[clang] [clang] Introduce [[clang::lifetime_capture_by(X)]] (PR #111499)

[Gábor Horváth via cfe-commits]

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@@ -1873,6 +1873,46 @@ def LifetimeBound : DeclOrTypeAttr {
   let SimpleHandler = 1;
 }
 
+def LifetimeCaptureBy : DeclOrTypeAttr {
+  let Spellings = [Clang<"lifetime_capture_by", 0>];
+  let Subjects = SubjectList<[ParmVar, ImplicitObjectParameter], ErrorDiag>;
+  let Args = [VariadicParamOrParamIdxArgument<"Params">];
+  let Documentation = [LifetimeBoundDocs];
+  let LangOpts = [CPlusPlus];
+
+  // let SimpleHandler = 1;
+  // let LateParsed = LateAttrParseStandard;
+  // let HasCustomParsing = 1;
+  // let ParseArgumentsAsUnevaluated = 1;
+
+  let AdditionalMembers = [{
+private:
+  SmallVector<IdentifierInfo*, 1> ArgIdents;
+  SmallVector<SourceLocation, 1> ArgLocs;
+
+public:
+  static constexpr int INVALID = -2;
+  static constexpr int UNKNOWN = -1;
+  static constexpr int GLOBAL = -1;
+  static constexpr int THIS = 0;
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Xazax-hun wrote:

I wish we had one universal way of indexing parameters in Clang. I think probably most attributes start from 1, but there are APINotes that start from 0. Not really an actionable comment here, more like a rant. 

https://github.com/llvm/llvm-project/pull/111499