Add slang-wasm target (#5237)

Support for exceptions is enabled, since Slang uses them for diagnostics.
The size optimization arguments ('-Os') resolves some internal emscripten error during the
slang-wasm.wasm linking step, which happens when enabling exceptions.
("parse exception: too many locals")

7 files changed, 372 insertions, 5 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b505cbf53..da22ec19a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -372,6 +372,22 @@ if(SLANG_ENABLE_SLANGC)
 endif()
 
 #
+# WebAssembly bindings for Slang
+#
+# This is an executable target because emcmake produces .a files without bindings if you just create a static library
+# https://stackoverflow.com/questions/63622009/static-library-built-with-cmake-as-a-with-emscripten-instead-of-wasm-js
+slang_add_target(
+  source/slang-wasm
+  EXECUTABLE
+  EXCLUDE_FROM_ALL
+  USE_FEWER_WARNINGS
+  LINK_WITH_PRIVATE miniz lz4_static slang core compiler-core
+  INCLUDE_DIRECTORIES_PUBLIC include source/slang-wasm
+)
+# To generate binding code
+target_link_options(slang-wasm PUBLIC "--bind")
+
+#
 # Our wrappers for glslang and llvm
 #
 if(SLANG_ENABLE_SLANG_GLSLANG)
diff --git a/CMakePresets.json b/CMakePresets.json
index 7b847e03e..47a733ee2 100644
--- a/CMakePresets.json
+++ b/CMakePresets.json
@@ -22,7 +22,9 @@
       "binaryDir": "${sourceDir}/build.em",
       "cacheVariables": {
         "SLANG_SLANG_LLVM_FLAVOR": "DISABLE",
-        "CMAKE_EXE_LINKER_FLAGS": "-sASSERTIONS -sALLOW_MEMORY_GROWTH"
+        "CMAKE_C_FLAGS_INIT": "-fwasm-exceptions -Os",
+        "CMAKE_CXX_FLAGS_INIT": "-fwasm-exceptions -Os",
+        "CMAKE_EXE_LINKER_FLAGS": "-sASSERTIONS -sALLOW_MEMORY_GROWTH -fwasm-exceptions --export=__cpp_exception"
       }
     },
     {
@@ -89,7 +91,7 @@
       "configurePreset": "emscripten",
       "configuration": "Release",
       "targets": [
-        "slang"
+        "slang-wasm"
       ]
     },
     {
diff --git a/docs/building.md b/docs/building.md
index da55f57aa..fa18ef60f 100644
--- a/docs/building.md
+++ b/docs/building.md
@@ -75,8 +75,8 @@ source ./emsdk_env # For Windows, emsdk_env.bat
 popd
 emcmake cmake -DSLANG_GENERATORS_PATH=generators/bin --preset emscripten -G "Ninja"
 
-# Build build.em/Release/bin/libslang.a
-cmake --build --preset emscripten --target slang
+# Build slang-wasm.js and slang-wasm.wasm in build.em/Release/bin
+cmake --build --preset emscripten --target slang-wasm
 ```
 
 **Note:** If the last build step fails, try running the command that `emcmake` outputs, directly.
diff --git a/source/compiler-core/slang-diagnostic-sink.cpp b/source/compiler-core/slang-diagnostic-sink.cpp
index 7e3c286eb..a4cbce22f 100644
--- a/source/compiler-core/slang-diagnostic-sink.cpp
+++ b/source/compiler-core/slang-diagnostic-sink.cpp
@@ -574,7 +574,8 @@ bool DiagnosticSink::diagnoseImpl(DiagnosticInfo const& info, const UnownedStrin
     if (info.severity >= Severity::Fatal)
     {
         // TODO: figure out a better policy for aborting compilation
-        SLANG_ABORT_COMPILATION("");
+        std::string message(formattedMessage.begin(), formattedMessage.end());
+        SLANG_ABORT_COMPILATION(message.c_str());
     }
     return true;
 }
diff --git a/source/slang-wasm/slang-wasm-bindings.cpp b/source/slang-wasm/slang-wasm-bindings.cpp
new file mode 100644
index 000000000..4880596a9
--- /dev/null
+++ b/source/slang-wasm/slang-wasm-bindings.cpp
@@ -0,0 +1,59 @@
+#include <emscripten/bind.h>
+#include <slang-com-ptr.h>
+#include "slang-wasm.h"
+
+using namespace emscripten;
+
+EMSCRIPTEN_BINDINGS(slang)
+{
+    constant("SLANG_OK", SLANG_OK);
+
+    function(
+        "createGlobalSession",
+        &slang::wgsl::createGlobalSession,
+        return_value_policy::take_ownership());
+
+    function(
+        "getLastError",
+        &slang::wgsl::getLastError);
+
+    class_<slang::wgsl::GlobalSession>("GlobalSession")
+        .function(
+            "createSession",
+            &slang::wgsl::GlobalSession::createSession,
+            return_value_policy::take_ownership());
+
+    class_<slang::wgsl::Session>("Session")
+        .function(
+            "loadModuleFromSource",
+            &slang::wgsl::Session::loadModuleFromSource,
+            return_value_policy::take_ownership())
+        .function(
+            "createCompositeComponentType",
+            &slang::wgsl::Session::createCompositeComponentType,
+            return_value_policy::take_ownership());
