[NFC][Attr TableGen] Emit Spelling Enum for Attr types if there >1

[erichkeane]

Summary

Discovered in a downstream, it is often useful to have slightly
different semantics for an attribute based on its namespace, however our
spelling infrastructure doesn't consider namespace when deciding to
elide the enum list. The result is that the solution for a case where
an attribute has slightly different semantics based on a namespace
requires checking against the integer value, which is fragile.

This patch makes us always emit the spelling enum if there is more than
1 and we're generating the header.

[rnk]

clang/utils/TableGen/ClangAttrEmitter.cpp

2333

I had to call this function during both header and cpp file generation because some code later used the SemanticToSyntacticMap it fills in.

2534

Won't this assert? I think we come here even if !Header.

[aaron.ballman]

I cannot think of a way to add test coverage for this change, can you?

clang/utils/TableGen/ClangAttrEmitter.cpp

2332

Looks like there is a little extra whitespace after the << that can be removed.

[erichkeane]

Did as @rnk suggested, and it fixed all the problems. Just changed the logic for emitting the enum.

[erichkeane]

clang/utils/TableGen/ClangAttrEmitter.cpp

2333

Ah! I didn't see anywhere that SpellingEnum was created. Perhaps thats my issue.

2534

I haven't got any asserts here, but I'm having weird problems from tablegen not getting recreated. I'll put the run-in-both-cases code back which should fix this anyway. New patch incoming as soon as it passes LIT.

[aaron.ballman]

LGTM!

clang/utils/TableGen/ClangAttrEmitter.cpp

for (const auto *Attr : Attrs) {
     // can be elided. If all of the spellings share the same name, the spelling
     // functionality can also be elided.
     bool ElideSpelling = (Spellings.size() <= 1) ||
                          SpellingNamesAreCommon(Spellings);
 
     // This maps spelling index values to semantic Spelling enumerants.
     SemanticSpellingMap SemanticToSyntacticMap;
 
-    std::string SpellingEnum;
-    if (!ElideSpelling)
-      SpellingEnum = CreateSemanticSpellings(Spellings, SemanticToSyntacticMap);
-    if (Header)
-      OS << SpellingEnum;
+    if (Header && Spellings.size() > 1)
+      OS <<  CreateSemanticSpellings(Spellings, SemanticToSyntacticMap);
 
     const auto &ParsedAttrSpellingItr = llvm::find_if(
         AttrMap, [R](const std::pair<std::string, const Record *> &P) {
           return &R == P.second;
         });
 
     // Emit CreateImplicit factory methods.
     auto emitCreate = [&](bool Implicit, bool emitFake) {
if (Header) {
       OS << '\n';
       OS << "  " << R.getName() << "Attr *clone(ASTContext &C) const;\n";
       OS << "  void printPretty(raw_ostream &OS,\n"
          << "                   const PrintingPolicy &Policy) const;\n";
       OS << "  const char *getSpelling() const;\n";
     }
 
     if (!ElideSpelling) {
       assert(!SemanticToSyntacticMap.empty() && "Empty semantic mapping list");
       if (Header)
         OS << "  Spelling getSemanticSpelling() const;\n";
       else {
         OS << R.getName() << "Attr::Spelling " << R.getName()
            << "Attr::getSemanticSpelling() const {\n";
         WriteSemanticSpellingSwitch("getAttributeSpellingListIndex()",
                                     SemanticToSyntacticMap, OS);
         OS << "}\n";