gh-126187 Add emscripten.py script to automate emscripten build (#126190)

Add emscripten.py script to automate emscripten build.

This is modeled heavily on `Tools/wasm/wasi.py`. This will form the basis of an Emscripten build bot.

2 files changed, 353 insertions, 136 deletions

diff --git a/Tools/wasm/README.md b/Tools/wasm/README.md
index bc3e4ba..4c9a643 100644
--- a/Tools/wasm/README.md
+++ b/Tools/wasm/README.md
@@ -1,7 +1,7 @@
 # Python WebAssembly (WASM) build
 
 **WASI support is [tier 2](https://peps.python.org/pep-0011/#tier-2).**
-**Emscripten is NOT officially supported as of Python 3.13.**
+**Emscripten support is [tier 3](https://peps.python.org/pep-0011/#tier-3).**
 
 This directory contains configuration and helpers to facilitate cross
 compilation of CPython to WebAssembly (WASM). Python supports Emscripten
@@ -27,154 +27,57 @@ It comes with a reduced and preloaded stdlib without tests and threading
 support. The ``Emscripten/node`` target has threading enabled and can
 access the file system directly.
 
-Cross compiling to the wasm32-emscripten platform needs the
-[Emscripten](https://emscripten.org/) SDK and a build Python interpreter.
-Emscripten 3.1.19 or newer are recommended. All commands below are relative
-to a repository checkout.
+To cross compile to the ``wasm32-emscripten`` platform you need
+[the Emscripten compiler toolchain](https://emscripten.org/), 
+a Python interpreter, and an installation of Node version 18 or newer. Emscripten
+version 3.1.42 or newer is recommended. All commands below are relative to a checkout
+of the Python repository.
 
-#### Toolchain
+#### Install [the Emscripten compiler toolchain](https://emscripten.org/docs/getting_started/downloads.html)
 
