[clang] [Attributes] Support Attributes being declared as only supporting late parsing when passing an experimental feature flag (PR #88596)

[Dan Liew via cfe-commits]

================
@@ -1822,28 +1822,106 @@ void WriteSemanticSpellingSwitch(const std::string &VarName,
   OS << "  }\n";
 }
 
+enum class LateAttrParseKind {
+  LateAttrParsingNever = 0,
+  LateAttrParsingAlways = 1,
+  LateAttrParsingExperimentalOnly = 2
+};
+
+static LateAttrParseKind getLateAttrParseKind(const Record *Attr) {
+  // This function basically does
+  // `Attr->getValueAsDef("LateParsed")->getValueAsInt("Mode")` but does
+  // a bunch of sanity checking to ensure that
+  // `LateAttrParseMode` in `Attr.td` is in sync with the `LateAttrParseKind`
+  // enum in this source file.
+
+  const char *LateParsedStr = "LateParsed";
+  auto *LAPK = Attr->getValueAsDef(LateParsedStr);
+
+  // Typecheck the `LateParsed` field.
+  SmallVector<Record *, 1> SuperClasses;
+  LAPK->getDirectSuperClasses(SuperClasses);
+  if (SuperClasses.size() != 1) {
+    PrintFatalError(Attr, "Field `" + llvm::Twine(LateParsedStr) +
+                              "`should only have one super class");
+  }
+  const char *LateAttrParseKindStr = "LateAttrParseKind";
+  if (SuperClasses[0]->getName().compare(LateAttrParseKindStr) != 0) {
+    PrintFatalError(Attr, "Field `" + llvm::Twine(LateParsedStr) +
+                              "`should only have type `" +
+                              llvm::Twine(LateAttrParseKindStr) +
+                              "` but found type `" +
+                              SuperClasses[0]->getName() + "`");
+  }
+
+  // Get Kind and verify the enum name matches the name in `Attr.td`.
+  const char *KindFieldStr = "Kind";
+  unsigned Kind = LAPK->getValueAsInt(KindFieldStr);
+  switch (LateAttrParseKind(Kind)) {
+#define CASE(X)                                                                \
+  case LateAttrParseKind::X:                                                   \
+    if (LAPK->getName().compare(#X) != 0) {                                    \
+      PrintFatalError(Attr,                                                    \
+                      "Field `" + llvm::Twine(LateParsedStr) + "` set to `" +  \
+                          LAPK->getName() +                                    \
+                          "` but this converts to `LateAttrParseKind::" +      \
+                          llvm::Twine(#X) + "`");                              \
+    }                                                                          \
+    return LateAttrParseKind::X;
+
+    CASE(LateAttrParsingNever)
+    CASE(LateAttrParsingAlways)
+    CASE(LateAttrParsingExperimentalOnly)
+#undef CASE
+  }
+
+  // The Kind value is completely invalid
+  auto KindValueStr = llvm::utostr(Kind);
+  PrintFatalError(Attr, "Field `" + llvm::Twine(LateParsedStr) + "` set to `" +
+                            LAPK->getName() + "` has unexpected `" +
+                            llvm::Twine(KindFieldStr) + "` value of " +
+                            KindValueStr);
+}
+
 // Emits the LateParsed property for attributes.
-static void emitClangAttrLateParsedList(RecordKeeper &Records, raw_ostream &OS) {
-  OS << "#if defined(CLANG_ATTR_LATE_PARSED_LIST)\n";
-  std::vector<Record*> Attrs = Records.getAllDerivedDefinitions("Attr");
+static void emitClangAttrLateParsedListImpl(RecordKeeper &Records,
+                                            raw_ostream &OS,
+                                            LateAttrParseKind LateParseMode) {
+  std::vector<Record *> Attrs = Records.getAllDerivedDefinitions("Attr");
 
   for (const auto *Attr : Attrs) {
-    bool LateParsed = Attr->getValueAsBit("LateParsed");
+    auto LateParsed = getLateAttrParseKind(Attr);
 
-    if (LateParsed) {
-      std::vector<FlattenedSpelling> Spellings = GetFlattenedSpellings(*Attr);
+    if (LateParsed != LateParseMode)
+      continue;
 
-      // FIXME: Handle non-GNU attributes
-      for (const auto &I : Spellings) {
-        if (I.variety() != "GNU")
-          continue;
-        OS << ".Case(\"" << I.name() << "\", " << LateParsed << ")\n";
-      }
+    std::vector<FlattenedSpelling> Spellings = GetFlattenedSpellings(*Attr);
+
+    // FIXME: Handle non-GNU attributes
+    for (const auto &I : Spellings) {
+      if (I.variety() != "GNU")
+        continue;
+      OS << ".Case(\"" << I.name() << "\", 1)\n";
     }
   }
+}
+
+static void emitClangAttrLateParsedList(RecordKeeper &Records,
+                                        raw_ostream &OS) {
+  OS << "#if defined(CLANG_ATTR_LATE_PARSED_LIST)\n";
+  emitClangAttrLateParsedListImpl(Records, OS,
+                                  LateAttrParseKind::LateAttrParsingAlways);
   OS << "#endif // CLANG_ATTR_LATE_PARSED_LIST\n\n";
 }
----------------
delcypher wrote:

By "inling" I assume you mean duplicating `emitClangAttrLateParsedListImpl` into `emitClangAttrLateParsedList` and `emitClangAttrLateParsedExperimentalList`. I've deliberately avoided doing that to avoid duplicating code. Another reason for avoiding the duplication is that the code has a `FIXME` and its probably best to avoid duplicating that if it's not necessary.

https://github.com/llvm/llvm-project/pull/88596