CMakeLists.txt

cmake_minimum_required(VERSION 3.2)
project(url-function-bug)

set(CMAKE_BUILD_TYPE Debug)
set(SOURCE_FILES url-function-bug.c empty.cpp)

include_directories("../libsass/include")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")

message("search for libsass static library in: ${CMAKE_SOURCE_DIR}/../libsass/lib")
find_library(SASS_EXT_LIBRARY NAMES sass libsass PATHS "${CMAKE_SOURCE_DIR}/../libsass/lib" NO_DEFAULT_PATH)
message(STATUS "libsass library: ${SASS_EXT_LIBRARY}")
add_library(sass UNKNOWN IMPORTED)
set_property(TARGET sass PROPERTY IMPORTED_LOCATION "${SASS_EXT_LIBRARY}")

file(WRITE empty.cpp "")

if(APPLE)
    add_executable(url-function-bug MACOSX_BUNDLE ${SOURCE_FILES})
elseif(WIN32)
    add_executable(url-function-bug WIN32 ${SOURCE_FILES})
else()
    add_executable(url-function-bug ${SOURCE_FILES})
endif()

set_property(TARGET url-function-bug PROPERTY C_STANDARD 99)

set(LINK_FLAGS ${LINK_FLAGS} "-Wl,--whole-archive")

if(APPLE)
    target_link_libraries(url-function-bug sass)
else()
    target_link_libraries(url-function-bug "-Wl,--whole-archive" sass "-Wl,--no-whole-archive")
endif()

url-function-bug.c

#include <stdio.h>
#include <string.h>
#include <sass.h>
#include <sass2scss.h>
#include <stdlib.h>

union Sass_Value *custom_function(
        const union Sass_Value *sass_arguments,
        Sass_Function_Entry sass_function_entry,
        struct Sass_Compiler *sass_compiler
) {
    union Sass_Value *value = sass_list_get_value(sass_arguments, 0);
    printf("call function with %s\n", sass_string_get_value(value));
    return sass_make_qstring(sass_string_get_value(value));
}

int main() {
    char* scss =
        ".item1 {\n"
        "    background: url(item1.jpg);\n"
        "}\n"
        ".item2 {\n"
        "    background: url('item2.jpg');\n"
        "}\n"
        ".item3 {\n"
        "    background: url(\"item3.jpg\");\n"
        "}\n"
        // This item fails with a parsing exception
        // ".item4 {\n"
        // "    background: func(item4.jpg);\n"
        // "}\n"
        ".item5 {\n"
        "    background: func('item5.jpg');\n"
        "}\n"
        ".item6 {\n"
        "    background: func(\"item6.jpg\");\n"
        "}\n";

    struct Sass_Data_Context *sass_context = sass_make_data_context(scss);
    struct Sass_Options *sass_options = sass_data_context_get_options(sass_context);

    // Register the custom function
    Sass_Function_List sass_function_list = sass_make_function_list(2);

    {
        printf("Register url($url) function\n");
        Sass_Function_Entry sass_function_entry = sass_make_function(
            "url($url)", (Sass_Function_Fn) custom_function, 0
        );
        sass_function_set_list_entry(sass_function_list, 0, sass_function_entry);
    }

    {
        printf("Register func($value) function\n");
        Sass_Function_Entry sass_function_entry = sass_make_function(
            "func($value)", (Sass_Function_Fn) custom_function, 0
        );
        sass_function_set_list_entry(sass_function_list, 1, sass_function_entry);
    }

    sass_option_set_c_functions(sass_options, sass_function_list);

    // Compile
    sass_data_context_set_options(sass_context, sass_options);
    struct Sass_Compiler *sass_compiler = sass_make_data_compiler(sass_context);
    sass_compiler_parse(sass_compiler);
    sass_compiler_execute(sass_compiler);

    const char *css = sass_context_get_output_string((struct Sass_Context *) sass_context);
    const char *error_json = sass_context_get_error_json((struct Sass_Context *) sass_context);

    printf("Result: %s\n", css);
    printf("Error: %s\n", error_json);

    return 0;
}