Proposal: root spec import mode to replace legacy importing and importmode

doc/en/proposals/importmode_root_spec.rst

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+:orphan:
+
+===================================
+PROPOSAL: Parametrize with fixtures
+===================================
+
+.. warning::
+
+    This document outlines a proposal around creating a new import mode that supports pep420 and
+    supports the dissonance between installed and editable installed
+
+
+Problem
+=======
+
+test module discovery in pytest currently is is pre-pep40 and create pains for users
+by adding anything things to sys.path and creating easy conflicts in sys.modules
+
+Additionally this will not solve the dissonance between doctest tests vs installed modules
+
+The importlib mode in contrast breaks all kinds of expectations by importing test modules in a magical way
+that breaks relative imports and leaves them out of ``sys.modules``
+
+
+Proposed Solution
+=================
+
+A new import mode take a definition of import roots.
+
+a import root is either a folder in the worktree that will no be installed,
+or a folder that will be installed either normally or editable.
+
+In any case pytest will collect the file tree in the working directory.
+
+If normal install us used and the content of the imported file differs from the working directory,
+pytest will fail collection with a "ContentMissmatch" error.
+
+When import roots are specified, nothing will be added to sys.path
+instead installable content will rely in installs, and local content will create namespace packages that limit the path of subitems
+
+everything else will be discovered using normal imports
+
+
+
+
+.. code-block::
+
+  # contents of pytest.ini
+  [pytest]
+  import-roots =
+    testing/ local
+    src/mypkg installed as mypkg
+    # alterntively
+    src/ installed
+
+## todo testcases
+
+* handle install vs editable install
+
+    * when installed - imported name will differe from name in soruce tree
+      fail collection when content differs
+      (optional strictly check all files/missing files)
+    * when installed editable - import using the right name
+
+   * when not installed:
+
+* testing folders
+  * if no __init__.py -> create fake namespace, use it for importing
+  * if __init__.py -> create normal package, dont change sys.path
+
+* ensure each folder gets a collection package