GeezerVison is showing github.com — Emscripten buildbot: Support multiple Emscripten versions · Issue #145177 · python/cpython
Emscripten buildbot: Support multiple Emscripten versions #145177DescriptionWe want to allow different branches to use different Emscripten versions. The plan is as follows:
- Add
emscripten_version.txt file and add --emsdk-cache argument to emscripten/__main__.py. If --emsdk-cache is passed, the build script will require that the appropriate emsdk version is found in that directory.
- Backport this to 3.14.x
- Set up buildbot cache dir
- Make a PR to buildmaster config to pass the
--emsdk-cache argument
cc @freakboy3742
Linked PRs
Activityfreakboy3742 commented on Feb 25, 2026 I did some preliminary work on the buildbot in preparation for this about 6 months ago, and then got distracted by other things. Thanks for picking this up again, @hoodmane.
Agreed that this is something that needs to be addressed, as it's a blocker on us bumping the Emscripten version. I don't recall if we were going to lock the Emscripten version for the pyodide_2025_0 tag at beta 1 or RC1 - but if it's beta 1, time is obviously a factor.
The one question I've got about the design specification here is whether a separate file is the best way to handle version specification. Having it in a separate file isn't a huge problem to parse... but if it was a constant in the Emscripten build script to start with that you can access with python -m emscripten --emdsk-version, doesn't that simplify the common use cases (in that it doesn't need independent file access and parsing)?
On the subject of the build script - there are some other housekeeping items that I'd like to address:
clean should be a little more selective. It currently destroys all of cross-build; it should only be purging the parts of cross-build that are emscripten specific (so that Emscripten, iOS and Android builds can co-exist). This is admittedly a "me" problem... but it's a problem I have :-)- The
cross-build directory name should be configurable. Again, this is somewhat a "me" problem... but I currently need to have cross builds for 3.10-3.15, and they can't currently co-exist.
- We shouldn't be building dependencies (libFFI and mpdec) on every build. A similar caching strategy to the one described for EMSDK should be possible - look to this directory; if the cache has a build for the right emscripten version, use it rather than rebuilding.
- @brettcannon has been trying to move all the platform build tooling to the
Platforms folder;
These issues don't necessarily need to be handled all in one PR - and I'm happy to deal with the ones that are me problems :-) However, we do want to minimize the number of changes that are needed in the buildbot configuration, and we need to be aware how the impact of changes in the interface to building will impact on the ability of the buildbot configuration to identify which Python version is being built. hoodmane commented on Feb 25, 2026 ContributorAuthor More actions
a separate file is the best way to handle version specification. Having it in a separate file isn't a huge problem to parse... but if it was a constant in the Emscripten build script to start with that you can access with python -m emscripten --emdsk-version, doesn't that simplify the common use cases (in that it doesn't need independent file access and parsing)?
I don't think it matters that much, but sure I can switch to that approach. hoodmane commented on Feb 25, 2026 ContributorAuthor More actions hoodmane commented on Feb 25, 2026 ContributorAuthor More actions @freakboy3742 should clean only remove cross-build/wasm32-emscripten and leave alone cross-build/build for now? hoodmane commented on Feb 25, 2026 ContributorAuthor More actions
there are some other housekeeping items that I'd like to address:
I opened #145219 for items 1-3. Item 4 is tracked as #145176. brettcannon commented on Feb 25, 2026
The one question I've got about the design specification here is whether a separate file is the best way to handle version specification.
WASI does it in a separate file to make backports easier; you can just copy the file blindly as a backport if the per-Python variance is separate from the code. added a commit that references this issue on Mar 6, 2026gh-145177: Support multiple Emscripten versions for Emscripten buildb…
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