[Buildroot] [PATCH v3 1/1] package/pkg-python: migrate flit to new bootstrapping sequence

[James Hilliard]

There are a number of flit toolchain dependencies currently in the
process of deprecating distutils based fallbacks.

This will be needed in order to update tomli.

We need to migrate these to use a new bootstrap based build+install
sequence which relies on flit's bootstrap wheel build+install
features to build and install host-python-pypa-build and
host-python-installer which gives us a full pep517 toolchain.

Note that one can run host-python-flit-core commands for building
and installing itself since the package build directory is the cwd.

We need to add a special flit-bootstrap SETUP_TYPE for dependencies
of host-python-pypa-build and host-python-installer which can not
use the normal flit SETUP_TYPE which would cause a circular dependency
issue.

We need to special case dependency exclusions for
host-python-flit-core and host-python-installer to avoid circular
dependencies in the flit-bootstrap SETUP_TYPE.

We also need to special case the installation command for
host-python-flit-core since it can not depend on host-python-installer
due to host-python-installer requiring host-python-flit-core.

Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
Cc: "Yann E. MORIN" <yann.morin.1998 at free.fr>
Cc: Arnout Vandecappelle <arnout at mind.be>
---
Changes v2 -> v3:
  - add special flit-bootstrap SETUP_TYPE
  - don't change package SETUP_TYPE's yet
Changes v1 -> v2:
  - formatting/cleanup
  - add comments
---
 package/pkg-python.mk | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/package/pkg-python.mk b/package/pkg-python.mk
index 52ce402281..353bbada65 100644
--- a/package/pkg-python.mk
+++ b/package/pkg-python.mk
@@ -154,6 +154,9 @@ HOST_PKG_PYTHON_PEP517_INSTALL_OPTS = \
 	--scripts=$(HOST_DIR)/usr/bin \
 	--data=$(HOST_DIR)/usr
 
+HOST_PKG_PYTHON_PEP517_BOOTSTRAP_INSTALL_OPTS = \
+	--installdir=$(HOST_DIR)/lib/python$(PYTHON3_VERSION_MAJOR)/site-packages
+
 ################################################################################
 # inner-python-package -- defines how the configuration, compilation
 # and installation of a Python package should be done, implements a
@@ -203,7 +206,7 @@ $(2)_BASE_ENV = $$(HOST_PKG_PYTHON_SETUPTOOLS_ENV)
 $(2)_BASE_BUILD_CMD = setup.py build
 $(2)_BASE_INSTALL_CMD = setup.py install $$(HOST_PKG_PYTHON_SETUPTOOLS_INSTALL_OPTS)
 endif
-else ifneq ($$(filter flit pep517,$$($(2)_SETUP_TYPE)),)
+else ifneq ($$(filter flit flit-bootstrap pep517,$$($(2)_SETUP_TYPE)),)
 ifeq ($(4),target)
 $(2)_BASE_ENV = $$(PKG_PYTHON_PEP517_ENV)
 $(2)_BASE_BUILD_CMD = -m build -n -w
@@ -211,9 +214,24 @@ $(2)_BASE_INSTALL_TARGET_CMD = $(TOPDIR)/support/scripts/pyinstaller.py dist/* $
 $(2)_BASE_INSTALL_STAGING_CMD = $(TOPDIR)/support/scripts/pyinstaller.py dist/* $$(PKG_PYTHON_PEP517_INSTALL_STAGING_OPTS)
 else
 $(2)_BASE_ENV = $$(HOST_PKG_PYTHON_PEP517_ENV)
+# Use flit built in wheel builder for packages that are flit-bootstrap packages.
+# This is needed to avoid a circular with host-python-pypa-build and those dependencies.
+#
+ifeq ($$($(2)_SETUP_TYPE),flit-bootstrap)
+$(2)_BASE_BUILD_CMD = -m flit_core.wheel
+ifeq ($(1),host-python-flit-core)
+# Use flit built in bootstrap_install for installing host-python-flit-core.
+# This is due to host-python-installer depending on host-python-flit-core.
+#
+$(2)_BASE_INSTALL_CMD = -m bootstrap_install dist/* $$(HOST_PKG_PYTHON_PEP517_BOOTSTRAP_INSTALL_OPTS)
+else
+$(2)_BASE_INSTALL_CMD = $(TOPDIR)/support/scripts/pyinstaller.py dist/* $$(HOST_PKG_PYTHON_PEP517_INSTALL_OPTS)
+endif
+else
 $(2)_BASE_BUILD_CMD = -m build -n -w
 $(2)_BASE_INSTALL_CMD = $(TOPDIR)/support/scripts/pyinstaller.py dist/* $$(HOST_PKG_PYTHON_PEP517_INSTALL_OPTS)
 endif
+endif
 else
 $$(error "Invalid $(2)_SETUP_TYPE. Valid options are 'distutils', 'setuptools', 'pep517' or 'flit'.")
 endif
@@ -239,6 +257,12 @@ $(2)_DEPENDENCIES += host-python-pypa-build host-python-installer
 ifeq ($$($(2)_SETUP_TYPE),flit)
 $(2)_DEPENDENCIES += host-python-flit-core
 endif
+else ifeq ($$($(2)_SETUP_TYPE),flit-bootstrap)
+ifneq ($$(filter host-python-flit-core host-python-installer,$(1)),)
+$(2)_DEPENDENCIES += $$(if $$(filter host-python-flit-core,$(1)),,host-python-flit-core)
+else
+$(2)_DEPENDENCIES += host-python-flit-core host-python-installer
+endif
 endif # SETUP_TYPE
 
 # Python interpreter to use for building the package.
-- 
2.25.1