diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -4459,6 +4459,12 @@
   "%0 in %1">;
 def note_using_value_decl_missing_typename : Note<
   "add 'typename' to treat this using declaration as a type">;
+def warn_cxx17_compat_implicit_typename : Warning<"use of implicit 'typename' is "
+  "incompatible with C++ standards before C++2a">, InGroup<CXX2aCompat>,
+  DefaultIgnore;
+def ext_implicit_typename : ExtWarn<"missing 'typename' prior to dependent "
+  "type name %0%1; implicit 'typename' is a C++2a extension">,
+  InGroup<CXX2a>;
 
 def err_template_kw_refers_to_non_template : Error<
   "%0 following the 'template' keyword does not refer to a template">;
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -771,9 +771,10 @@
 public:
   // If NeedType is true, then TryAnnotateTypeOrScopeToken will try harder to
   // find a type name by attempting typo correction.
-  bool TryAnnotateTypeOrScopeToken();
+  bool TryAnnotateTypeOrScopeToken(bool AllowImplicitTypename = false);
   bool TryAnnotateTypeOrScopeTokenAfterScopeSpec(CXXScopeSpec &SS,
-                                                 bool IsNewScope);
+                                                 bool IsNewScope,
+                                                 bool AllowImplicitTypename);
   bool TryAnnotateCXXScopeToken(bool EnteringContext = false);
 
 private:
@@ -2019,6 +2020,7 @@
     DSC_alias_declaration, // C++11 type-specifier-seq in an alias-declaration
     DSC_top_level, // top-level/namespace declaration context
     DSC_template_param, // template parameter context
+    DSC_template_arg, // template argument context
     DSC_template_type_arg, // template type argument context
     DSC_objc_method_result, // ObjC method result context, enables 'instancetype'
     DSC_condition // condition declaration context
@@ -2030,6 +2032,7 @@
     switch (DSC) {
     case DeclSpecContext::DSC_normal:
     case DeclSpecContext::DSC_template_param:
+    case DeclSpecContext::DSC_template_arg:
     case DeclSpecContext::DSC_class:
     case DeclSpecContext::DSC_top_level:
     case DeclSpecContext::DSC_objc_method_result:
@@ -2051,6 +2054,7 @@
     switch (DSC) {
     case DeclSpecContext::DSC_normal:
     case DeclSpecContext::DSC_template_param:
+    case DeclSpecContext::DSC_template_arg:
     case DeclSpecContext::DSC_class:
     case DeclSpecContext::DSC_top_level:
     case DeclSpecContext::DSC_condition:
@@ -2066,6 +2070,27 @@
     llvm_unreachable("Missing DeclSpecContext case");
   }
 
+  // Is this a context in which an implicit 'typename' is allowed?
+  static bool isImplicitTypenameContext(DeclSpecContext DSC) {
+    switch (DSC) {
+    case DeclSpecContext::DSC_class:
+    case DeclSpecContext::DSC_top_level:
+    case DeclSpecContext::DSC_type_specifier:
+    case DeclSpecContext::DSC_template_type_arg:
+    case DeclSpecContext::DSC_trailing:
+    case DeclSpecContext::DSC_alias_declaration:
+    case DeclSpecContext::DSC_template_param:
+      return true;
+
+    case DeclSpecContext::DSC_normal:
+    case DeclSpecContext::DSC_objc_method_result:
+    case DeclSpecContext::DSC_condition:
+    case DeclSpecContext::DSC_template_arg:
+      return false;
+    }
+    llvm_unreachable("Missing DeclSpecContext case");
+  }
+
   /// Information on a C++0x for-range-initializer found while parsing a
   /// declaration which turns out to be a for-range-declaration.
   struct ForRangeInit {
@@ -2117,7 +2142,18 @@
       const ParsedTemplateInfo &TemplateInfo = ParsedTemplateInfo(),
       AccessSpecifier AS = AS_none,
       DeclSpecContext DSC = DeclSpecContext::DSC_normal,
-      LateParsedAttrList *LateAttrs = nullptr);
+      LateParsedAttrList *LateAttrs = nullptr) {
+    return ParseDeclarationSpecifiers(DS, TemplateInfo, AS, DSC, LateAttrs,
+                                      isImplicitTypenameContext(DSC));
+  }
+  void ParseDeclarationSpecifiers(
+      DeclSpec &DS,
+      const ParsedTemplateInfo &TemplateInfo,
+      AccessSpecifier AS,
+      DeclSpecContext DSC,
+      LateParsedAttrList *LateAttrs,
+      bool AllowImplicitTypename);
+
   bool DiagnoseMissingSemiAfterTagDefinition(
       DeclSpec &DS, AccessSpecifier AS, DeclSpecContext DSContext,
       LateParsedAttrList *LateAttrs = nullptr);
@@ -2242,7 +2278,8 @@
   /// might be a constructor-style initializer.
   /// If during the disambiguation process a parsing error is encountered,
   /// the function returns true to let the declaration parsing code handle it.
-  bool isCXXFunctionDeclarator(bool *IsAmbiguous = nullptr);
+  bool isCXXFunctionDeclarator(bool *IsAmbiguous = nullptr,
+                               bool AllowImplicitTypename = false);
 
   struct ConditionDeclarationOrInitStatementState;
   enum class ConditionOrInitStatement {
@@ -2292,7 +2329,8 @@
   /// Doesn't consume tokens.
   TPResult
   isCXXDeclarationSpecifier(TPResult BracedCastResult = TPResult::False,
-                            bool *HasMissingTypename = nullptr);
+                            bool *HasMissingTypename = nullptr,
+                            bool AllowImplicitTypename = false);
 
   /// Given that isCXXDeclarationSpecifier returns \c TPResult::True or
   /// \c TPResult::Ambiguous, determine whether the decl-specifier would be
@@ -2321,7 +2359,8 @@
                               bool mayHaveDirectInit = false);
   TPResult
   TryParseParameterDeclarationClause(bool *InvalidAsDeclaration = nullptr,
-                                     bool VersusTemplateArg = false);
+                                     bool VersusTemplateArg = false,
+                                     bool AllowImplicitTypename = false);
   TPResult TryParseFunctionDeclarator();
   TPResult TryParseBracketDeclarator();
   TPResult TryConsumeDeclarationSpecifier();
diff --git a/clang/include/clang/Sema/DeclSpec.h b/clang/include/clang/Sema/DeclSpec.h
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -39,6 +39,7 @@
   class CXXRecordDecl;
   class TypeLoc;
   class LangOptions;
+  class LookupResult;
   class IdentifierInfo;
   class NamespaceAliasDecl;
   class NamespaceDecl;
@@ -1834,6 +1835,9 @@
   /// this declarator as a parameter pack.
   SourceLocation EllipsisLoc;
 
