Implement variable typing (sync from OE)

This implementation consists of two components:

- Type creation python modules, 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.data
    for pkg in oe.data.typed_value("PACKAGES", d):
        bb.note("package: %s" % pkg)
}

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

python () {
    import oe.data
    assert(oe.data.typed_value("LIBTOOL_HAS_SYSROOT", d) == True)
}

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

1 files changed, 13 insertions, 0 deletions

diff --git a/meta/lib/oe/data.py b/meta/lib/oe/data.py
new file mode 100644
index 0000000000..8b7c3cd789
--- /dev/null
+++ b/meta/lib/oe/data.py
@@ -0,0 +1,13 @@
+import oe.maketype
+import bb.msg
+
+def typed_value(key, d):
+    """Construct a value for the specified metadata variable, using its flags
+    to determine the type and parameters for construction."""
+    var_type = d.getVarFlag(key, 'type')
+    flags = d.getVarFlags(key)
+
+    try:
+        return oe.maketype.create(d.getVar(key, True) or '', var_type, **flags)
+    except (TypeError, ValueError), exc:
+        bb.msg.fatal(bb.msg.domain.Data, "%s: %s" % (key, str(exc)))