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, 12 insertions, 0 deletions

diff --git a/classes/typecheck.bbclass b/classes/typecheck.bbclass
new file mode 100644
index 0000000000..646cd4eed2
--- /dev/null
+++ b/classes/typecheck.bbclass
@@ -0,0 +1,12 @@
+# Check types of bitbake configuration variables
+#
+# See oe.types for details.
+
+python check_types() {
+    import oe.types
+    if isinstance(e, bb.event.ConfigParsed):
+        for key in e.data.keys():
+            if e.data.getVarFlag(key, "type"):
+                oe.types.value(key, e.data)
+}
+addhandler check_types