The following scenario would fail compiling to C++ because we failed to
determine the return type of the conditional expression:
Test := Rectangle {
property<bool> condition;
property<color> extra_color;
color: condition ? root.extra_color : 4289374890;
}
The type of the true branch would be color and the false branch would be
a float. Since they "disagree", ty() on the expression would return
Type::Invalid. This was temporarily worked around in the C++ generator
by always returning the type of the true branch, but that's wrong.
Instead this patch changes maybe_convert_to to apply the Cast expression
to the individual branches, placing the cast only to the numberic
literal and correcting the return value of ty() on the conditional
expression.
The Image's source property used to be a string. Now it is a Resource
enum, which can either be None or an absolute file path to the image on
disk. This also replaces the internal Image type.
The compiler internally resolves the img bang expression to a resource
reference, which shall remain just an absolute path. For now the target
generator passes that through, but in the future the target generator
may choose a target specific way of embedding the data and thus
generating a different Resource type in the final code (through
compile_expression in the cpp and rust generator).
The C++ binding is a bit messy as cbindgen doesn't really support
exporting enums that can be constructed on the C++ side. So instead we
use cbindgen to merely export the type internally and only use the tag
from it then. The public API is then a custom Resource type that is
meant to be binary compatible.
