gh-127503 Don't propagate native PATH to Emscripten Python

[hoodmane]

The native PATH makes shutil.which() pick up native executables which is inconvenient.

While I'm at it, I also set thisProgram incorrectly in the final version of #127506.

• Issue: Emscripten: Make python.sh function as proper Python CLI #127503

[freakboy3742]

I thinks this change makes sense; however, in trying to test it, I've hit an issue.

I don't think the problem is related to this change specifically; I can't tell if it's related to #127506, or if I've done something to my EMSDK config. I suspect it's manifesting now because I had to do a complete rebuild of both the host and build Python, whereas during my testing of #127506 I had a pre-existing build, and I was only testing the script updates.

The problem manifests as an error during python Tools/wasm/emscripten make-host. I had to remove the --jobs flag to get an error that made any sense; when I do, I get:

...
_PYTHON_HOSTRUNNER='node' _PYTHON_PROJECT_BASE=/Users/rkm/projects/python/cpython/cross-build/wasm32-emscripten _PYTHON_HOST_PLATFORM=emscripten-wasm32 PYTHONPATH=../../Lib _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata__emscripten_wasm32-emscripten _PYTHON_SYSCONFIGDATA_PATH= /Users/rkm/projects/python/cpython/cross-build/build/python.exe -S -m sysconfig --generate-posix-vars ;\
        if test $? -ne 0 ; then \
                echo "generate-posix-vars failed" ; \
                rm -f ./pybuilddir.txt ; \
                exit 1 ; \
        fi
Written build/lib.emscripten-wasm32-3.14/_sysconfigdata__emscripten_wasm32-emscripten.py
Written build/lib.emscripten-wasm32-3.14/_sysconfig_vars__emscripten_wasm32-emscripten.json
_PYTHON_HOSTRUNNER='node' _PYTHON_PROJECT_BASE=/Users/rkm/projects/python/cpython/cross-build/wasm32-emscripten _PYTHON_HOST_PLATFORM=emscripten-wasm32 PYTHONPATH=../../Lib _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata__emscripten_wasm32-emscripten _PYTHON_SYSCONFIGDATA_PATH=/Users/rkm/projects/python/cpython/cross-build/wasm32-emscripten/build/lib.emscripten-wasm32-3.14 /Users/rkm/projects/python/cpython/cross-build/build/python.exe -c 'import sys ; from sysconfig import get_platform ; print("%s-%d.%d" % (get_platform(), *sys.version_info[:2]))' >platform
/Users/rkm/projects/emsdk/upstream/emscripten/emcc  -fno-strict-overflow -Wsign-compare -Wunreachable-code -DNDEBUG -g -O3 -Wall -DPY_CALL_TRAMPOLINE -sUSE_BZIP2   -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I../../Include/internal -I../../Include/internal/mimalloc -IObjects -IInclude -IPython -I. -I../../Include   -fPIC -fPIC -c ../../Modules/_testimportmultiple.c -o Modules/_testimportmultiple.o
/Users/rkm/projects/emsdk/upstream/emscripten/emcc -shared -sSIDE_MODULE=1   -sALLOW_MEMORY_GROWTH -sINITIAL_MEMORY=20971520 -sWASM_BIGINT -sFORCE_FILESYSTEM -lidbfs.js -lnodefs.js -lproxyfs.js -lworkerfs.js -sEXPORTED_RUNTIME_METHODS=FS,callMain,ENV -sEXPORTED_FUNCTIONS=_main,_Py_Version -sSTACK_SIZE=5MB -sEXIT_RUNTIME   Modules/_testimportmultiple.o   -o Modules/_testimportmultiple.cpython-314-wasm32-emscripten.so
emcc: warning: EXPORTED_FUNCTIONS is not valid with LINKABLE set (normally due to SIDE_MODULE=1/MAIN_MODULE=1) since all functions are exported this mode.  To export only a subset use SIDE_MODULE=2/MAIN_MODULE=2 [-Wunused-command-line-argument]
emcc: error: undefined exported symbol: "_Py_Version" [-Wundefined] [-Werror]
make: *** [Modules/_testimportmultiple.cpython-314-wasm32-emscripten.so] Error 1
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/Users/rkm/projects/python/cpython/Tools/wasm/emscripten/__main__.py", line 357, in <module>
    main()
  File "/Users/rkm/projects/python/cpython/Tools/wasm/emscripten/__main__.py", line 353, in main
    dispatch[context.subcommand](context)
  File "/Users/rkm/projects/python/cpython/Tools/wasm/emscripten/__main__.py", line 83, in wrapper
    return func(context, working_dir)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/rkm/projects/python/cpython/Tools/wasm/emscripten/__main__.py", line 252, in make_emscripten_python
    call(
  File "/Users/rkm/projects/python/cpython/Tools/wasm/emscripten/__main__.py", line 110, in call
    subprocess.check_call(command, **kwargs, stdout=stdout, stderr=stderr)
  File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/subprocess.py", line 413, in check_call
    raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['make', 'all']' returned non-zero exit status 2.

Any ideas where that could be coming from? It looks like it's a misconfiguration of the -sEXPORTED_FUNCTIONS setting... but that's not a recent change, AFAICT

[hoodmane]

I think the problem was introduced in the web_example PR here:
https://github.com/python/cpython/pull/127113/files#diff-49473dca262eeab3b4a43002adb08b4db31020d190caaad1594b47f1d5daa810R2336

The issue is that -sEXPORTED_FUNCTIONS (and the majority of the other Emscripten-specific settings) should only be added when linking python.mjs not when linking the various shared libraries. Here it's failing to link _testimportmultiple.so because it doesn't define a symbol called Py_Version. I think the solution is to put those flags into LINKFORSHARED and not LDFLAGS_NODIST. (The variable names in configure.ac can be a bit hard to understand.)

[hoodmane]

Opened #127666 with a fix.

[freakboy3742]

👍 With the fix from #127666, I can now confirm this works as expected.