[RFC,2/2] oe-setup-build: add a tool for discovering config templates and setting up builds

diff --git a/meta/lib/oeqa/selftest/cases/bblayers.py b/meta/lib/oeqa/selftest/cases/bblayers.py
index 65426a6782..73fefb5d19 100644
--- a/meta/lib/oeqa/selftest/cases/bblayers.py
+++ b/meta/lib/oeqa/selftest/cases/bblayers.py
@@ -151,12 +151,12 @@  class BitbakeLayers(OESelftestTestCase):
         self.validate_layersjson(jsonfile)
 
         # The revision-under-test may not necessarily be available on the remote server,
-        # so replace it with a revision that has a yocto-4.0 tag.
+        # so replace it with a revision that has a yocto-4.1 tag.
         import json
         with open(jsonfile) as f:
             data = json.load(f)
         for s in data['sources']:
-            data['sources'][s]['git-remote']['rev'] = '00cfdde791a0176c134f31e5a09eff725e75b905'
+            data['sources'][s]['git-remote']['rev'] = '5200799866b92259e855051112520006e1aaaac0'
         with open(jsonfile, 'w') as f:
             json.dump(data, f)
 
@@ -164,3 +164,22 @@  class BitbakeLayers(OESelftestTestCase):
         result = runCmd('{}/setup-layers --destdir {}'.format(self.testlayer_path, testcheckoutdir))
         layers_json = os.path.join(testcheckoutdir, ".oe-layers.json")
         self.assertTrue(os.path.exists(layers_json), "File {} not found in test layer checkout".format(layers_json))
+
+        # As setup-layers checkout out an old revision of poky, there is no setup-build symlink,
+        # and we need to run oe-setup-build directly from the current poky tree under test
+        oe_setup_build = os.path.join(get_bb_var('COREBASE'), 'scripts/oe-setup-build')
+        oe_setup_build_l = os.path.join(testcheckoutdir, 'setup-build')
+        os.symlink(oe_setup_build,oe_setup_build_l)
+
+        cmd = '{} list-config-templates --layerlist {}'.format(oe_setup_build_l, layers_json)
+        result = runCmd(cmd)
+        cond = "setup-build setup-build-env -c " in result.output and "conf/templates/default" in result.output
+        self.assertTrue(cond, "Incorrect output from {}: {}".format(cmd, result.output))
+
+        # rather than hardcode the build setup cmdline here, let's actually run what the tool suggests to the user
+        cmd = None
+        for l in result.output.splitlines():
+            if "setup-build setup-build-env -c " in l:
+                cmd = l + " --no-shell"
+        self.assertIsNotNone(cmd, "Could not find the command to set up a build in the output: {}".format(result.output))
+        result = runCmd(cmd)
diff --git a/scripts/oe-setup-build b/scripts/oe-setup-build
new file mode 100755
index 0000000000..4cfc002de3
--- /dev/null
+++ b/scripts/oe-setup-build
@@ -0,0 +1,77 @@ 
+#!/usr/bin/env python3
+#
+# Copyright OpenEmbedded Contributors
+#
+# SPDX-License-Identifier: MIT
+#
+
+import argparse
+import json
+import os
+import subprocess
+
+def defaultlayers():
+    return os.path.abspath(os.path.join(os.path.dirname(__file__), '.oe-layers.json'))
+
+def makebuildpath(topdir, templatelocation, template):
+    return os.path.join(topdir, "build-{}-{}".format(os.path.basename(os.path.abspath(os.path.join(templatelocation,'..','..'))), template))
+
+def print_templates(args):
+    layers_file = args.layerlist
+    verbose = args.v
+    if not os.path.exists(layers_file):
+        print("List of layers {} does not exist; were they set up using the setup-layers script?".format(layers_file))
+        return
+    layers_list = json.load(open(layers_file))["layers"]
+    print("Available build configuration templates (re-run with 'list-config-templates -v' to see their descriptions):\n")
+    for layer in layers_list:
+        template_dir = os.path.join(os.path.dirname(layers_file), layer, 'conf','templates')
+        if os.path.exists(template_dir):
+            for d in os.listdir(template_dir):
+                if not os.path.isdir(os.path.join(template_dir,d)):
+                    continue
+                print("{} setup-build-env -c {}\nwill create a build configuration in {}\n".format(__file__, os.path.join(template_dir, d), makebuildpath(os.path.dirname(defaultlayers()), template_dir, d)))
+                if verbose:
+                    if os.path.join(template_dir, d).endswith('meta-poky/conf/templates/default'):
+                        print("Description: this is the reference configuration of the poky reference distribution (choose this if you are uncertain).")
