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gh-90539: doc: Expand on what should not go into CFLAGS, LDFLAGS #92754

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gh-90539: doc: Expand on what should not go into CFLAGS, LDFLAGS #92754

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Doc/using/configure.rst: Expand on what should not go into CFLAGS, LD…
mkoeppe May 12, 2022
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📜🤖 Added by blurb_it.
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Doc/using/configure.rst: Fix rst markup
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Doc/using/configure.rst: Fixup: LDFLAGS, not CFLAGS
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Doc/using/configure.rst: Break a long sentence
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Doc/using/configure.rst: Break another long sentence
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18 changes: 18 additions & 0 deletions Doc/using/configure.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -747,6 +747,17 @@ Compiler flags
extensions. Use it when a compiler flag should *not* be part of the
distutils :envvar:`CFLAGS` once Python is installed (:issue:`21121`).

In particular, :envvar:`CFLAGS` should not contain:

* the compiler flag `-I` (for setting the search path for include files).
The `-I` flags are processed from left to right, and any flags in
:envvar:`CFLAGS` would take precedence over user- and package-supplied `-I`
flags.
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* hardening flags such as `-Werror` because distributions cannot control
whether packages installed by users conform to such heightened
standards.

.. versionadded:: 3.5

.. envvar:: EXTRA_CFLAGS
Expand Down Expand Up @@ -859,6 +870,13 @@ Linker flags
:envvar:`CFLAGS_NODIST`. Use it when a linker flag should *not* be part of
the distutils :envvar:`LDFLAGS` once Python is installed (:issue:`35257`).

In particular, :envvar:`LDFLAGS` should not contain:

* the compiler flag `-L` (for setting the search path for libraries).
The `-L` flags are processed from left to right, and any flags in
:envvar:`LDFLAGS` would take precedence over user- and package-supplied `-L`
flags.
Comment on lines +873 to +878
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@native-api native-api Jun 13, 2022 •
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In pyenv/pyenv#2381, we found out that at least one -L flag from LDFLAGS was required when linking against Python to find libintl. We even had to add it to python-config --ldflags via a hack since python-config ignores compile-time LDFLAGS for some reason.

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Do you think we should add guidance here for downstream packagers that informs them of other, more suitable ways to set flags -- namely setting environment variables CFLAGS, LDFLAGS, CPATH, LIBRARY_PATH at the runtime of Python?

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setting environment variables CFLAGS, LDFLAGS, CPATH, LIBRARY_PATH at the runtime of Python?

I'm not sure how you expect downstream packagers to do that -- and why they need to do that in the first place since distutils and python-config specifically exist to take care of providing all the necessary flags to link against a specific Python installation.

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Aren't the pyenv shims already setting environment variables? Specifically, they are setting PATH. https://trac.sagemath.org/ticket/29285#comment:20

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I'm not sure how you expect downstream packagers to do that

conda and nix use activation scripts for their environments. homebrew provides brew sh for this purpose.

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If we set the flags in an envvar, they would likely still override package-supplied flags (skimmed through distutils sources, it looks like that). If so, that won't help your original problem.

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That may be true for CFLAGS, but definitely not for CPATH. By the way, https://github.com/pypa/setuptools/blob/main/docs/userguide/ext_modules.rst now has some info (from my PR pypa/setuptools#3368); we can expand it to cover all necessary details to resolve this discussion.

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This is now pypa/setuptools#3387


.. envvar:: CONFIGURE_LDFLAGS_NODIST

Value of :envvar:`LDFLAGS_NODIST` variable passed to the ``./configure``
Expand Down