Explicit build-time features by orlitzky · Pull Request #41550 · sagemath/sage

orlitzky · 2026-01-28T20:20:07Z

Implement Option 3 from #41067.

Add a new meson option defer_feature_checks that defaults to false in meson, and true in the sage distro (for backwards compatibility). Record its value in sage/config.py.
For all of the existing features in meson.options, define variables in sage/config.py stating whether or not they were enabled in the build.
Add a new sage.features.build_feature.BuildFeature class to handle the processing.
Subclass the new BuildFeature in the sage features for things in meson.options.
Add missing features for eclib, mwrank, and rankwidth.
Don't spam build-only features in the output from sage -t.

All permutations of the options should work, but for an example using the meson build, meson setup -Dauto_features=disabled ... will disable everything at build-time, and not check for it again at run-time. You should be able to see the values foo_enabled = 0 in sage/config.py. The feature objects (BuildFeature subclasses) will consult these variables to determine if the feature is enabled.

An example of a feature that can be detected at runtime is the mwrank executable. In the current scenario, its BuildFeature checks sage.config.eclib_enabled, so even if eclib is installed, the mwank executable will not be used. However, if you rebuild with meson setup -Ddefer_feature_checks=true ..., then mwrank will be detected at run-time.

The other features can also be detected at run-time, but they are linked to various python modules at build time. To test the runtime detection, one option is to uninstall the library that the feature uses (say, sirocco). This will cause the import test of sage.libs.sirocco to fail at runtime, leading to the feature being disabled. Reinstall sirocco and the feature should re-enable itself.

Relevant docs:

github-actions · 2026-01-28T21:36:05Z

Documentation preview for this PR (built with commit bead86a; changes) is ready! 🎉
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orlitzky · 2026-01-30T20:25:08Z

The distro CI is hosed, but I think this works now and there are no major problems with the docs. Please play around and let me know your thoughts. The implementation was straightforward so far, but I haven't tried to convert any other runtime features yet, only the ones with existing meson options/checks.

antonio-rojas · 2026-01-30T23:11:26Z

I would expect defer_feature_checks=true to keep the current status quo, that is, runtime detection of all optional features, including linked ones. Otherwise this is an important regression for my packaging use case: I build all optional features and then users can optionally enable or disable them at runtime.

antonio-rojas · 2026-01-30T23:14:36Z

This doesn't look right:

sage: from sage.features.mwrank import Mwrank
sage: Mwrank().is_present()
---------------------------------------------------------------------------
RecursionError                            Traceback (most recent call last)
Cell In[2], line 1
----> 1 Mwrank().is_present()

File /usr/lib/python3.14/site-packages/sage/features/__init__.py:211, in Feature.is_present(self)
    208 # We do not use @cached_method here because we wish to use
    209 # Feature early in the build system of sagelib.
    210 if self._cache_is_present is None:
--> 211     res = self._is_present()
    212     if not isinstance(res, FeatureTestResult):
    213         res = FeatureTestResult(self, res)

File /usr/lib/python3.14/site-packages/sage/features/build_feature.py:130, in BuildFeature._is_present(self)
    108 r"""
    109 Default presence check for build features.
    110 
   (...)    127 
    128 """
    129 if self.is_runtime_detectable():
--> 130     return self.is_present_at_runtime()
    131 else:
    132     import sage.config

File /usr/lib/python3.14/site-packages/sage/features/mwrank.py:39, in Mwrank.is_present_at_runtime(self)
     38 def is_present_at_runtime(self):
---> 39     return Executable.is_present(self)

File /usr/lib/python3.14/site-packages/sage/features/__init__.py:211, in Feature.is_present(self)
    208 # We do not use @cached_method here because we wish to use
    209 # Feature early in the build system of sagelib.
    210 if self._cache_is_present is None:
--> 211     res = self._is_present()
    212     if not isinstance(res, FeatureTestResult):
    213         res = FeatureTestResult(self, res)

File /usr/lib/python3.14/site-packages/sage/features/build_feature.py:130, in BuildFeature._is_present(self)
    108 r"""
    109 Default presence check for build features.
    110 
   (...)    127 
    128 """
    129 if self.is_runtime_detectable():
--> 130     return self.is_present_at_runtime()
    131 else:
    132     import sage.config

File /usr/lib/python3.14/site-packages/sage/features/mwrank.py:39, in Mwrank.is_present_at_runtime(self)
     38 def is_present_at_runtime(self):
---> 39     return Executable.is_present(self)

    [... skipping similar frames: Feature.is_present at line 211 (991 times), BuildFeature._is_present at line 130 (990 times), Mwrank.is_present_at_runtime at line 39 (990 times)]

File /usr/lib/python3.14/site-packages/sage/features/build_feature.py:130, in BuildFeature._is_present(self)
    108 r"""
    109 Default presence check for build features.
    110 
   (...)    127 
    128 """
    129 if self.is_runtime_detectable():
--> 130     return self.is_present_at_runtime()
    131 else:
    132     import sage.config