+  /// Lookup result of declarator, if any.
+  LookupResult *PrevLookupResult;
+
   friend struct DeclaratorChunk;
 
 public:
@@ -1843,7 +1847,8 @@
         GroupingParens(false), FunctionDefinition(FDK_Declaration),
         Redeclaration(false), Extension(false), ObjCIvar(false),
         ObjCWeakProperty(false), InlineStorageUsed(false),
-        Attrs(ds.getAttributePool().getFactory()), AsmLabel(nullptr) {}
+        Attrs(ds.getAttributePool().getFactory()), AsmLabel(nullptr),
+        PrevLookupResult(nullptr) {}
 
   ~Declarator() {
     clear();
@@ -2482,6 +2487,17 @@
 
   void setRedeclaration(bool Val) { Redeclaration = Val; }
   bool isRedeclaration() const { return Redeclaration; }
+
+  void setPrevLookupResult(LookupResult *LR) { PrevLookupResult = LR; }
+  LookupResult &getPrevLookupResult() {
+    assert(PrevLookupResult);
+    return *PrevLookupResult;
+  }
+  const LookupResult &getPrevLookupResult() const {
+    assert(PrevLookupResult);
+    return *PrevLookupResult;
+  }
+  bool hasPrevLookupResult() const { return PrevLookupResult; }
 };
 
 /// This little struct is used to capture information about
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -1781,6 +1781,7 @@
                          bool IsCtorOrDtorName = false,
                          bool WantNontrivialTypeSourceInfo = false,
                          bool IsClassTemplateDeductionContext = true,
+                         bool AllowImplicitTypename = false,
                          IdentifierInfo **CorrectedII = nullptr);
   TypeSpecifierType isTagName(IdentifierInfo &II, Scope *S);
   bool isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S);
@@ -2122,6 +2123,10 @@
   /// \c constexpr in C++11 or has an 'auto' return type in C++14).
   bool canSkipFunctionBody(Decl *D);
 
+  /// Determine whether \param D is function like (function or function
+  /// template) for parsing.
+  bool isDeclaratorFunctionLike(Declarator &D);
+
   void computeNRVO(Stmt *Body, sema::FunctionScopeInfo *Scope);
   Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body);
   Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body, bool IsInstantiation);
@@ -6618,10 +6623,10 @@
   /// \param SS the nested-name-specifier following the typename (e.g., 'T::').
   /// \param II the identifier we're retrieving (e.g., 'type' in the example).
   /// \param IdLoc the location of the identifier.
-  TypeResult
-  ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
-                    const CXXScopeSpec &SS, const IdentifierInfo &II,
-                    SourceLocation IdLoc);
+  TypeResult ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
+                               const CXXScopeSpec &SS, const IdentifierInfo &II,
+                               SourceLocation IdLoc,
+                               bool IsImplicitTypename = false);
 
   /// Called when the parser has parsed a C++ typename
   /// specifier that ends in a template-id, e.g.,
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -2649,6 +2649,9 @@
     case tok::semi:
       // This looks like a variable or function declaration. The type is
       // probably missing. We're done parsing decl-specifiers.
+      // But only if we are not in a function prototype scope.
+      if (getCurScope()->isFunctionPrototypeScope())
+        break;
       if (SS)
         AnnotateScopeToken(*SS, /*IsNewAnnotation*/false);
       return false;
@@ -2712,22 +2715,46 @@
 /// DeclaratorContext enumerator values.
 Parser::DeclSpecContext
 Parser::getDeclSpecContextFromDeclaratorContext(DeclaratorContext Context) {
-  if (Context == DeclaratorContext::MemberContext)
+  switch (Context) {
+  case DeclaratorContext::MemberContext:
     return DeclSpecContext::DSC_class;
-  if (Context == DeclaratorContext::FileContext)
+  case DeclaratorContext::FileContext:
     return DeclSpecContext::DSC_top_level;
-  if (Context == DeclaratorContext::TemplateParamContext)
+  case DeclaratorContext::TemplateParamContext:
     return DeclSpecContext::DSC_template_param;
-  if (Context == DeclaratorContext::TemplateArgContext ||
-      Context == DeclaratorContext::TemplateTypeArgContext)
+  case DeclaratorContext::TemplateArgContext:
+    return DeclSpecContext::DSC_template_arg;
+  case DeclaratorContext::TemplateTypeArgContext:
     return DeclSpecContext::DSC_template_type_arg;
-  if (Context == DeclaratorContext::TrailingReturnContext ||
-      Context == DeclaratorContext::TrailingReturnVarContext)
+  case DeclaratorContext::TrailingReturnContext:
+  case DeclaratorContext::TrailingReturnVarContext:
     return DeclSpecContext::DSC_trailing;
-  if (Context == DeclaratorContext::AliasDeclContext ||
-      Context == DeclaratorContext::AliasTemplateContext)
+  case DeclaratorContext::AliasDeclContext:
+  case DeclaratorContext::AliasTemplateContext:
     return DeclSpecContext::DSC_alias_declaration;
-  return DeclSpecContext::DSC_normal;
+  case DeclaratorContext::TypeNameContext:
+    return DeclSpecContext::DSC_type_specifier;
+  case DeclaratorContext::ConditionContext:
+    return DeclSpecContext::DSC_condition;
+  case DeclaratorContext::PrototypeContext:
+  case DeclaratorContext::ObjCResultContext:
+  case DeclaratorContext::ObjCParameterContext:
+  case DeclaratorContext::KNRTypeListContext:
+  case DeclaratorContext::FunctionalCastContext:
+  case DeclaratorContext::BlockContext:
+  case DeclaratorContext::ForContext:
+  case DeclaratorContext::InitStmtContext:
+  case DeclaratorContext::CXXNewContext:
+  case DeclaratorContext::CXXCatchContext:
+  case DeclaratorContext::ObjCCatchContext:
+  case DeclaratorContext::BlockLiteralContext:
+  case DeclaratorContext::LambdaExprContext:
+  case DeclaratorContext::LambdaExprParameterContext:
+  case DeclaratorContext::ConversionIdContext:
+    return DeclSpecContext::DSC_normal;
+  }
+
+  llvm_unreachable("Missing DeclaratorContext case");
 }
 
 /// ParseAlignArgument - Parse the argument to an alignment-specifier.
@@ -2944,7 +2971,8 @@
                                         const ParsedTemplateInfo &TemplateInfo,
                                         AccessSpecifier AS,
                                         DeclSpecContext DSContext,
-                                        LateParsedAttrList *LateAttrs) {
+                                        LateParsedAttrList *LateAttrs,
+                                        bool AllowImplicitTypename) {
   if (DS.getSourceRange().isInvalid()) {
     // Start the range at the current token but make the end of the range
     // invalid.  This will make the entire range invalid unless we successfully
@@ -3132,12 +3160,13 @@
           isConstructorDeclarator(/*Unqualified*/ false))
         goto DoneWithDeclSpec;
 
