Refactor: Implement bash completion for stbt config in Python

The current bash implementation calls `stbt config` so we may as well do
all the work there.  This removes the need for `__system_config` to be in
`stbt.conf`.

stbt-completion

@@ -279,25 +279,7 @@ _stbt_control_recorder_file() {
 }
 
 _stbt_config_keys() {
-    _stbt_config_file_contents |
-    grep -v ^__system_config |
-    perl -lne '
-        $section = $1 if /^\s*\[([a-zA-Z0-9_]+)\]\s*$/;
-        print "$section.$1" if /^\s*([a-zA-Z0-9_]+)\s*=/;'
-}
-
-_stbt_config_file_contents() {
-    [ -n "$in_unit_test" ] && { cat; return; }
-
-    local defaults=$(
-        awk '/stbt-"\$@"/ { print $NF }' "$(which stbt)" |
-        xargs dirname
-        )/stbt.conf
-    local system_config=$(stbt config global.__system_config)
-    local user_config="${XDG_CONFIG_HOME:-$HOME/.config}/stbt/stbt.conf"
-    for f in "$defaults" "$system_config" "$user_config" "$STBT_CONFIG_FILE"; do
-        [ -r "$f" ] && cat "$f"
-    done
+    stbt config --bash-completion ""
 }
 
 _stbt_power_outlet_uri() {

stbt-config

@@ -9,7 +9,7 @@ https://github.com/stb-tester/stb-tester/blob/master/LICENSE for details).
 import argparse
 import sys
 
-from _stbt.config import ConfigurationError, get_config
+from _stbt.config import _config_init, ConfigurationError, get_config
 
 
 def error(s):
@@ -23,11 +23,20 @@ parser.description = """Prints the value of the specified key from the stbt
     configuration file. See 'configuration' in the stbt(1) man page."""
 parser.epilog = \
     "Returns non-zero exit status if the specified key or section isn't found."
+parser.add_argument(
+    "--bash-completion", action="store_true", help=argparse.SUPPRESS)
 parser.add_argument(
     "name", metavar="section.key",
     help="e.g. 'global.source_pipeline' or 'record.control_recorder'")
 args = parser.parse_args(sys.argv[1:])
 
+if args.bash_completion:
+    cfg = _config_init()
+    for section in cfg.sections():
+        for option in cfg.options(section):
+            print "%s.%s" % (section, option)
+    sys.exit(0)
+
 if args.name.rfind(".") == -1:
     error(
         "'name' parameter must contain the section and key separated by a dot")

tests/completion-test.conf

@@ -0,0 +1,8 @@
+[global]
+key1 = hi there
+key2=hi there
+key3 = hi there
+key4	= hi there
+
+[run]
+key5 = hi there

tests/test-stbt-completion.sh

@@ -128,23 +128,11 @@ test_completion_filenames() {
     fail "unexpected completions for files + directories"
 }
 
-completion_config_for_tests() {
-    cat <<-EOF
-	[global]
-	key1 = hi there
-	key2=hi there
-	  key3 = hi there
-	  	key4	= hi there
-	  	[run]
-	key5 = hi there
-	EOF
-}
-
 test_completion_config_keys() {
     cd "$srcdir" && . stbt-completion
-    diff \
-        <(completion_config_for_tests | in_unit_test=yes _stbt_config_keys) \
-        <(printf '%s\n' \
-            global.key1 global.key2 global.key3 global.key4 run.key5) ||
+    diff -u \
+        <(printf '%s\n' global.key1 global.key2 global.key3 global.key4 run.key5) \
+        <(STBT_CONFIG_FILE="tests/completion-test.conf" _stbt_config_keys | grep 'key[0-9]') \
+         ||
     fail "_stbt_config_keys unexpected output"
 }