gh-127111: Make web example work again

I moved the web example from `Tools/wasm` into `Tools/wasm/emscripten/web_example`.
I also added a new target `build_emscripten` which is `build_wasm` but also
builds the web_example. The web_example needs:
1. python.html, copied
2. python.worker.mjs copied
3. python.mjs and python.wasm output from the main linking of the Python interpreter
4. The webserver that sets COOP and COEP
5. python3.14.zip

This last is created by the `wasm_assets.py` script, which required a pretty
small set of changes to work fine for us.

The last thing that should be done is the `python.worker.mjs` script should be
made independent of the Python version: currently 3.14 is hard coded. I ran
into trouble doing this, so maybe I can leave it to a followup.

Makefile.pre.in

@@ -269,10 +269,6 @@ SRCDIRS= 	@SRCDIRS@
 # Other subdirectories
 SUBDIRSTOO=	Include Lib Misc
 
-# assets for Emscripten browser builds
-WASM_ASSETS_DIR=.$(prefix)
-WASM_STDLIB=$(WASM_ASSETS_DIR)/lib/python$(VERSION)/os.py
-
 # Files and directories to be distributed
 CONFIGFILES=	configure configure.ac acconfig.h pyconfig.h.in Makefile.pre.in
 DISTFILES=	README.rst ChangeLog $(CONFIGFILES)
@@ -737,6 +733,9 @@ build_all:	check-clean-src check-app-store-compliance $(BUILDPYTHON) platform sh
 build_wasm: check-clean-src $(BUILDPYTHON) platform sharedmods \
 		python-config checksharedmods
 
+.PHONY: build_emscripten
+build_emscripten: build_wasm web_example
+
 # Check that the source is clean when building out of source.
 .PHONY: check-clean-src
 check-clean-src:
@@ -1016,23 +1015,38 @@ $(DLLLIBRARY) libpython$(LDVERSION).dll.a: $(LIBRARY_OBJS)
 	else true; \
 	fi
 
-# wasm32-emscripten browser build
-# wasm assets directory is relative to current build dir, e.g. "./usr/local".
-# --preload-file turns a relative asset path into an absolute path.
+# wasm32-emscripten browser web example
+
+WEBEX_DIR=$(srcdir)/Tools/wasm/emscripten/web_example/
+web_example/python.html: $(WEBEX_DIR)/python.html
+	@mkdir -p web_example
+	@cp $< $@
+
+web_example/python.worker.mjs: $(WEBEX_DIR)/python.worker.mjs
+	@mkdir -p web_example
+	@cp $< $@
 
-.PHONY: wasm_stdlib
-wasm_stdlib: $(WASM_STDLIB)
-$(WASM_STDLIB): $(srcdir)/Lib/*.py $(srcdir)/Lib/*/*.py \
-	    $(srcdir)/Tools/wasm/wasm_assets.py \
+web_example/server.py: $(WEBEX_DIR)/server.py
+	@mkdir -p web_example
+	@cp $< $@
+
+WEB_STDLIB=web_example/python$(VERSION)$(ABI_THREAD).zip
+$(WEB_STDLIB): $(srcdir)/Lib/*.py $(srcdir)/Lib/*/*.py \
+	    $(WEBEX_DIR)/wasm_assets.py \
 	    Makefile pybuilddir.txt Modules/Setup.local
-	$(PYTHON_FOR_BUILD) $(srcdir)/Tools/wasm/wasm_assets.py \
-	    --buildroot . --prefix $(prefix)
+	$(PYTHON_FOR_BUILD) $(WEBEX_DIR)/wasm_assets.py \
+	    --buildroot . --prefix $(prefix) -o $@
 
-python.html: $(srcdir)/Tools/wasm/python.html python.worker.js
-	@cp $(srcdir)/Tools/wasm/python.html $@
+web_example/python.mjs web_example/python.wasm: $(BUILDPYTHON)
+	@if test $(HOST_GNU_TYPE) != 'wasm32-unknown-emscripten' ; then \
+		echo "Can only build web_example when target is Emscripten" ;\
+		exit 1 ;\
+	fi
+	cp python.mjs web_example/python.mjs
+	cp python.wasm web_example/python.wasm
 
-python.worker.js: $(srcdir)/Tools/wasm/python.worker.js
-	@cp $(srcdir)/Tools/wasm/python.worker.js $@
+.PHONY: web_example
+web_example: web_example/python.mjs web_example/python.worker.mjs web_example/python.html web_example/server.py $(WEB_STDLIB)
 
