Crashes with Julia 1.12 and Revise.jl

I have been using PyPlot (with PyCall) with Revise.jl quite well in the past years, but after the upgrade to Julia 1.12 I see now constant crashes. I've tried to debug these, but they happen quite randomly. I was about to point the issue as happening only in IJulia kernels, when I started seeing them in Julia REPL as well.

These crashes can happen whenever, and are not related to calling "plot" functions.

I have tried reinstalling PyCall and PyPlot with ENV["PYTHON"] = "" (today) and verified the installation happens with a clean Conda.jl environment.

Here is an example of simple commands that trigger the crash:

```
$ julia
_
_ _ _(_)_ | Documentation: https://docs.julialang.org
(_) | (_) (_) |
_ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 1.12.3 (2025-12-15)
_/ |\__'_|_|_|\__'_| | Official https://julialang.org release
|__/ |

julia> using Base.Threads

julia> threadpool()
:interactive

julia> nthreads()
1

julia> Threads.nthreads(:default)
1

julia> using Revise

julia> using PyPlot

[857707] signal 11 (1): Segmentation fault
in expression starting at REPL[6]:1
_PyInterpreterState_GET at /usr/local/src/conda/python-3.12.12/Include/internal/pycore_pystate.h:133 [inlined]
notify_code_watchers at /usr/local/src/conda/python-3.12.12/Objects/codeobject.c:32
code_dealloc at /usr/local/src/conda/python-3.12.12/Objects/codeobject.c:1705
pydecref_ at /home/mazza/.julia/packages/PyCall/1gn3u/src/PyCall.jl:118 [inlined]
pydecref at /home/mazza/.julia/packages/PyCall/1gn3u/src/PyCall.jl:123
jfptr_pydecref_8808 at /home/mazza/.julia/compiled/v1.12/PyCall/GkzkC_o0cEr.so (unknown line)
run_finalizer at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/gc-common.c:180
jl_gc_run_finalizers_in_list at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/gc-common.c:270
run_finalizers at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/gc-common.c:316
ijl_gc_collect at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/gc-stock.c:3483
maybe_collect at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/gc-stock.c:349 [inlined]
ijl_gc_managed_malloc at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/gc-stock.c:3811
jl_alloc_genericmemory_unchecked at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/genericmemory.c:38
_new_genericmemory_ at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/genericmemory.c:68 [inlined]
jl_alloc_genericmemory at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/genericmemory.c:101
ijl_array_grow_end at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/array.c:222
_append_symbol_to_bindings_array at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/module.c:1958 [inlined]
append_module_names at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/module.c:1980
ijl_module_names at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/module.c:2001
#unsorted_names#4 at ./runtime_internals.jl:119 [inlined]
unsorted_names at ./runtime_internals.jl:119 [inlined]
#names#3 at ./runtime_internals.jl:118 [inlined]
names at ./runtime_internals.jl:118 [inlined]
_subtypes_in! at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/usr/share/julia/stdlib/v1.12/InteractiveUtils/src/InteractiveUtils.jl:266
subtypes at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/usr/share/julia/stdlib/v1.12/InteractiveUtils/src/InteractiveUtils.jl:303 [inlined]
_foreach_subtype! at /home/mazza/.julia/packages/Revise/icvyF/src/visit.jl:43
_foreach_subtype! at /home/mazza/.julia/packages/Revise/icvyF/src/visit.jl:49
_foreach_subtype! at /home/mazza/.julia/packages/Revise/icvyF/src/visit.jl:49
foreach_subtype at /home/mazza/.julia/packages/Revise/icvyF/src/visit.jl:38 [inlined]
#__init__##2 at /home/mazza/.julia/packages/Revise/icvyF/src/packagedef.jl:1658
unknown function (ip: 0x7f711c6a894f) at (unknown file)
jl_apply at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/julia.h:2391 [inlined]
start_task at /cache/build/tester-amdci4-9/julialang/julia-release-1-dot-12/src/task.c:1249
Allocations: 5202189 (Pool: 5202112; Big: 77); GC: 7
Segmentation fault (core dumped)
```

Start by reproducing the Julia REPL sequence with Revise and PyPlot shown in the issue. Read Revise's src/visit.jl and src/packagedef.jl, then PyCall's src/PyCall.jl around pydecref and compare them with the reported Julia 1.12 and Python stack frames. Done means the reproducible segmentation fault is isolated and no longer occurs in the demonstrated setup.

Scritto dal modello di indicizzazione a partire dal testo della issue.