-##### Container image
-
-Christian Heimes maintains a container image with Emscripten SDK, Python
-build dependencies, WASI-SDK, wasmtime, and several additional tools.
-
-From within your local CPython repo clone, run one of the following commands:
-
-```
-# Fedora, RHEL, CentOS
-podman run --rm -ti -v $(pwd):/python-wasm/cpython:Z -w /python-wasm/cpython quay.io/tiran/cpythonbuild:emsdk3
-
-# other
-docker run --rm -ti -v $(pwd):/python-wasm/cpython -w /python-wasm/cpython quay.io/tiran/cpythonbuild:emsdk3
+You can install the Emscripten toolchain as follows:
+```shell
+git clone https://github.com/emscripten-core/emsdk.git --depth 1
+./emsdk/emsdk install latest
+./emsdk/emsdk activate latest
 ```
-
-##### Manually
-
-###### Install [Emscripten SDK](https://emscripten.org/docs/getting_started/downloads.html)
-
-**NOTE**: Follow the on-screen instructions how to add the SDK to ``PATH``.
-
+To add the Emscripten compiler to your path:
 ```shell
-git clone https://github.com/emscripten-core/emsdk.git /opt/emsdk
-/opt/emsdk/emsdk install latest
-/opt/emsdk/emsdk activate latest
+source ./emsdk/emsdk_env.sh
 ```
+This adds `emcc` and `emconfigure` to your path.
 
-###### Optionally: enable ccache for EMSDK
+##### Optionally: enable ccache for EMSDK
 
 The ``EM_COMPILER_WRAPPER`` must be set after the EMSDK environment is
 sourced. Otherwise the source script removes the environment variable.
 
-```
-. /opt/emsdk/emsdk_env.sh
-EM_COMPILER_WRAPPER=ccache
-```
-
-###### Optionally: pre-build and cache static libraries
-
-Emscripten SDK provides static builds of core libraries without PIC
-(position-independent code). Python builds with ``dlopen`` support require
-PIC. To populate the build cache, run:
-
 ```shell
-. /opt/emsdk/emsdk_env.sh
-embuilder build zlib bzip2 MINIMAL_PIC
-embuilder --pic build zlib bzip2 MINIMAL_PIC
+export EM_COMPILER_WRAPPER=ccache
 ```
 
-
 ### Compile and build Python interpreter
 
-From within the container, run the following command:
-
-```shell
-./Tools/wasm/wasm_build.py build
-```
-
-The command is roughly equivalent to:
-
-```shell
-mkdir -p builddir/build
-pushd builddir/build
-../../configure -C
-make -j$(nproc)
-popd
-```
-
-#### Cross-compile to wasm32-emscripten for browser
-
-```shell
-./Tools/wasm/wasm_build.py emscripten-browser
-```
-
-The command is roughly equivalent to:
-
+You can use `python Tools/wasm/emscripten` to compile and build targetting
+Emscripten. You can do everything at once with:
 ```shell
-mkdir -p builddir/emscripten-browser
-pushd builddir/emscripten-browser
-
-CONFIG_SITE=../../Tools/wasm/config.site-wasm32-emscripten \
-  emconfigure ../../configure -C \
-    --host=wasm32-unknown-emscripten \
-    --build=$(../../config.guess) \
-    --with-emscripten-target=browser \
-    --with-build-python=$(pwd)/../build/python
-
-emmake make -j$(nproc)
-popd
+python Tools/wasm/emscripten build
 ```
-
-Serve `python.html` with a local webserver and open the file in a browser.
-Python comes with a minimal web server script that sets necessary HTTP
-headers like COOP, COEP, and mimetypes. Run the script outside the container
-and from the root of the CPython checkout.
-
+or you can break it out into four separate steps:
 ```shell
-./Tools/wasm/wasm_webserver.py
+python Tools/wasm/emscripten configure-build-python
+python Tools/wasm/emscripten make-build-python
+python Tools/wasm/emscripten configure-host
+python Tools/wasm/emscripten make-host
 ```
-
-and open http://localhost:8000/builddir/emscripten-browser/python.html . This
-directory structure enables the *C/C++ DevTools Support (DWARF)* to load C
-and header files with debug builds.
-
-
-#### Cross compile to wasm32-emscripten for node
-
+Extra arguments to the configure steps are passed along to configure. For
+instance, to do a debug build, you can use:
 ```shell
-./Tools/wasm/wasm_build.py emscripten-node-dl
+python Tools/wasm/emscripten build --with-py-debug
 ```
 
-The command is roughly equivalent to:
-
-```shell
-mkdir -p builddir/emscripten-node-dl
-pushd builddir/emscripten-node-dl
-
-CONFIG_SITE=../../Tools/wasm/config.site-wasm32-emscripten \
-  emconfigure ../../configure -C \