File /usr/lib/python3.14/site-packages/sage/features/mwrank.py:39, in Mwrank.is_present_at_runtime(self)
     38 def is_present_at_runtime(self):
---> 39     return Executable.is_present(self)

File /usr/lib/python3.14/site-packages/sage/features/__init__.py:211, in Feature.is_present(self)
    208 # We do not use @cached_method here because we wish to use
    209 # Feature early in the build system of sagelib.
    210 if self._cache_is_present is None:
--> 211     res = self._is_present()
    212     if not isinstance(res, FeatureTestResult):
    213         res = FeatureTestResult(self, res)

File /usr/lib/python3.14/site-packages/sage/features/build_feature.py:129, in BuildFeature._is_present(self)
    107 def _is_present(self):
    108     r"""
    109     Default presence check for build features.
    110 
   (...)    127 
    128     """
--> 129     if self.is_runtime_detectable():
    130         return self.is_present_at_runtime()
    131     else:

RecursionError: maximum recursion depth exceeded

orlitzky · 2026-01-31T00:10:02Z

I would expect defer_feature_checks=true to keep the current status quo, that is, runtime detection of all optional features, including linked ones. Otherwise this is an important regression for my packaging use case: I build all optional features and then users can optionally enable or disable them at runtime.

No problem, I didn't realize anyone was doing this yet. How is it implemented, are you packaging the optional python modules (like sage.libs.sirocco) separately? If so I'll put back the python module check as is_present_at_runtime() and that should be enough.

This doesn't look right:

Ugh, no, I'll take a look. I have a feeling that this was caused by changing from . import Executable to from sage.features import Executable, which should be a no-op, but was needed to fix a heisenbug metaclass TypeError in pytest.

antonio-rojas · 2026-01-31T08:59:50Z

I would expect defer_feature_checks=true to keep the current status quo, that is, runtime detection of all optional features, including linked ones. Otherwise this is an important regression for my packaging use case: I build all optional features and then users can optionally enable or disable them at runtime.

No problem, I didn't realize anyone was doing this yet. How is it implemented, are you packaging the optional python modules (like sage.libs.sirocco) separately? If so I'll put back the python module check as is_present_at_runtime() and that should be enough.

For now I'm shipping everything together (and the features are enabled by installing the corresponding libraries), but I may move to split packages soon as our tooling is moving towards automatic detection of link libraries at packaging time. Since sage Features check for the modules loadability (as opposed to their presence), this works fine either way (currently).

orlitzky · 2026-01-31T14:54:28Z

Ok, runtime detection probably works. Tested with the ones I happen to have installed (bliss, brial, eclib, rankwidth).

orlitzky · 2026-01-31T14:55:52Z

(And the Mrwank bug is fixed.)

src/sage/features/coxeter3.py

antonio-rojas · 2026-01-31T19:30:48Z

Thanks. Besides the coxeter issue, everything works fine here with defer_feature_checks=true (as in, same as before)

orlitzky · 2026-01-31T21:55:27Z

On 2026-01-31 11:31:11, Antonio Rojas wrote: antonio-rojas left a comment (sagemath/sage#41550) Thanks. Besides the coxeter issue, everything works fine here with `defer_feature_checks=true` (as in, same as before)

Coxeter should be fixed now too, thanks a lot for testing.

The meson build system is now capable of building sagelib without linking to libec, which means that the mwrank program may not be installed. Here we add a new feature to represent it. In particular this allows us to use "needs mwrank" in tests.

The meson build system is now capable of building sagelib without sage.libs.eclib. Here we add a new feature to represent it. In particular this allows us to use "needs sage.libs.eclib" in tests.

When a feature is not runtime-detectable, don't include it in the list of features to be detected. This keeps the list, $ sage -t src ... Features to be detected: 32_bit,4ti2,benzene,buckygen, ... ... Features detected for doctesting: database_ellcurves, ... free of misleading information and clutter.

If the feature for sage.libs.foo is enabled, we shouldn't skip over files that fail to collect with an ImportError for sage.libs.foo.

When sage.libs.eclib doesn't exist, pytest will still try to collect *.py files that import it, leading to an ImportError. We add eclib to the list of feature-backed modules with workarounds for this issue.

For backwards compatibility, defer all possible build-time feature checks to run-time. (For now this only affects the detection of the mwrank program.)

A trick is needed to dynamically add a method to an object.

Call Executable._is_present() instead of Executable.is_present() to avoid infinite recursion. Somehow this worked before I replaced the relative import of Executable with an absolute one.

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

The module name that we check for in this case is the same as the feature name, so we can subclass the feature from PythonModule and use PythonModule's _is_present() in is_present_at_runtime().