-      ParsedType TypeRep =
-          Actions.getTypeName(*Next.getIdentifierInfo(), Next.getLocation(),
-                              getCurScope(), &SS, false, false, nullptr,
-                              /*IsCtorOrDtorName=*/false,
-                              /*WantNonTrivialSourceInfo=*/true,
-                              isClassTemplateDeductionContext(DSContext));
+      ParsedType TypeRep = Actions.getTypeName(
+          *Next.getIdentifierInfo(), Next.getLocation(), getCurScope(), &SS,
+          false, false, nullptr,
+          /*IsCtorOrDtorName=*/false,
+          /*WantNonTrivialSourceInfo=*/true,
+          isClassTemplateDeductionContext(DSContext),
+          AllowImplicitTypename);
 
       // If the referenced identifier is not a type, then this declspec is
       // erroneous: We already checked about that it has no type specifier, and
@@ -4827,7 +4856,7 @@
   case tok::kw_typename: // typename T::type
     // Annotate typenames and C++ scope specifiers.  If we get one, just
     // recurse to handle whatever we get.
-    if (TryAnnotateTypeOrScopeToken())
+    if (TryAnnotateTypeOrScopeToken(!getCurScope()->isTemplateParamScope()))
       return true;
     if (Tok.is(tok::identifier))
       return false;
@@ -5850,10 +5879,17 @@
       // is not, the declarator has been fully parsed.
       bool IsAmbiguous = false;
       if (getLangOpts().CPlusPlus && D.mayBeFollowedByCXXDirectInit()) {
+        bool AllowImplicitTypename = false;
+        if (D.getCXXScopeSpec().isSet())
+          AllowImplicitTypename = Actions.isDeclaratorFunctionLike(D);
+        else if (D.getContext() == DeclaratorContext::MemberContext)
+          AllowImplicitTypename = true;
+
         // The name of the declarator, if any, is tentatively declared within
         // a possible direct initializer.
         TentativelyDeclaredIdentifiers.push_back(D.getIdentifier());
-        bool IsFunctionDecl = isCXXFunctionDeclarator(&IsAmbiguous);
+        bool IsFunctionDecl =
+            isCXXFunctionDeclarator(&IsAmbiguous, AllowImplicitTypename);
         TentativelyDeclaredIdentifiers.pop_back();
         if (!IsFunctionDecl)
           break;
@@ -6404,6 +6440,15 @@
        ParsedAttributes &FirstArgAttrs,
        SmallVectorImpl<DeclaratorChunk::ParamInfo> &ParamInfo,
        SourceLocation &EllipsisLoc) {
+
+  bool AllowImplicitTypename;
+  if (D.getContext() == DeclaratorContext::MemberContext ||
+      D.getContext() == DeclaratorContext::LambdaExprContext)
+    AllowImplicitTypename = true;
+  else
+    AllowImplicitTypename = D.getCXXScopeSpec().isSet() &&
+                            D.isFunctionDeclaratorAFunctionDeclaration();
+
   do {
     // FIXME: Issue a diagnostic if we parsed an attribute-specifier-seq
     // before deciding this was a parameter-declaration-clause.
@@ -6429,8 +6474,9 @@
     // too much hassle.
     DS.takeAttributesFrom(FirstArgAttrs);
 
-    ParseDeclarationSpecifiers(DS);
-
+    ParseDeclarationSpecifiers(DS, /*TemplateInfo=*/ParsedTemplateInfo(),
+                               AS_none, DeclSpecContext::DSC_normal,
+                               /*LateAttrs=*/nullptr, AllowImplicitTypename);
 
     // Parse the declarator.  This is "PrototypeContext" or
     // "LambdaExprParameterContext", because we must accept either
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -1199,7 +1199,8 @@
       *Id, IdLoc, getCurScope(), &SS, /*IsClassName=*/true, false, nullptr,
       /*IsCtorOrDtorName=*/false,
       /*NonTrivialTypeSourceInfo=*/true,
-      /*IsClassTemplateDeductionContext*/ false, &CorrectedII);
+      /*IsClassTemplateDeductionContext*/ false,
+      /*AllowImplicitTypename=*/false, &CorrectedII);
   if (!Type) {
     Diag(IdLoc, diag::err_expected_class_name);
     return true;
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1343,7 +1343,8 @@
 
   // Parse the common declaration-specifiers piece.
   DeclSpec DS(AttrFactory);
-  ParseSpecifierQualifierList(DS);
+  ParseSpecifierQualifierList(DS, /*AccessSpecifier=*/AS_none,
+                              DeclSpecContext::DSC_type_specifier);
 
   // Parse the abstract-declarator, if present.
   Declarator DeclaratorInfo(DS, DeclaratorContext::TypeNameContext);
diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -16,6 +16,7 @@
 #include "clang/Parse/Parser.h"
 #include "clang/Parse/RAIIObjectsForParser.h"
 #include "clang/Sema/DeclSpec.h"
+#include "clang/Sema/Lookup.h"
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Scope.h"
 using namespace clang;
diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -1275,7 +1275,10 @@
 ///
 Parser::TPResult
 Parser::isCXXDeclarationSpecifier(Parser::TPResult BracedCastResult,
-                                  bool *HasMissingTypename) {
+                                  bool *HasMissingTypename,
+                                  bool AllowImplicitTypename) {
+  const bool NoImplicitTypename = !HasMissingTypename || !AllowImplicitTypename;
+
   switch (Tok.getKind()) {
   case tok::identifier: {
     // Check for need to substitute AltiVec __vector keyword
@@ -1305,7 +1308,7 @@
         // template template argument, we'll undo this when checking the
         // validity of the argument.
         if (getLangOpts().CPlusPlus17) {
-          if (TryAnnotateTypeOrScopeToken())
+          if (TryAnnotateTypeOrScopeToken(!NoImplicitTypename))
             return TPResult::Error;
           if (Tok.isNot(tok::identifier))
             break;
@@ -1326,7 +1329,7 @@
       // a missing 'typename' keyword. Don't use TryAnnotateName in this case,
       // since it will annotate as a primary expression, and we want to use the
       // "missing 'typename'" logic.
-      if (TryAnnotateTypeOrScopeToken())
+      if (TryAnnotateTypeOrScopeToken(!NoImplicitTypename))
         return TPResult::Error;
       // If annotation failed, assume it's a non-type.
       // FIXME: If this happens due to an undeclared identifier, treat it as
@@ -1342,7 +1345,7 @@
   case tok::kw_typename:  // typename T::type
     // Annotate typenames and C++ scope specifiers.  If we get one, just
     // recurse to handle whatever we get.
-    if (TryAnnotateTypeOrScopeToken())
+    if (TryAnnotateTypeOrScopeToken(/*AllowImplicitTypename=*/true))
       return TPResult::Error;
     return isCXXDeclarationSpecifier(BracedCastResult, HasMissingTypename);
 