-    --host=wasm32-unknown-emscripten \
-    --build=$(../../config.guess) \
-    --with-emscripten-target=node \
-    --enable-wasm-dynamic-linking \
-    --with-build-python=$(pwd)/../build/python
-
-emmake make -j$(nproc)
-popd
-```
-
-```shell
-node --experimental-wasm-threads --experimental-wasm-bulk-memory --experimental-wasm-bigint builddir/emscripten-node-dl/python.js
-```
-
-(``--experimental-wasm-bigint`` is not needed with recent NodeJS versions)
-
 ### Limitations and issues
 
-Emscripten before 3.1.8 has known bugs that can cause memory corruption and
-resource leaks. 3.1.8 contains several fixes for bugs in date and time
-functions.
-
 #### Network stack
 
 - Python's socket module does not work with Emscripten's emulated POSIX
@@ -241,8 +144,6 @@ functions.
   [gh-90548](https://github.com/python/cpython/issues/90548).
 - Python's object allocator ``obmalloc`` is disabled by default.
 - ``ensurepip`` is not available.
-- Some ``ctypes`` features like ``c_longlong`` and ``c_longdouble`` may need
-   NodeJS option ``--experimental-wasm-bigint``.
 
 #### In the browser
 
@@ -263,15 +164,6 @@ Node builds use ``NODERAWFS``.
 - Node RawFS allows direct access to the host file system without need to
   perform ``FS.mount()`` call.
 
-### wasm64-emscripten
-
-- wasm64 requires recent NodeJS and ``--experimental-wasm-memory64``.
-- ``EM_JS`` functions must return ``BigInt()``.
-- ``Py_BuildValue()`` format strings must match size of types. Confusing 32
-  and 64 bits types leads to memory corruption, see
-  [gh-95876](https://github.com/python/cpython/issues/95876) and
-  [gh-95878](https://github.com/python/cpython/issues/95878).
-
 ### Hosting Python WASM builds
 
 The simple REPL terminal uses SharedArrayBuffer. For security reasons
diff --git a/Tools/wasm/emscripten/__main__.py b/Tools/wasm/emscripten/__main__.py
new file mode 100644
index 0000000..2015a37
--- /dev/null
+++ b/Tools/wasm/emscripten/__main__.py
@@ -0,0 +1,325 @@
+#!/usr/bin/env python3
+
+import argparse
+import contextlib
+import functools
+import os
+
+try:
+    from os import process_cpu_count as cpu_count
+except ImportError:
+    from os import cpu_count
+from pathlib import Path
+import shutil
+import subprocess
+import sys
+import sysconfig
+import tempfile
+
+WASM_DIR = Path(__file__).parent.parent
+CHECKOUT = WASM_DIR.parent.parent
+
+CROSS_BUILD_DIR = CHECKOUT / "cross-build"
+BUILD_DIR = CROSS_BUILD_DIR / "build"
+HOST_TRIPLE = "wasm32-emscripten"
+HOST_DIR = CROSS_BUILD_DIR / HOST_TRIPLE
+
+LOCAL_SETUP = CHECKOUT / "Modules" / "Setup.local"
+LOCAL_SETUP_MARKER = "# Generated by Tools/wasm/emscripten.py\n".encode("utf-8")
+
+
+def updated_env(updates={}):
+    """Create a new dict representing the environment to use.
+
+    The changes made to the execution environment are printed out.
+    """
+    env_defaults = {}
+    # https://reproducible-builds.org/docs/source-date-epoch/
+    git_epoch_cmd = ["git", "log", "-1", "--pretty=%ct"]
+    try:
+        epoch = subprocess.check_output(git_epoch_cmd, encoding="utf-8").strip()
+        env_defaults["SOURCE_DATE_EPOCH"] = epoch
+    except subprocess.CalledProcessError:
+        pass  # Might be building from a tarball.
+    # This layering lets SOURCE_DATE_EPOCH from os.environ takes precedence.
+    environment = env_defaults | os.environ | updates
+
+    env_diff = {}
+    for key, value in environment.items():
+        if os.environ.get(key) != value:
+            env_diff[key] = value
+
+    print("🌎 Environment changes:")
+    for key in sorted(env_diff.keys()):
+        print(f"  {key}={env_diff[key]}")
+
+    return environment
+
+
+def subdir(working_dir, *, clean_ok=False):
+    """Decorator to change to a working directory."""
+
+    def decorator(func):
+        @functools.wraps(func)
+        def wrapper(context):
+            try:
+                tput_output = subprocess.check_output(
+                    ["tput", "cols"], encoding="utf-8"
+                )
+                terminal_width = int(tput_output.strip())
+            except subprocess.CalledProcessError:
+                terminal_width = 80
+            print("⎯" * terminal_width)
