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Expose emscripten_dir variable via config #321

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Merged
agriyakhetarpal merged 5 commits into from
Apr 3, 2026
Merged

Expose emscripten_dir variable via config #321

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2a858c9
Expose `emcc_path` variable via config
agriyakhetarpal Apr 3, 2026
e67ca5a
Add CHANGELOG entry for #321
agriyakhetarpal Apr 3, 2026
a80547d
Some changes
agriyakhetarpal Apr 3, 2026
7a5c6f2
More changes
agriyakhetarpal Apr 3, 2026
6ebfa5e
Update CHANGELOG
agriyakhetarpal Apr 3, 2026
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9 changes: 9 additions & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0

## [Unreleased]

## [0.34.1] - 2026/04/03

### Added

- `pyodide config` exposes a variable `emscripten_dir` that points to the Emscripten installation
directory in the xbuildenv (this is only available after Emscripten gets installed into the
xbuildenv via the `pyodide xbuildenv install-emscripten` command).
[#321](https://github.com/pyodide/pyodide-build/pull/321)

### Changed

- Platform name for the Pyodide wheel is now `pyemscripten` instead of `pyodide`, following the PEP 783 standard.
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13 changes: 13 additions & 0 deletions pyodide_build/config.py
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Expand Up @@ -112,6 +112,17 @@ def _load_cross_build_envs(self) -> Mapping[str, str]:
for k, v in DEFAULT_CONFIG_COMPUTED.items()
}

# Compute the Emscripten directory from pyodide_root. The emsdk directory
# is a sibling of the xbuildenv directory, both living under the versioned
# xbuildenv root (pyodide_root/../../emsdk/upstream/emscripten).
# We compute this here rather than via Makefile.envs or DEFAULT_CONFIG so
# that the path is always the resolved, versioned path – not the shared
# xbuildenv symlink, because there are some issues I have noticed with
# concurrent builds especially when being used in cibuildwheel etc.
Comment on lines +118 to +121
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@ryanking13 ryanking13 Apr 3, 2026

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Could you elaborate on this?

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@agriyakhetarpal agriyakhetarpal Apr 3, 2026

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This is because the Emscripten version was being mis-found during concurrent builds. For example, in pypa/cibuildwheel#2800, we were previously relying on the symlinks. When running the test suite in parallel, it would find Emscripten 3.1.58 when we would need 4.0.9 and cause weird failures in the tests. I kept the comment a bit vague, though, indeed. Happy to add more details if you need me to?

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@ryanking13 ryanking13 Apr 3, 2026

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I see. Makes sense, thanks!

computed_vars["emscripten_dir"] = str(
self.pyodide_root.parent.parent / "emsdk" / "upstream" / "emscripten"
)

return {
BUILD_VAR_TO_KEY[k]: v
for k, v in makefile_vars.items()
Expand Down Expand Up @@ -250,6 +261,7 @@ def _parse_makefile_envs(
"build_dependency_index_url": "BUILD_DEPENDENCY_INDEX_URL",
"default_cross_build_env_url": "DEFAULT_CROSS_BUILD_ENV_URL",
"xbuildenv_path": "PYODIDE_XBUILDENV_PATH",
"emscripten_dir": "PYODIDE_EMSCRIPTEN_DIR",
"dist_dir": "PYODIDE_DIST_DIR",
"ignored_build_requirements": "IGNORED_BUILD_REQUIREMENTS",
"use_legacy_platform": "USE_LEGACY_PLATFORM",
Expand Down Expand Up @@ -340,6 +352,7 @@ def _parse_makefile_envs(
"ldflags": "SIDE_MODULE_LDFLAGS",
"meson_cross_file": "MESON_CROSS_FILE",
"xbuildenv_path": "PYODIDE_XBUILDENV_PATH",
"emscripten_dir": "PYODIDE_EMSCRIPTEN_DIR",
"pyodide_abi_version": "PYODIDE_ABI_VERSION",
"pyodide_root": "PYODIDE_ROOT",
"dist_dir": "PYODIDE_DIST_DIR",
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17 changes: 17 additions & 0 deletions pyodide_build/tests/test_config.py
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Expand Up @@ -117,6 +117,23 @@ def test_computed_vars(self, dummy_xbuildenv, reset_env_vars, reset_cache):
assert makefile_vars[k] != v # The template should have been substituted
assert "$(" not in makefile_vars[k]

def test_emscripten_dir(self, dummy_xbuildenv, reset_env_vars, reset_cache):
xbuildenv_manager = CrossBuildEnvManager(
dummy_xbuildenv / common.xbuildenv_dirname()
)
config_manager = CrossBuildEnvConfigManager(
pyodide_root=xbuildenv_manager.pyodide_root
)

expected = str(
xbuildenv_manager.pyodide_root.parent.parent
/ "emsdk"
/ "upstream"
/ "emscripten"
)
assert config_manager.config["emscripten_dir"] == expected
assert config_manager.to_env()["PYODIDE_EMSCRIPTEN_DIR"] == expected

def test_load_config_from_env(self, dummy_xbuildenv, reset_env_vars, reset_cache):
xbuildenv_manager = CrossBuildEnvManager(
dummy_xbuildenv / common.xbuildenv_dirname()
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