Fix warning in MSVC

Currently there is no PrintOnLeft attribute set, which results in an
empty switch-case. When compiling this, MSVC issues a warning saying
that the switch-case is empty. Fix this by using a macro and checking
if this macro is defined or not.

Links to D157394

Author: giulianobelinassi

clang/lib/AST/DeclPrinter.cpp

@@ -250,13 +250,23 @@ raw_ostream& DeclPrinter::Indent(unsigned Indentation) {
   return Out;
 }
 
+// For CLANG_ATTR_LIST_CanPrintOnLeft macro.
+#include "clang/Basic/AttrLeftSideCanPrintList.inc"
+
+// For CLANG_ATTR_LIST_PrintOnLeft macro.
+#include "clang/Basic/AttrLeftSideMustPrintList.inc"
+
 static bool canPrintOnLeftSide(attr::Kind kind) {
+#ifdef CLANG_ATTR_LIST_CanPrintOnLeft
   switch (kind) {
-#include "clang/Basic/AttrLeftSideCanPrintList.inc"
+  CLANG_ATTR_LIST_CanPrintOnLeft
     return true;
   default:
     return false;
   }
+#else
+  return false;
+#endif
 }
 
 static bool canPrintOnLeftSide(const Attr *A) {
@@ -268,11 +278,16 @@ static bool canPrintOnLeftSide(const Attr *A) {
 
 static bool mustPrintOnLeftSide(attr::Kind kind) {
   switch (kind) {
-#include "clang/Basic/AttrLeftSideMustPrintList.inc"
+#ifdef CLANG_ATTR_LIST_PrintOnLeft
+  switch (kind) {
+  CLANG_ATTR_LIST_PrintOnLeft
     return true;
   default:
     return false;
   }
+#else
+  return false;
+#endif
 }
 
 static bool mustPrintOnLeftSide(const Attr *A) {
@@ -314,7 +329,6 @@ void DeclPrinter::prettyPrintAttributes(Decl *D, llvm::raw_ostream &Out,
                    VD->getInitStyle() == VarDecl::CallInit)
           AttrLoc = AttrPrintLoc::Left;
       }
-
       // Only print the side matches the user requested.
       if ((Loc & AttrLoc) != AttrPrintLoc::None)
         A->printPretty(Out, Policy);

clang/utils/TableGen/ClangAttrEmitter.cpp

@@ -3217,15 +3217,24 @@ void EmitClangAttrPrintList(const std::string &FieldName, RecordKeeper &Records,
 
   std::vector<Record *> Attrs = Records.getAllDerivedDefinitions("Attr");
   std::vector<Record *> PragmaAttrs;
+  bool first = false;
+
   for (auto *Attr : Attrs) {
     if (!Attr->getValueAsBit("ASTNode"))
       continue;
 
     if (!Attr->getValueAsBit(FieldName))
       continue;
 
-    OS << "case attr::" << Attr->getName() << ":\n";
+    if (!first) {
+      first = true;
+      OS << "#define CLANG_ATTR_LIST_" << FieldName;
+    }
+
+    OS << " \\\n case attr::" << Attr->getName() << ":";
   }
+
+  OS << '\n';
 }
 
 // Emits the enumeration list for attributes.