+
+    class_<slang::wgsl::ComponentType>("ComponentType")
+        .function(
+            "link",
+            &slang::wgsl::ComponentType::link,
+            return_value_policy::take_ownership())
+        .function(
+            "getEntryPointCode",
+            &slang::wgsl::ComponentType::getEntryPointCode);
+
+    class_<slang::wgsl::Module, base<slang::wgsl::ComponentType>>("Module")
+        .function(
+            "findEntryPointByName",
+            &slang::wgsl::Module::findEntryPointByName,
+            return_value_policy::take_ownership());
+
+    value_object<slang::wgsl::Error>("Error")
+        .field("type", &slang::wgsl::Error::type)
+        .field("result", &slang::wgsl::Error::result)
+        .field("message", &slang::wgsl::Error::message);
+
+    class_<slang::wgsl::EntryPoint, base<slang::wgsl::ComponentType>>("EntryPoint");
+
+    register_vector<slang::wgsl::ComponentType*>("ComponentTypeList");
+}
diff --git a/source/slang-wasm/slang-wasm.cpp b/source/slang-wasm/slang-wasm.cpp
new file mode 100644
index 000000000..c2cbe66b6
--- /dev/null
+++ b/source/slang-wasm/slang-wasm.cpp
@@ -0,0 +1,182 @@
+#include <vector>
+#include <string>
+#include <slang.h>
+#include <slang-com-ptr.h>
+#include "slang-wasm.h"
+#include "../core/slang-blob.h"
+#include "../core/slang-exception.h"
+
+using namespace slang;
+
+namespace slang
+{
+namespace wgsl
+{
+
+Error g_error;
+
+Error getLastError()
+{
+    Error currentError = g_error;
+    g_error = {};
+    return currentError;
+}
+
+GlobalSession* createGlobalSession()
+{
+    IGlobalSession* globalSession = nullptr;
+    {
+        SlangResult result = slang::createGlobalSession(&globalSession);
+        if (result != SLANG_OK)
+        {
+            g_error.type = std::string("USER");
+            g_error.result = result;
+            return nullptr;
+        }
+    }
+
+    return new GlobalSession(globalSession);
+}
+
+Session* GlobalSession::createSession()
+{
+    ISession* session = nullptr;
+    {
+        SessionDesc sessionDesc = {};
+        sessionDesc.structureSize = sizeof(sessionDesc);
+        constexpr SlangInt targetCount = 1;
+        TargetDesc targets[targetCount] = {
+            {.structureSize = sizeof(TargetDesc), .format = SLANG_WGSL}
+        };
+        sessionDesc.targets = targets;
+        sessionDesc.targetCount = targetCount;
+        SlangResult result = m_interface->createSession(sessionDesc, &session);
+        if (result != SLANG_OK)
+        {
+            g_error.type = std::string("USER");
+            g_error.result = result;
+            return nullptr;
+        }
+    }
+
+    return new Session(session);
+}
+
+Module* Session::loadModuleFromSource(const std::string& slangCode)
+{
+    Slang::ComPtr<IModule> module;
+    {
+        const char * name = "";
+        const char * path = "";
+        Slang::ComPtr<slang::IBlob> diagnosticsBlob;
+        Slang::ComPtr<ISlangBlob> slangCodeBlob = Slang::RawBlob::create(
+            slangCode.c_str(), slangCode.size());
+        module = m_interface->loadModuleFromSource(
+            name, path, slangCodeBlob, diagnosticsBlob.writeRef());
+        if (!module)
+        {
+            g_error.type = std::string("USER");
+            g_error.message = std::string(
+                (char*)diagnosticsBlob->getBufferPointer(),
+                (char*)diagnosticsBlob->getBufferPointer() +
+                diagnosticsBlob->getBufferSize());
+            return nullptr;
+        }
+    }
+
+    return new Module(module);
+}
+
+EntryPoint* Module::findEntryPointByName(const std::string& name)
+{
+    Slang::ComPtr<IEntryPoint> entryPoint;
+    {
+        SlangResult result = moduleInterface()->findEntryPointByName(
+            name.c_str(), entryPoint.writeRef());
+        if (result != SLANG_OK)
+        {
+            g_error.type = std::string("USER");
+            g_error.result = result;
+            return nullptr;
+        }
+    }
+
+    return new EntryPoint(entryPoint);
+}
+
+ComponentType* Session::createCompositeComponentType(
+    const std::vector<ComponentType*>& components)
+{
+    Slang::ComPtr<IComponentType> composite;
+    {
+        std::vector<IComponentType*> nativeComponents(components.size());
+        for (size_t i = 0U; i < components.size(); i++)
+            nativeComponents[i] = components[i]->interface();
+        SlangResult result = m_interface->createCompositeComponentType(