 ############################################################################
 # Header files
@@ -3053,8 +3067,7 @@ clean-retain-profile: pycremoval
 	find build -name '*.py[co]' -exec rm -f {} ';' || true
 	-rm -f pybuilddir.txt
 	-rm -f _bootstrap_python
-	-rm -f python.html python*.js python.data python*.symbols python*.map
-	-rm -f $(WASM_STDLIB)
+	-rm -rf web_example python.mjs python.wasm python*.symbols python*.map
 	-rm -f Programs/_testembed Programs/_freeze_module
 	-rm -rf Python/deepfreeze
 	-rm -f Python/frozen_modules/*.h

Tools/wasm/python.html → Tools/wasm/emscripten/web_example/python.html

@@ -47,7 +47,7 @@
 
     async initialiseWorker() {
         if (!this.worker) {
-            this.worker = new Worker(this.workerURL)
+            this.worker = new Worker(this.workerURL, {type: "module"})
             this.worker.addEventListener('message', this.handleMessageFromWorker)
         }
     }
@@ -347,7 +347,7 @@
         programRunning(false)
     }
 
-    const pythonWorkerManager = new WorkerManager('./python.worker.js', stdio, readyCallback, finishedCallback)
+    const pythonWorkerManager = new WorkerManager('./python.worker.mjs', stdio, readyCallback, finishedCallback)
 }
     </script>
 </head>

Tools/wasm/python.worker.js → Tools/wasm/emscripten/web_example/python.worker.mjs

@@ -1,3 +1,5 @@
+import createEmscriptenModule from "./python.mjs";
+
 class StdinBuffer {
     constructor() {
         this.sab = new SharedArrayBuffer(128 * Int32Array.BYTES_PER_ELEMENT)
@@ -59,29 +61,42 @@ const stderr = (charCode) => {
 
 const stdinBuffer = new StdinBuffer()
 
-var Module = {
+const emscriptenSettings = {
     noInitialRun: true,
     stdin: stdinBuffer.stdin,
     stdout: stdout,
     stderr: stderr,
     onRuntimeInitialized: () => {
         postMessage({type: 'ready', stdinBuffer: stdinBuffer.sab})
+    },
+    async preRun(Module) {
+        // TODO: remove fixed version number
+        // Prevent complaints about not finding exec-prefix by making a lib-dynload directory
+        Module.FS.mkdirTree("/lib/python3.14/lib-dynload/");
+        Module.addRunDependency("install-stdlib");
+        const resp = await fetch("python3.14.zip");
+        const stdlibBuffer = await resp.arrayBuffer();
+        Module.FS.writeFile(`/lib/python314.zip`, new Uint8Array(stdlibBuffer), { canOwn: true });
+        Module.removeRunDependency("install-stdlib");
     }
 }
 
-onmessage = (event) => {
+const modulePromise = createEmscriptenModule(emscriptenSettings);
+
+
+onmessage = async (event) => {
     if (event.data.type === 'run') {
+        const Module = await modulePromise;
         if (event.data.files) {
             for (const [filename, contents] of Object.entries(event.data.files)) {
                 Module.FS.writeFile(filename, contents)
             }
         }
-        const ret = callMain(event.data.args)
+        const ret = Module.callMain(event.data.args);
         postMessage({
             type: 'finished',
             returnCode: ret
         })
     }
 }
 
-importScripts('python.js')

Tools/wasm/wasm_webserver.py → Tools/wasm/emscripten/web_example/server.py

@@ -14,13 +14,6 @@
 
 
 class MyHTTPRequestHandler(server.SimpleHTTPRequestHandler):
-    extensions_map = server.SimpleHTTPRequestHandler.extensions_map.copy()
-    extensions_map.update(
-        {
-            ".wasm": "application/wasm",
-        }
-    )
-
     def end_headers(self) -> None:
         self.send_my_headers()
         super().end_headers()
@@ -42,5 +35,6 @@ def main() -> None:
         bind=args.bind,
     )
 
+
 if __name__ == "__main__":
     main()

Tools/wasm/wasm_assets.py → Tools/wasm/emscripten/web_example/wasm_assets.py

@@ -19,7 +19,7 @@
 from typing import Dict
 
 # source directory
-SRCDIR = pathlib.Path(__file__).parent.parent.parent.absolute()
+SRCDIR = pathlib.Path(__file__).parents[4].absolute()
 SRCDIR_LIB = SRCDIR / "Lib"
 
