cooker: Ensure bbappend files are processed in a determistic order

self.appendlist is a dict and as such unordered. This can lead to cases
where appends with different names (e.g. x_%.bbappend vs. x_123.bbappend)
can be reordered in application which in turn reorders the variables
that those bbappend files might touch. Reorderd variables changes the sstate
cache signatures causing real world issues.

To avoid this, use a list for the append files instead.

This patch is conservative and just adds a new data structure alongside
the existing one and uses it to resolve the core issue. Later patches
(post release) can handle some of the wider but less problematic ones
(e.g. issues in bitbake-layers flatten).

[YOCTO #7511]

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

lib/bb/cooker.py

@@ -1573,6 +1573,7 @@ def __init__(self):
 class CookerCollectFiles(object):
     def __init__(self, priorities):
         self.appendlist = {}
+        self.bbappends = []
         self.appliedappendlist = []
         self.bbfile_config_priorities = priorities
 
@@ -1667,6 +1668,7 @@ def collect_bbfiles(self, config, eventdata):
         # Build a list of .bbappend files for each .bb file
         for f in bbappend:
             base = os.path.basename(f).replace('.bbappend', '.bb')
+            self.bbappends.append((base, f))
             if not base in self.appendlist:
                self.appendlist[base] = []
             if f not in self.appendlist[base]:
@@ -1692,11 +1694,11 @@ def get_file_appends(self, fn):
         """
         filelist = []
         f = os.path.basename(fn)
-        for bbappend in self.appendlist:
+        for b in self.bbappends:
+            (bbappend, filename) = b
             if (bbappend == f) or ('%' in bbappend and bbappend.startswith(f[:bbappend.index('%')])):
                 self.appliedappendlist.append(bbappend)
-                for filename in self.appendlist[bbappend]:
-                    filelist.append(filename)
+                filelist.append(filename)
         return filelist
 
     def collection_priorities(self, pkgfns, d):
@@ -1716,10 +1718,10 @@ def collection_priorities(self, pkgfns, d):
                 unmatched.add(regex)
 
         def findmatch(regex):
-            for bbfile in self.appendlist:
-                for append in self.appendlist[bbfile]:
-                    if regex.match(append):
-                        return True
+            for b in self.bbappends:
+                (bbfile, append) = b
+                if regex.match(append):
+                    return True
             return False
 
         for unmatch in unmatched.copy():