+                    elif os.path.join(template_dir, d).endswith('meta/conf/templates/default'):
+                        print("Description: this is the reference configuration of the openembedded-core layer (choose this if you are uncertain).")
+                    else:
+                        print("Description:", open(os.path.join(template_dir, d, 'conf-notes.txt')).read())
+                    print("---")
+
+def setup_build_env(args):
+    template = args.c
+    builddir = args.b
+    no_shell = args.no_shell
+    if not builddir:
+        builddir = makebuildpath(os.path.dirname(defaultlayers()), os.path.dirname(template), os.path.basename(template))
+    coredir = os.path.abspath(os.path.join(os.path.dirname(os.path.realpath(__file__)), '..'))
+    cmd = "TEMPLATECONF={} . {} {}".format(template, os.path.join(coredir, 'oe-init-build-env'), builddir)
+    if not no_shell:
+        cmd = cmd + " && {}".format(os.environ['SHELL'])
+    print("Running:", cmd)
+    subprocess.run(cmd, shell=True, executable=os.environ['SHELL'])
+
+parser = argparse.ArgumentParser(description="A script that discovers available build configuration templates and sets up a build environment based on one of them")
+subparsers = parser.add_subparsers()
+parser_list_templates = subparsers.add_parser('list-config-templates', help='List available configuration templates')
+
+parser_list_templates.add_argument("--layerlist", default=defaultlayers(), help='Where to look for available layers (as written out by setup-layers script) (default is {}).'.format(defaultlayers()))
+parser_list_templates.add_argument('-v', action='store_true',
+        help='Print a description for each available build configuration template.')
+parser_list_templates.set_defaults(func=print_templates)
+
+parser_setup_env = subparsers.add_parser('setup-build-env', help='Set up a build environment and open a shell session with it, ready to run builds.')
+parser_setup_env.add_argument('-c', metavar='template_path', required=True, help="Use a build configuration template in template_path to set up a build environment (run this script with 'list-config-templates' to see what is available)")
+parser_setup_env.add_argument('-b', metavar='build_path', help="Set up a build directory in build_path (run this script with 'list-config-templates' to see where it would be by default)")
+parser_setup_env.add_argument('--no-shell', action='store_true',
+        help='Create a build directory but do not start a shell session with the build environment from it.')
+parser_setup_env.set_defaults(func=setup_build_env)
+
+args = parser.parse_args()
+if 'func' in args:
+    args.func(args)
+else:
+    from argparse import Namespace
+    print_templates(Namespace(layerlist=defaultlayers(), v=False))
diff --git a/scripts/oe-setup-layers b/scripts/oe-setup-layers
index cbf94ddb08..97e13fc03b 100755
--- a/scripts/oe-setup-layers
+++ b/scripts/oe-setup-layers
@@ -63,6 +63,7 @@  def _write_layer_list(dest, repodirs):
 def _do_checkout(args, json):
     repos = json['sources']
     repodirs = []
+    oesetupbuild = None
     for r_name in repos:
         r_data = repos[r_name]
         repodir = os.path.abspath(os.path.join(args['destdir'], r_data['path']))
@@ -108,9 +109,18 @@  def _do_checkout(args, json):
 
             if _contains_submodules(repodir):
                 print("Repo {} contains submodules, use 'git submodule update' to ensure they are up to date".format(repodir))
+        if os.path.exists(os.path.join(repodir, 'scripts/oe-setup-build')):
+            oesetupbuild = os.path.join(repodir, 'scripts/oe-setup-build')
 
     _write_layer_list(args['destdir'], repodirs)
 
+    if oesetupbuild:
+        oesetupbuild_symlink = os.path.join(args['destdir'], 'setup-build')
+        if os.path.exists(oesetupbuild_symlink):
+            os.remove(oesetupbuild_symlink)
+        os.symlink(os.path.relpath(oesetupbuild,args['destdir']),oesetupbuild_symlink)
+        print("\nRun '{}' to list available build configuration templates and set up a build from one of them.".format(oesetupbuild_symlink))
+
 parser = argparse.ArgumentParser(description="A self contained python script that fetches all the needed layers and sets them to correct revisions using data in a json format from a separate file. The json data can be created from an active build directory with 'bitbake-layers create-layers-setup destdir' and there's a sample file and a schema in meta/files/")
 
 parser.add_argument('--force-bootstraplayer-checkout', action='store_true',