To detect coxeter3 at runtime, we should check for a module that won't be present when coxeter3 support is disabled. This feature now checks for a conditionally-compiled cython module beneath sage.libs.coxeter3, rather than for sage.libs.coxeter3 itself.

Add the "needs rankwidth" tags for the doctests in this module, all of which need rankwidth. At first a one-line magic sage.doctest header appears to make more sense, but pytest does not understand these and needs workarounds (see conftest.py). Given the small number of tests in this module, individual annotations seem like less of a hassle.

github-actions bot added the s: needs review label Jan 28, 2026

orlitzky marked this pull request as draft January 28, 2026 20:20

github-actions bot removed the s: needs review label Jan 28, 2026

orlitzky mentioned this pull request Jan 28, 2026

New feature for eclib/mwrank #41042

Closed

orlitzky force-pushed the build-time-features branch 2 times, most recently from 2b669f7 to d045aee Compare January 29, 2026 14:23

orlitzky mentioned this pull request Jan 29, 2026

Add "needs" tags for eclib and mwrank #40546

Draft

orlitzky force-pushed the build-time-features branch from d045aee to 5b776af Compare January 29, 2026 17:46

orlitzky added the c: build label Jan 29, 2026

orlitzky force-pushed the build-time-features branch 3 times, most recently from cc97f87 to fba22ba Compare January 30, 2026 20:19

orlitzky marked this pull request as ready for review January 30, 2026 20:20

github-actions bot added the s: needs review label Jan 30, 2026

orlitzky requested review from antonio-rojas, dimpase, kiwifb, tobiasdiez and tornaria January 30, 2026 20:21

antonio-rojas suggested changes Jan 31, 2026

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src/sage/features/coxeter3.py Outdated Show resolved Hide resolved

orlitzky added 29 commits February 20, 2026 08:12

src/sage/features/coxeter3.py: convert to a BuildFeature

0608eeb

src/sage/features/mcqd.py: convert to a BuildFeature

e62d5c6

src/sage/features/meataxe.py: convert to a BuildFeature

bf38da2

src/sage/features/sirocco.py: convert to a BuildFeature

25f3844

src/sage/features/tdlib.py: convert to a BuildFeature

580453c

src/sage/features/rankwidth.py: new BuildFeature

260a586

src/sage/features/sagemath.py: new feature for sage.libs.eclib

a2e3826

The meson build system is now capable of building sagelib without sage.libs.eclib. Here we add a new feature to represent it. In particular this allows us to use "needs sage.libs.eclib" in tests.

src/doc/en/reference/spkg/index.rst: add sage.features.mwrank

6c56185

src/doc/en/reference/spkg/index.rst: add sage.features.build_feature

b6d3eea

src/doc/en/reference/spkg/index.rst: add sage.features.rankwidth

a5aed67

conftest.py: only ignore ImportErrors for disabled features

576e2a6

If the feature for sage.libs.foo is enabled, we shouldn't skip over files that fail to collect with an ImportError for sage.libs.foo.

conftest.py: ignore ImportErrors for sage.libs.eclib if disabled

0e8efbe

When sage.libs.eclib doesn't exist, pytest will still try to collect *.py files that import it, leading to an ImportError. We add eclib to the list of feature-backed modules with workarounds for this issue.

build/pkgs/sagelib: defer feature checks to runtime

afe3b43

For backwards compatibility, defer all possible build-time feature checks to run-time. (For now this only affects the detection of the mwrank program.)

src/sage/features/build_feature.py: fix is_present() doctest

ca6bc31

A trick is needed to dynamically add a method to an object.

src/sage/features/mwrank.py: fix is_present_at_runtime()

3752036

Call Executable._is_present() instead of Executable.is_present() to avoid infinite recursion. Somehow this worked before I replaced the relative import of Executable with an absolute one.

src/sage/features/sagemath.py: make eclib runtime-detectable

86d20c3

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/sirocco.py: make sirocco runtime-detectable

1bb60a8

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/mcqd.py: make mcqd runtime-detectable

c9a099e

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/meataxe.py: make meataxe runtime-detectable

1d22a0d

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/bliss.py: make bliss runtime-detectable

9eb9e06

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/tdlib.py: make tdlib runtime-detectable

cc2da29

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/coxeter3.py: make coxeter3 runtime-detectable

86bb563

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/rankwidth.py: make rankwidth runtime-detectable

24d5e0e

The result of _is_present() is cached and we want to check for a module with a different name than that of the feature, so we create a new PythonModule on the fly for this.

src/sage/features/sagemath.py: make brial runtime-detectable

2f1486d

The module name that we check for in this case is the same as the feature name, so we can subclass the feature from PythonModule and use PythonModule's _is_present() in is_present_at_runtime().

src/sage/features/bliss.py: don't import PythonModule twice

927a70f

orlitzky force-pushed the build-time-features branch from a947492 to bead86a Compare February 20, 2026 13:12

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Explicit build-time features#41550

Explicit build-time features#41550
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