[Sema] typecheck implicit extensions too

When asking about the Copyable conformance for a nominal, we will end up
 synthesizing a conditional conformance to Copyable depending on the
 presence of ~Copyable in a generic param. We were not actually checking
 that conformance for validity (i.e., the containment rule) because we
were skipping over implicit ExtensionDecl's at a high level, but only
during Sema.

  There doesn't appear to be a fundamental issue with also checking the
  implicit decls; it just requires care when dealing with the
  inheritance clause's lack of TypeRepr's. Perhaps it's debatable
  whether the inheritance clause should have any entries at all for an
  implicit extension, if it's generic signature has already been set.
  It's where-clause isn't populated either.

Author: kavon

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -1640,7 +1640,7 @@ static void diagnoseRetroactiveConformances(
   // We better only be conforming it to protocols declared within this module.
   llvm::SmallSetVector<ProtocolDecl *, 8> externalProtocols;
   for (const InheritedEntry &entry : ext->getInherited().getEntries()) {
-    if (entry.getType().isNull()) {
+    if (entry.getType().isNull() || !entry.getTypeRepr()) {
       continue;
     }
 
@@ -3821,7 +3821,7 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
       auto *extTypeNominal = extType->getAnyNominal();
       bool firstNominalIsNotMostSpecific =
         extTypeNominal && extTypeNominal != nominal;
-      if (isa<CompositionTypeRepr>(extTypeRepr)
+      if ((extTypeRepr && isa<CompositionTypeRepr>(extTypeRepr))
           || firstNominalIsNotMostSpecific) {
         auto diag = ED->diagnose(diag::composition_in_extended_type,
                                  nominal->getDeclaredType());

lib/Sema/TypeCheckInvertible.cpp

@@ -78,7 +78,6 @@ static void tryEmitContainmentFixits(NominalTypeDecl *enclosingNom,
   }
     break;
   case InverseMarking::Kind::Explicit:
-    assert(false && "how did it become Copyable?");
     break;
   };
 
@@ -326,11 +325,11 @@ ProtocolConformance *deriveConformanceForInvertible(Evaluator &evaluator,
     ext->setExtendedNominal(nominal);
     nominal->addExtension(ext);
 
-    // Make it accessible to getTopLevelDecls()
-    if (auto file = dyn_cast<FileUnit>(nominal->getModuleScopeContext()))
-      file->getOrCreateSynthesizedFile().addTopLevelDecl(ext);
+    // Make it accessible to getTopLevelDecls() so it gets type-checked.
+    auto file = cast<FileUnit>(nominal->getModuleScopeContext());
+    file->getOrCreateSynthesizedFile().addTopLevelDecl(ext);
 
-    // Then reate the conformance using the extension as the conformance's
+    // Then create the conformance using the extension as the conformance's
     // DeclContext, which is how we register these conditional requirements
     // with the conformance.
     return generateConformance(ext);

lib/Sema/TypeChecker.cpp

@@ -290,13 +290,11 @@ TypeCheckSourceFileRequest::evaluate(Evaluator &eval, SourceFile *SF) const {
       }
     }
 
-    // Type-check macro-generated extensions.
+    // Type-check macro-generated or implicitly-synthesized extensions.
     if (auto *synthesizedSF = SF->getSynthesizedFile()) {
       for (auto *decl : synthesizedSF->getTopLevelDecls()) {
-        if (!decl->isImplicit()) {
-          assert(isa<ExtensionDecl>(decl));
-          TypeChecker::typeCheckDecl(decl);
-        }
+        assert(isa<ExtensionDecl>(decl));
+        TypeChecker::typeCheckDecl(decl);
       }
     }
     SF->typeCheckDelayedFunctions();