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|
/// @file WASM export surface for the gonix evaluator.
/// These are the C entry points that the Go host (wazero) calls into.
/// Handles are indices into a GC-rooted handle table.
#include "lix/libexpr/eval.hh"
#include "lix/libexpr/value.hh"
#include "lix/libexpr/wasm-codec.hh"
#include "lix/libstore/globals.hh"
#include "lix/libstore/store-api.hh"
#include "lix/libstore/wasm-store.hh"
#include "lix/libutil/async.hh"
#include "lix/libutil/box_ptr.hh"
#include "lix/libutil/error.hh"
#include "lix/libutil/logging.hh"
#include "lix/libutil/config.hh"
#include <cstdint>
#include <cstring>
#include <string>
#include <vector>
#include <memory>
#ifdef __EMSCRIPTEN__
#include <emscripten.h>
#define WASM_EXPORT EMSCRIPTEN_KEEPALIVE
#else
#define WASM_EXPORT
#endif
namespace {
// ---------------------------------------------------------------------------
// Global evaluator state
// ---------------------------------------------------------------------------
std::unique_ptr<nix::AsyncIoRoot> g_aio;
std::unique_ptr<nix::Evaluator> g_evaluator;
std::optional<nix::box_ptr<nix::EvalState>> g_state;
std::string g_last_error;
// Handle table — keeps Values alive across calls from Go.
// Index 0 is reserved (invalid handle).
std::vector<nix::RootValue> g_handles;
int32_t newHandle(nix::Value v)
{
g_handles.push_back(nix::allocRootValue(v));
return static_cast<int32_t>(g_handles.size() - 1);
}
nix::Value * getHandle(int32_t h)
{
if (h <= 0 || static_cast<size_t>(h) >= g_handles.size()) {
return nullptr;
}
return g_handles[h].get();
}
// Write a string into a caller-provided buffer, null-terminate, return length.
int32_t writeStr(const std::string & s, char * buf, int32_t max_len)
{
int32_t n = std::min(static_cast<int32_t>(s.size()), max_len - 1);
memcpy(buf, s.data(), n);
buf[n] = '\0';
return n;
}
// Record an error for later retrieval by nix_last_error().
#define CATCH_INTO_LAST_ERROR(ret) \
catch (nix::Error & e) \
{ \
g_last_error = e.msg(); \
return ret; \
} \
catch (std::exception & e) \
{ \
g_last_error = e.what(); \
return ret; \
} \
catch (...) \
{ \
g_last_error = "unknown error"; \
return ret; \
}
} // anonymous namespace
extern "C" {
// ---------------------------------------------------------------------------
// nix_init: initialise the evaluator with the store directory.
// Called once by Go before any eval calls.
// ---------------------------------------------------------------------------
WASM_EXPORT
void nix_init(const char * store_dir, int32_t /*len*/)
{
try {
nix::initLibStore();
nix::initLibExpr();
// Build a WasmStore — all store I/O goes through the Go host.
nix::WasmStoreConfig cfg(nix::StringMap{});
auto store = nix::make_ref<nix::WasmStore>("wasm", "wasm://", std::move(cfg));
// Reserve handle 0 as invalid.
g_handles.emplace_back();
// Set up the async I/O root (KJ shim — no real event loop in WASM).
g_aio = std::make_unique<nix::AsyncIoRoot>();
// Create the evaluator.
nix::SearchPath searchPath;
g_evaluator = std::make_unique<nix::Evaluator>(*g_aio, searchPath, nix::ref<nix::Store>(store));
// Create an EvalState via the Evaluator's begin() factory.
g_state.emplace(g_evaluator->begin(*g_aio));
} catch (...) {
g_last_error = "nix_init failed";
}
}
// ---------------------------------------------------------------------------
// nix_eval_expr: parse and evaluate a Nix expression string.
// Returns a handle, or -1 on error.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_eval_expr(const char * expr, int32_t /*len*/)
try {
if (!g_state || !g_evaluator) {
g_last_error = "not initialised";
return -1;
}
nix::Expr & e = g_evaluator->parseExprFromString(std::string(expr), nix::CanonPath::root);
nix::Value v = (*g_state)->eval(e);
return newHandle(v);
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_force_value: force a value to WHNF.
