
+If you are going to compile C/C++ code, you will need to
+install this package, as Erlang.mk cannot use the normal
+"gcc" package:
+
+[source,bash]
+$ pacman -S mingw-w64-x86_64-gcc
+
 You can also run commands under the MSYS2 environment from
 the Windows command line or batch files. This command will
 install GNU Make and Git:

doc/src/guide/ports.asciidoc

@@ -64,9 +64,19 @@ before including Erlang.mk:
 [source,make]
 C_SRC_TYPE = executable
 
-The generated file will be saved to '$(C_SRC_OUTPUT)'. It
-defaults to '$(CURDIR)/priv/$(PROJECT).so', the filename
-adequately fitting a Unix shared library.
+The generated file name varies depending on the type of project
+you have (shared library or executable) and on the platform you
+build the project on.
+
+For shared libraries, the generated file name will be
+'$(C_SRC_OUTPUT)$(C_SRC_SHARED_EXTENSION)', with the default
+being '$(CURDIR)/priv/$(PROJECT)' followed by the extension:
+`.dll` on Windows, `.so` everywhere else.
+
+For executables, the generated file name is
+'$(C_SRC_OUTPUT)$(C_SRC_EXECUTABLE_EXTENSION)', with the same
+default except for the extension: `.exe` on Windows, and otherwise
+nothing.
 
 Erlang.mk sets appropriate compile and linker flags by default.
 These flags vary depending on the platform, and can of course

plugins/c_src.mk

@@ -7,12 +7,32 @@
 
 C_SRC_DIR ?= $(CURDIR)/c_src
 C_SRC_ENV ?= $(C_SRC_DIR)/env.mk
-C_SRC_OUTPUT ?= $(CURDIR)/priv/$(PROJECT).so
+C_SRC_OUTPUT ?= $(CURDIR)/priv/$(PROJECT)
 C_SRC_TYPE ?= shared
 
 # System type and C compiler/flags.
 
-ifeq ($(PLATFORM),darwin)
+ifeq ($(PLATFORM),msys2)
+	C_SRC_OUTPUT_EXECUTABLE_EXTENSION ?= .exe
+	C_SRC_OUTPUT_SHARED_EXTENSION ?= .dll
+else
+	C_SRC_OUTPUT_EXECUTABLE_EXTENSION ?=
+	C_SRC_OUTPUT_SHARED_EXTENSION ?= .so
+endif
+
+ifeq ($(C_SRC_TYPE),shared)
+	C_SRC_OUTPUT_FILE = $(C_SRC_OUTPUT)$(C_SRC_OUTPUT_SHARED_EXTENSION)
+else
+	C_SRC_OUTPUT_FILE = $(C_SRC_OUTPUT)$(C_SRC_OUTPUT_EXECUTABLE_EXTENSION)
+endif
+
+ifeq ($(PLATFORM),msys2)
+# We hardcode the compiler used on MSYS2. The default CC=cc does
+# not produce working code. The "gcc" MSYS2 package also doesn't.
+	CC = /mingw64/bin/gcc
+	CFLAGS ?= -O3 -std=c99 -finline-functions -Wall -Wmissing-prototypes
+	CXXFLAGS ?= -O3 -finline-functions -Wall
+else ifeq ($(PLATFORM),darwin)
 	CC ?= cc
 	CFLAGS ?= -O3 -std=c99 -arch x86_64 -finline-functions -Wall -Wmissing-prototypes
 	CXXFLAGS ?= -O3 -arch x86_64 -finline-functions -Wall
@@ -27,10 +47,15 @@ else ifeq ($(PLATFORM),linux)
 	CXXFLAGS ?= -O3 -finline-functions -Wall
 endif
 
-CFLAGS += -fPIC -I $(ERTS_INCLUDE_DIR) -I $(ERL_INTERFACE_INCLUDE_DIR)
-CXXFLAGS += -fPIC -I $(ERTS_INCLUDE_DIR) -I $(ERL_INTERFACE_INCLUDE_DIR)
+ifneq ($(PLATFORM),msys2)
+	CFLAGS += -fPIC
+	CXXFLAGS += -fPIC
+endif
+
+CFLAGS += -I"$(ERTS_INCLUDE_DIR)" -I"$(ERL_INTERFACE_INCLUDE_DIR)"
+CXXFLAGS += -I"$(ERTS_INCLUDE_DIR)" -I"$(ERL_INTERFACE_INCLUDE_DIR)"
 