+            print("📁", working_dir)
+            if clean_ok and getattr(context, "clean", False) and working_dir.exists():
+                print(f"🚮 Deleting directory (--clean)...")
+                shutil.rmtree(working_dir)
+
+            working_dir.mkdir(parents=True, exist_ok=True)
+
+            with contextlib.chdir(working_dir):
+                return func(context, working_dir)
+
+        return wrapper
+
+    return decorator
+
+
+def call(command, *, quiet, **kwargs):
+    """Execute a command.
+
+    If 'quiet' is true, then redirect stdout and stderr to a temporary file.
+    """
+    print("❯", " ".join(map(str, command)))
+    if not quiet:
+        stdout = None
+        stderr = None
+    else:
+        stdout = tempfile.NamedTemporaryFile(
+            "w",
+            encoding="utf-8",
+            delete=False,
+            prefix="cpython-emscripten-",
+            suffix=".log",
+        )
+        stderr = subprocess.STDOUT
+        print(f"📝 Logging output to {stdout.name} (--quiet)...")
+
+    subprocess.check_call(command, **kwargs, stdout=stdout, stderr=stderr)
+
+
+def build_platform():
+    """The name of the build/host platform."""
+    # Can also be found via `config.guess`.`
+    return sysconfig.get_config_var("BUILD_GNU_TYPE")
+
+
+def build_python_path():
+    """The path to the build Python binary."""
+    binary = BUILD_DIR / "python"
+    if not binary.is_file():
+        binary = binary.with_suffix(".exe")
+        if not binary.is_file():
+            raise FileNotFoundError("Unable to find `python(.exe)` in " f"{BUILD_DIR}")
+
+    return binary
+
+
+@subdir(BUILD_DIR, clean_ok=True)
+def configure_build_python(context, working_dir):
+    """Configure the build/host Python."""
+    if LOCAL_SETUP.exists():
+        print(f"👍 {LOCAL_SETUP} exists ...")
+    else:
+        print(f"📝 Touching {LOCAL_SETUP} ...")
+        LOCAL_SETUP.write_bytes(LOCAL_SETUP_MARKER)
+
+    configure = [os.path.relpath(CHECKOUT / "configure", working_dir)]
+    if context.args:
+        configure.extend(context.args)
+
+    call(configure, quiet=context.quiet)
+
+
+@subdir(BUILD_DIR)
+def make_build_python(context, working_dir):
+    """Make/build the build Python."""
+    call(["make", "--jobs", str(cpu_count()), "all"], quiet=context.quiet)
+
+    binary = build_python_path()
+    cmd = [
+        binary,
+        "-c",
+        "import sys; " "print(f'{sys.version_info.major}.{sys.version_info.minor}')",
+    ]
+    version = subprocess.check_output(cmd, encoding="utf-8").strip()
+
+    print(f"🎉 {binary} {version}")
+
+
+@subdir(HOST_DIR, clean_ok=True)
+def configure_emscripten_python(context, working_dir):
+    """Configure the emscripten/host build."""
+    config_site = os.fsdecode(
+        CHECKOUT / "Tools" / "wasm" / "config.site-wasm32-emscripten"
+    )
+
+    emscripten_build_dir = working_dir.relative_to(CHECKOUT)
+
+    python_build_dir = BUILD_DIR / "build"
+    lib_dirs = list(python_build_dir.glob("lib.*"))
+    assert (
+        len(lib_dirs) == 1
+    ), f"Expected a single lib.* directory in {python_build_dir}"
+    lib_dir = os.fsdecode(lib_dirs[0])
+    pydebug = lib_dir.endswith("-pydebug")
+    python_version = lib_dir.removesuffix("-pydebug").rpartition("-")[-1]
+    sysconfig_data = (
+        f"{emscripten_build_dir}/build/lib.emscripten-wasm32-{python_version}"
+    )
+    if pydebug:
+        sysconfig_data += "-pydebug"
+
+    host_runner = context.host_runner
+    env_additions = {"CONFIG_SITE": config_site, "HOSTRUNNER": host_runner}
+    build_python = os.fsdecode(build_python_path())
+    configure = [
+        "emconfigure",
+        os.path.relpath(CHECKOUT / "configure", working_dir),
+        "CFLAGS=-DPY_CALL_TRAMPOLINE -sUSE_BZIP2",
+        f"--host={HOST_TRIPLE}",
+        f"--build={build_platform()}",
+        f"--with-build-python={build_python}",
+        "--without-pymalloc",
+        "--disable-shared",
+        "--disable-ipv6",
+        "--enable-big-digits=30",
+        "--enable-wasm-dynamic-linking",
+        f"--prefix={HOST_DIR}",
+    ]
+    if pydebug:
+        configure.append("--with-pydebug")
