scipy: Developer installation fails with poetry

I followed the instructions from this guide Building from source for SciPy development and everything worked well including the actual build via:

python dev.py build

Note that I did NOT install the doc and typing/linting dependencies, as I only need the latest main branch to work inside a python environment for some testing regarding #14740 . This is the terminal output directly after the build, which for me looks good:

[1606/1606] Linking target scipy/optimize/_highs/_highs_wrapper.cpython-310-x86_64-linux-gnu.so
Build OK
💻  meson install -C build --only-changed
Installing, see meson-install.log...
Installation OK

To get an interpreter with the latest SciPy source, I tried

python dev.py ipython

and also

python dev.py python

but both fail with

 ...
  File "/home/xxx/scipy/dev.py", line 536, in install_project                                                              
    raise RuntimeError("Can't install in non-empty directory: "                                                            
RuntimeError: Can't install in non-empty directory: '/home/xxx/scipy/build-install' 

I was so bold and deleted the build-install directory, repeating python dev.py ipython then gives:

 ...
  File "/home/xxx/scipy/dev.py", line 1161, in run                                                                         
    import IPython                                                                                                         
ModuleNotFoundError: No module named 'IPython'  

however python dev.py python then actually spawns an interpreter, but then I get

>>> import scipy                                                                                                           
Traceback (most recent call last):                                                                                         
  File "/home/xxx/scipy/__init__.py", line 51, in <module>                                                                 
    from scipy.__config__ import show as show_config                                                                       
ModuleNotFoundError: No module named 'scipy.__config__'                                                                    
                                                                                                                           
The above exception was the direct cause of the following exception:                                                       
                                                                                                                           
Traceback (most recent call last):                                                                                         
  File "<console>", line 1, in <module>                                                                                    
  File "/home/xxx/scipy/__init__.py", line 56, in <module>                                                                 
    raise ImportError(msg) from e                                                                                          
ImportError: Error importing SciPy: you cannot import SciPy while                                                          
    being in scipy source directory; please exit the SciPy source                                                          
    tree first and relaunch your Python interpreter.

So here I am stuck, as executing

python -c "import scipy; print(scipy.__version__)"

outside the source directory gives me the correct 1.11.4, but(this was due to an pre-installed binary of the latest scipy release)

python -c "import scipy.signal; scipy.signal.ShortTimeFFT"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: module 'scipy.signal' has no attribute 'ShortTimeFFT'

which should be there as it was merged with PR #17408 and I can also see it here

EDIT: So the problem is: build works, but installing ipython and getting an import scipy to work fails

@lucascolley advised to fire up a git clean -xdf, then repeating python dev.py ipython lead to the exact same error as above (ModuleNotFoundError: No module named 'IPython').

My system:

• OS: Ubuntu 22.04
• virtual env.: poetry