[Incremental] Introducing: DependencyVerifier

The DependencyVerifier is a DiagnosticVerifier-alike utility that takes annotations in user code and transforms them into a set of expectations. Those expectations are met by corresponding "obligations", which are constructed by reading the contents of the referenced name tracker associated with the source files for each of the primary inputs to a frontend job. The verifier will then pair off expectations and obligations, and ensure that any remaining unpaired obligations are diagnosed as failures.

This tool will not only ensure the correctness of the referenced name tracker's output, it will provide us with tests that ensure its output is stable, and give us the confidence to replace it with an evaluator-based tracking scheme in the future.

Resolves rdar://59773883

Author: CodaFi

lib/Frontend/CMakeLists.txt

@@ -3,6 +3,7 @@ add_swift_host_library(swiftFrontend STATIC
   ArgsToFrontendOptionsConverter.cpp
   ArgsToFrontendOutputsConverter.cpp
   CompilerInvocation.cpp
+  DependencyVerifier.cpp
   DiagnosticVerifier.cpp
   Frontend.cpp
   FrontendInputsAndOutputs.cpp