gh-127111: Emscripten Make web example work again (#127113)

Moves the Emscripten web example into a standalone folder, and updates 
Makefile targets to build the web example. Instructions for usage have
also been added.

1 files changed, 245 insertions, 0 deletions

diff --git a/Tools/wasm/emscripten/web_example/wasm_assets.py b/Tools/wasm/emscripten/web_example/wasm_assets.py
new file mode 100755
index 00000000000..7f0fa7ae7c1
--- /dev/null
+++ b/Tools/wasm/emscripten/web_example/wasm_assets.py
@@ -0,0 +1,245 @@
+#!/usr/bin/env python
+"""Create a WASM asset bundle directory structure.
+
+The WASM asset bundles are pre-loaded by the final WASM build. The bundle
+contains:
+
+- a stripped down, pyc-only stdlib zip file, e.g. {PREFIX}/lib/python311.zip
+- os.py as marker module {PREFIX}/lib/python3.11/os.py
+- empty lib-dynload directory, to make sure it is copied into the bundle:
+    {PREFIX}/lib/python3.11/lib-dynload/.empty
+"""
+
+import argparse
+import pathlib
+import shutil
+import sys
+import sysconfig
+import zipfile
+from typing import Dict
+
+# source directory
+SRCDIR = pathlib.Path(__file__).parents[4].absolute()
+SRCDIR_LIB = SRCDIR / "Lib"
+
+
+# Library directory relative to $(prefix).
+WASM_LIB = pathlib.PurePath("lib")
+WASM_STDLIB_ZIP = (
+    WASM_LIB / f"python{sys.version_info.major}{sys.version_info.minor}.zip"
+)
+WASM_STDLIB = WASM_LIB / f"python{sys.version_info.major}.{sys.version_info.minor}"
+WASM_DYNLOAD = WASM_STDLIB / "lib-dynload"
+
+
+# Don't ship large files / packages that are not particularly useful at
+# the moment.
+OMIT_FILES = (
+    # regression tests
+    "test/",
+    # package management
+    "ensurepip/",
+    "venv/",
+    # other platforms
+    "_aix_support.py",
+    "_osx_support.py",
+    # webbrowser
+    "antigravity.py",
+    "webbrowser.py",
+    # Pure Python implementations of C extensions
+    "_pydecimal.py",
+    "_pyio.py",
+    # concurrent threading
+    "concurrent/futures/thread.py",
+    # Misc unused or large files
+    "pydoc_data/",
+)
+
+# Synchronous network I/O and protocols are not supported; for example,
+# socket.create_connection() raises an exception:
+# "BlockingIOError: [Errno 26] Operation in progress".
+OMIT_NETWORKING_FILES = (
+    "email/",
+    "ftplib.py",
+    "http/",
+    "imaplib.py",
+    "mailbox.py",
+    "poplib.py",
+    "smtplib.py",
+    "socketserver.py",
+    # keep urllib.parse for pydoc
+    "urllib/error.py",
+    "urllib/request.py",
+    "urllib/response.py",
+    "urllib/robotparser.py",
+    "wsgiref/",
+)
+
+OMIT_MODULE_FILES = {
+    "_asyncio": ["asyncio/"],
+    "_curses": ["curses/"],
+    "_ctypes": ["ctypes/"],
+    "_decimal": ["decimal.py"],
+    "_dbm": ["dbm/ndbm.py"],
+    "_gdbm": ["dbm/gnu.py"],
+    "_json": ["json/"],
+    "_multiprocessing": ["concurrent/futures/process.py", "multiprocessing/"],
+    "pyexpat": ["xml/", "xmlrpc/"],
+    "readline": ["rlcompleter.py"],
+    "_sqlite3": ["sqlite3/"],
+    "_ssl": ["ssl.py"],
+    "_tkinter": ["idlelib/", "tkinter/", "turtle.py", "turtledemo/"],
+    "_zoneinfo": ["zoneinfo/"],
+}
+
+SYSCONFIG_NAMES = (
+    "_sysconfigdata__emscripten_wasm32-emscripten",
+    "_sysconfigdata__emscripten_wasm32-emscripten",
+    "_sysconfigdata__wasi_wasm32-wasi",
+    "_sysconfigdata__wasi_wasm64-wasi",
+)
+
+
+def get_builddir(args: argparse.Namespace) -> pathlib.Path:
+    """Get builddir path from pybuilddir.txt"""
+    with open("pybuilddir.txt", encoding="utf-8") as f:
+        builddir = f.read()
+    return pathlib.Path(builddir)
+
+
+def get_sysconfigdata(args: argparse.Namespace) -> pathlib.Path:
+    """Get path to sysconfigdata relative to build root"""
+    assert isinstance(args.builddir, pathlib.Path)
+    data_name: str = sysconfig._get_sysconfigdata_name()  # type: ignore[attr-defined]
+    if not data_name.startswith(SYSCONFIG_NAMES):
+        raise ValueError(f"Invalid sysconfig data name '{data_name}'.", SYSCONFIG_NAMES)
+    filename = data_name + ".py"
+    return args.builddir / filename
+
+
+def create_stdlib_zip(
