Add warning for 'using' keyword before hlsl2021. (#4312)

tools/clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1027,6 +1027,8 @@ def warn_hlsl_semantic_identifier_collision : Warning <
   InGroup< HLSLSemanticIdentifierCollision >;
 def err_hlsl_enum : Error<
   "enum is unsupported in HLSL before 2017">;
+def warn_hlsl_new_feature : Warning <
+  "%0 is a HLSL %1 feature, and is available in older versions as a non-portable extension.">;
 
 // OpenMP support.
 def warn_pragma_omp_ignored : Warning<

tools/clang/lib/Parse/ParseDeclCXX.cpp

@@ -438,6 +438,13 @@ Decl *Parser::ParseUsingDirective(unsigned Context,
 
   // Eat 'namespace'.
   SourceLocation NamespcLoc = ConsumeToken();
+  // HLSL change begin -warning ext before HLSL2021.
+  if (getLangOpts().HLSL) {
+    if (getLangOpts().HLSLVersion < hlsl::LangStd::v2021)
+      Diag(UsingLoc, diag::warn_hlsl_new_feature) << "keyword 'using'"
+                                                  << "2021";
+  }
+  // HLSL change end.
 
   if (Tok.is(tok::code_completion)) {
     Actions.CodeCompleteUsingDirective(getCurScope());
@@ -584,7 +591,13 @@ Decl *Parser::ParseUsingDeclaration(unsigned Context,
     }
 
     ConsumeToken();
-
+    // HLSL change begin -warning ext before HLSL2021.
+    if (getLangOpts().HLSL) {
+      if (getLangOpts().HLSLVersion < hlsl::LangStd::v2021)
+        Diag(UsingLoc, diag::warn_hlsl_new_feature) << "keyword 'using'"
+                                                  << "2021";
+    } else
+    // HLSL change end.
     Diag(Tok.getLocation(), getLangOpts().CPlusPlus11 ?
          diag::warn_cxx98_compat_alias_declaration :
          diag::ext_alias_declaration);

tools/clang/test/HLSL/cpp-errors-hv2015.hlsl

@@ -292,7 +292,7 @@ namespace MyNs {
 // namespace alias definition.
 namespace NamespaceAlias = MyNs; // expected-error {{expected identifier}}
 
-using namespace MyNS;
+using namespace MyNS;  // expected-warning {{keyword 'using' is a HLSL 2021 feature, and is available in older versions as a non-portable extension}}
 int using; // expected-error {{'using' is a reserved keyword in HLSL}}
 
 struct my_struct { };

tools/clang/test/HLSL/cpp-errors.hlsl

@@ -288,7 +288,7 @@ namespace MyNs {
 // namespace alias definition.
 namespace NamespaceAlias = MyNs; // expected-error {{expected identifier}}
 
-using namespace MyNS;
+using namespace MyNS; // expected-warning {{keyword 'using' is a HLSL 2021 feature, and is available in older versions as a non-portable extension}}
 int using; // expected-error {{'using' is a reserved keyword in HLSL}}
 
 struct my_struct { };

tools/clang/test/HLSLFileCheck/hlsl/diagnostics/warnings/using.hlsl

@@ -0,0 +1,30 @@
+// RUN: %dxc -E main -T ps_6_0 %s -HV 2021  | FileCheck -check-prefix=HV2021 %s
+
+// RUN: %dxc -E main -T ps_6_0 %s  | FileCheck %s
+
+// CHECK:using.hlsl:14:5: warning: keyword 'using' is a HLSL 2021 feature, and is available in older versions as a non-portable extension.
+// CHECK:using.hlsl:21:1: warning: keyword 'using' is a HLSL 2021 feature, and is available in older versions as a non-portable extension.
+// CHECK:using.hlsl:22:1: warning: keyword 'using' is a HLSL 2021 feature, and is available in older versions as a non-portable extension.
+
+// CHECK:error: control reaches end of non-void function
+
+// HV2021-NOT:keyword 'using' is a HLSL 2021 feature, and is available in older versions as a non-portable extension
+// HV2021:error: control reaches end of non-void function
+namespace n {
+    using f = float;
+    namespace n2 {
+       f foo(f a) { return sin(a); }
+    }
+
+}
+
+using namespace n;
+using f32 = n::f;
+
+
+using n2::foo;
+
+f32 main(f32 a:A) : SV_Target {
+
+  f32 r = foo(a);
+}