build(wasm): add wasm_stubs for Emscripten build

build.zig

@@ -613,16 +613,15 @@ pub fn build(b: *std.Build) !void {
             "-sALLOW_MEMORY_GROWTH=1",
             "--profiling-funcs",
             "-sEXPORTED_FUNCTIONS=_main,_malloc,_free",
-            "-sEXPORTED_RUNTIME_METHODS=stringToUTF8,lengthBytesUTF8,setValue,getValue,UTF8ToString,callMain,ENV,FS",
-            "-sSTACK_SIZE=134217728", // 64MB — emscripten's own flag, overrides its 65536
-            "-sINITIAL_MEMORY=536870912", // 256MB — stack(64MB) + data(12MB) + heap room
+            "-sEXPORTED_RUNTIME_METHODS=stringToUTF8,lengthBytesUTF8,setValue,getValue,UTF8ToString,callMain,ENV,FS,HEAPU8",
+            "-sSTACK_SIZE=8388608",
+            "-sINITIAL_MEMORY=268435456",
             "-sMAXIMUM_MEMORY=2147483648",
             "-sFORCE_FILESYSTEM=1",
             "-sNODERAWFS=0",
-            "-sERROR_ON_UNDEFINED_SYMBOLS=0",
+            "-sERROR_ON_UNDEFINED_SYMBOLS=1",
             "-sEXIT_RUNTIME=0",
             "-sINVOKE_RUN=0",
-            "-sGLOBAL_BASE=134217728",
             "-sMODULARIZE=1",
             "-sEXPORT_NAME=createNvim",
             "-Wl,--unresolved-symbols=ignore-all",
@@ -631,6 +630,8 @@ pub fn build(b: *std.Build) !void {
             "-flto",
             "-sSTACK_OVERFLOW_CHECK=2",
             "-sASSERTIONS=1",
+            "-sASYNCIFY=1",
+            "-sASYNCIFY_STACK_SIZE=65536",
         });
 
         emcc.addArg("-o");

src/wasm_stubs.c

@@ -0,0 +1,126 @@
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <time.h>
+#include <sys/time.h>
+#include <uv.h>
+#include <pthread.h>
+#include <emscripten.h> 
+
+uint64_t uv_get_free_memory(void)       { return 8 * 1024 * 1024; } 
+uint64_t uv_get_total_memory(void)      { return 256 * 1024 * 1024; } 
+uint64_t uv_get_available_memory(void)  { return uv_get_free_memory(); }
+uint64_t uv_get_constrained_memory(void)  { return uv_get_total_memory(); }
+
+// Report an idle virtual system
+void uv_loadavg(double avg[3])
+{
+    avg[0] = 0.0; avg[1] = 0.0; avg[2] = 0.0;
+}
+
+int uv_uptime(double* uptime)
+{
+    if (!uptime) return UV_EINVAL;
+    *uptime = emscripten_get_now() / 1000.0; 
+    return 0;
+}
+
+int uv_resident_set_memory(size_t* rss)
+{
+    if (!rss) return UV_EINVAL;
+    *rss = uv_get_total_memory() / 2; 
+    return 0;
+}
+
+int uv_exepath(char* buffer, size_t* size)
+{
+    if (!buffer || !size) return UV_EINVAL;
+    const char* exepath = "/nvim.wasm";
+    size_t len = strlen(exepath);
+    if (*size <= len) {
+        *size = len + 1;
+        return UV_ENOBUFS;
+    }
+    memcpy(buffer, exepath, len);
+    buffer[len] = '\0';
+    *size = len;
+    return 0;
+}
+
+int uv__io_fork(uv_loop_t* loop) {
+    (void)loop;
+    return 0;
+}
+
+int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count)
+{
+    if (!cpu_infos || !count) return UV_EINVAL;
+    *cpu_infos = (uv_cpu_info_t*) malloc(sizeof(uv_cpu_info_t));
+    if (!*cpu_infos) return UV_ENOMEM;
+
+    uv_cpu_info_t* cpu = *cpu_infos;
+    cpu->model = "WebAssembly Virtual CPU"; 
+    cpu->speed = 0;
+    cpu->cpu_times.user = 0; cpu->cpu_times.nice = 0; cpu->cpu_times.sys = 0;   
+    cpu->cpu_times.idle = 0; cpu->cpu_times.irq = 0;      
+    *count = 1;
+    return 0;
+}
+
+int uv_interface_addresses(uv_interface_address_t** addresses, int* count)
+{
+    if (!addresses || !count) return UV_EINVAL;
+    *addresses = (uv_interface_address_t*) malloc(sizeof(uv_interface_address_t));
+    if (!*addresses) return UV_ENOMEM;
+
+    uv_interface_address_t* addr = *addresses;
+    memset(addr, 0, sizeof(uv_interface_address_t));
+    addr->name = strdup("lo");
+    if (!addr->name) { free(addr); return UV_ENOMEM; }
+    addr->is_internal = 1;
+    uv_ip4_addr("127.0.0.1", 0, (struct sockaddr_in*)&addr->address);
+    uv_ip4_addr("255.0.0.0", 0, (struct sockaddr_in*)&addr->netmask);  
+    *count = 1;
+    return 0;
+}
+
+void uv__platform_invalidate_fd(uv_loop_t* loop, int fd) { (void)loop; (void)fd; }
+int uv__io_check_fd(uv_loop_t* loop, void* w)           { (void)loop; (void)w; return 0; }
+
+// Replaces the kernel poll() call
+void uv__io_poll(uv_loop_t* loop, int timeout) {
+    if (timeout > 0) {
+        emscripten_sleep(timeout); 
+        uv_update_time(loop);    
+        emscripten_sleep(10);     
+        uv_update_time(loop);      
+    } else if (timeout == 0) {
+        emscripten_sleep(0);
+    }
+}
+
+int uv__platform_loop_init(uv_loop_t* loop)
+{
+    if (!loop) return UV_EINVAL;
+    loop->backend_fd = -1; 
+    return 0;
+}
+
+void uv__platform_loop_delete(uv_loop_t* loop) { (void)loop; }
+
+// Fakes thread names when nvim tracks or debugs its internal processes
+int pthread_getname_np(pthread_t thread, char* name, size_t len)
+{
+    (void)thread;
+    if (!name || len < 1) return EINVAL;
+    strncpy(name, "nvim-main", len - 1);
+    name[len - 1] = '\0';
+    return 0;
+}
+
+int pthread_setname_np(pthread_t thread, const char* name) { (void)thread; (void)name; return 0; }
+int pthread_setschedparam(pthread_t thread, int policy, const struct sched_param* param) { (void)thread; (void)policy; (void)param; return 0; }
+int sched_get_priority_max(int policy) { (void)policy; return 1; }
+int sched_get_priority_min(int policy) { (void)policy; return 1; }