ast/BBHandler: Add inherit_defer support

Add support for an inherit_defer statement which works as
inherit does but is only evaulated at the end of parsing.

This allows conditional expressions to be evaulated 'late' meaning changes
to PACKAGECONFIG from bbappends can be applied for example. This addresses
a usability/confusion issue users have with the current conditional
inherit mechanism since they don't realise the condition has to be
expanded immediately with the current model.

There is a commented out warning we could enable in future which
warns about the use of a conditional inherit that isn't deferred.

There is a behaviour difference in the placement of the inherit,
particularly around variables set using ?= which means wen swapping
from one to the other, caution must be used as values can change.

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

2 files changed, 31 insertions, 1 deletions

diff --git a/lib/bb/parse/ast.py b/lib/bb/parse/ast.py
index d30b68896..7581d003f 100644
--- a/lib/bb/parse/ast.py
+++ b/lib/bb/parse/ast.py
@@ -314,6 +314,16 @@ class InheritNode(AstNode):
     def eval(self, data):
         bb.parse.BBHandler.inherit(self.classes, self.filename, self.lineno, data)
 
+class InheritDeferredNode(AstNode):
+    def __init__(self, filename, lineno, classes):
+        AstNode.__init__(self, filename, lineno)
+        self.inherit = (classes, filename, lineno)
+
+    def eval(self, data):
+        inherits = data.getVar('__BBDEFINHERITS', False) or []
+        inherits.append(self.inherit)
+        data.setVar('__BBDEFINHERITS', inherits)
+
 def handleInclude(statements, filename, lineno, m, force):
     statements.append(IncludeNode(filename, lineno, m.group(1), force))
 
@@ -364,6 +374,10 @@ def handleInherit(statements, filename, lineno, m):
     classes = m.group(1)
     statements.append(InheritNode(filename, lineno, classes))
 
+def handleInheritDeferred(statements, filename, lineno, m):
+    classes = m.group(1)
+    statements.append(InheritDeferredNode(filename, lineno, classes))
+
 def runAnonFuncs(d):
     code = []
     for funcname in d.getVar("__BBANONFUNCS", False) or []:
@@ -430,6 +444,14 @@ def multi_finalize(fn, d):
         logger.debug("Appending .bbappend file %s to %s", append, fn)
         bb.parse.BBHandler.handle(append, d, True)
 
+    while True:
+        inherits = d.getVar('__BBDEFINHERITS', False) or []
+        if not inherits:
+            break
+        inherit, filename, lineno = inherits.pop(0)
+        d.setVar('__BBDEFINHERITS', inherits)
+        bb.parse.BBHandler.inherit(inherit, filename, lineno, d, deferred=True)
+
     onlyfinalise = d.getVar("__ONLYFINALISE", False)
 
     safe_d = d
diff --git a/lib/bb/parse/parse_py/BBHandler.py b/lib/bb/parse/parse_py/BBHandler.py
index 4d5b45e1e..cd1c998f8 100644
--- a/lib/bb/parse/parse_py/BBHandler.py
+++ b/lib/bb/parse/parse_py/BBHandler.py
@@ -21,6 +21,7 @@ from .ConfHandler import include, init
 
 __func_start_regexp__    = re.compile(r"(((?P<py>python(?=(\s|\()))|(?P<fr>fakeroot(?=\s)))\s*)*(?P<func>[\w\.\-\+\{\}\$:]+)?\s*\(\s*\)\s*{$" )
 __inherit_regexp__       = re.compile(r"inherit\s+(.+)" )
+__inherit_def_regexp__   = re.compile(r"inherit_defer\s+(.+)" )
 __export_func_regexp__   = re.compile(r"EXPORT_FUNCTIONS\s+(.+)" )
 __addtask_regexp__       = re.compile(r"addtask\s+(?P<func>\w+)\s*((before\s*(?P<before>((.*(?=after))|(.*))))|(after\s*(?P<after>((.*(?=before))|(.*)))))*")
 __deltask_regexp__       = re.compile(r"deltask\s+(.+)")
@@ -40,8 +41,10 @@ def supports(fn, d):
     """Return True if fn has a supported extension"""
     return os.path.splitext(fn)[-1] in [".bb", ".bbclass", ".inc"]
 
-def inherit(files, fn, lineno, d):
+def inherit(files, fn, lineno, d, deferred=False):
     __inherit_cache = d.getVar('__inherit_cache', False) or []
+    #if "${" in files and not deferred:
+    #    bb.warn("%s:%s has non deferred conditional inherit" % (fn, lineno))
     files = d.expand(files).split()
     for file in files:
         classtype = d.getVar("__bbclasstype", False)
@@ -265,6 +268,11 @@ def feeder(lineno, s, fn, root, statements, eof=False):
         ast.handleInherit(statements, fn, lineno, m)
         return
 
+    m = __inherit_def_regexp__.match(s)
+    if m:
+        ast.handleInheritDeferred(statements, fn, lineno, m)
+        return
+
     return ConfHandler.feeder(lineno, s, fn, statements, conffile=False)
 
 # Add us to the handlers list