[clang] Reapply "[clang] Introduce [[clang::lifetime_capture_by(X)]] (PR #115823)

[Haojian Wu via cfe-commits]

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@@ -1889,6 +1889,43 @@ 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 = [LifetimeCaptureByDocs];
+  let AdditionalMembers = [{
+private:
+  MutableArrayRef<IdentifierInfo*> ArgIdents;
+  MutableArrayRef<SourceLocation> ArgLocs;
+
+public:
+  static constexpr int THIS = 0;
+  static constexpr int INVALID = -1;
+  static constexpr int UNKNOWN = -2;
+  static constexpr int GLOBAL = -3;
+
+  void CreateArgs(ASTContext &Ctx) {
+    ArgIdents =
+      MutableArrayRef<IdentifierInfo *>(new (Ctx) IdentifierInfo *[params_Size], params_Size);
+    ArgLocs =
+      MutableArrayRef<SourceLocation>(new (Ctx) SourceLocation[params_Size], params_Size);
+  }
+  auto getArgIdents() const { 
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hokein wrote:

Returning a `MutableArrayRef` and allowing mutations in the caller seems to break the encapsulation from a getter.

I’d prefer using an `ArrayRef` and adding a setter like `setArgIdents(ArrayRef<IdentifierInfo*> Args)`. While this means we’d allocate the array in the caller, I think it is fine.


https://github.com/llvm/llvm-project/pull/115823