+    if context.args:
+        configure.extend(context.args)
+    call(
+        configure,
+        env=updated_env(env_additions),
+        quiet=context.quiet,
+    )
+
+    python_js = working_dir / "python.js"
+    exec_script = working_dir / "python.sh"
+    exec_script.write_text(f'#!/bin/sh\nexec {host_runner} {python_js} "$@"\n')
+    exec_script.chmod(0o755)
+    print(f"🏃‍♀️ Created {exec_script} ... ")
+    sys.stdout.flush()
+
+
+@subdir(HOST_DIR)
+def make_emscripten_python(context, working_dir):
+    """Run `make` for the emscripten/host build."""
+    call(
+        ["make", "--jobs", str(cpu_count()), "commoninstall"],
+        env=updated_env(),
+        quiet=context.quiet,
+    )
+
+    exec_script = working_dir / "python.sh"
+    subprocess.check_call([exec_script, "--version"])
+
+
+def build_all(context):
+    """Build everything."""
+    steps = [
+        configure_build_python,
+        make_build_python,
+        configure_emscripten_python,
+        make_emscripten_python,
+    ]
+    for step in steps:
+        step(context)
+
+
+def clean_contents(context):
+    """Delete all files created by this script."""
+    if CROSS_BUILD_DIR.exists():
+        print(f"🧹 Deleting {CROSS_BUILD_DIR} ...")
+        shutil.rmtree(CROSS_BUILD_DIR)
+
+    if LOCAL_SETUP.exists():
+        with LOCAL_SETUP.open("rb") as file:
+            if file.read(len(LOCAL_SETUP_MARKER)) == LOCAL_SETUP_MARKER:
+                print(f"🧹 Deleting generated {LOCAL_SETUP} ...")
+
+
+def main():
+    default_host_runner = "node"
+
+    parser = argparse.ArgumentParser()
+    subcommands = parser.add_subparsers(dest="subcommand")
+    build = subcommands.add_parser("build", help="Build everything")
+    configure_build = subcommands.add_parser(
+        "configure-build-python", help="Run `configure` for the " "build Python"
+    )
+    make_build = subcommands.add_parser(
+        "make-build-python", help="Run `make` for the build Python"
+    )
+    configure_host = subcommands.add_parser(
+        "configure-host",
+        help="Run `configure` for the host/emscripten (pydebug builds are inferred from the build Python)",
+    )
+    make_host = subcommands.add_parser("make-host", help="Run `make` for the host/emscripten")
+    clean = subcommands.add_parser(
+        "clean", help="Delete files and directories created by this script"
+    )
+    for subcommand in build, configure_build, make_build, configure_host, make_host:
+        subcommand.add_argument(
+            "--quiet",
+            action="store_true",
+            default=False,
+            dest="quiet",
+            help="Redirect output from subprocesses to a log file",
+        )
+    for subcommand in configure_build, configure_host:
+        subcommand.add_argument(
+            "--clean",
+            action="store_true",
+            default=False,
+            dest="clean",
+            help="Delete any relevant directories before building",
+        )
+    for subcommand in build, configure_build, configure_host:
+        subcommand.add_argument(
+            "args", nargs="*", help="Extra arguments to pass to `configure`"
+        )
+    for subcommand in build, configure_host:
+        subcommand.add_argument(
+            "--host-runner",
+            action="store",
+            default=default_host_runner,
+            dest="host_runner",
+            help="Command template for running the emscripten host"
+            f"`{default_host_runner}`)",
+        )
+
+    context = parser.parse_args()
+
+    dispatch = {
+        "configure-build-python": configure_build_python,
+        "make-build-python": make_build_python,
+        "configure-host": configure_emscripten_python,
+        "make-host": make_emscripten_python,
+        "build": build_all,
+        "clean": clean_contents,
+    }
+
+    if not context.subcommand:
+        # No command provided, display help and exit
+        print("Expected one of", ", ".join(sorted(dispatch.keys())), file=sys.stderr)
+        parser.print_help(sys.stderr)
+        sys.exit(1)
+    dispatch[context.subcommand](context)
+
+
+if __name__ == "__main__":
+    main()