Add Wasm32 as target for cross compiling

[kjartanm]

This PR adds Wasm32 as target for cross compiling, Emscripten setup, and fences off some Emscripten-incompatible elements.

See Feature request pyodide/pyodide#1670

[akutruff]

What's blocking WASM support right now? Is this dead?

[Mizux]

mostly lack of human ressource (i.e. lack of time) to work on it + fear of the technical debt increase to maintain it.

BTW I'm not against it, on the contrary I'd love to have an ortools-lite running on the edge on client side web browser...

[akutruff]

Wish I could help on the build errors - Seems like there's some simple permissions error somewhere?

[chadbrewbaker]

I have an immediate need for this. What is the blocker?

This is how Z3 does it, they provide not just a WASM build but also a JS interface. I agree this should be effectively an or-tools-lite in the default build, you should have to pass some extra flag to build a really fat binary.

Minimal viable commit is defining a JSON for an or-tools graph format and having it pass some unit tests?

[Mizux]

My 2 cents,

We have a job to test emscripten build
https://github.com/google/or-tools/actions/workflows/amd64_web.yml
src: https://github.com/google/or-tools/blob/stable/.github/workflows/amd64_web.yml

using:
make --directory=cmake web_build
src:

or-tools/cmake/Makefile

Lines 660 to 698 in ef7bb07

	#########
	## WEB ##
	#########
	WEB_STAGES := env devel build test
	define make-web-stage-target =
	#$$(info STAGE: $1)
	#$$(info Create target: web_$1.)
	.PHONY: web_$1
	web_$1: docker/web/Dockerfile
	#@docker image rm -f ${IMAGE}:web_$1 2>/dev/null
	${DOCKER_BUILD_CMD} --target=$1 --tag ${IMAGE}:web_$1 -f $$< ..
	#$$(info Create target: save_web_$1 (debug).)
	.PHONY: save_web_$1
	save_web_$1: cache/web/docker_$1.tar
	cache/web/docker_$1.tar: web_$1
	@rm -f $$@
	mkdir -p cache/web
	docker save ${IMAGE}:web_$1 -o $$@
	#$$(info Create target: sh_web_$1 (debug).)
	.PHONY: sh_web_$1
	sh_web_$1: web_$1
	${DOCKER_RUN_CMD} -it --name ${IMAGE}_web_$1 ${IMAGE}:web_$1
	#$$(info Create target: clean_web_$1.)
	.PHONY: clean_web_$1
	clean_web_$1:
	docker image rm -f ${IMAGE}:web_$1 2>/dev/null
	rm -f cache/web/docker_$1.tar
	endef
	$(foreach stage,$(WEB_STAGES),$(eval $(call make-web-stage-target,$(stage))))
	## MERGE ##
	.PHONY: clean_web
	clean_web: $(addprefix clean_web_, $(WEB_STAGES))
	rm -f cache/web

Dockerfile: https://github.com/google/or-tools/blob/stable/cmake/docker/web/Dockerfile
cmake config:

or-tools/cmake/docker/web/Dockerfile

Lines 18 to 25 in ef7bb07

	RUN emcmake cmake -S. -Bbuild \
	-DCMAKE_BUILD_TYPE=Release -DBUILD_DEPS=ON \
	-DBUILD_EXAMPLES=OFF \
	-DUSE_COINOR=OFF \
	-DUSE_GLPK=OFF \
	-DUSE_HIGHS=OFF \
	-DUSE_PDLP=OFF \
	-DUSE_SCIP=OFF

Need to compare/test with this PR...

[Mizux]

Last Tag as of 2024 June 07
https://github.com/emscripten-core/emsdk/releases/tag/3.1.61

[airen1986]

Hi Mizux,
Is it planned for next release or will it take time? Also, is this command work with stable branch:
emcmake cmake -S . -B build -DBUILD_DEPS=ON -DBUILD_PYTHON=ON

I tried after making changes in cross_compile.sh and I am getting error as:
Could NOT find Python3 (missing: Python3_INCLUDE_DIRS Python3_LIBRARIES Development Development.Module Development.Embed) (found version "3.11.9")

However, I don't see such error when using just cmake?

[Mizux]

Sorry, I don't get it, what did you try to do/expect ?

BUILD_PYTHON is used to generate automatically python wrapper on top of the C++ library to have access to ortools in python (which is just a wrapper on top of the native library, since we won't reimplement ortools in pure Python/Java nor .Net).

On the other side, AFAIK, emcmake is used to transpile C++ code into wasm byte code to have a "browser compatible" source code so there is no point to try to build a python wrapper on top of this wasm library.

[agriyakhetarpal]

Hi there, I recently pointed @airen1986 to this issue from https://github.com/pyodide/pyodide/issues/5013. If configured correctly, Pyodide would allow runtime for a Python interface for this WASM library through an Emscripten-compiled Python extension module.

[Mizux]

ok, I guess I understand what you want to do:
0. This is not something we support

1. currently our wrapper is generated by swig which is currently use to build 64bit code -> don't know how it work with WASM32 ptr size etc...
2. IIRC emcmake is working by injecting a CMake cross toolchain thus my bet is the Toolchainfile do not provide a python thus the issue.
3. I would suggest to play with my pet project: https://github.com/Mizux/python-native which should have the same cmake stuff than or-tools so once you have something work there it should be easier to patch/fixup or-tools and dev iteration should be faster IMHO...

sorry this comment is little bit dry, will try to reformulate if you want...

[Mizux]

note for myself, emscripten generate wasm32 by default
ref: https://emscripten.org/docs/tools_reference/settings_reference.html#memory64