// Returns the same handle, or -1 on error.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_force_value(int32_t handle)
try {
if (!g_state) {
g_last_error = "not initialised";
return -1;
}
nix::Value * v = getHandle(handle);
if (!v) {
g_last_error = "invalid handle";
return -1;
}
(*g_state)->forceValue(*v, nix::noPos);
return handle;
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_value_type: return the ValueType of a forced value as an int.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_value_type(int32_t handle)
{
nix::Value * v = getHandle(handle);
if (!v) {
return -1;
}
return static_cast<int32_t>(v->type());
}
// ---------------------------------------------------------------------------
// nix_value_ptr: return the WASM linear-memory address of the identity of a
// value for cycle/repeat detection — mirroring cppnix print.cc's ValuesSeen.
//
// For attrs values, returns the Bindings* pointer: two Value objects wrapping
// the same underlying attribute set share a Bindings* and will return the
// same address. This is the key to detecting the derivation `all` cycle,
// where `all[0]` is a different Value* than the top-level output attrset but
// both share the same Bindings*.
//
// For list values, returns the list-items pointer.
//
// For all other types (or invalid handles), returns 0 (no cycle tracking).
// ---------------------------------------------------------------------------
WASM_EXPORT
uint32_t nix_value_ptr(int32_t handle)
{
nix::Value * v = getHandle(handle);
if (!v) {
return 0;
}
switch (v->type()) {
case nix::nAttrs:
if (!v->attrs()) {
return 0;
}
return static_cast<uint32_t>(reinterpret_cast<uintptr_t>(v->attrs()));
case nix::nList:
// Use the raw list-element array pointer (unique per list allocation).
return static_cast<uint32_t>(reinterpret_cast<uintptr_t>(v->listElems()));
case nix::nThunk:
case nix::nInt:
case nix::nFloat:
case nix::nBool:
case nix::nString:
case nix::nPath:
case nix::nNull:
case nix::nFunction:
case nix::nExternal:
return 0;
}
}
// ---------------------------------------------------------------------------
// nix_get_string / nix_get_int / nix_get_float / nix_get_bool
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_get_string(int32_t handle, char * buf, int32_t max_len)
try {
nix::Value * v = getHandle(handle);
if (!v) {
g_last_error = "invalid handle";
return -1;
}
return writeStr(std::string(v->str()), buf, max_len);
}
CATCH_INTO_LAST_ERROR(-1)
WASM_EXPORT
int64_t nix_get_int(int32_t handle)
{
nix::Value * v = getHandle(handle);
if (!v) {
return 0;
}
return v->integer().value;
}
WASM_EXPORT
double nix_get_float(int32_t handle)
{
nix::Value * v = getHandle(handle);
if (!v) {
return 0.0;
}
return v->fpoint();
}
WASM_EXPORT
int32_t nix_get_bool(int32_t handle)
{
nix::Value * v = getHandle(handle);
if (!v) {
return 0;
}
return v->boolean() ? 1 : 0;
}
// ---------------------------------------------------------------------------
// nix_get_attr: look up an attribute by name, return a new handle.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_get_attr(int32_t handle, const char * name, int32_t /*name_len*/)
try {
if (!g_state) {
g_last_error = "not initialised";
return -1;
}
nix::Value * v = getHandle(handle);
if (!v) {
g_last_error = "invalid handle";
return -1;
}
(*g_state)->forceAttrs(*v, nix::noPos, "while getting attribute");
auto sym = (*g_state)->ctx.symbols.create(name);
auto * attr = v->attrs()->get(sym);
if (!attr) {
g_last_error = std::string("missing attribute: ") + name;
return -1;
}
return newHandle(attr->value);
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_get_attr_names: write newline-separated attribute names into buf.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_get_attr_names(int32_t handle, char * buf, int32_t max_len)
try {
if (!g_state) {
g_last_error = "not initialised";
return -1;
}
nix::Value * v = getHandle(handle);
if (!v) {
g_last_error = "invalid handle";
return -1;
}
(*g_state)->forceAttrs(*v, nix::noPos, "while listing attributes");
std::string result;
for (auto & attr : *v->attrs()) {
result += (*g_state)->ctx.symbols[attr.name];
result += '\n';
}
return writeStr(result, buf, max_len);
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_list_length / nix_list_get
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_list_length(int32_t handle)
try {
if (!g_state) {
g_last_error = "not initialised";
return -1;
}
nix::Value * v = getHandle(handle);
if (!v) {
g_last_error = "invalid handle";
return -1;
}
(*g_state)->forceList(*v, nix::noPos, "while getting list length");
return static_cast<int32_t>(v->listSize());
}
CATCH_INTO_LAST_ERROR(-1)
WASM_EXPORT
int32_t nix_list_get(int32_t handle, int32_t idx)
try {
if (!g_state) {
g_last_error = "not initialised";
return -1;
}
nix::Value * v = getHandle(handle);
if (!v) {
g_last_error = "invalid handle";
return -1;
}
(*g_state)->forceList(*v, nix::noPos, "while indexing list");
if (idx < 0 || static_cast<size_t>(idx) >= v->listSize()) {
g_last_error = "list index out of range";
return -1;
}
return newHandle(v->listElems()[idx]);
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_builtin_names: return the ordered list of builtin names (in the same
// order as the C++ base environment) as a codec-encoded list of scalars.
