Slow re-linking of python bindings on build with no changes

[traversaro]

I noticed that somehow the latest version of blf a build with no changes always result in re-liking the python bindings:

Finished <<< ICUB [0.43s]
[ 62%] Linking CXX shared module ../../bipedal_locomotion_framework/bindings.cpython-311-x86_64-linux-gnu.so
lto-wrapper: warning: using serial compilation of 43 LTRANS jobs
lto-wrapper: note: see the '-flto' option documentation for more information
[Processing: BipedalLocomotionFramework]
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 8 bytes into a region of size 7 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 16 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 16 into destination object 'buf' of size 7
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 17 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset [1, 7] into destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 17 into destination object 'buf' of size 7
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 18 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset [2, 7] into destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 18 into destination object 'buf' of size 7
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 19 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset [3, 7] into destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 19 into destination object 'buf' of size 7
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 20 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset [4, 7] into destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 20 into destination object 'buf' of size 7
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 21 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset [5, 7] into destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 21 into destination object 'buf' of size 7
In function 'copy',
    inlined from 'for_each_codepoint' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:677:15,
    inlined from 'find_escape' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1794:21,
    inlined from 'write_escaped_string' at /home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:1886:30:
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/base.h:1213:31: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
 1213 |   while (begin != end) *out++ = static_cast<T>(*begin++);
      |                               ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h: In function 'write_escaped_string':
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 22 into destination object 'buf' of size 7
  676 |     char buf[2 * block_size - 1] = {};
      |          ^
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset [6, 7] into destination object 'buf' of size 7
/home/traversaro/gb-monorepo-demo/.pixi/envs/default/include/fmt/format.h:676:10: note: at offset 22 into destination object 'buf' of size 7
[100%] Built target pybind11_blf

At least on my machine (with WSL, so probably it has a sub-optimal filesystem performance) this step always takes ~50 seconds.

[traversaro]

The fact that re-link is slow may be related to pybind/pybind11#5223, but the fact that is happening everytime seems unrelated.