@@ -1357,7 +1360,7 @@
   case tok::kw_decltype:
     // Annotate typenames and C++ scope specifiers.  If we get one, just
     // recurse to handle whatever we get.
-    if (TryAnnotateTypeOrScopeToken())
+    if (TryAnnotateTypeOrScopeToken(!NoImplicitTypename))
       return TPResult::Error;
     return isCXXDeclarationSpecifier(BracedCastResult, HasMissingTypename);
 
@@ -1469,7 +1472,7 @@
 
   case tok::annot_cxxscope: // foo::bar or ::foo::bar, but already parsed
     // We've already annotated a scope; try to annotate a type.
-    if (TryAnnotateTypeOrScopeToken())
+    if (TryAnnotateTypeOrScopeToken(!NoImplicitTypename))
       return TPResult::Error;
     if (!Tok.is(tok::annot_typename)) {
       // If the next token is an identifier or a type qualifier, then this
@@ -1778,7 +1781,8 @@
 /// '(' parameter-declaration-clause ')' cv-qualifier-seq[opt]
 ///         exception-specification[opt]
 ///
-bool Parser::isCXXFunctionDeclarator(bool *IsAmbiguous) {
+bool Parser::isCXXFunctionDeclarator(bool *IsAmbiguous,
+                                     bool AllowImplicitTypename) {
 
   // C++ 8.2p1:
   // The ambiguity arising from the similarity between a function-style cast and
@@ -1793,7 +1797,9 @@
 
   ConsumeParen();
   bool InvalidAsDeclaration = false;
-  TPResult TPR = TryParseParameterDeclarationClause(&InvalidAsDeclaration);
+  TPResult TPR = TryParseParameterDeclarationClause(
+      &InvalidAsDeclaration, /*VersusTemplateArgument=*/false,
+      AllowImplicitTypename);
   if (TPR == TPResult::Ambiguous) {
     if (Tok.isNot(tok::r_paren))
       TPR = TPResult::False;
@@ -1839,7 +1845,8 @@
 ///
 Parser::TPResult
 Parser::TryParseParameterDeclarationClause(bool *InvalidAsDeclaration,
-                                           bool VersusTemplateArgument) {
+                                           bool VersusTemplateArgument,
+                                           bool AllowImplicitTypename) {
 
   if (Tok.is(tok::r_paren))
     return TPResult::Ambiguous;
@@ -1872,8 +1879,8 @@
     // decl-specifier-seq
     // A parameter-declaration's initializer must be preceded by an '=', so
     // decl-specifier-seq '{' is not a parameter in C++11.
-    TPResult TPR = isCXXDeclarationSpecifier(TPResult::False,
-                                             InvalidAsDeclaration);
+    TPResult TPR = isCXXDeclarationSpecifier(
+        TPResult::False, InvalidAsDeclaration, AllowImplicitTypename);
 
     if (VersusTemplateArgument && TPR == TPResult::True) {
       // Consume the decl-specifier-seq. We have to look past it, since a
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1500,7 +1500,8 @@
     return ANK_Error;
 
   if (Tok.isNot(tok::identifier) || SS.isInvalid()) {
-    if (TryAnnotateTypeOrScopeTokenAfterScopeSpec(SS, !WasScopeAnnotation))
+    if (TryAnnotateTypeOrScopeTokenAfterScopeSpec(
+            SS, !WasScopeAnnotation, /*AllowImplicitTypename=*/false))
       return ANK_Error;
     return ANK_Unresolved;
   }
@@ -1510,10 +1511,11 @@
 
   // FIXME: Move the tentative declaration logic into ClassifyName so we can
   // typo-correct to tentatively-declared identifiers.
-  if (isTentativelyDeclared(Name)) {
+  if (isTentativelyDeclared(Name) && SS.isEmpty()) {
     // Identifier has been tentatively declared, and thus cannot be resolved as
     // an expression. Fall back to annotating it as a type.
-    if (TryAnnotateTypeOrScopeTokenAfterScopeSpec(SS, !WasScopeAnnotation))
+    if (TryAnnotateTypeOrScopeTokenAfterScopeSpec(
+            SS, !WasScopeAnnotation, /*AllowImplicitTypename=*/false))
       return ANK_Error;
     return Tok.is(tok::annot_typename) ? ANK_Success : ANK_TentativeDecl;
   }
@@ -1651,7 +1653,7 @@
 ///
 /// Note that this routine emits an error if you call it with ::new or ::delete
 /// as the current tokens, so only call it in contexts where these are invalid.
-bool Parser::TryAnnotateTypeOrScopeToken() {
+bool Parser::TryAnnotateTypeOrScopeToken(bool AllowImplicitTypename) {
   assert((Tok.is(tok::identifier) || Tok.is(tok::coloncolon) ||
           Tok.is(tok::kw_typename) || Tok.is(tok::annot_cxxscope) ||
           Tok.is(tok::kw_decltype) || Tok.is(tok::annot_template_id) ||
@@ -1668,7 +1670,7 @@
     if (getLangOpts().MSVCCompat && NextToken().is(tok::kw_typedef)) {
       Token TypedefToken;
       PP.Lex(TypedefToken);
-      bool Result = TryAnnotateTypeOrScopeToken();
+      bool Result = TryAnnotateTypeOrScopeToken(AllowImplicitTypename);
       PP.EnterToken(Tok);
       Tok = TypedefToken;
       if (!Result)
@@ -1693,7 +1695,8 @@
           Tok.is(tok::annot_decltype)) {
         // Attempt to recover by skipping the invalid 'typename'
         if (Tok.is(tok::annot_decltype) ||
-            (!TryAnnotateTypeOrScopeToken() && Tok.isAnnotation())) {
+            (!TryAnnotateTypeOrScopeToken(AllowImplicitTypename) &&
+             Tok.isAnnotation())) {
           unsigned DiagID = diag::err_expected_qualified_after_typename;
           // MS compatibility: MSVC permits using known types with typename.
           // e.g. "typedef typename T* pointer_type"
@@ -1759,22 +1762,23 @@
     if (ParseOptionalCXXScopeSpecifier(SS, nullptr, /*EnteringContext*/false))
       return true;
 
-  return TryAnnotateTypeOrScopeTokenAfterScopeSpec(SS, !WasScopeAnnotation);
+  return TryAnnotateTypeOrScopeTokenAfterScopeSpec(SS, !WasScopeAnnotation,
+                                                   AllowImplicitTypename);
 }
 
