Field offset vectors are always filled out with either zero or the static layout's offset, depending on the metadata initialization strategy. This change means that the static layout's offset will only be non-zero for properties with a statically-known layout. Existing runtimes doing dynamic class layout assign class properties a zero offset if the field offset vector entry is zero and the property is zero-sized. So this effectively brings the compiler into accord with the runtime (for all newly-compiled Swift code, which will eventually be all Swift code because the current public releases of Swift 5 are not yet considered ABI-stable) and guarantees a zero value for the offset everywhere.
Since the runtime will agree with the compiler about the zero value of the offset, the compiler can continue to emit such offset variables as constant. The exception to this rule is if the class has non-fragile ObjC ancestry, in which case the ObjC runtime (which is not aware of this special rule for empty fields) will attempt to slide it along with everything else.
Fixes rdar://48031465, in which the `FixedClassMetadataBuilder` for a class with a legacy-fixed layout was writing a non-zero offset for an empty field into the field offset vector, causing the runtime to not apply the special case and thus to compute a non-zero offset, which it then attempted to copy into the global field offset variable, which the compiler had emitted as a true-constant zero.
Create a new capturing substitution for adding a rpath to a target
library. This is needed as Windows doesn't really support the concept
of a rpath. This also makes it possible to remove the parameter from
the command line on windows.
Thanks to @jrose for the hint about the substitution ordering, the new
substitution now works even inside the capture group. Replace the
remaining uses to the new macro.
The naming convention is different on Windows than on Unix-like
environments. In order to follow the convention we need to substitute
the prefix and the suffix. Take the opportunity to rename the
`target-dylib-extension` to the CMake-like variable
`target-shared-library-suffix` and introduce
`target-shared-library-prefix`. This helps linking the test suite
binaries on Windows.
Previously we were only doing this in assert builds, or if the
new Objective-C runtime metadata update hook mechanism was
available.
However, swift_checkMetadataState() gets called on the superclass
of a class, and it assumes that the metadata entry for the
superclass already exists in the singleton cache.
So even on an older runtime when there's no initialization work
to be done, we have to realize the superclass to populate the
singleton cache so that the check can succeed.
Fixes <rdar://problem/45569020>.
Instead of just making sure IRGen correctly executes the fix
(performing fully fragile layout for all classes with
resiliently-sized fields, not just those with Objective-C ancestry)
actually add a test case for the reported bug -- that Objective-C
categories on classes with resiliently-sized fields work.
