pythongh-126898 Switch to exporting an es6 module and using a node_entry script

Author: hoodmane

Tools/wasm/emscripten/__main__.py

@@ -16,8 +16,8 @@
 import sysconfig
 import tempfile
 
-WASM_DIR = Path(__file__).parent.parent
-CHECKOUT = WASM_DIR.parent.parent
+EMSCRIPTEN_DIR = Path(__file__).parent
+CHECKOUT = EMSCRIPTEN_DIR.parent.parent.parent
 
 CROSS_BUILD_DIR = CHECKOUT / "cross-build"
 BUILD_DIR = CROSS_BUILD_DIR / "build"
@@ -207,7 +207,9 @@ def configure_emscripten_python(context, working_dir):
         quiet=context.quiet,
     )
 
-    python_js = working_dir / "python.js"
+    shutil.copy(EMSCRIPTEN_DIR / "node_entry.mjs", working_dir / "node_entry.mjs")
+
+    python_js = working_dir / "node_entry.mjs"
     exec_script = working_dir / "python.sh"
     exec_script.write_text(f'#!/bin/sh\nexec {host_runner} {python_js} "$@"\n')
     exec_script.chmod(0o755)

Tools/wasm/emscripten/node_entry.mjs

@@ -0,0 +1,23 @@
+import EmscriptenModule from "./python.mjs";
+import { dirname } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+if (typeof process !== "undefined") {
+  const nodeVersion = Number(process.versions.node.split(".", 1)[0]);
+  if (nodeVersion < 18) {
+      process.stderr.write(
+          `Node version must be >= 18, got version ${process.version}\n`,
+      );
+      process.exit(1);
+  }
+}
+
+const settings = {
+  preRun(Module) {
+    const __dirname = dirname(fileURLToPath(import.meta.url));
+    Module.FS.mkdirTree("/lib/");
+    Module.FS.mount(Module.FS.filesystems.NODEFS, { root: __dirname + "/lib/" }, "/lib/");
+  }
+};
+
+await EmscriptenModule(settings);

Tools/wasm/emscripten/node_pre.js

@@ -1327,7 +1327,7 @@ AC_ARG_WITH([suffix],
   )
 ], [
   AS_CASE([$ac_sys_system],
-    [Emscripten], [EXEEXT=.js],
+    [Emscripten], [EXEEXT=.mjs],
     [WASI], [EXEEXT=.wasm],
     [EXEEXT=]
   )
@@ -2328,6 +2328,7 @@ AS_CASE([$ac_sys_system],
 
     dnl Include file system support
     AS_VAR_APPEND([LDFLAGS_NODIST], [" -sFORCE_FILESYSTEM -lidbfs.js -lnodefs.js -lproxyfs.js -lworkerfs.js"])
+    AS_VAR_APPEND([LDFLAGS_NODIST], [" -sEXPORTED_RUNTIME_METHODS=FS"])
 
     AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
       AS_VAR_APPEND([LINKFORSHARED], [" -sMAIN_MODULE"])
@@ -2341,7 +2342,6 @@ AS_CASE([$ac_sys_system],
     AS_VAR_APPEND([LDFLAGS_NODIST], [" -sALLOW_MEMORY_GROWTH"])
     dnl not completely sure whether or not we want -sEXIT_RUNTIME, keeping it for now.
     AS_VAR_APPEND([LDFLAGS_NODIST], [" -sEXIT_RUNTIME"])
-    AS_VAR_APPEND([LDFLAGS_NODIST], [" --pre-js=\$(srcdir)/Tools/wasm/emscripten/node_pre.js"])
     WASM_LINKFORSHARED_DEBUG="-gseparate-dwarf --emit-symbol-map"
 
     AS_VAR_IF([wasm_debug], [yes], [