AAPT2 Macros are compile-time resources definitions that are expanded
when referenced during the link phase.
A macro must be defined in the res/values.xml directory. A macro
definition for a macro named "foo" looks like the following:
<macro name="foo">contents</macro>
When "@macro/foo" is used in the res/values directory or in a compiled
XML file, the contents of the macro replace the macro reference and
then the substituted contents are compiled and linked. If the macro
contents reference xml namespaces from its original definition, the
namespaces of the original macro definition will be used to determine
which package is being referenced.
Macros can be used anywhere resources can be referenced using the
@package:type/entry syntax.
Macros are not included in the final resource table or the R.java since
they are not actual resources.
Bug: 175616308
Test: aapt2_tests
Change-Id: I48b29ab6564357b32b4b4e32bff7ef06036382bc
For future macro support, aapt2 must be able to convert Reference
values into other Value types. Currently a DescendingValueVisitor is
used to visit all of the References in a ResourceTable or a compiled
XML file to set their resource ids during the link phase. This was fine
since we were only mutating the resource id of the visited Reference.
A macro may reference a String, BinaryPrimitive, or any other Item
type. During the link phase, we will need to transform references to
macros into the values of the macros.
The only parameter in the methods of the ValueVisitor interface is a
raw pointer to the type being visited. The visitor interface does not
support reassigning the visited type to a different type.
ValueTransformer is a new interface for consuming a Value type and
transforming it into a compatible Value type. This change refactors
Value::Clone to use this interface.
Bug: 175616308
Test: aapt2_tests
Change-Id: Ic1b9d718b932c208764114cd9c74d880e189ccb0