 /// Try to annotate a type or scope token, having already parsed an
 /// optional scope specifier. \p IsNewScope should be \c true unless the scope
 /// specifier was extracted from an existing tok::annot_cxxscope annotation.
-bool Parser::TryAnnotateTypeOrScopeTokenAfterScopeSpec(CXXScopeSpec &SS,
-                                                       bool IsNewScope) {
+bool Parser::TryAnnotateTypeOrScopeTokenAfterScopeSpec(
+    CXXScopeSpec &SS, bool IsNewScope, bool AllowImplicitTypename) {
   if (Tok.is(tok::identifier)) {
     // Determine whether the identifier is a type name.
     if (ParsedType Ty = Actions.getTypeName(
             *Tok.getIdentifierInfo(), Tok.getLocation(), getCurScope(), &SS,
             false, NextToken().is(tok::period), nullptr,
             /*IsCtorOrDtorName=*/false,
-            /*NonTrivialTypeSourceInfo*/true,
-            /*IsClassTemplateDeductionContext*/true)) {
+            /*NonTrivialTypeSourceInfo*/ true,
+            /*IsClassTemplateDeductionContext*/ true, AllowImplicitTypename)) {
       SourceLocation BeginLoc = Tok.getLocation();
       if (SS.isNotEmpty()) // it was a C++ qualified type name.
         BeginLoc = SS.getBeginLoc();
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -18,6 +18,7 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/TargetInfo.h"
+#include "clang/Sema/Lookup.h"
 #include "clang/Sema/ParsedTemplate.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/SemaDiagnostic.h"
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -2191,3 +2191,28 @@
   return checkOpenCLDisabledTypeOrDecl(&D, E.getBeginLoc(), FnName,
                                        OpenCLDeclExtMap, 1, D.getSourceRange());
 }
+
+bool Sema::isDeclaratorFunctionLike(Declarator &D) {
+  assert(D.getCXXScopeSpec().isSet() &&
+         "can only be called for qualified names");
+  LookupResult LR(*this, D.getIdentifier(), D.getBeginLoc(), LookupOrdinaryName,
+                  forRedeclarationInCurContext());
+  DeclContext *DC = computeDeclContext(D.getCXXScopeSpec(),
+                                       !D.getDeclSpec().isFriendSpecified());
+  if (!DC)
+    return false;
+
+  LookupQualifiedName(LR, DC);
+  bool Result = std::all_of(LR.begin(), LR.end(), [](Decl *Dcl) {
+    if (NamedDecl *ND = dyn_cast<NamedDecl>(Dcl)) {
+      ND = ND->getUnderlyingDecl();
+      return isa<FunctionDecl>(ND) || isa<FunctionTemplateDecl>(ND) ||
+             isa<UsingDecl>(ND);
+    }
+    return false;
+  });
+
+  
+  D.setPrevLookupResult(new LookupResult(std::move(LR)));
+  return Result;
+}
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -280,6 +280,7 @@
                              bool IsCtorOrDtorName,
                              bool WantNontrivialTypeSourceInfo,
                              bool IsClassTemplateDeductionContext,
+                             bool AllowImplicitTypename,
                              IdentifierInfo **CorrectedII) {
   // FIXME: Consider allowing this outside C++1z mode as an extension.
   bool AllowDeducedTemplate = IsClassTemplateDeductionContext &&
@@ -306,17 +307,32 @@
         //
         // We therefore do not perform any name lookup if the result would
         // refer to a member of an unknown specialization.
-        if (!isClassName && !IsCtorOrDtorName)
+        // In C++2a, in several contexts a 'typename' is not required. Also
+        // allow this as an extension.
+        if (!AllowImplicitTypename && !isClassName && !IsCtorOrDtorName)
           return nullptr;
+        bool IsImplicitTypename = !isClassName && !IsCtorOrDtorName;
+        if (IsImplicitTypename) {
+          SourceLocation QualifiedLoc = SS->getRange().getBegin();
+          if (getLangOpts().CPlusPlus2a)
+            Diag(QualifiedLoc, diag::warn_cxx17_compat_implicit_typename);
+          else
+            Diag(QualifiedLoc, diag::ext_implicit_typename)
+                << SS->getScopeRep() << II.getName()
+                << FixItHint::CreateInsertion(QualifiedLoc, "typename ");
+        }
 
         // We know from the grammar that this name refers to a type,
         // so build a dependent node to describe the type.
         if (WantNontrivialTypeSourceInfo)
-          return ActOnTypenameType(S, SourceLocation(), *SS, II, NameLoc).get();
+          return ActOnTypenameType(S, SourceLocation(), *SS, II, NameLoc,
+                                   IsImplicitTypename)
+              .get();
 
         NestedNameSpecifierLoc QualifierLoc = SS->getWithLocInContext(Context);
-        QualType T = CheckTypenameType(ETK_None, SourceLocation(), QualifierLoc,
-                                       II, NameLoc);
+        QualType T =
+            CheckTypenameType(IsImplicitTypename ? ETK_Typename : ETK_None,
+                              SourceLocation(), QualifierLoc, II, NameLoc);
         return ParsedType::make(T);
       }
 
@@ -5438,7 +5454,12 @@
 
     LookupName(Previous, S, CreateBuiltins);
   } else { // Something like "int foo::x;"
-    LookupQualifiedName(Previous, DC);
+    if (D.hasPrevLookupResult()) {
+      Previous = std::move(D.getPrevLookupResult());
+      D.setPrevLookupResult(nullptr);
+    }
+    else
+      LookupQualifiedName(Previous, DC);
 
     // C++ [dcl.meaning]p1:
     //   When the declarator-id is qualified, the declaration shall refer to a
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -9483,10 +9483,11 @@
   return CreateParsedType(Result, TLB.getTypeSourceInfo(Context, Result));
 }
 
-TypeResult
-Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
-                        const CXXScopeSpec &SS, const IdentifierInfo &II,
-                        SourceLocation IdLoc) {
+TypeResult Sema::ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
+                                   const CXXScopeSpec &SS,
+                                   const IdentifierInfo &II,
+                                   SourceLocation IdLoc,
+                                   bool IsImplicitTypename) {
   if (SS.isInvalid())
     return true;
 
@@ -9498,8 +9499,9 @@
       << FixItHint::CreateRemoval(TypenameLoc);
 
