[facebook#38] Clone shell_builder as system builder base

Currently the build_script 'build_openr.sh' is broken (facebook#38). Create a
debian system builder that creates a build_script from the
fbcode_builder. The shell_builder does something very similar. However,
the shell_builder doesn't install dependencies and programs to the
system, but to a temp directory.

To initialize the debian system builder, clone the shell_builder to make
changes more traceable.

build/fbcode_builder/debian_system_builder.py

@@ -0,0 +1,112 @@
+#!/usr/bin/env python
+# Copyright (c) Facebook, Inc. and its affiliates.
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+'''
+shell_builder.py allows running the fbcode_builder logic
+on the host rather than in a container.
+
+It emits a bash script with set -exo pipefail configured such that
+any failing step will cause the script to exit with failure.
+
+== How to run it? ==
+
+cd build
+python fbcode_builder/shell_builder.py > ~/run.sh
+bash ~/run.sh
+'''
+
+import os
+import distutils.spawn
+
+from fbcode_builder import FBCodeBuilder
+from shell_quoting import (
+    raw_shell, shell_comment, shell_join, ShellQuoted
+)
+from utils import recursively_flatten_list
+
+
+class ShellFBCodeBuilder(FBCodeBuilder):
+    def _render_impl(self, steps):
+        return raw_shell(shell_join('\n', recursively_flatten_list(steps)))
+
+    def workdir(self, dir):
+        return [
+            ShellQuoted('mkdir -p {d} && cd {d}').format(
+                d=dir
+            ),
+        ]
+
+    def run(self, shell_cmd):
+        return ShellQuoted('{cmd}').format(cmd=shell_cmd)
+
+    def step(self, name, actions):
+        assert '\n' not in name, 'Name {0} would span > 1 line'.format(name)
+        b = ShellQuoted('')
+        return [ShellQuoted('### {0} ###'.format(name)), b] + actions + [b]
+
+    def setup(self):
+        steps = [
+            ShellQuoted('set -exo pipefail'),
+        ]
+        if self.has_option('ccache_dir'):
+            ccache_dir = self.option('ccache_dir')
+            steps += [
+                ShellQuoted(
+                    # Set CCACHE_DIR before the `ccache` invocations below.
+                    'export CCACHE_DIR={ccache_dir} '
+                    'CC="ccache ${{CC:-gcc}}" CXX="ccache ${{CXX:-g++}}"'
+                ).format(ccache_dir=ccache_dir)
+            ]
+        return steps
+
+    def comment(self, comment):
+        return shell_comment(comment)
+
+    def copy_local_repo(self, dir, dest_name):
+        return [
+            ShellQuoted('cp -r {dir} {dest_name}').format(
+                dir=dir,
+                dest_name=dest_name
+            ),
+        ]
+
+
+def find_project_root():
+    here = os.path.dirname(os.path.realpath(__file__))
+    maybe_root = os.path.dirname(os.path.dirname(here))
+    if os.path.isdir(os.path.join(maybe_root, '.git')):
+        return maybe_root
+    raise RuntimeError(
+        "I expected shell_builder.py to be in the "
+        "build/fbcode_builder subdir of a git repo")
+
+
+def persistent_temp_dir(repo_root):
+    escaped = repo_root.replace('/', 'sZs').replace('\\', 'sZs').replace(':', '')
+    return os.path.join(os.path.expandvars("$HOME"), '.fbcode_builder-' + escaped)
+
+
+if __name__ == '__main__':
+    from utils import read_fbcode_builder_config, build_fbcode_builder_config
+    repo_root = find_project_root()
+    temp = persistent_temp_dir(repo_root)
+
+    config = read_fbcode_builder_config('fbcode_builder_config.py')
+    builder = ShellFBCodeBuilder()
+
+    builder.add_option('projects_dir', temp)
+    if distutils.spawn.find_executable('ccache'):
+        builder.add_option('ccache_dir',
+            os.environ.get('CCACHE_DIR', os.path.join(temp, '.ccache')))
+    builder.add_option('prefix', os.path.join(temp, 'installed'))
+    builder.add_option('make_parallelism', 4)
+    builder.add_option(
+        '{project}:local_repo_dir'.format(project=config['github_project']),
+        repo_root)
+    make_steps = build_fbcode_builder_config(config)
+    steps = make_steps(builder)
+    print(builder.render(steps))