-LDLIBS += -L $(ERL_INTERFACE_LIB_DIR) -lerl_interface -lei
+LDLIBS += -L"$(ERL_INTERFACE_LIB_DIR)" -lerl_interface -lei
 
 # Verbosity.
 
@@ -67,15 +92,15 @@ OBJECTS = $(addsuffix .o, $(basename $(SOURCES)))
 COMPILE_C = $(c_verbose) $(CC) $(CFLAGS) $(CPPFLAGS) -c
 COMPILE_CPP = $(cpp_verbose) $(CXX) $(CXXFLAGS) $(CPPFLAGS) -c
 
-app:: $(C_SRC_ENV) $(C_SRC_OUTPUT)
+app:: $(C_SRC_ENV) $(C_SRC_OUTPUT_FILE)
 
-test-build:: $(C_SRC_ENV) $(C_SRC_OUTPUT)
+test-build:: $(C_SRC_ENV) $(C_SRC_OUTPUT_FILE)
 
-$(C_SRC_OUTPUT): $(OBJECTS)
+$(C_SRC_OUTPUT_FILE): $(OBJECTS)
 	$(verbose) mkdir -p priv/
 	$(link_verbose) $(CC) $(OBJECTS) \
 		$(LDFLAGS) $(if $(filter $(C_SRC_TYPE),shared),-shared) $(LDLIBS) \
-		-o $(C_SRC_OUTPUT)
+		-o $(C_SRC_OUTPUT_FILE)
 
 %.o: %.c
 	$(COMPILE_C) $(OUTPUT_OPTION) $<
@@ -92,13 +117,13 @@ $(C_SRC_OUTPUT): $(OBJECTS)
 clean:: clean-c_src
 
 clean-c_src:
-	$(gen_verbose) rm -f $(C_SRC_OUTPUT) $(OBJECTS)
+	$(gen_verbose) rm -f $(C_SRC_OUTPUT_FILE) $(OBJECTS)
 
 endif
 
 ifneq ($(wildcard $(C_SRC_DIR)),)
 $(C_SRC_ENV):
-	$(verbose) $(ERL) -eval "file:write_file(\"$(C_SRC_ENV)\", \
+	$(verbose) $(ERL) -eval "file:write_file(\"$(call core_native_path,$(C_SRC_ENV))\", \
 		io_lib:format( \
 			\"ERTS_INCLUDE_DIR ?= ~s/erts-~s/include/~n\" \
 			\"ERL_INTERFACE_INCLUDE_DIR ?= ~s~n\" \

test/plugin_c_src.mk

@@ -34,7 +34,11 @@ c-src-nif: build clean-c-src-nif
 	$t test -f $(APP)/c_src/env.mk
 	$t test -f $(APP)/ebin/$(APP).app
 	$t test -f $(APP)/ebin/$(APP).beam
+ifeq ($(PLATFORM),msys2)
+	$t test -f $(APP)/priv/$(APP).dll
+else
 	$t test -f $(APP)/priv/$(APP).so
+endif
 
 	$i "Check that the application was compiled correctly"
 	$t $(ERL) -pa $(APP)/ebin/ -eval " \
@@ -55,7 +59,11 @@ c-src-nif: build clean-c-src-nif
 	$t test -f $(APP)/c_src/env.mk
 	$t test -f $(APP)/ebin/$(APP).app
 	$t test -f $(APP)/ebin/$(APP).beam
+ifeq ($(PLATFORM),msys2)
+	$t test -f $(APP)/priv/$(APP).dll
+else
 	$t test -f $(APP)/priv/$(APP).so
+endif
 
 	$i "Check that the application was compiled correctly"
 	$t $(ERL) -pa $(APP)/ebin/ -eval " \
@@ -75,7 +83,11 @@ c-src-nif: build clean-c-src-nif
 	$t test ! -e $(APP)/c_src/$(APP).o
 	$t test ! -e $(APP)/ebin/$(APP).app
 	$t test ! -e $(APP)/ebin/$(APP).beam
+ifeq ($(PLATFORM),msys2)
+	$t test ! -e $(APP)/priv/$(APP).dll
+else
 	$t test ! -e $(APP)/priv/$(APP).so
+endif
 
 	$i "Distclean the application"
 	$t $(MAKE) -C $(APP) distclean $v