Implement variable typing

This implementation consists of two components:

- oe.types python module, whose job it is to construct objects of the defined
  type for a given variable in the metadata
- typecheck.bbclass, which iterates over all configuration variables with a
  type defined and uses oe.types to check the validity of the values

This gives us a few benefits:

- Automatic sanity checking of all configuration variables with a defined type
- Avoid duplicating the "how do I make use of the value of this variable"
  logic between its users.  For variables like PATH, this is simply a split(),
  for boolean variables, the duplication can result in confusing, or even
  mismatched semantics (is this 0/1, empty/nonempty, what?)
- Make it easier to create a configuration UI, as the type information could
  be used to provide a better interface than a text edit box (e.g checkbox for
  'boolean', dropdown for 'choice')

This functionality is entirely opt-in right now.  To enable the configuration
variable type checking, simply INHERIT += "typecheck".  Example of a failing
type check:

BAZ = "foo"
BAZ[type] = "boolean"

$ bitbake -p
FATAL: BAZ: Invalid boolean value 'foo'
$

Examples of leveraging oe.types in a python snippet:

PACKAGES[type] = "list"

python () {
    import oe.types
    for pkg in oe.types.value("PACKAGES", d):
        bb.note("package: %s" % pkg)
}

LIBTOOL_HAS_SYSROOT = "yes"
LIBTOOL_HAS_SYSROOT[type] = "boolean"

python () {
    import oe.types
    assert(oe.types.value("LIBTOOL_HAS_SYSROOT", d) == True)
}

Signed-off-by: Chris Larson <chris_larson@mentor.com>

1 files changed, 97 insertions, 0 deletions

diff --git a/lib/oe/types.py b/lib/oe/types.py
new file mode 100644
index 0000000000..963e964212
--- /dev/null
+++ b/lib/oe/types.py
@@ -0,0 +1,97 @@
+# Constructs objects of the specified type for a given variable in the
+# metadata.  The 'type' flag of the variable defines which of the factory
+# functions in this module will be called.
+#
+# If no type is defined, the value() function will simply return the expanded
+# string value as is.
+
+import bb
+import inspect
+import _types
+
+types = {}
+
+class MissingFlag(TypeError):
+    def __init__(self, flag, type):
+        self.flag = flag
+        self.type = type
+        TypeError.__init__(self)
+
+    def __str__(self):
+        return "Type '%s' requires flag '%s'" % (self.type, self.flag)
+
+def factory(var_type):
+    try:
+        return types[var_type]
+    except KeyError:
+        raise TypeError("Invalid type '%s'" % var_type)
+
+def create(value, var_type, **flags):
+    obj = factory(var_type)
+    objflags = {}
+    for flag in obj.flags:
+        if flag not in flags:
+            if flag not in obj.optflags:
+                raise MissingFlag(flag, var_type)
+        else:
+            objflags[flag] = flags[flag]
+
+    return obj(value, **objflags)
+
+def value(key, d):
+    """Construct a value for a metadata variable, based upon its flags"""
+
+    var_type = d.getVarFlag(key, 'type')
+    flags = d.getVarFlags(key)
+
+    try:
+        return create(d.getVar(key, True) or '', var_type, **flags)
+    except (TypeError, ValueError), exc:
+        bb.fatal("%s: %s" % (key, str(exc)))
+
+def get_callable_args(obj):
+    """Grab all but the first argument of the specified callable, returning
+    the list, as well as a list of which of the arguments have default
+    values."""
+    if type(obj) is type:
+        obj = obj.__init__
+
+    args, varargs, keywords, defaults = inspect.getargspec(obj)
+    flaglist = []
+    if args:
+        if len(args) > 1 and args[0] == 'self':
+            args = args[1:]
+        flaglist.extend(args)
+
+    optional = set()
+    if defaults:
+        optional |= set(flaglist[-len(defaults):])
+    return flaglist, optional
+
+def factory_setup(name, obj):
+    """Prepare a factory for use by oe.types"""
+    args, optional = get_callable_args(obj)
+    extra_args = args[1:]
+    if extra_args:
+        obj.flags, optional = extra_args, optional
+        obj.optflags = set(optional)
+    else:
+        obj.flags = obj.optflags = ()
+
+    if not hasattr(obj, 'name'):
+        obj.name = name
+
+def register(name, factory):
+    factory_setup(name, factory)
+    types[factory.name] = factory
+
+# Set the 'flags' and 'optflags' attributes of all our types
+for name in dir(_types):
+    if name.startswith('_'):
+        continue
+
+    obj = getattr(_types, name)
+    if not callable(obj):
+        continue
+
+    register(name, obj)