Feature: Web REPL using Emscripten (#138)

Currently doesn't include the new page into navigation since we aren't building the .js files anywhere.

.gitignore

@@ -5,3 +5,4 @@
 ^default.prof*
 ^fuzz-*
 ^luau$
+/.vs

CLI/Repl.cpp

@@ -198,6 +198,11 @@ static std::string runCode(lua_State* L, const std::string& source)
         error += "\nstack backtrace:\n";
         error += lua_debugtrace(T);
 
+#ifdef __EMSCRIPTEN__
+        // nicer formatting for errors in web repl
+        error = "Error:" + error;
+#endif
+
         fprintf(stdout, "%s", error.c_str());
     }
 
@@ -205,6 +210,44 @@ static std::string runCode(lua_State* L, const std::string& source)
     return std::string();
 }
 
+#ifdef __EMSCRIPTEN__
+extern "C"
+{
+    const char* executeScript(const char* source)
+    {
+        // static string for caching result (prevents dangling ptr on function exit)
+        static std::string result;
+
+        // setup flags
+        for (Luau::FValue<bool>* flag = Luau::FValue<bool>::list; flag; flag = flag->next)
+            if (strncmp(flag->name, "Luau", 4) == 0)
+                flag->value = true;
+
+        // create new state
+        std::unique_ptr<lua_State, void (*)(lua_State*)> globalState(luaL_newstate(), lua_close);
+        lua_State* L = globalState.get();
+
+        // setup state
+        setupState(L);
+
+        // sandbox thread
+        luaL_sandboxthread(L);
+
+        // run code + collect error
+        std::string error = runCode(L, source);
+        result  = error;
+        
+        if (error.length())
+        {
+            return result.c_str();
+        }
+        return NULL;
+    }
+}
+#endif
+
+// Excluded from emscripten compilation to avoid -Wunused-function errors.
+#ifndef __EMSCRIPTEN__
 static void completeIndexer(lua_State* L, const char* editBuffer, size_t start, std::vector<std::string>& completions)
 {
     std::string_view lookup = editBuffer + start;
@@ -547,3 +590,4 @@ int main(int argc, char** argv)
         return failed;
     }
 }
+#endif

CMakeLists.txt

@@ -17,17 +17,26 @@ add_library(Luau.VM STATIC)
 
 if(LUAU_BUILD_CLI)
     add_executable(Luau.Repl.CLI)
+    if(NOT EMSCRIPTEN)
         add_executable(Luau.Analyze.CLI)
+    else()
+        # add -fexceptions for emscripten to allow exceptions to be caught in C++
+        set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
+    endif()
 
     # This also adds target `name` on Linux/macOS and `name.exe` on Windows
     set_target_properties(Luau.Repl.CLI PROPERTIES OUTPUT_NAME luau)
+
+    if(NOT EMSCRIPTEN)
         set_target_properties(Luau.Analyze.CLI PROPERTIES OUTPUT_NAME luau-analyze)
+    endif()
 endif()
 
-if(LUAU_BUILD_TESTS)
+if(LUAU_BUILD_TESTS AND NOT EMSCRIPTEN)
     add_executable(Luau.UnitTest)
     add_executable(Luau.Conformance)
 endif()
+
 include(Sources.cmake)
 
 target_compile_features(Luau.Ast PUBLIC cxx_std_17)
@@ -53,10 +62,6 @@ if(MSVC)
 else()
     list(APPEND LUAU_OPTIONS -Wall) # All warnings
     list(APPEND LUAU_OPTIONS -Werror) # Warnings are errors
-
-    if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
-        list(APPEND LUAU_OPTIONS -Wno-unused) # GCC considers variables declared/checked in if() as unused
-    endif()
 endif()
 
 target_compile_options(Luau.Ast PRIVATE ${LUAU_OPTIONS})
@@ -65,7 +70,10 @@ target_compile_options(Luau.VM PRIVATE ${LUAU_OPTIONS})
 
 if(LUAU_BUILD_CLI)
     target_compile_options(Luau.Repl.CLI PRIVATE ${LUAU_OPTIONS})
+
+    if(NOT EMSCRIPTEN)
         target_compile_options(Luau.Analyze.CLI PRIVATE ${LUAU_OPTIONS})
+    endif()
 
     target_include_directories(Luau.Repl.CLI PRIVATE extern)
     target_link_libraries(Luau.Repl.CLI PRIVATE Luau.Compiler Luau.VM)
@@ -74,10 +82,20 @@ if(LUAU_BUILD_CLI)
         target_link_libraries(Luau.Repl.CLI PRIVATE pthread)
     endif()
 
+    if(NOT EMSCRIPTEN)
         target_link_libraries(Luau.Analyze.CLI PRIVATE Luau.Analysis)
+    endif()
+
+    if(EMSCRIPTEN)
+        # declare exported functions to emscripten
+        target_link_options(Luau.Repl.CLI PRIVATE -sEXPORTED_FUNCTIONS=['_executeScript'] -sEXPORTED_RUNTIME_METHODS=['ccall','cwrap'] -fexceptions)
+
+        # custom output directory for wasm + js file
+        set_target_properties(Luau.Repl.CLI PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_SOURCE_DIR}/docs/assets/luau)
+    endif()
 endif()
 
-if(LUAU_BUILD_TESTS)
+if(LUAU_BUILD_TESTS AND NOT EMSCRIPTEN)
     target_compile_options(Luau.UnitTest PRIVATE ${LUAU_OPTIONS})
     target_include_directories(Luau.UnitTest PRIVATE extern)
     target_link_libraries(Luau.UnitTest PRIVATE Luau.Analysis Luau.Compiler)

docs/_data/navigation.yml

@@ -27,3 +27,7 @@ pages:
     url: /profile
   - title: Library
     url: /library
+
+# Remove demo pages until solution is found
+#  - title: Demo
+#    url: /demo

docs/_includes/repl.html

@@ -0,0 +1,50 @@
+<form>
+    <div>
+        <label>Script:</label>
+        <br>
+        <textarea rows="10" cols="70" id="script">print("Hello World!")</textarea>
+        <br><br>
+        <button onclick="clearInput(); return false;">
+            Clear Input
+        </button>
+        <button onclick="executeScript(); return false;">
+            Run
+        </button>
+    </div>
+    <br><br>
+    <div>
+        <label>Output:</label>
+        <br>
+        <textarea readonly rows="10" cols="70" id="output"></textarea>
+        <br><br>
+        <button onclick="clearOutput(); return false;">
+            Clear Output
+        </button>
+    </div>
+</form>
+
+<script>
+    function output(text) {
+        document.getElementById("output").value += "[" + new Date().toLocaleTimeString() + "] " + text.replace('stdin:', '') + "\n";
+    }
+
+    var Module = {
+        'print': function (msg) { output(msg) }
+    };
+
+    function clearInput() {
+        document.getElementById("script").value = "";
+    }
+
+    function clearOutput() {
+        document.getElementById("output").value = "";
+    }
+
+    function executeScript() {
+        var err = Module.ccall('executeScript', 'string', ['string'], [document.getElementById("script").value]);
+        if (err) {
+            output('Error:' + err.replace('stdin:', ''));
+        }
+    }
+</script>
+<script async src="assets/luau/luau.js"></script>

docs/_pages/demo.md

@@ -0,0 +1,6 @@
+---
+permalink: /demo
+title: Demo
+---
+
+{% include repl.html %}