Protocol requirements may not necessarily add new entries to the witness table if
it's inherited from super protocol. This patch teaches the json dump to
include a flag indicating whether a protocol requirement requires new
witness table entry and diagnoses the change of such flag as ABI
breakages.
rdar://47657204
Rather than using the `LINK_LIBRARIES` option, use target_link_libraries
like clang does. Because these are all host tools, there is no name
mangling done for the libraries making this a no-op change.
Before this patch, we used to define tooling-specific diagnostics. With adding more
checking logics, we found this mechanism hard to extend. This patch
eliminates the home-made diagnostics model to use the one from compiler, which provides
several benefits: less boiler-templates, better integration with DiagnosticConsumer,
and easy ordering of detected issues.
[Tools] Add a tool to detect source-breaking API changes introduced from libraries.
swift-api-digester is a test utility to detect source-breaking API changes
during the evolution of a swift library. The tool works on two phases:
(1) dumping library contents as a json file, and (2) comparing two json
files textually to report interesting changes.
During phase (1), the api-digester looks up every declarations inside
a module and outputs a singly-rooted tree that encloses interesting
details of the API level.
During phase (2), api-digester applies structure-information comparision
algorithms on two given singly root trees, trying to figure out, as
precise as possible, the branches/leaves in the trees that differ from
each other. Further analysis decides whether the changed leaves/branches
can be reflected as source-breaking changes for API users. If they are,
the output of api-digester will include such changes.
Also, this commit includes a regression test that make sure API changes
from the Swift stdlib are expected.
