WebAssembly: Prepare library to be used with wasm32-wasi

It is the changes I made to make compilation work for clang with "wasm32-wasi" target and the wasi-sdk.

Makefile

@@ -27,6 +27,14 @@ else
 endif
 CAT ?= $(if $(filter $(OS),Windows_NT),type,cat)
 
+ifdef WASM
+  CFLAGS   += -D_WASM
+  CXXFLAGS += -D_WASM
+endif
+
+ifdef WASM
+	UNAME := WebAssembly
+else
 ifneq (,$(findstring /cygdrive/,$(PATH)))
 	UNAME := Cygwin
 else
@@ -44,6 +52,7 @@ endif
 endif
 endif
 endif
+endif
 
 ifndef LIBSASS_VERSION
 	ifneq ($(wildcard ./.git/ ),)
@@ -161,18 +170,28 @@ ifeq (Windows,$(UNAME))
 		LIB_SHARED  = $(SASS_LIBSASS_PATH)/lib/libsass.dll
 	endif
 else
+ifdef WASM
+	SASSC_BIN = $(SASS_SASSC_PATH)/bin/sassc.wasm
+	SHAREDLIB  = lib/libsass.wasm
+	LIB_SHARED  = $(SASS_LIBSASS_PATH)/lib/libsass.wasm
+else
 ifneq (Cygwin,$(UNAME))
 	CFLAGS   += -fPIC
 	CXXFLAGS += -fPIC
 	LDFLAGS  += -fPIC
 endif
 endif
+endif
 
 include Makefile.conf
 OBJECTS = $(addprefix src/,$(SOURCES:.cpp=.o))
 COBJECTS = $(addprefix src/,$(CSOURCES:.c=.o))
 RCOBJECTS = $(RESOURCES:.rc=.o)
 
+ifdef WASM
+WASMOBJECTS = wasm/libcxxabi_stubs.o
+endif
+
 DEBUG_LVL ?= NONE
 
 CLEANUPS ?=
@@ -198,15 +217,18 @@ debug-shared: shared
 lib:
 	$(MKDIR) lib
 
-lib/libsass.a: $(COBJECTS) $(OBJECTS) | lib
-	$(AR) rcvs $@ $(COBJECTS) $(OBJECTS)
+lib/libsass.a: $(COBJECTS) $(OBJECTS) $(WASMOBJECTS) | lib
+	$(AR) rcvs $@ $(COBJECTS) $(OBJECTS) $(WASMOBJECTS)
 
 lib/libsass.so: $(COBJECTS) $(OBJECTS) | lib
 	$(CXX) -shared $(LDFLAGS) -o $@ $(COBJECTS) $(OBJECTS) $(LDLIBS)
 
 lib/libsass.dll: $(COBJECTS) $(OBJECTS) $(RCOBJECTS) | lib
 	$(CXX) -shared $(LDFLAGS) -o $@ $(COBJECTS) $(OBJECTS) $(RCOBJECTS) $(LDLIBS) -s -Wl,--subsystem,windows,--out-implib,lib/libsass.a
 
+lib/libsass.wasm: $(COBJECTS) $(OBJECTS) $(WASMOBJECTS) | lib
+	$(CXX) $(LDFLAGS) -o $@ $(COBJECTS) $(OBJECTS) $(WASMOBJECTS) $(LDLIBS)
+
 %.o: %.c
 	$(CC) $(CFLAGS) -c -o $@ $<
 
@@ -269,7 +291,9 @@ $(SASSC_BIN): $(BUILD)
 	$(MAKE) -C $(SASS_SASSC_PATH) build-$(BUILD)-dev
 
 sassc: $(SASSC_BIN)
+ifndef WASM
 	$(SASSC_BIN) -v
+endif
 
 version: $(SASSC_BIN)
 	$(SASSC_BIN) -v
@@ -286,7 +310,7 @@ test_probe: $(SASSC_BIN)
 	$(RUBY_BIN) $(SASS_SPEC_PATH)/sass-spec.rb -c $(SASSC_BIN) --impl libsass --probe-todo $(LOG_FLAGS) $(SASS_SPEC_PATH)/$(SASS_SPEC_SPEC_DIR)
 
