Bug#1127672: nanobind: multiple regressions with MPI

[Timo Röhling]

On Sat, 14 Feb 2026 12:26:13 +0100 Timo Röhling <roehling at debian.org> 
wrote:
> nanobind 2.11.0 introduced some internal changes which break MPI code.
> I am yet uncertain what the underlying cause is, but nanobind added 
> immutability to internal classes, which trigger certain fast paths in 
> CPython and might cause issues with MPI.

I have bisected the nanobind upstream repository and traced the i386 
unit test regression to 
https://github.com/wjakob/nanobind/commit/ac63d3a63dfec1be5c1129fa6be3ee35d5ac13ed
[Implicit nb::none() annotation for std::optional<T>-typed arguments]


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