   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
-  QualType T = CheckTypenameType(TypenameLoc.isValid()? ETK_Typename : ETK_None,
-                                 TypenameLoc, QualifierLoc, II, IdLoc);
+  QualType T = CheckTypenameType(
+      TypenameLoc.isValid() || IsImplicitTypename ? ETK_Typename : ETK_None,
+      TypenameLoc, QualifierLoc, II, IdLoc);
   if (T.isNull())
     return true;
 
diff --git a/clang/test/CXX/drs/dr1xx.cpp b/clang/test/CXX/drs/dr1xx.cpp
--- a/clang/test/CXX/drs/dr1xx.cpp
+++ b/clang/test/CXX/drs/dr1xx.cpp
@@ -58,7 +58,7 @@
 namespace dr108 { // dr108: yes
   template<typename T> struct A {
     struct B { typedef int X; };
-    B::X x; // expected-error {{missing 'typename'}}
+    B::X x; // expected-error {{implicit 'typename' is a C++2a extension}}
     struct C : B { X x; }; // expected-error {{unknown type name}}
   };
   template<> struct A<int>::B { int X; };
diff --git a/clang/test/CXX/drs/dr2xx.cpp b/clang/test/CXX/drs/dr2xx.cpp
--- a/clang/test/CXX/drs/dr2xx.cpp
+++ b/clang/test/CXX/drs/dr2xx.cpp
@@ -242,7 +242,7 @@
       typedef int type;
       A::type a;
       A<T>::type b;
-      A<T*>::type c; // expected-error {{missing 'typename'}}
+      A<T*>::type c; // expected-error {{implicit 'typename' is a C++2a extension}}
       ::dr224::example1::A<T>::type d;
 
       class B {
@@ -250,12 +250,12 @@
 
         A::type a;
         A<T>::type b;
-        A<T*>::type c; // expected-error {{missing 'typename'}}
+        A<T*>::type c; // expected-error {{implicit 'typename' is a C++2a extension}}
         ::dr224::example1::A<T>::type d;
 
         B::type e;
         A<T>::B::type f;
-        A<T*>::B::type g; // expected-error {{missing 'typename'}}
+        A<T*>::B::type g; // expected-error {{implicit 'typename' is a C++2a extension}}
         typename A<T*>::B::type h;
       };
     };
@@ -263,21 +263,21 @@
     template <class T> class A<T*> {
       typedef int type;
       A<T*>::type a;
-      A<T>::type b; // expected-error {{missing 'typename'}}
+      A<T>::type b; // expected-error {{implicit 'typename' is a C++2a extension}}
     };
 
     template <class T1, class T2, int I> struct B {
       typedef int type;
       B<T1, T2, I>::type b1;
-      B<T2, T1, I>::type b2; // expected-error {{missing 'typename'}}
+      B<T2, T1, I>::type b2; // expected-error {{implicit 'typename' is a C++2a extension}}
 
       typedef T1 my_T1;
       static const int my_I = I;
       static const int my_I2 = I+0;
       static const int my_I3 = my_I;
-      B<my_T1, T2, my_I>::type b3; // FIXME: expected-error {{missing 'typename'}}
-      B<my_T1, T2, my_I2>::type b4; // expected-error {{missing 'typename'}}
-      B<my_T1, T2, my_I3>::type b5; // FIXME: expected-error {{missing 'typename'}}
+      B<my_T1, T2, my_I>::type b3; // FIXME: expected-error {{implicit 'typename' is a C++2a extension}}
+      B<my_T1, T2, my_I2>::type b4; // expected-error {{implicit 'typename' is a C++2a extension}}
+      B<my_T1, T2, my_I3>::type b5; // FIXME: expected-error {{implicit 'typename' is a C++2a extension}}
     };
   }
 
@@ -285,10 +285,10 @@
     template <int, typename T> struct X { typedef T type; };
     template <class T> class A {
       static const int i = 5;
-      X<i, int>::type w; // FIXME: expected-error {{missing 'typename'}}
-      X<A::i, char>::type x; // FIXME: expected-error {{missing 'typename'}}
-      X<A<T>::i, double>::type y; // FIXME: expected-error {{missing 'typename'}}
-      X<A<T*>::i, long>::type z; // expected-error {{missing 'typename'}}
+      X<i, int>::type w; // FIXME: expected-error {{implicit 'typename' is a C++2a extension}}
+      X<A::i, char>::type x; // FIXME: expected-error {{implicit 'typename' is a C++2a extension}}
+      X<A<T>::i, double>::type y; // FIXME: expected-error {{implicit 'typename' is a C++2a extension}}
+      X<A<T*>::i, long>::type z; // expected-error {{implicit 'typename' is a C++2a extension}}
       int f();
     };
     template <class T> int A<T>::f() {
diff --git a/clang/test/CXX/drs/dr4xx.cpp b/clang/test/CXX/drs/dr4xx.cpp
--- a/clang/test/CXX/drs/dr4xx.cpp
+++ b/clang/test/CXX/drs/dr4xx.cpp
@@ -173,7 +173,7 @@
     B b1;
     A::B b2;
     A<T>::B b3;
-    A<T*>::B b4; // expected-error {{missing 'typename'}}
+    A<T*>::B b4; // expected-error {{implicit 'typename' is a C++2a extension}}
   };
 }
 
diff --git a/clang/test/CXX/drs/dr5xx.cpp b/clang/test/CXX/drs/dr5xx.cpp
--- a/clang/test/CXX/drs/dr5xx.cpp
+++ b/clang/test/CXX/drs/dr5xx.cpp
@@ -228,8 +228,8 @@
   template<int N> struct X {
     typedef int type;
     X<N>::type v1;
-    X<(N)>::type v2; // expected-error {{missing 'typename'}}
-    X<+N>::type v3; // expected-error {{missing 'typename'}}
+    X<(N)>::type v2; // expected-error {{implicit 'typename' is a C++2a extension}}
+    X<+N>::type v3; // expected-error {{implicit 'typename' is a C++2a extension}}
   };
 }
 