 clean-objects: | lib
-	-$(RM) lib/*.a lib/*.so lib/*.dll lib/*.la
+	-$(RM) lib/*.a lib/*.so lib/*.dll lib/*.la lib/*.wasm
 	-$(RMDIR) lib
 clean: clean-objects
 	$(RM) $(CLEANUPS)

src/file.cpp

@@ -18,6 +18,7 @@
 #include <cctype>
 #include <vector>
 #include <algorithm>
+#include <stdlib.h>
 #include <sys/stat.h>
 #include "file.hpp"
 #include "context.hpp"
@@ -49,6 +50,15 @@ inline static std::string wstring_to_string(const std::wstring &wstr)
 # endif
 #endif
 
+#ifdef _WASM
+inline static std::string get_cwd_from_env()
+{
+  char* value = getenv("PWD");
+  if (!value) return "/";
+  return value;
+}
+#endif
+
 namespace Sass {
   namespace File {
 
@@ -57,6 +67,11 @@ namespace Sass {
     // always with trailing slash
     std::string get_cwd()
     {
+      #ifdef _WASM
+        // the WASI does not implement getcwd() yet --
+        // check the environment variables or default to "/".
+        std::string cwd = get_cwd_from_env();
+      #else
       const size_t wd_len = 4096;
       #ifndef _WIN32
         char wd[wd_len];
@@ -73,6 +88,7 @@ namespace Sass {
         //convert backslashes to forward slashes
         replace(cwd.begin(), cwd.end(), '\\', '/');
       #endif
+      #endif
       if (cwd[cwd.length() - 1] != '/') cwd += '/';
       return cwd;
     }

src/plugins.cpp

@@ -13,8 +13,10 @@
 #include <sys/types.h>
 #include <dirent.h>
 #include <errno.h>
+#ifndef _WASM
 #include <dlfcn.h>
 #endif
+#endif
 
 namespace Sass {
 
@@ -57,7 +59,7 @@ namespace Sass {
   // load one specific plugin
   bool Plugins::load_plugin (const std::string& path)
   {
-
+#ifdef ENABLE_LOAD_PLUGINS
     typedef const char* (*__plugin_version__)(void);
     typedef Sass_Function_List (*__plugin_load_fns__)(void);
     typedef Sass_Importer_List (*__plugin_load_imps__)(void);
@@ -107,6 +109,9 @@ namespace Sass {
       std::cerr << "failed loading plugin <" << path << ">" << std::endl;
       if (const char* dlopen_error = dlerror()) std::cerr << dlopen_error << std::endl;
     }
+#else
+    std::cerr << "plugins loading is unsupported <" << path << ">" << std::endl;
+#endif
 
     return false;
 

src/plugins.hpp

@@ -6,6 +6,7 @@
 #include "utf8_string.hpp"
 #include "sass/functions.h"
 
+#ifdef ENABLE_LOAD_PLUGINS
 #ifdef _WIN32
 
   #define LOAD_LIB(var, path) HMODULE var = LoadLibraryW(UTF_8::convert_to_utf16(path).c_str())
@@ -24,6 +25,7 @@
   #define CLOSE_LIB(var) dlclose(var)
 
 #endif
+#endif
 
 namespace Sass {
 

src/sass.hpp

@@ -38,6 +38,11 @@
 # endif
 #endif
 
+// enable loading of plugins for non-wasm
+#ifndef _WASM
+# define ENABLE_LOAD_PLUGINS
+#endif
+
 // path separation char
 #ifndef PATH_SEP
 # ifdef _WIN32

wasm/libcxxabi_stubs.c

@@ -0,0 +1,25 @@
+#include <stdlib.h> 
+
+// -fno-exceptions is not an option with libsass yet,
+// stubbing libc++abi functions
+
+void __cxa_throw(void *thrown_exception, void *tinfo,
+                 void (*dest)(void *))
+{
+    abort();
+}
+
+void *__cxa_allocate_exception(size_t thrown_size)
+{
+    abort();
+}
+
+void __cxa_rethrow()
+{
+    abort();
+}
+
+void* __cxa_begin_catch(void* exceptionObject)
+{
+    abort();
+}