AssociatedTypeInference: Add -dump-type-witness-systems flag to enable debug output

Author: AnthonyLatsis

include/swift/Basic/LangOptions.h

@@ -534,6 +534,9 @@ namespace swift {
     RequirementMachineMode RequirementMachineInferredSignatures =
         RequirementMachineMode::Disabled;
 
+    /// Enables dumping type witness systems from associated type inference.
+    bool DumpTypeWitnessSystems = false;
+
     /// Sets the target we are building for and updates platform conditions
     /// to match.
     ///

include/swift/Option/FrontendOptions.td

@@ -356,6 +356,9 @@ def requirement_machine_max_concrete_nesting : Joined<["-"], "requirement-machin
   Flags<[FrontendOption, HelpHidden, DoesNotAffectIncrementalBuild]>,
   HelpText<"Set the maximum concrete type nesting depth before giving up">;
 
+def dump_type_witness_systems : Flag<["-"], "dump-type-witness-systems">,
+  HelpText<"Enables dumping type witness systems from associated type inference">;
+
 def debug_generic_signatures : Flag<["-"], "debug-generic-signatures">,
   HelpText<"Debug generic signatures">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -955,6 +955,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+  Opts.DumpTypeWitnessSystems = Args.hasArg(OPT_dump_type_witness_systems);
+
   return HadError || UnsupportedOS || UnsupportedArch;
 }
 

lib/Sema/TypeCheckProtocolInference.cpp

@@ -1225,6 +1225,10 @@ AssociatedTypeDecl *AssociatedTypeInference::inferAbstractTypeWitnesses(
   TypeWitnessSystem system(unresolvedAssocTypes);
   collectAbstractTypeWitnesses(system, unresolvedAssocTypes);
 
+  if (ctx.LangOpts.DumpTypeWitnessSystems) {
+    system.dump(llvm::dbgs(), conformance);
+  }
+
   // If we couldn't resolve an associated type, bail out.
   for (auto *assocType : unresolvedAssocTypes) {
     if (!system.hasResolvedTypeWitness(assocType->getName())) {