Kavon Farvardin
b7d57f3bcd
Ordinary base protocols use fixed-indexing to access the base index. That means adding another base protocol to an existing protocol can break the order of the entries, and thus clients, because we otherwise order the base entires with TypeDecl::compare. Reparentable protocols are meant to be resilient to that, so we order them at the end of the base entries list, just before the other resilient entries in the witness table. This patch completes the picture, by having the reparentable protocol entries be indexed resiliently, in the same manner as associated conformances. The difference is that we can skip the call to `swift_getAssociatedConformanceWitness` and compute the index directly by finding the distance of the descriptors, because we know all base protocol witness table entries are eagarly instantiated. Using this distance protects us from the ordering problems of entries among all of the reparentable base protocols. resolves rdar://173409851
Resilient Library Evolution Tests
This directory tests for the correctness of resilience, which is a
broad term for Swift maximizing binary compatibility of a dependency
while maintaining the freedom to do things that would normally break
clients in other languages, such as changing the layout of nominal
types. The detailed explanation of resilience is out of scope of this
little readme and can be found in docs/LibraryEvolution.rst.
Each main test file should compile against "before" and "after" versions of the corresponding library file. The old and new versions are selected via the BEFORE or AFTER preprocessor variables.
In the library, going from BEFORE to AFTER must be an ABI-compatible change, as documented in the library evolution specification.
In the main program, going from BEFORE to AFTER does not have to be backward compatible.
In the main file, use your test library's getVersion helper function
to know which version of the library to expect at runtime.
There are four valid combinations for each test:
- Main file compiled against old library, linked against old library a.k.a. "before before"
- Main file compiled against old library, linked against new library, a.k.a. "before after"
- Main file compiled against new library, linked against old library, a.k.a. "after before"
- Main file compiled against new library, linked against new library, a.k.a. "after after"
The version of the library available at compile time determines which serialized declarations and transparent function bodies are visible.
When adding a new test, see the boilerplate at the top of each file for
the general pattern for this kind of test. Use the StdlibUnittest
library for assertions.