+    args: argparse.Namespace,
+    *,
+    optimize: int = 0,
+) -> None:
+    def filterfunc(filename: str) -> bool:
+        pathname = pathlib.Path(filename).resolve()
+        return pathname not in args.omit_files_absolute
+
+    with zipfile.PyZipFile(
+        args.output,
+        mode="w",
+        compression=args.compression,
+        optimize=optimize,
+    ) as pzf:
+        if args.compresslevel is not None:
+            pzf.compresslevel = args.compresslevel
+        pzf.writepy(args.sysconfig_data)
+        for entry in sorted(args.srcdir_lib.iterdir()):
+            entry = entry.resolve()
+            if entry.name == "__pycache__":
+                continue
+            if entry.name.endswith(".py") or entry.is_dir():
+                # writepy() writes .pyc files (bytecode).
+                pzf.writepy(entry, filterfunc=filterfunc)
+
+
+def detect_extension_modules(args: argparse.Namespace) -> Dict[str, bool]:
+    modules = {}
+
+    # disabled by Modules/Setup.local ?
+    with open(args.buildroot / "Makefile") as f:
+        for line in f:
+            if line.startswith("MODDISABLED_NAMES="):
+                disabled = line.split("=", 1)[1].strip().split()
+                for modname in disabled:
+                    modules[modname] = False
+                break
+
+    # disabled by configure?
+    with open(args.sysconfig_data) as f:
+        data = f.read()
+    loc: Dict[str, Dict[str, str]] = {}
+    exec(data, globals(), loc)
+
+    for key, value in loc["build_time_vars"].items():
+        if not key.startswith("MODULE_") or not key.endswith("_STATE"):
+            continue
+        if value not in {"yes", "disabled", "missing", "n/a"}:
+            raise ValueError(f"Unsupported value '{value}' for {key}")
+
+        modname = key[7:-6].lower()
+        if modname not in modules:
+            modules[modname] = value == "yes"
+    return modules
+
+
+def path(val: str) -> pathlib.Path:
+    return pathlib.Path(val).absolute()
+
+
+parser = argparse.ArgumentParser()
+parser.add_argument(
+    "--buildroot",
+    help="absolute path to build root",
+    default=pathlib.Path(".").absolute(),
+    type=path,
+)
+parser.add_argument(
+    "--prefix",
+    help="install prefix",
+    default=pathlib.Path("/usr/local"),
+    type=path,
+)
+parser.add_argument(
+    "-o",
+    "--output",
+    help="output file",
+    type=path,
+)
+
+
+def main() -> None:
+    args = parser.parse_args()
+
+    relative_prefix = args.prefix.relative_to(pathlib.Path("/"))
+    args.srcdir = SRCDIR
+    args.srcdir_lib = SRCDIR_LIB
+    args.wasm_root = args.buildroot / relative_prefix
+    args.wasm_stdlib = args.wasm_root / WASM_STDLIB
+    args.wasm_dynload = args.wasm_root / WASM_DYNLOAD
+
+    # bpo-17004: zipimport supports only zlib compression.
+    # Emscripten ZIP_STORED + -sLZ4=1 linker flags results in larger file.
+    args.compression = zipfile.ZIP_DEFLATED
+    args.compresslevel = 9
+
+    args.builddir = get_builddir(args)
+    args.sysconfig_data = get_sysconfigdata(args)
+    if not args.sysconfig_data.is_file():
+        raise ValueError(f"sysconfigdata file {args.sysconfig_data} missing.")
+
+    extmods = detect_extension_modules(args)
+    omit_files = list(OMIT_FILES)
+    if sysconfig.get_platform().startswith("emscripten"):
+        omit_files.extend(OMIT_NETWORKING_FILES)
+    for modname, modfiles in OMIT_MODULE_FILES.items():
+        if not extmods.get(modname):
+            omit_files.extend(modfiles)
+
+    args.omit_files_absolute = {
+        (args.srcdir_lib / name).resolve() for name in omit_files
+    }
+
+    # Empty, unused directory for dynamic libs, but required for site initialization.
+    args.wasm_dynload.mkdir(parents=True, exist_ok=True)
+    marker = args.wasm_dynload / ".empty"
+    marker.touch()
+    # The rest of stdlib that's useful in a WASM context.
+    create_stdlib_zip(args)
+    size = round(args.output.stat().st_size / 1024**2, 2)
+    parser.exit(0, f"Created {args.output} ({size} MiB)\n")
+
+
+if __name__ == "__main__":
+    main()