diff --git a/clang/test/CXX/temp/temp.res/p5.cpp b/clang/test/CXX/temp/temp.res/p5.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/CXX/temp/temp.res/p5.cpp
@@ -0,0 +1,159 @@
+// RUN: %clang_cc1 -std=c++2a -pedantic -verify %s
+
+struct X {
+  using type = int;
+  static constexpr int value = 1;
+  class tclass {};
+};
+
+// [temp.res]p5
+//   A qualified-id is assumed to name a type if
+
+template <typename T>
+void f() {
+  // it is a qualified name in a type-id-only context (see below), or
+  // [its smallest enclosing [/new/defining/]-type-id is]:
+  // - a new-type-id
+  auto *Ptr = new T::type();
+  // - a defining-type-id
+  class T::tclass Empty1;
+  T::tclass Empty2; // expected-error{{missing 'typename'}}
+  // - a trailing-return-type
+  auto f()->T::type;
+  // - default argument of a type-parameter of a template [see below]
+
+  // - type-id of a
+  // static_cast,
+  auto StaticCast = static_cast<T::type>(1.2);
+  // const_cast,
+  const auto *ConstCast = const_cast<const T::type *>(Ptr);
+  // reinterpret_cast,
+  int ReinterpretCast = reinterpret_cast<T::type>(4);
+  // dynamic_cast
+  struct B {
+    virtual ~B() = default;
+  };
+  struct D : T::tclass {};
+  auto *Base = dynamic_cast<T::tclass *>(new B);
+
+  T::type Invalid; // expected-error{{missing 'typename'}}
+}
+
+template void f<X>();
+
+// As default argument.
+template <typename T, typename = T::type>
+struct DefaultArg {};
+
+template struct DefaultArg<X>;
+
+// it is a decl-specifier of the decl-specifier-seq of a
+// - simple-declaration or a function-definition in namespace scope
+template <typename T>
+T::type VarTemp = 1;
+
+template int VarTemp<X>;
+
+template <typename T>
+T::type FuncDef() { return 1; }
+
+template int FuncDef<X>();
+
+template <typename T>
+T::type funcDecl();
+
+template <typename T>
+void FuncParam(T::type); // ok, but variable template
+// expected-error@-1{{variable has incomplete type 'void'}}
+
+template <typename T>
+void FuncParam2(const T::type, int); // expected-error{{missing 'typename'}}
+
+template <typename T>
+struct MemberDecl {
+  // member-declaration,
+  T::type Member;
+
+  // parameter-declaration in a member-declaration, unless that
+  // parameter-declaration appears in a default argument
+  void NoDefault(T::type);
+  void Default(int A = T::value);
+};
+
+template struct MemberDecl<X>;
+
+// parameter-declaration in a declarator of a function or function template
+// declaration where the declarator-id is qualified, unless that
+// parameter-declaration appears in a default argument,
+struct QualifiedFunc {
+  template <typename T>
+  void foo(typename T::type);
+  template <typename T>
+  void bar(T::type);
+};
+
+template <typename T>
+void QualifiedFunc::foo(T::type) {}
+template <typename T>
+void QualifiedFunc::bar(typename T::type) {}
+
+template <typename T>
+void g() {
+  // parameter-declaration in a lambda-declarator, unless that
+  // parameter-declaration appears in a default argument, or
+  auto Lambda1 = [](T::type) {};
+  auto Lambda2 = [](int A = T::value) {};
+}
+
+template void g<X>();
+
+// parameter-declaration of a (non-type) template-parameter.
+template <typename T, T::type>
+void NonTypeArg() {}
+
+template void NonTypeArg<X, 0>();
+
+template <typename T>
+void f(T::type) {} // expected-error {{missing 'typename'}}
+
+namespace N {
+  template <typename T>
+  int f(typename T::type);
+  template <typename T>
+  extern int Var;
+}
+
+template <typename T>
+int N::f(T::type); // ok, function
+template <typename T>
+int N::Var(T::value); // ok, variable
+
+int h() {
+  return N::f<X>(10) + N::Var<X>;
+}
+
+namespace NN {
+  inline namespace A { template <typename T> int f(typename T::type); } // expected-note{{previous definition is here}}
+  inline namespace B { template <typename T> int f(T::type); }
+}
+
+template <typename T>
+int NN::f(T::type); // expected-error{{redefinition of 'f' as different kind of symbol}}
+
+template <auto V>
+struct videntity {
+  static constexpr auto value = V;
+};
+
+template <typename T,
+    bool = T::value,
+    bool = bool(T::value),
+    bool = videntity<bool(T::value)>::value>
+void f(int = T::value) {}
+
+template <typename> int test() = delete;
+template <auto> int test();
+
+template <typename T>
+int Test = test<int(T::value)>();
+template int Test<X>;
diff --git a/clang/test/CXX/temp/temp.res/temp.dep/temp.dep.type/p1.cpp b/clang/test/CXX/temp/temp.res/temp.dep/temp.dep.type/p1.cpp
--- a/clang/test/CXX/temp/temp.res/temp.dep/temp.dep.type/p1.cpp
+++ b/clang/test/CXX/temp/temp.res/temp.dep/temp.dep.type/p1.cpp
@@ -17,7 +17,7 @@
 
   template<class T> struct A<A<A<T>>> {
     struct C {};
-    B<B<T>>::C bc; // expected-error {{missing 'typename'}}
+    B<B<T>>::C bc; // expected-warning {{implicit 'typename' is a C++2a extension}}
   };
 }
 
diff --git a/clang/test/FixIt/fixit.cpp b/clang/test/FixIt/fixit.cpp
--- a/clang/test/FixIt/fixit.cpp
+++ b/clang/test/FixIt/fixit.cpp
@@ -211,7 +211,7 @@
 template<class T> struct Mystery;
 template<class T> typedef Mystery<T>::type getMysteriousThing() { // \
   expected-error {{function definition declared 'typedef'}} \
-  expected-error {{missing 'typename' prior to dependent}}
+  expected-warning {{implicit 'typename' is a C++2a extension}}
   return Mystery<T>::get();
 }
 
diff --git a/clang/test/Parser/cxx-member-initializers.cpp b/clang/test/Parser/cxx-member-initializers.cpp
--- a/clang/test/Parser/cxx-member-initializers.cpp
+++ b/clang/test/Parser/cxx-member-initializers.cpp
@@ -103,5 +103,5 @@
   void l(int x = C<int, C<int, int>::C1>().f()) {}
 
   // This isn't, but it shouldn't crash. The diagnostics don't matter much.
-  void m(int x = C<int, union int>().f()) {} // expected-error {{declaration of anonymous union must be a definition}} expected-error {{expected a type}}
+  void m(int x = C<int, union int>().f()) {} // expected-error {{declaration of anonymous union must be a definition}} expected-error {{type name requires a specifier or qualifier}}
 };
diff --git a/clang/test/Parser/editor-placeholder-recovery.cpp b/clang/test/Parser/editor-placeholder-recovery.cpp
--- a/clang/test/Parser/editor-placeholder-recovery.cpp
+++ b/clang/test/Parser/editor-placeholder-recovery.cpp
@@ -64,7 +64,7 @@
     }
 }
 
-void Struct::method(<#Struct &x#>, noSupressionHere) { // expected-error {{unknown type name 'noSupressionHere'}} expected-error {{C++ requires a type specifier for all declarations}}
+void Struct::method(<#Struct &x#>, noSupressionHere) { // expected-error {{unknown type name 'noSupressionHere'}}
 #ifndef SUPPRESS
   // expected-error@-2 {{editor placeholder in source file}}
 #endif
diff --git a/clang/test/SemaCXX/MicrosoftCompatibility.cpp b/clang/test/SemaCXX/MicrosoftCompatibility.cpp
--- a/clang/test/SemaCXX/MicrosoftCompatibility.cpp
+++ b/clang/test/SemaCXX/MicrosoftCompatibility.cpp
@@ -199,14 +199,14 @@
    typedef B<U> Base2;
    typedef A<U> Base3;
 
