[VOL-5285] - JJB Upgrade toward v5

makefiles/include.mk
--------------------
  o Define new lib var sandbox-root= pointing at the build directory.
  o Added a comment section at the bottom to document declared vars.

makefiles/virtualenv/requirements-txt.mk
----------------------------------------
  o Rework pip -r requirements.txt logic to be dependency driven.
  o pip install will be run when requirements.txt is modified.

makefiles/virtualenv/include.mk
-------------------------------
  o Populate venv-abs-path= with sandbox-root= to insulate against
    $(PWD) path changes.
  o Split logic into separate makefiles so include.mk remains small.
  o Rework dependencies to leverage the new requirements-txt.mk logic.

Misc
----
  o Rework help help-* targets to not display everything, all the time.
  o make help      : display venv (primary target).
  o make venv-help : display exteneded help, venv targets and flags.

[HOWTO: test]
  % git clone onf-make
  % cd onf-make
  % touch requirements.txt

  % make help | grep venv
  % make venv-help

  % make venv
  % make venv-requirements

  % touch requirements.txt
  % make venv-requirements

Change-Id: I9e12bc45c73a0e2bc90b1fd11c87ccffc7ebe57a
diff --git a/makefiles/virtualenv/virtualenv.mk b/makefiles/virtualenv/virtualenv.mk
new file mode 100644
index 0000000..0667f68
--- /dev/null
+++ b/makefiles/virtualenv/virtualenv.mk
@@ -0,0 +1,138 @@
+# -*- makefile -*-
+## -----------------------------------------------------------------------
+# Copyright 2017-2024 Open Networking Foundation (ONF) and the ONF Contributors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# -----------------------------------------------------------------------
+# https://gerrit.opencord.org/plugins/gitiles/onf-make
+# ONF.makefile.version = 1.2
+# -----------------------------------------------------------------------
+
+$(if $(DEBUG),$(warning ENTER))
+
+##-------------------##
+##---]  GLOBALS  [---##
+##-------------------##
+.PHONY: venv
+
+##------------------##
+##---]  LOCALS  [---##
+##------------------##
+venv-name             ?= .venv#                            # default install directory
+venv-abs-path         := $(PWD)/$(venv-name)
+venv-activate-bin     := $(venv-name)/bin
+venv-activate-script  := $(venv-activate-bin)/activate#    # dependency
+
+# Intent: activate= is a macro for accessing the virtualenv activation script#
+#  Usage: $(activate) && python
+activate             ?= set +u && source $(venv-activate-script) && set -u
+
+venv-version      : venv-requirements
+venv-requirements : venv-install
+venv-install      : $(venv-activate-script)
+
+## -----------------------------------------------------------------------
+## Intent: Activate script path dependency
+## Usage:
+##    o place on the right side of colon as a target dependency
+##    o When the script does not exist install the virtual env and display.
+## -----------------------------------------------------------------------
+$(venv-activate-script) :
+
+	$(call banner-enter,(virtualenv -p python))
+	virtualenv -p python3 $(venv-name)
+	$(activate) && python -m pip install --upgrade pip
+	$(activate) && pip install --upgrade setuptools
+
+	@$(MAKE) --no-print-directory venv-requirements venv-version
+	$(call banner-leave,(virtualenv -t python))
+
+## ----------------------------------------------------------------------
+## Intent: pip install with dependencies
+## ----------------------------------------------------------------------
+# venv-requirements-txt    := .venv/makedep/requirements.txt.ts
+# venv-requirements        : $(venv-requirements-txt)
+# venv-install             : $(venv-activate-script)
+# venv-requirements        : venv-install
+
+$(venv-requirements-txt) : requirements.txt
+
+	$(activate) && python -m pip install -r requirements.txt
+	@mkdir -p $(dir $@)
+	@touch $@
+
+## ----------------------------------------------------------------------
+## ----------------------------------------------------------------------
+venv-version :
+	$(activate) && python --version
+
+## -----------------------------------------------------------------------
+## Intent: Activate script path dependency
+## Usage:
+##    o place on the right side of colon as a target dependency
+##    o When the script does not exist install the virtual env and display.
+## ----------------------------------------------------------------------
+$(venv-activate-script)-orig :
+	@echo
+	@echo "============================="
+	@echo "Installing python virtual env"
+	@echo "============================="
+	virtualenv -p python3 $(venv-name)
+	$(activate) && python -m pip install --upgrade pip
+	$(activate) && pip install --upgrade setuptools
+	$(activate) && [[ -r requirements.txt ]] \
+	    && { python -m pip install -r requirements.txt; } \
+	    || { /bin/true; }
+
+	$(activate) && python --version
+
+## -----------------------------------------------------------------------
+## Intent: Explicit named installer target w/o dependencies.
+##         Makefile targets should depend on venv-activate-script.
+## -----------------------------------------------------------------------
+venv-activate-patched := $(venv-activate-script).patched
+venv-activate-patched : $(venv-activate-patched)
+$(venv-activate-patched) : $(venv-activate-script)
+	$(call banner-enter,Target $@)
+	$(onf-mk-top)/../patches/python_310_migration.sh --venv "$(venv-name)" 'apply'
+	touch $@
+	$(call banner-leave,Target $@)
+
+## -----------------------------------------------------------------------
+## Intent: Explicit named installer target w/o dependencies.
+##         Makefile targets should depend on venv-activate-script.
+## -----------------------------------------------------------------------
+venv += $(venv-activate-script)
+venv += $(venv-requirements-txt)
+venv: $(venv)
+
+## -----------------------------------------------------------------------
+## Intent: Revert installation to a clean checkout
+## -----------------------------------------------------------------------
+sterile :: clean
+	$(RM) -r "$(venv-abs-path)"
+
+## -----------------------------------------------------------------------
+## -----------------------------------------------------------------------
+help ::
+	@echo
+	@echo '[VIRTUAL ENV]'
+	@echo '  venv                Create a python virtual environment'
+	@echo '    venv-name=        Subdir name for virtualenv install'
+	@echo '  venv-activate-script         make macro name'
+	@echo '      $$(target) dependency    install python virtualenv'
+	@echo '      source $$(macro) && cmd  configure env and run cmd'
+
+$(if $(DEBUG),$(warning LEAVE))
+
+# [EOF]