bitbake: build/data: Don't expand python functions before execution [API change]

Right now, if you have some python code like:

X = "a"

def somefunction(d):
    d.setVar("X", "b")
    d.setVar("Y", "${X}")

then any sane person would expect that Y = "b" at the end of the
function. This is not the case, Y = "a".

This is due to the python function being expanded before execution, the
executed code would read d.setVar("Y", "a"). This understandably
confuses people, it also makes it near impossible to write ${} in a
python function without unintended things happening.

I think there is general agreement we should fix this and standardise
on non-expansion of python functions. We already don't expand anonymous
python (mostly).

I've checked OE-Core with buildhistory before and after this change and
there were a small number of issues this exposed which I've sent
patches for.

I propose we default to not expanding python code and then deal with
any consequences from that if/as/where identified. This will improve
new user understanding and usability of the system, it also allows
several long standing weird expansion issues to be fixed.

(Bitbake rev: 8bf33a8e92c0e188fa392030025756196c96fcbb)

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

bitbake/lib/bb/data.py

@@ -298,7 +298,7 @@ def emit_func_python(func, o=sys.__stdout__, d = init()):
     """Emits all items in the data store in a format such that it can be sourced by a shell."""
 
     def write_func(func, o, call = False):
-        body = d.getVar(func, True)
+        body = d.getVar(func, False)
         if not body.startswith("def"):
             body = _functionfmt.format(function=func, body=body)
 
@@ -308,7 +308,7 @@ def emit_func_python(func, o=sys.__stdout__, d = init()):
 
     write_func(func, o, True)
     pp = bb.codeparser.PythonParser(func, logger)
-    pp.parse_python(d.getVar(func, True))
+    pp.parse_python(d.getVar(func, False))
     newdeps = pp.execs
     newdeps |= set((d.getVarFlag(func, "vardeps", True) or "").split())
     seen = set()
@@ -320,7 +320,7 @@ def emit_func_python(func, o=sys.__stdout__, d = init()):
             if d.getVarFlag(dep, "func", False) and d.getVarFlag(dep, "python", False):
                write_func(dep, o)
                pp = bb.codeparser.PythonParser(dep, logger)
-               pp.parse_python(d.getVar(dep, True))
+               pp.parse_python(d.getVar(dep, False))
                newdeps |= pp.execs
                newdeps |= set((d.getVarFlag(dep, "vardeps", True) or "").split())
         newdeps -= seen