Build isolation

[sr-murthy]

Can someone please explain the exact difference in behaviour of pdm build between using the --no-isolation option, and leaving it out? I've tried to build wheels in my project (using PDM 2.9.2) in a pre-existing Python 3.9.6 virtual env. (created using virtualenv) using both options and the behaviour seems to be the same. Confusingly, the CLI output seems to indicate it is trying to create an isolated build env. in both cases:

$ pdm build -v --no-sdist -d build
Building wheel...
pdm.termui: Preparing isolated env for PEP 517 build...
...

and

$ pdm build -v --no-isolation --no-sdist -d build
Building wheel...
pdm.termui: Preparing isolated env for PEP 517 build...
...

Is this simply a CLI output inconsistency, or is something else going on behind the scenes?

[frostming]

Is this simply a CLI output inconsistency

That's the case

[sr-murthy]

@frostming OK, but with --no-isolation, which I assume means it does the build in the current virtual env., which already has the build backend dependencies:importlib-metadata, pdm-backend, zipp etc., I see that it is trying to install these:

...
pdm.termui: Installing importlib-metadata@6.8.0...
...
pdm.termui: Installing pdm-backend@2.1.6...
...
pdm.termui: Installing zipp@3.17.0...
...

If they already exist in the current virtual env., and we are using --no-isolation, why does it need to install them again?

[sr-murthy]

I think these build backend dependencies existed in the virtual env. prior to running the command above:

(venv) $ pdm show pdm-backend
Name:                  pdm-backend                                                           
Latest version:        2.1.6
...

(venv) $ pdm show importlib-metadata
Name:                  importlib-metadata                          
Latest version:        6.8.0
...

(venv) $ pdm show zipp
Name:                  zipp                                                       
Latest version:        3.17.0
...

I'm just trying to understand the actual difference in build environments and behaviour with and without --no-isolation.

[frostming]

I think these build backend dependencies existed in the virtual env.

It can't be proven by the information given. pdm show will show the PyPI version if not installed. The package is installed only if Installed version exists in the output

[sr-murthy]

I'll update here after retesting this is a new virtual env.