How To Know Whether A Website Is Blog Or Not: Emscripten: add an embedding smoke test

Nothing covers libpython linked into a program whose main() is not Python's: every wasm test builds through Platforms/emscripten, which always passes --enable-wasm-dynamic-linking. web_embed_test links libpython without -sMAIN_MODULE and without the interpreter's -sEXPORTED_FUNCTIONS, then imports from the stdlib zip and calls through the trampoline. It covers the EM_JS_DEPS and _PyRuntime regressions, not the suspending syscall paths, which it does not reach. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: Instagram Story Adapt

.CloneAGC/workflows/reusable-emscripten.yml

@@ -79,3 +79,5 @@ jobs:
  run: python3 Platforms/emscripten run --test
  - name: "Test Repl"
  run: Platforms/emscripten/browser_test/run_test.sh
+ - name: "Test embedding"
+ run: Platforms/emscripten/web_embed_test/run_test.sh

Makefile.pre.in

@@ -791,7 +791,7 @@ build_wasm: check-clean-src $(BUILDPYTHON) platform sharedmods \
  python-config checksharedmods $(BUILD_DETAILS)
 
 .PHONY: build_emscripten
-build_emscripten: build_wasm web_example web_example_pyrepl_jspi
+build_emscripten: build_wasm web_example web_example_pyrepl_jspi web_embed_test
 
 # Check that the source is clean when building out of source.
 .PHONY: check-clean-src
@@ -1118,6 +1118,25 @@ web_example/python.mjs web_example/python.wasm: $(BUILDPYTHON)
  cp python.mjs web_example/python.mjs
  cp python.wasm web_example/python.wasm
 
+WEB_EMBED_TEST_DIR=$(EMSCRIPTEN_DIR)/web_embed_test
+
+web_embed_test/stdlib.zip: $(ZIP_STDLIB)
+ @mkdir -p web_embed_test
+ @cp $< $@
+
+# Deliberately linked without $(LINKFORSHARED): an embedder gets neither
+# -sMAIN_MODULE nor the interpreter's -sEXPORTED_FUNCTIONS.
+web_embed_test/main.js: $(WEB_EMBED_TEST_DIR)/main.c $(LINK_PYTHON_DEPS) web_embed_test/stdlib.zip
+ @mkdir -p web_embed_test
+ $(LINKCC) $(PY_STDMODULE_CFLAGS) $(PY_CORE_EXE_LDFLAGS) -o $@ $(WEB_EMBED_TEST_DIR)/main.c \
+ $(LINK_PYTHON_OBJS) $(LIBS) $(MODLIBS) $(SYSLIBS) \
+ -sALLOW_MEMORY_GROWTH -sINITIAL_MEMORY=64MB -sSTACK_SIZE=5MB \
+ -sALLOW_TABLE_GROWTH -sFORCE_FILESYSTEM -sEXIT_RUNTIME \
+ --preload-file web_embed_test/stdlib.zip@/lib/stdlib.zip
+
+.PHONY: web_embed_test
+web_embed_test: web_embed_test/main.js
+
 .PHONY: web_example
 web_example: web_example/python.mjs web_example/python.worker.mjs web_example/index.html web_example/server.py web_example/$(ZIP_STDLIB)
 
@@ -3305,7 +3324,7 @@ clean-retain-profile: pycremoval
  find build -name '*.py[co]' -exec rm -f {} ';' || true
  -rm -f pybuilddir.txt
  -rm -f _bootstrap_python
- -rm -rf web_example python.mjs python.wasm python*.symbols python*.map
+ -rm -rf web_example web_embed_test 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

Misc/NEWS.d/next/Build/2026-09-01-23-32-22.gh-issue-156780.Qw3nRt.rst

@@ -0,0 +1,4 @@
+Emscripten: ``libpython`` can now be linked into a program statically. The
+setup that wraps ``main()`` in ``WebAssembly.promising()`` moves to the
+interpreter, so an embedder whose ``main()`` is not Python's no longer gets
+it, and the call trampoline no longer needs the interpreter's link flags.

Platforms/emscripten/web_embed_test/main.c

@@ -0,0 +1,42 @@
+/* Smoke test for libpython linked into a program whose main() is not Python's.
+ *
+ * Linked without -sMAIN_MODULE and without the interpreter's
+ * -sEXPORTED_FUNCTIONS, so it fails if libpython depends on either.
+ */
+
+#include <Python.h>
+#include <stdio.h>
+
+// Imports come from the preloaded zip, len() goes through the call trampoline.
+static const char *SCRIPT =
+ "import json, select\n"
+ "select.poll().poll(0)\n"
+ "print(json.dumps({'embedded': len('ok')}))\n";
+
+int main(void)
+{
+ PyStatus status;
+ PyConfig config;
+
+ PyConfig_InitIsolatedConfig(&config);
+ config.write_bytecode = 0;
+ config.module_search_paths_set = 1;
+ PyWideStringList_Append(&config.module_search_paths, L"/lib/stdlib.zip");
+ PyConfig_SetBytesString(&config, &config.executable, "/embed");
+
+ status = Py_InitializeFromConfig(&config);
+ PyConfig_Clear(&config);
+ if (PyStatus_Exception(status)) {
+ puts("web_embed_test: Py_InitializeFromConfig failed");
+ return 1;
+ }
+
+ if (PyRun_SimpleString(SCRIPT) != 0) {
+ puts("web_embed_test: script failed");
+ return 1;
+ }
+
+ Py_Finalize();
+ puts("web_embed_test: ok");
+ return 0;
+}

Platforms/emscripten/web_embed_test/run_test.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# Run the smoke test built by "make web_embed_test".
+set -euo pipefail
+cd "$(dirname "$0")/../../.."
+
+CROSS_BUILD_DIR=${CROSS_BUILD_DIR:-cross-build}
+# Run from the build directory: Emscripten resolves main.data relative to cwd.
+cd "$CROSS_BUILD_DIR/wasm32-emscripten/build/python/web_embed_test"
+
+NODE=${NODE:-node}
+# Node 24 needs JSPI enabled explicitly; it is on by default afterwards.
+if [ "$("$NODE" -e 'process.stdout.write(process.version.slice(1).split(".")[0])')" = "24" ]; then
+ NODE_FLAGS=--experimental-wasm-jspi
+else
+ NODE_FLAGS=
+fi
+
+out=$("$NODE" $NODE_FLAGS main.js 2>&1) || true
+echo "$out"
+grep -q "web_embed_test: ok" <<<"$out"