Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -985,6 +985,9 @@
 // A warning group for warnings about using C99 features as extensions.
 def C99 : DiagGroup<"c99-extensions", [C99Designator]>;
 
+// A warning group for warnings about using C2x features as extensions.
+def C2x : DiagGroup<"c2x-extensions">;
+
 // A warning group for warnings about GCC extensions.
 def GNU : DiagGroup<"gnu", [GNUAlignofExpression, GNUAnonymousStruct,
                             GNUAutoType,
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -275,7 +275,9 @@
   "%0 cannot be the name of a parameter">;
 def err_bad_parameter_name_template_id : Error<
   "parameter name cannot have template arguments">;
-def err_parameter_name_omitted : Error<"parameter name omitted">;
+def ext_parameter_name_ommitted_c2x : ExtWarn<
+  "omitting the parameter name in a function definition is a C2x extension">,
+  InGroup<C2x>;
 def err_anyx86_interrupt_attribute : Error<
   "%select{x86|x86-64}0 'interrupt' attribute only applies to functions that "
   "have %select{a 'void' return type|"
Index: clang/lib/Sema/SemaChecking.cpp
===================================================================
--- clang/lib/Sema/SemaChecking.cpp
+++ clang/lib/Sema/SemaChecking.cpp
@@ -12860,11 +12860,12 @@
 
     // C99 6.9.1p5: If the declarator includes a parameter type list, the
     // declaration of each parameter shall include an identifier.
-    if (CheckParameterNames &&
-        Param->getIdentifier() == nullptr &&
-        !Param->isImplicit() &&
-        !getLangOpts().CPlusPlus)
-      Diag(Param->getLocation(), diag::err_parameter_name_omitted);
+    if (CheckParameterNames && Param->getIdentifier() == nullptr &&
+        !Param->isImplicit() && !getLangOpts().CPlusPlus) {
+      // Diagnose this as an extension in C17 and earlier.
+      if (!getLangOpts().C2x)
+        Diag(Param->getLocation(), diag::ext_parameter_name_ommitted_c2x);
+    }
 
     // C99 6.7.5.3p12:
     //   If the function declarator is not part of a definition of that
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -14645,11 +14645,12 @@
   if (ExplicitSignature) {
     for (unsigned I = 0, E = ExplicitSignature.getNumParams(); I != E; ++I) {
       ParmVarDecl *Param = ExplicitSignature.getParam(I);
-      if (Param->getIdentifier() == nullptr &&
-          !Param->isImplicit() &&
-          !Param->isInvalidDecl() &&
-          !getLangOpts().CPlusPlus)
-        Diag(Param->getLocation(), diag::err_parameter_name_omitted);
+      if (Param->getIdentifier() == nullptr && !Param->isImplicit() &&
+          !Param->isInvalidDecl() && !getLangOpts().CPlusPlus) {
+        // Diagnose this as an extension in C17 and earlier.
+        if (!getLangOpts().C2x)
+          Diag(Param->getLocation(), diag::ext_parameter_name_ommitted_c2x);
+      }
       Params.push_back(Param);
     }
 
Index: clang/test/Sema/block-args.c
===================================================================
--- clang/test/Sema/block-args.c
+++ clang/test/Sema/block-args.c
@@ -31,8 +31,8 @@
 
 // radar 7528255
 void f0() {
-  ^(int, double d, char) {}(1, 1.34, 'a'); // expected-error {{parameter name omitted}} \
-				 	   // expected-error {{parameter name omitted}}
+  ^(int, double d, char) {}(1, 1.34, 'a'); // expected-warning {{omitting the parameter name in a function definition is a C2x extension}} \
+                                           // expected-warning {{omitting the parameter name in a function definition is a C2x extension}}
 }
 
 // rdar://problem/8962770
Index: clang/test/Sema/c89.c
===================================================================
--- clang/test/Sema/c89.c
+++ clang/test/Sema/c89.c
@@ -45,7 +45,7 @@
 
 typedef int sometype;
 int a(sometype, y) {return 0;}  /* expected-warning {{declaration specifier missing, defaulting to 'int'}} \
-                                   expected-error {{parameter name omitted}}*/
+                                   expected-warning {{omitting the parameter name in a function definition is a C2x extension}}*/
 
 
 
Index: clang/test/Sema/function.c
===================================================================
--- clang/test/Sema/function.c
+++ clang/test/Sema/function.c
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic
+// RUN: %clang_cc1 %s -fsyntax-only -verify -verify=c2x -pedantic
+// RUN: %clang_cc1 %s -fsyntax-only -std=c2x -verify -pedantic
 
 // PR1892, PR11354
 void f(double a[restrict][5]) { __typeof(a) x = 10; } // expected-warning {{(aka 'double (*restrict)[5]')}}
@@ -30,7 +31,7 @@
 void t11(){t10(1);} // expected-warning{{too many arguments}}
 
 // PR3208
-void t12(int) {}  // expected-error{{parameter name omitted}}
+void t12(int) {}  // c2x-warning{{omitting the parameter name in a function definition is a C2x extension}}
 
 // PR2790
 void t13() {
@@ -80,7 +81,8 @@
 fn_t t17;
 
 // PR4049
-unknown_type t18(void*) {   // expected-error {{unknown type name 'unknown_type'}} expected-error{{parameter name omitted}}
+unknown_type t18(void*) {   // expected-error {{unknown type name 'unknown_type'}} \
+                            // c2x-warning {{omitting the parameter name in a function definition is a C2x extension}}
 }
 
 unknown_type t19(int* P) {   // expected-error {{unknown type name 'unknown_type'}}