+            nativeComponents.data(),
+            (SlangInt)nativeComponents.size(),
+            composite.writeRef());
+        if (result != SLANG_OK)
+        {
+            g_error.type = std::string("USER");
+            g_error.result = result;
+            return nullptr;
+        }
+    }
+
+    return new ComponentType(composite);
+}
+
+ComponentType* ComponentType::link()
+{
+    Slang::ComPtr<IComponentType> linkedProgram;
+    {
+        Slang::ComPtr<ISlangBlob> diagnosticBlob;
+        SlangResult result = interface()->link(
+            linkedProgram.writeRef(), diagnosticBlob.writeRef());
+        if (result != SLANG_OK)
+        {
+            g_error.type = std::string("USER");
+            g_error.result = result;
+            g_error.message = std::string(
+                (char*)diagnosticBlob->getBufferPointer(),
+                (char*)diagnosticBlob->getBufferPointer() +
+                diagnosticBlob->getBufferSize());
+            return nullptr;
+        }
+    }
+
+    return new ComponentType(linkedProgram);
+}
+
+std::string ComponentType::getEntryPointCode(int entryPointIndex, int targetIndex)
+{
+    {
+        Slang::ComPtr<IBlob> kernelBlob;
+        Slang::ComPtr<ISlangBlob> diagnosticBlob;
+        SlangResult result = interface()->getEntryPointCode(
+            entryPointIndex,
+            targetIndex,
+            kernelBlob.writeRef(),
+            diagnosticBlob.writeRef());
+        if (result != SLANG_OK)
+        {
+            g_error.type = std::string("USER");
+            g_error.result = result;
+            g_error.message = std::string(
+                (char*)diagnosticBlob->getBufferPointer(),
+                (char*)diagnosticBlob->getBufferPointer() +
+                diagnosticBlob->getBufferSize());
+            return "";
+        }
+        std::string wgslCode = std::string(
+            (char*)kernelBlob->getBufferPointer(),
+            (char*)kernelBlob->getBufferPointer() + kernelBlob->getBufferSize());
+        return wgslCode;
+    }
+
+    return {};
+}
+
+} // namespace wgsl
+} // namespace slang
diff --git a/source/slang-wasm/slang-wasm.h b/source/slang-wasm/slang-wasm.h
new file mode 100644
index 000000000..24ce62392
--- /dev/null
+++ b/source/slang-wasm/slang-wasm.h
@@ -0,0 +1,107 @@
+#pragma once
+
+#include <slang.h>
+
+namespace slang
+{
+namespace wgsl
+{
+
+class Error
+{
+public:
+    // Can be
+    // "USER": User did not call the API correctly
+    // "INTERNAL": Slang failed due to a bug
+    std::string type;
+    std::string message;
+    SlangResult result;
+};
+
+Error getLastError();
+
+class ComponentType
+{
+public:
+
+    ComponentType(slang::IComponentType* interface) :
+        m_interface(interface) {}
+
+    ComponentType* link();
+
+    std::string getEntryPointCode(int entryPointIndex, int targetIndex);
+
+    slang::IComponentType* interface() const {return m_interface;}
+
+    virtual ~ComponentType() = default;
+
+private:
+
+    Slang::ComPtr<slang::IComponentType> m_interface;
+};
+
+class EntryPoint : public ComponentType
+{
+public:
+
+    EntryPoint(slang::IEntryPoint* interface) : ComponentType(interface) {}
+
+private:
+
+    slang::IEntryPoint* entryPointInterface() const {
+        return static_cast<slang::IEntryPoint*>(interface());
+    }
+};
+
+class Module : public ComponentType
+{
+public:
+
+    Module(slang::IModule* interface) : ComponentType(interface) {}
+
+    EntryPoint* findEntryPointByName(const std::string& name);
+
+    slang::IModule* moduleInterface() const {
+        return static_cast<slang::IModule*>(interface());
+    }
+};
+
+class Session
+{
+public:
+
+    Session(slang::ISession* interface)
+        : m_interface(interface) {}
+
+    Module* loadModuleFromSource(const std::string& slangCode);
+
+    ComponentType* createCompositeComponentType(
+        const std::vector<ComponentType*>& components);
+
+    slang::ISession* interface() const {return m_interface;}
+
+private:
+
+    Slang::ComPtr<slang::ISession> m_interface;
+};
+
+class GlobalSession
+{
+public:
+
+    GlobalSession(slang::IGlobalSession* interface)
+        : m_interface(interface) {}
+
+    Session* createSession();
+
+    slang::IGlobalSession* interface() const {return m_interface;}
+
+private:
+
+    Slang::ComPtr<slang::IGlobalSession> m_interface;
+};
+
+GlobalSession* createGlobalSession();
+
+} // namespace wgsl
+} // namespace slang