 
@@ -131,7 +131,7 @@ def filterfunc(filename: str) -> bool:
         return pathname not in args.omit_files_absolute
 
     with zipfile.PyZipFile(
-        args.wasm_stdlib_zip,
+        args.output,
         mode="w",
         compression=args.compression,
         optimize=optimize,
@@ -195,6 +195,12 @@ def path(val: str) -> pathlib.Path:
     default=pathlib.Path("/usr/local"),
     type=path,
 )
+parser.add_argument(
+    "-o", "--output",
+    help="output file",
+    type=path,
+)
+
 
 
 def main() -> None:
@@ -204,7 +210,6 @@ def main() -> None:
     args.srcdir = SRCDIR
     args.srcdir_lib = SRCDIR_LIB
     args.wasm_root = args.buildroot / relative_prefix
-    args.wasm_stdlib_zip = args.wasm_root / WASM_STDLIB_ZIP
     args.wasm_stdlib = args.wasm_root / WASM_STDLIB
     args.wasm_dynload = args.wasm_root / WASM_DYNLOAD
 
@@ -234,12 +239,10 @@ def main() -> None:
     args.wasm_dynload.mkdir(parents=True, exist_ok=True)
     marker = args.wasm_dynload / ".empty"
     marker.touch()
-    # os.py is a marker for finding the correct lib directory.
-    shutil.copy(args.srcdir_lib / "os.py", args.wasm_stdlib)
     # The rest of stdlib that's useful in a WASM context.
     create_stdlib_zip(args)
-    size = round(args.wasm_stdlib_zip.stat().st_size / 1024**2, 2)
-    parser.exit(0, f"Created {args.wasm_stdlib_zip} ({size} MiB)\n")
+    size = round(args.output.stat().st_size / 1024**2, 2)
+    parser.exit(0, f"Created {args.output} ({size} MiB)\n")
 
 
 if __name__ == "__main__":

configure.ac

@@ -1854,9 +1854,13 @@ if test "$Py_OPT" = 'true' ; then
       LDFLAGS_NODIST="$LDFLAGS_NODIST -fno-semantic-interposition"
       ], [], [-Werror])
   ])
-elif test "$ac_sys_system" = "Emscripten" -o "$ac_sys_system" = "WASI"; then
-  dnl Emscripten does not support shared extensions yet. Build
-  dnl "python.[js,wasm]", "pybuilddir.txt", and "platform" files.
+elif test "$ac_sys_system" = "Emscripten"; then
+  dnl Build "python.[js,wasm]", "pybuilddir.txt", and "platform" files.
+  DEF_MAKE_ALL_RULE="build_emscripten"
+  REQUIRE_PGO="no"
+  DEF_MAKE_RULE="all"
+elif test "$ac_sys_system" = "WASI"; then
+  dnl Build "python.wasm", "pybuilddir.txt", and "platform" files.
   DEF_MAKE_ALL_RULE="build_wasm"
   REQUIRE_PGO="no"
   DEF_MAKE_RULE="all"
@@ -2321,14 +2325,14 @@ AS_CASE([$ac_sys_system],
     AS_VAR_IF([Py_DEBUG], [yes], [wasm_debug=yes], [wasm_debug=no])
 
     dnl Start with 20 MB and allow to grow
-    AS_VAR_APPEND([LDFLAGS_NODIST], [" -sALLOW_MEMORY_GROWTH -sTOTAL_MEMORY=20971520"])
+    AS_VAR_APPEND([LDFLAGS_NODIST], [" -sALLOW_MEMORY_GROWTH -sINITIAL_MEMORY=20971520"])
 
     dnl map int64_t and uint64_t to JS bigint
     AS_VAR_APPEND([LDFLAGS_NODIST], [" -sWASM_BIGINT"])
 
     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_APPEND([LDFLAGS_NODIST], [" -sEXPORTED_RUNTIME_METHODS=FS,callMain"])
 
     AS_VAR_IF([enable_wasm_dynamic_linking], [yes], [
       AS_VAR_APPEND([LINKFORSHARED], [" -sMAIN_MODULE"])
@@ -2339,7 +2343,6 @@ AS_CASE([$ac_sys_system],
       AS_VAR_APPEND([LDFLAGS_NODIST], [" -sUSE_PTHREADS"])
       AS_VAR_APPEND([LINKFORSHARED], [" -sPROXY_TO_PTHREAD"])
     ])
-    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"])
     WASM_LINKFORSHARED_DEBUG="-gseparate-dwarf --emit-symbol-map"