wic: allow bitbake variables in kickstarter files

image_types_wic.bbclass has a mechanism for doing variable substitution
on .wks files by simply letting the input file be called
.wks.in. However, that doesn't allow using variables in files included
via the include directive. This is unfortunate, because lacking either
the ability to include other files or variable substitution leads to
fragile and error-prone duplication between kickstarter files and
recipes/configuration files used for various boards.

This adds (somewhat naive) support for variable substitution in all
files parsed by wic. The user should add all required variables to
WICVARS to get them exported appropriately.

(From OE-Core rev: 8a75d614a8a1ff72c4af448ac3e1292d0e1d1a79)

Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/ksparser.py

@@ -28,14 +28,30 @@
 import os
 import shlex
 import logging
+import re
 
 from argparse import ArgumentParser, ArgumentError, ArgumentTypeError
 
 from wic.engine import find_canned
 from wic.partition import Partition
+from wic.misc import get_bitbake_var
 
 logger = logging.getLogger('wic')
 
+__expand_var_regexp__ = re.compile(r"\${[^{}@\n\t :]+}")
+
+def expand_line(line):
+    while True:
+        m = __expand_var_regexp__.search(line)
+        if not m:
+            return line
+        key = m.group()[2:-1]
+        val = get_bitbake_var(key)
+        if val is None:
+            logger.warning("cannot expand variable %s" % key)
+            return line
+        line = line[:m.start()] + val + line[m.end():]
+
 class KickStartError(Exception):
     """Custom exception."""
     pass
@@ -190,6 +206,7 @@ class KickStart():
                 line = line.strip()
                 lineno += 1
                 if line and line[0] != '#':
+                    line = expand_line(line)
                     try:
                         line_args = shlex.split(line)
                         parsed = parser.parse_args(line_args)