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

[Dan Liew via cfe-commits]

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@@ -2101,9 +2179,20 @@ bool PragmaClangAttributeSupport::isAttributedSupported(
     return SpecifiedResult;
 
   // Opt-out rules:
-  // An attribute requires delayed parsing (LateParsed is on)
-  if (Attribute.getValueAsBit("LateParsed"))
+
+  // An attribute requires delayed parsing (LateParsed is on).
+  switch (getLateAttrParseKind(&Attribute)) {
+  case LateAttrParseKind::LateAttrParsingNever:
+    break;
+  case LateAttrParseKind::LateAttrParsingAlways:
+    return false;
+  case LateAttrParseKind::LateAttrParsingExperimentalOnly:
+    // FIXME: This is only late parsed when
+    // `-fexperimental-late-parse-attributes` is on. If that option is off
+    // then we shouldn't return here.
     return false;
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delcypher wrote:

So you're saying I should drop the `FIXME`?

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