// This lets the Go evaluator construct a builtins env with matching displacements.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_builtin_names(char * resp, int32_t resp_max)
try {
if (!g_evaluator) {
g_last_error = "not initialised";
return -1;
}
// Walk the static env to collect names sorted by displacement value.
const auto & se = *g_evaluator->builtins.staticEnv;
std::vector<std::pair<uint32_t, std::string>> byDispl;
for (auto it = se.vars.cbegin(); it != se.vars.cend(); ++it) {
byDispl.push_back({static_cast<uint32_t>(it->second), std::string(g_evaluator->symbols[it->first])});
}
std::sort(byDispl.begin(), byDispl.end());
// Encode as a codec list of scalars: "[" *( len ":" name ";" ) "]"
std::string items;
for (const auto & [displ, name] : byDispl) {
std::string item = nix::wasm_codec::encScalar(name);
items += std::to_string(item.size()) + ":" + item + ";";
}
std::string inner = "[" + items + "]";
std::string msg = nix::wasm_codec::message(inner);
if (static_cast<int32_t>(msg.size()) > resp_max) {
g_last_error = "builtin names too large for buffer";
return -1;
}
memcpy(resp, msg.data(), msg.size());
return static_cast<int32_t>(msg.size());
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_parse_expr: parse a Nix expression and return the post-finalize AST
// in codec wire format. Returns bytes written, or negative on error.
//
// base_path is an absolute directory path (e.g. "/testfs/sub/") used to
// resolve relative path literals like ./foo.nix. Pass "/" for the legacy
// behaviour where ./foo → /foo in the AST.
//
// file_path is the absolute path of the file being parsed (e.g. "/testfs/sub/foo.nix").
// It is used only for position information (file field in {file, line, column} attrs).
// Pass an empty string or "/" if unknown.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_parse_expr(
const char * expr,
int32_t expr_len,
const char * base_path,
int32_t base_path_len,
const char * file_path,
int32_t file_path_len,
char * resp,
int32_t resp_max
)
try {
if (!g_state || !g_evaluator) {
g_last_error = "not initialised";
return -1;
}
std::string src(expr, static_cast<size_t>(expr_len));
std::string base(base_path, static_cast<size_t>(base_path_len));
std::string filePath(file_path, static_cast<size_t>(file_path_len));
nix::CanonPath basePath(base);
nix::Expr & e = g_evaluator->parseExprFromString(src, nix::SourcePath(basePath));
std::string encoded =
nix::wasm_codec::encodeExpr(e, g_evaluator->symbols, g_evaluator->positions, filePath);
std::string msg = nix::wasm_codec::message(encoded);
if (static_cast<int32_t>(msg.size()) > resp_max) {
g_last_error = "parse result too large for buffer";
return -1;
}
memcpy(resp, msg.data(), msg.size());
return static_cast<int32_t>(msg.size());
}
CATCH_INTO_LAST_ERROR(-1)
// ---------------------------------------------------------------------------
// nix_free_value: release a handle.
// ---------------------------------------------------------------------------
WASM_EXPORT
void nix_free_value(int32_t handle)
{
if (handle > 0 && static_cast<size_t>(handle) < g_handles.size()) {
g_handles[handle].reset();
}
}
// ---------------------------------------------------------------------------
// nix_last_error: retrieve the last error message.
// ---------------------------------------------------------------------------
WASM_EXPORT
int32_t nix_last_error(char * buf, int32_t max_len)
{
return writeStr(g_last_error, buf, max_len);
}
} // extern "C"
|