project: add NIAR_WORKING_DIRECTORY support.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## 0.1.3 (unreleased)
 
+New:
+
+* project: `NIAR_WORKING_DIRECTORY` can be used to override the origin.
+
 ## 0.1.2
 
 New:

niar/project.py

@@ -1,3 +1,4 @@
+import os
 import sys
 from pathlib import Path
 from typing import Optional
@@ -100,6 +101,9 @@ class Project:
     ]
 
     def __init_subclass__(cls):
+        if origin := os.getenv("NIAR_WORKING_DIRECTORY"):
+            cls.origin = Path(origin).absolute()
+        else:
             # We expect to be called from project-root/module/__init.py__ or similar;
             # cls.origin is project-root. Keep going up until we find pyproject.toml.
             origin = Path(sys._getframe(1).f_code.co_filename).absolute().parent
@@ -111,6 +115,8 @@ class Project:
                     assert False, "could not find pyproject.toml"
                 origin = origin.parent
 
+        os.chdir(cls.origin)
+
         extras = cls.__dict__.keys() - {"__module__", "__doc__", "origin"}
         for prop in cls.PROPS:
             prop.validate(cls)