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

[Boaz Brickner via cfe-commits]

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@@ -3223,6 +3225,49 @@ void Sema::CheckArgAlignment(SourceLocation Loc, NamedDecl *FDecl,
         << ParamName << (FDecl != nullptr) << FDecl;
 }
 
+void Sema::checkLifetimeCaptureBy(FunctionDecl *FD, bool IsMemberFunction,
+                                  const Expr *ThisArg,
+                                  ArrayRef<const Expr *> Args) {
+  auto GetArgAt = [&](int Idx) {
+    if (IsMemberFunction && Idx == 0)
+      return const_cast<Expr *>(ThisArg);
+    return const_cast<Expr *>(Args[Idx - int(IsMemberFunction)]);
+  };
+  for (unsigned I = 0; I < FD->getNumParams(); ++I) {
+    auto *CapturedByAttr =
+        FD->getParamDecl(I)->getAttr<LifetimeCaptureByAttr>();
+    if (!CapturedByAttr)
+      continue;
+    for (int CapturingParamIdx : CapturedByAttr->params()) {
+      Expr *Capturing = GetArgAt(CapturingParamIdx);
+      Expr *Captured = GetArgAt(I + IsMemberFunction);
+      CapturingEntity CE{Capturing};
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bricknerb wrote:

Consider making this initialization clearer by writing .Expression = Capturing

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