-   A<T>::TYPE a1; // expected-warning {{missing 'typename' prior to dependent type name}}
-   Base1::TYPE a2; // expected-warning {{missing 'typename' prior to dependent type name}}
+   A<T>::TYPE a1; // expected-warning {{implicit 'typename' is a C++2a extension}}
+   Base1::TYPE a2; // expected-warning {{implicit 'typename' is a C++2a extension}}
 
-   B<U>::TYPE a3; // expected-warning {{missing 'typename' prior to dependent type name}}
-   Base2::TYPE a4; // expected-warning {{missing 'typename' prior to dependent type name}}
+   B<U>::TYPE a3; // expected-warning {{implicit 'typename' is a C++2a extension}}
+   Base2::TYPE a4; // expected-warning {{implicit 'typename' is a C++2a extension}}
 
-   A<U>::TYPE a5; // expected-error {{missing 'typename' prior to dependent type name}}
-   Base3::TYPE a6; // expected-error {{missing 'typename' prior to dependent type name}}
+   A<U>::TYPE a5; // expected-warning {{implicit 'typename' is a C++2a extension}}
+   Base3::TYPE a6; // expected-warning {{implicit 'typename' is a C++2a extension}}
  };
 
 class D {
@@ -215,9 +215,9 @@
 };
 
 template <class T>
-void function_missing_typename(const T::Type param)// expected-warning {{missing 'typename' prior to dependent type name}}
+void function_missing_typename(const T::Type param)// expected-warning {{missing 'typename'}}
 {
-    const T::Type var = 2; // expected-warning {{missing 'typename' prior to dependent type name}}
+    const T::Type var = 2; // expected-warning {{missing 'typename'}}
 }
 
 template void function_missing_typename<D>(const D::Type param);
diff --git a/clang/test/SemaCXX/MicrosoftExtensions.cpp b/clang/test/SemaCXX/MicrosoftExtensions.cpp
--- a/clang/test/SemaCXX/MicrosoftExtensions.cpp
+++ b/clang/test/SemaCXX/MicrosoftExtensions.cpp
@@ -526,7 +526,7 @@
 
 namespace PR32750 {
 template<typename T> struct A {};
-template<typename T> struct B : A<A<T>> { A<T>::C::D d; }; // expected-error {{missing 'typename' prior to dependent type name 'A<T>::C::D'}}
+template<typename T> struct B : A<A<T>> { A<T>::C::D d; }; // expected-warning {{implicit 'typename' is a C++2a extension}}
 }
 
 #else
diff --git a/clang/test/SemaCXX/MicrosoftSuper.cpp b/clang/test/SemaCXX/MicrosoftSuper.cpp
--- a/clang/test/SemaCXX/MicrosoftSuper.cpp
+++ b/clang/test/SemaCXX/MicrosoftSuper.cpp
@@ -108,8 +108,8 @@
   typename __super::XXX a;
   typedef typename __super::XXX b;
 
-  __super::XXX c;         // expected-error {{missing 'typename'}}
-  typedef __super::XXX d; // expected-error {{missing 'typename'}}
+  __super::XXX c;         // expected-warning {{implicit 'typename' is a C++2a extension}}
+  typedef __super::XXX d; // expected-warning {{implicit 'typename' is a C++2a extension}}
 
   void foo() {
     typename __super::XXX e;
@@ -127,8 +127,8 @@
   typename __super::XXX a;
   typedef typename __super::XXX b;
 
-  __super::XXX c;         // expected-error {{missing 'typename'}}
-  typedef __super::XXX d; // expected-error {{missing 'typename'}}
+  __super::XXX c;         // expected-warning {{implicit 'typename' is a C++2a extension}}
+  typedef __super::XXX d; // expected-warning {{implicit 'typename' is a C++2a extension}}
 
   void foo() {
     typename __super::XXX e;
diff --git a/clang/test/SemaCXX/unknown-type-name.cpp b/clang/test/SemaCXX/unknown-type-name.cpp
--- a/clang/test/SemaCXX/unknown-type-name.cpp
+++ b/clang/test/SemaCXX/unknown-type-name.cpp
@@ -36,15 +36,15 @@
 
   static int n;
   static type m;
-  static int h(T::type, int); // expected-error{{missing 'typename'}}
-  static int h(T::type x, char); // expected-error{{missing 'typename'}}
+  static int h(T::type, int); // expected-warning{{implicit 'typename' is a C++2a extension}}
+  static int h(T::type x, char); // expected-warning{{implicit 'typename' is a C++2a extension}}
 };
 
 template<typename T>
-A<T>::type g(T t) { return t; } // expected-error{{missing 'typename'}}
+A<T>::type g(T t) { return t; } // expected-warning{{implicit 'typename' is a C++2a extension}}
 
 template<typename T>
-A<T>::type A<T>::f() { return type(); } // expected-error{{missing 'typename'}}
+A<T>::type A<T>::f() { return type(); } // expected-warning{{implicit 'typename' is a C++2a extension}}
 
 template<typename T>
 void f(T::type) { } // expected-error{{missing 'typename'}}
@@ -72,9 +72,7 @@
 
 int *p;
 
-// FIXME: We should assume that 'undeclared' is a type, not a parameter name
-//        here, and produce an 'unknown type name' diagnostic instead.
-int f1(undeclared, int); // expected-error{{requires a type specifier}}
+int f1(undeclared, int); // expected-error{{unknown type name 'undeclared'}}
 
 int f2(undeclared, 0); // expected-error{{undeclared identifier}}
 
@@ -86,11 +84,11 @@
 
 template<typename T> int A<T>::n(T::value); // ok
 template<typename T>
-A<T>::type // expected-error{{missing 'typename'}}
+A<T>::type // expected-warning {{implicit 'typename' is a C++2a extension}}
 A<T>::m(T::value, 0); // ok
 
-template<typename T> int A<T>::h(T::type, int) {} // expected-error{{missing 'typename'}}
-template<typename T> int A<T>::h(T::type x, char) {} // expected-error{{missing 'typename'}}
+template<typename T> int A<T>::h(T::type, int) {} // expected-warning{{implicit 'typename' is a C++2a extension}}
+template<typename T> int A<T>::h(T::type x, char) {} // expected-warning{{implicit 'typename' is a C++2a extension}}
 
 template<typename T> int h(T::type, int); // expected-error{{missing 'typename'}}
 template<typename T> int h(T::type x, char); // expected-error{{missing 'typename'}}
@@ -118,4 +116,5 @@
 // FIXME: We know which type specifier should have been specified here. Provide
 //        a fix-it to add 'typename A<T>::type'
 template<typename T>
-A<T>::g() { } // expected-error{{requires a type specifier}}
+A<T>::g() { } // expected-error{{expected unqualified-id}}
+// expected-warning@-1{{implicit 'typename' is a C++2a extension}}