Revert "devenv: Set PYTHONPATH where we install python modules"

This reverts commit 79c6075b560dbf1c3e4e0b30f1c472dc2086421e.

# Conflicts:
#	docs/markdown/snippets/devenv.md
#	mesonbuild/modules/python.py
#	test cases/unit/91 devenv/test-devenv.py

PYTHONPATH cannot be reliably determined. The standard use case for
installing python modules with Meson is mixed pure sources (at least
`__init__.py`) and compiled extension_modules or configured files.
Unfortunately that doesn't actually work because python will not load
the same package hierarchy from two different directories, one a source
directory and one a (mandatory) out of tree build directory.

(It kind of can, but you need to do what this test case accidentally
stumbled upon, which is namespace packages. Namespace packages are a
very specific use case and you are NOT SUPPOSED to use them outside that
use case, so people are not going to use them just to circumvent Meson
devenv stuff as that would have negative install-time effects.)

Adding PYTHONPATH anyway will just lead to documentation commitments
which we cannot actually uphold, and confusing issues at time of use
because some imports *will* work... and some will *not*. The end result
will be a half-created tree of modules which just doesn't work together
at all, but because it partially works, users attempting to debug it
will spend time wondering why parts of it do import.

For any case where the automatic devenv would work correctly, it will
also work correctly to use `meson.add_devenv()` a single time, which is
very easy to manually get correct and doesn't provide any significant
value to automate.

In the long run, an uninstalled python package environment will require
"editable installs" support.

2 files changed, 0 insertions, 15 deletions

diff --git a/docs/markdown/Commands.md b/docs/markdown/Commands.md
index f905d2c..b137166 100644
--- a/docs/markdown/Commands.md
+++ b/docs/markdown/Commands.md
@@ -340,15 +340,6 @@ These variables are set in environment in addition to those set using `meson.add
   schemas is compiled. This is automatically set when using `gnome.compile_schemas()`.
   Note that this requires GLib >= 2.64 when `gnome.compile_schemas()` is used in
   more than one directory.
-- `PYTHONPATH` *Since 0.62.0* includes every directory where a python module is being
-  installed using [`python.install_sources()`](Python-module.md#install_sources)
-  and [`python.extension_module()`](Python-module.md#extension_module). Python
-  modules installed by other means, such as `install_data()` or `install_subdir()`,
-  will not be included and should be added to `PYTHONPATH` manually using
-  [`meson.add_devenv()`](Reference-manual_builtin_meson.md#mesonadd_devenv).
-  Note that when modules are installed into subdirectories the source tree
-  layout must match the installed tree layout otherwise `import subdir.mod`
-  cannot work.
 
 Since *Since 0.62.0* if bash-completion scripts are being installed and the
 shell is bash, they will be automatically sourced.
diff --git a/docs/markdown/snippets/devenv.md b/docs/markdown/snippets/devenv.md
index 104cfd9..bffa5fa 100644
--- a/docs/markdown/snippets/devenv.md
+++ b/docs/markdown/snippets/devenv.md
@@ -1,9 +1,3 @@
-## `PYTHONPATH` automatically defined in `meson devenv`
-
-`PYTHONPATH` now includes every directory where a python module is being
-installed using [`python.install_sources()`](Python-module.md#install_sources)
-and [`python.extension_module()`](Python-module.md#extension_module).
-
 ## Bash completion scripts sourced in `meson devenv`
 
 If bash-completion scripts are being installed and the shell is bash, they will