[ArchetypeBuilder] Eliminate expandGenericEnvironment().

Remove the pre-expansion of all of the archetypes in a generic
environment; they can be constructed lazily from interface types.

Note that this only concerns the construction of the archetypes
themselves. The archetype builder is still pre-expanding all
*potential* archetypes.

"Fixes" rdar://problem/30351514, in the sense that the eager code and
the assertion that was getting tripped up are being eliminated
completely.

Author: DougGregor

include/swift/AST/ArchetypeBuilder.h

@@ -144,11 +144,6 @@ class ArchetypeBuilder {
                                  RequirementSource Source,
                                 llvm::SmallPtrSetImpl<ProtocolDecl *> &Visited);
 
-  /// "Expand" all of the archetypes in the generic environment.
-  /// FIXME: This is a hack we need until we're able to lazily create
-  /// archetypes.
-  void expandGenericEnvironment(GenericEnvironment *genericEnv);
-
 public:
   /// \brief Add a new conformance requirement specifying that the given
   /// potential archetypes are equivalent.

lib/AST/ArchetypeBuilder.cpp

@@ -2601,61 +2601,3 @@ GenericSignature *ArchetypeBuilder::getGenericSignature() {
   auto sig = GenericSignature::get(Impl->GenericParams, requirements);
   return sig;
 }
-
-void ArchetypeBuilder::expandGenericEnvironment(GenericEnvironment *env) {
-
-  assert(Impl->finalized && "Must finalize builder first");
-
-  // Force the creation of all of the archetypes.
-  // FIXME: This isn't a well-formed notion with recursive protocol constraints.
-  auto signature = env->getGenericSignature();
-  visitPotentialArchetypes([&](PotentialArchetype *pa) {
-    if (auto archetype =
-            env->mapTypeIntoContext(
-              pa->getDependentType(signature->getGenericParams(),
-                                  /*allowUnresolved=*/false),
-             getLookupConformanceFn())
-          ->getAs<ArchetypeType>())
-      (void)archetype->getAllNestedTypes();
-  });
-
-#ifndef NDEBUG
-  // FIXME: This property should be maintained when there are errors, too.
-  if (!Diags.hadAnyError()) {
-    auto genericParams = signature->getGenericParams();
-    visitPotentialArchetypes([&](PotentialArchetype *pa) {
-      if (pa->isConcreteType()) return;
-
-      auto depTy = pa->getDependentType(genericParams,
-                                        /*allowUnresolved=*/false);
-      auto inContext = env->mapTypeIntoContext(depTy, getLookupConformanceFn());
-
-      auto repDepTy = pa->getRepresentative()->getDependentType(
-                                                    genericParams,
-                                                    /*allowUnresolved=*/false);
-      auto repInContext =
-        env->mapTypeIntoContext(repDepTy, getLookupConformanceFn());
-      if (!(inContext->isEqual(repInContext) ||
-              inContext->hasError() ||
-            repInContext->hasError())) {
-        dump(llvm::errs());
-
-        llvm::errs() << "Dependent type:\n";
-        depTy->dump();
-
-        llvm::errs() << "Dependent type in context:\n";
-        inContext->dump();
-
-        llvm::errs() << "Representative dependent type:\n";
-        repDepTy->dump();
-
-        llvm::errs() << "Representative in context:\n";
-        repInContext->dump();
-
-        llvm_unreachable(
-                  "Potential archetype mapping differs from representative!");
-      }
-    });
-  }
-#endif
-}

lib/AST/GenericSignature.cpp

@@ -204,9 +204,7 @@ GenericSignature::getCanonicalSignature() const {
 GenericEnvironment *GenericSignature::createGenericEnvironment(
                                                              ModuleDecl &mod) {
   auto *builder = getArchetypeBuilder(mod);
-  auto env = GenericEnvironment::getIncomplete(this, builder);
-  builder->expandGenericEnvironment(env);
-  return env;
+  return GenericEnvironment::getIncomplete(this, builder);
 }